Introduction

The increase in the world population has intensified the demand for higher food production, while the agricultural land and essential resources, such as water for food production, are limited. Currently, agriculture consumes about 70% of the world’s freshwater, and contributes to water pollution in rivers, lakes, and oceans through the runoff of chemical fertilizer1. Moreover, climate change factors such as global warming, shifts in precipitation rate and pattern, and prolonged drought conditions are increasingly impacting agriculture and food production. These changes also affect food security and crop yields through extreme weather events, altered rainfall patterns, and the emergence of new pests and diseases. Agriculture is also a significant contributor to greenhouse gas emissions, accounting for 10.5% of U.S. emissions in 2022 and highlighting another key challenge facing the agriculture industry.

Statistics from the literature indicate that more than 10 million tons of food are wasted annually in the United States due to changes in the growing conditions (such as extreme weather, pest and disease infestation), high labor costs, and fluctuations in market price2. California produces more than 50% of the fruits, nuts, and vegetables in the United States (Pathak et al, 2018); and its main specialty crops are nuts (almonds, pistachios, walnuts) and fruits (apples, strawberries, cherries, citrus, grapes, peaches, plums, pomegranates, olives). According to a report of the United States Department of Agriculture (USDA), in 2011, California was the sole producer (99% or more) of many specialty crops, including almonds, plums, figs, olives, pomegranates, raisins, and walnuts. There is no established or reliable data that catalogs food loss and waste from these specialty crops. Most estimates of food loss and waste are based on survey data for specific crops and lack consistency in reporting methods. Different reporting approaches were used, including qualitative measures (such as amounts and percentages) or qualitative descriptions such as “good”. Various studies have defined loss and waste in different ways. Some studies3,4,5,6 measured crop waste based on the total marketable crop which considers the loss as a portion of the crop that becomes landfill. In contrast, other researchers defined loss as the portion of crops that cannot be eaten as food and did not consider the loss from other secondary uses, such as compost or valorization techniques.

Baker et al. provided one of the most comprehensive references on this subject. They investigated farm losses in northern and central California through direct interviews with selected growers and collected data from county pesticide release documents. They surveyed 123 fields with 20 crops that were hand-harvested single or multiple times (called multiple-cut crops) and reported an overall on-farm loss of 31.3%. Additionally, they reported that the growers dramatically underestimated the on-farm loss versus the real loss. Table 1 provides a summary of the waste generation stage and loss percentage of specialty crops in the United States. The losses reported in this table align well with findings from other studies4,5,7.

Table 1 Statistics and waste generation stages for specialty crops in the U.S
Full size table

A more general estimation of food waste was provided by Dou et al., in which the losses occurring in various agricultural commodities were divided into industry, retail, and consumer subgroups8. The industry level refers to all operations within the field, post-harvest processing, and packaging. Figure 1 illustrates an overall view of the waste and loss across the food chain in each sector from farm to fork.

Fig. 1
Fig. 1The alternative text for this image may have been generated using AI.
Full size image

Percentage of waste at different stages of agricultural activities.

Besides the financial losses caused by edible food waste, the Natural Resources Defense Council estimates that 18% of available cultivated lands, 21% of water, and 19% of fertilizer are consumed for the uneaten portion of agricultural products9. To address the large degree of food waste, it is essential to understand and implement effective waste management practices throughout the food chain. This includes utilizing crop residues and reducing post-harvest losses. Such strategies play a key role in enhancing food safety, optimizing resource efficiency, and minimizing pollution and greenhouse gas emissions.

This review article reports the significant food waste in specialty crop production and explores the critical paths to reduce food waste in agriculture and improve sustainability. Focusing on California’s specialty crops, the study examines factors throughout the food chain, from production and pre-harvest conditions to post-harvest handling that lead to food waste (“Challenges in agricultural practices”). This is followed by waste management strategies and advanced methods for reducing the waste (“Integrated strategies for food waste reduction and sustainability”). Central to this approach is Good Agricultural Practices. It also explores the critical consideration from a food safety point of view in reusing the wasted food. Lastly, the concept of circular economy is introduced with the objective of finding secondary uses for agricultural waste.

Challenges in agricultural practices

According to the Food and Agriculture Organization (FAO), about one-third of the food produced for human consumption (~1300 million tons) was wasted or lost in 2013. The impact of this loss on the global economy was estimated at about $750 billion U.S. dollars. In this section, we review the food waste at various stages from production to post-harvest in relation to food hazards.

Production and pre-harvest challenges

In the United States, ~7% of crops remain unharvested each year due to inefficient market management and limited knowledge of market demands. Overproduction often leads to surplus yield, which leads to price reduction and makes harvesting economically unfeasible. Therefore, growers prefer not to harvest their crops, leading to increased in-field waste and losses2. In recent decades, climate change and natural disasters have been the main driving factors in increased food loss and waste. These factors can directly or indirectly affect food loss and waste. Direct impacts occur due to sudden temperature changes, gusty winds, hail, or severe rainfall at the end of the season, before or during harvest. These conditions may lead to early fruit drop or unsynchronized fruit maturing, which makes them unharvestable. They could also alter crop suitability due to disease and insect infestation, or damage crops through issues such as sunscald10. Besides directly decreasing yield quantity, climate change can indirectly contribute to food waste through the creation of visually defective fruits and vegetables, which drastically reduce their marketability10,11.

Crop waste is also affected by crop type and how it develops during the growing period. These factors can lead to waste before, during, or after harvest. Early-season crops, in particular, are more vulnerable to severe weather events, such as heavy rain, storms, or hail, which can increase the risk of pre-harvest losses. As an example, orchards with nine different varieties of almonds were surveyed over two growing seasons (2019 and 2020) and it was found that the majority of them had less than 5% pre-harvest fall (also called windfalls) with late cultivars like Carmel and Monterrey varieties having fruit drop rates exceeding 10% in some extremely late harvest orchards12. The same phenomenon of variations in fruit drop amongst table olives varieties was reported by13,14.

Pests and diseases contribute to waste during the post-harvest stage of specialty crops in California. Almonds, one of the main products of Northern California, face significant challenges from navel orangeworm (NOW), which is one of the most damaging pests. Late harvesting after hull splitting can increase damage to the kernels, especially in soft-shell varieties such as ‘Nonpreil’15. Damages from NOW can be as high as 30%. This is particularly concerning given that 40% of annual almond production comes from NOW-susceptible varieties. While ‘Nonpreil’ variety is popular among California growers for its quality, it is also susceptible to hull rot disease. This pathogen-based disease is responsible for up to 70% of damages to almond yield in Australia16,17. Investigations revealed that practices such as deficit nitrogen, irrigation practices, and insecticide application at the hull splitting stage can reduce the damages due to this disease in almonds18. Regardless of sensory grading factors for the almond kernels, selection of the hard-shell varieties with a sealed shell would be a better practice to reduce crop waste due to pest pressure and disease outbreaks19,20,21,22,23,24,25. Additionally, early harvesting after hull splitting can reduce the risk of damage from disease and pest by up to 74% in susceptible varieties in California18.

Harvest and post-harvest challenges

Harvesting fruits at the right maturity level is important to reduce fruit loss. Harvesting immature fruits leads to low-quality products, which reduces the marketability of the crop and eventually turns a potentially consumable product into waste. Late harvesting of crops may also result in low-quality products. This factor is crucial for any harvesting practices. Over-ripening of crops can dramatically increase the rate of windfalls and lead to more in-field food loss and waste26. Furthermore, it may cause quality degradation due to physiological changes, which make crops more vulnerable to mechanical damage during harvest and post-harvest operations and decrease their shelf life27. As mentioned in “Production and pre-harvest challenges”, variety selection plays a vital role in determining the appropriate harvest time. Factors such as changes in quality, shelf life, crop type, and market potential drive growers’ decisions. Some growers prefer to plant two different varieties in their orchard to better manage ripening times and logistics of the harvesting process, especially for crops that require hand harvesting.

Over the past decades, labor costs have dramatically increased in California, partly due to labor shortages and COVID-19 breakouts. In 2012, the California Farm Bureau Federation reported that labor costs sometimes exceeded 50% to 70% of gross return, while crop values have not increased proportionally. That is a reason why some growers prefer to leave crops in the field rather than harvesting them. It has also led to increased interest in mechanical harvesting, described next.

There are two types of harvesting methods for specialty crops, as shown in Fig. 2. The majority of the crops for the fresh market are hand-harvested. Although this method can reduce in-farm crop waste by selectively picking properly mature produce with minimum damage, the hand-harvest crew must be properly trained to identify high-quality produce, harvest gently, and handle it with care28. Mechanical harvesting is divided into three subcategories. Harvesting aids are devices such as ladders, poles, and tractor-mounted structures that help the picking crew reach different parts of the canopy and make the harvest operation easier. Mechanical machines like robotic harvesters, mass harvesters, or shakers, perform the harvest process fully or semi-autonomously29.

Fig. 2
Fig. 2The alternative text for this image may have been generated using AI.
Full size image

Harvesting techniques for California specialty crops.

Mechanical harvesters are commonly used for nut trees and olive oil trees. However, other fruit trees, like peaches, plums, and apricots, are still hand-harvested since mechanical harvesting could damage the fruits and affect their marketability. In some crops, like table olives, the transition from hand harvesting to mechanical harvesting has begun. This transition necessitates pruning the canopy to control its size and maintain proper clearance around the trunk. In mechanized harvesting, fruit damages were reported to be significantly higher than in manual harvesting. For example, the bruising and skin injuries increased by 11% and 20%, respectively, in the mechanical harvesting of table olives, with the internal fruit damage leading to rapid softening and decay14,30.

Regardless of the harvesting method, cleaning and sanitation of all equipment that comes into direct contact with the produce is a crucial practice. Contaminants such as crop disease, human-based pathogens, and pest larvae can spread through contaminated tools, machine parts, and human hands or gloves, which reduce produce’s shelf life and affect other marketability metrics. A comprehensive literature review by Leaman et al. explained the good practices for equipment sanitation during harvest and post-harvest stages31.

Some specialty crops like berries and stone fruits require more care during handling and post-harvest processes. For berries, it is necessary to pack them in clamshell containers in the field and store them in refrigerated facilities. Field packaging reduces the time and handling needed to transport the produce to cold storage, but it limits the ability to sort and grade the fruit, which is a drawback of this method32. For stone fruits and other commodities with a lower risk of damage to fresh crops, collected fruits can be transferred to central packaging houses in larger bins. Timely handling and packaging of fresh crops can reduce the chances of deterioration during distribution to the final user28. For example, a study found that the two main causes of damage in sweet cherries during post-harvest operations were the speed of the cluster cutter machine’s belt and the fruit’s falling height in the hydrocooler, contributing to 23.7% and 28.2% of damage33. Additionally, increasing the throughput rate (tons per hour) led to a higher rate of damage. To reduce fruit loss, changing the equipment’s design and operating speed were suggested33.

Food safety hazards

A significant portion of agricultural waste and loss arises from crops that are damaged or contaminated by microbial agents or their toxins. Farm sanitation, along with good agricultural and harvest practices, plays a crucial role in preventing the spread of contamination to food products. In other words, food safety and waste prevention both start at the farm level. The more that is invested in strategies to prevent contamination and crop damage, the safer the food supply becomes, the less food waste is produced, and the less financial burden it places on producers. This section will focus on four microbial contaminants (Salmonella, Escherichia coli (E. coli), Listeria, and Aspergillus species), provide some examples related to contamination and recalls of California specialty crops, and the management techniques aimed at controlling or preventing these contaminants to reduce the likelihood of waste production.

Pathogens present in the intestinal tracts of humans and warm-blooded animals can easily enter water and soil, leading to the contamination of agricultural crops34. The presence of the above-mentioned bacteria is closely associated with inadequate sanitation practices at various stages of farming, both at the farm level and during handling processes. Mold contamination (particularly by Aspergillus species) is also a serious concern. Poor sanitation and farm management practices can lead to Aspergillus contamination and the formation and accumulation of mycotoxins in agricultural products.

Listeria infection (known as listeriosis) is fatal in high-risk individuals such as young children, the elderly, and pregnant women. Listeria outbreaks occur annually, and in a recent fruit-related outbreak, the Centers for Disease Control and Prevention (CDC) reported that Listeria monocytogenes infected eleven people across seven states, with the highest numbers in California and Florida. One death was reported, and all cases were linked to contaminated plums, peaches, and nectarines—specialty crops from California35. Multiple brands that sourced peaches and plums from the contaminated farm recalled their products from markets across seven states. This resulted in significant financial losses for the companies, who also had to implement specific measures to dispose of the contaminated waste in compliance with the U.S. Food and Drug Administration (FDA) guidelines.

Salmonella is the leading cause of foodborne gastrointestinal infections each year. Salmonellosis (also known as stomach flu or gastroenteritis) can be particularly dangerous for infants and the elderly36. Salmonella is a serious concern in nuts (particularly almonds), vegetables (such as lettuce and cucumber), and summer crops (like cantaloupe). In 2023, a nationwide Salmonella outbreak across 44 states was linked to cantaloupes, resulting in 158 hospitalizations and 6 deaths37. During 2003–2004, an outbreak of Salmonella associated with raw almonds (sourced from California) was reported in 12 states of the U.S. and Canada, leading to the recall and disposal of approximately 13 million pounds of raw almonds38. The CDC linked the source of Salmonella contamination in fruits and nuts to farm workers and food vehicles37. The agricultural water, soil, and harvest equipment have also been identified as the on-farm sources of Salmonella and other pathogens contamination in fruits39.

Infection with Shiga toxin-producing E, coli (STEC) can result in a serious health condition known as hemolytic uremic syndrome (HUS), which can lead to kidney failure. Infection with STEC is particularly dangerous for high-risk individuals. The most recent outbreak related to nuts occurred in April 2024, involving bulk organic walnuts contaminated with E. coli. In this outbreak, 12 people in California and Washington were hospitalized, with two developing severe kidney complications known as HUS (CDC, 2024). The organic walnuts were recalled from markets across multiple states and were disposed of in compliance with FDA guidelines. According to a multi-agency investigation by the U.S. FDA, CDC, Canadian Food Inspection Agency (CFIA), and Public Health Agency of Canada, contaminated irrigation water40 and manure41,42 were identified as the primary sources of E. coli contamination on the farm.

Aflatoxins are among the most toxic secondary metabolites produced by Aspergillus and Penicillium species43,44,45, and aflatoxin contamination has a significant impact on crop marketability. Products with contamination levels exceeding regulatory limits for human consumption are typically repurposed as animal feed, discarded, or, in some cases, are sold at a lower price for alternative uses in less developed countries46. As a result, substantial volumes of products can become waste, and this will lead to the generation of hazardous agricultural waste. The economic losses associated with aflatoxin contamination in agriculture are significant and cannot be overlooked47,48. Furthermore, with the rising global temperatures due to climate change, the prevalence of aflatoxin contamination is likely to increase. This will make this issue increasingly urgent and in need of immediate attention. The agricultural water, soil, weeds, and harvest equipment have been identified as the on-farm sources of Aspergillus contamination in fruits39. In addition to the previously mentioned sources of contamination, NOW infestations contribute to the spread of Aspergillus spores in tree nut farms49,50,51.

It is important to note that when dealing with toxin- or pathogen-contaminated food or crops, standard waste disposal methods cannot be used. Such waste is classified as biological waste and must be managed using specialized waste management techniques. These methods are often costly, require specific expertise, and can sometimes have negative environmental impacts. The FDA has specific regulations for disposing of contaminated or spoiled food. These regulations ensure that processors and growers treat the contaminated food waste appropriately, whether it is disposed of in a landfill, incinerated, or rendered52. Figure 3 outlines ten key questions that must be addressed when disposing of contaminated food or agricultural products in compliance with FDA requirements.

Fig. 3
Fig. 3The alternative text for this image may have been generated using AI.
Full size image

Key considerations for disposing of contaminated food (Questions are based on FDA-2018 guidelines).

Integrated strategies for food waste reduction and sustainability

In this section, various strategies for the reduction of food waste and strategies towards more sustainable food production are discussed.

Good agricultural practices and good handling practices

Good agricultural practices (GAPs) and good handling practices (GHPs) are key tools that help reduce food and crop waste during pre-harvest and harvest by keeping products safe, healthy, and of high quality. The key steps for GAPs include using clean water for irrigation, rotating crops to maintain healthy soil, and managing pests in ways that are safer for both the crops and the environment. These practices prevent biological and chemical contamination while also minimizing physical damage to crops and ensuring they grow and ripen without issues that could lead to waste. Once crops are harvested, GHPs play a crucial role in reducing post-harvest losses. This involves proper cleaning, packaging, and storage at optimal temperatures, all of which help prevent spoilage and extend the shelf life of food products53. By adhering to GAPs and GHPs, producers significantly reduce the risk of food loss due to decay, spoilage, or contamination, which in turn enhances food security and promotes sustainability. Reducing waste also conserves valuable resources such as water, energy, and labor, while maximizing productivity. Moreover, these practices help mitigate greenhouse gas emissions from decomposing organic waste in landfills and contribute to environmental sustainability.

In a comprehensive study, Parfitt et al. analyzed food waste within the food supply chain and classified kitchen wastes into two groups: edible wastes and inedible wastes54. According to them, edible waste falls under the ‘avoidable,’ and ‘potentially avoidable’ categories while inedible items are considered ‘unavoidable’ waste. Building on their framework and incorporating GAPs and GHPs at the harvest and post-harvest stages, we have classified crop wastes into three categories presented in Fig. 4. “Avoidable” crop wastes include any edible crops discarded at the pre-harvest and harvesting stages due to physiological conditions (such as overripe or underripe fruits that are lost due to timing errors in harvesting), mechanical damage (such as bruised apples), or chemical contamination (caused by pesticide application without adhering to the pre-harvest interval). The pre-harvest interval is the minimum waiting period between the last pesticide application and when the crop is safe to be harvested. “Possibly avoidable” crop waste is any edible crop that is lost due to improper processing, storage, handling, or transportation. This type of waste is mostly related to biological contamination. Examples are strawberries contaminated with E. coli due to contaminated water or unsanitary handling practices, or nuts that become moldy due to inadequate drying or incorrect storage conditions (e.g., high temp & humidity). The majority of agricultural waste falls under avoidable or possibly avoidable categories, and both of these types of waste can be reduced through special practices and proper management systems (such as GAPs, GHPs, and hazard analysis critical control point (HACCP)) and introduced into the food chain. “Unavoidable” crop waste refers to all non-edible parts of crops (such as stems or pits) and unwanted edible parts (such as fruit peels) that are discarded either due to their nature or as a result of the processing.

Fig. 4: Classification of agricultural waste based on waste generation potential, using apples as a model.
Fig. 4: Classification of agricultural waste based on waste generation potential, using apples as a model.The alternative text for this image may have been generated using AI.
Full size image

A Avoidable waste: includes fallen apples in orchards and mechanically bruised apples, which could potentially be avoided through improved harvesting practices. B Possibly avoidable waste: involves insect-infested or microbially contaminated apples, where preventive measures or processing innovations may reduce losses. C Unavoidable waste: refers to inedible parts such as apple seeds and stems, which are natural by-products of apple consumption and processing. Arrow size is scaled proportionally to the amount of waste generated by each category.

From a food safety perspective, biological contaminants play a significant role in the generation of agricultural waste. Therefore, it is essential to minimize the risk of infection and infestation by biological contaminants at every stage of the food chain. Rangarajan et al. thoroughly explored the sources of on-farm contamination that contribute to overall waste and highlighted 11 key factors that lead to both spoilage and crop loss41. Figure 5 provides a schematic representation of the key on-farm contaminants that lead to crop spoilage and contribute to waste generation through the GAP and GHP lenses.

Fig. 5
Fig. 5The alternative text for this image may have been generated using AI.
Full size image

Key sources of on-farm contaminants contributing to crop spoilage and waste generation.

To minimize the risk of biological contamination and reduce waste production, GAPs and GHPs should be followed by farmers, producers, and packers to ensure the safety of their products. The Institute of Food and Agricultural Sciences (IFAS) at the University of Florida has published guidelines on GAPs for ensuring food safety on the farm7. This document emphasizes the role of the above-mentioned factors and recommends a checklist as a preliminary assessment tool for producers to ensure the safety of their products and reduce waste generation. Table 2 outlines the key potential risk factors that must be addressed under GAPs (based on IFAS guidelines).

Table 2 Key risk factors to consider for ensuring safety and reducing waste under good agricultural practices (GAPs)
Full size table

Hazard analysis critical control point

According to the FDA, HACCP is a systematic management approach designed to ensure food safety after harvest by (1) identifying, (2) analyzing, and (3) controlling hazards (biological, chemical, and physical) across the entire food production chain. This system begins with the raw material sources and extends through handling, manufacturing, distribution, and final product consumption55. By identifying and controlling potential hazards throughout these stages, the HACCP system contributes to waste reduction and promotes the shift toward a more sustainable production process. Through the implementation of HACCP, growers and producers can accurately identify critical control points (CCPs) where hazards are most likely to occur and implement preventive measures to reduce risks. CCPs are determined through a series of structured questions and responses, and specific control actions are applied at these points to prevent contamination56,57.

HACCP directly contributes to reducing waste in food and agricultural crops by minimizing post-harvest losses related to spoilage or contamination. Ensuring proper handling, storage, and transportation conditions through HACCP protocols prevents degradation of crops, leading to improved quality and shelf life and reducing food waste. Studies show that up to 40% of global food waste occurs at the post-harvest stage due to spoilage with pathogens, poor handling, and inadequate storage conditions, which can effectively be addressed through the implementation of the HACCP system58.

Circular economy

The agricultural sector is one of the most resource-intensive industries and, as mentioned earlier, is responsible for 70% of freshwater usage, 50% of all habitable land usage, and 25% of the world’s greenhouse gas emissions. Given the need to increase food production by 70% by 205059, it is clear that the current linear economy model (Make, Use, and Dispose) in agriculture must be replaced by a more sustainable circular economy model (Reduce, Reuse, and Recycle) (Fig. 6).

Fig. 6
Fig. 6The alternative text for this image may have been generated using AI.
Full size image

Circular economy model for agricultural crop production.

In the circular economy, resources are recovered rather than being provided from outside the system. This approach can reduce production costs and minimize or eliminate waste. The main concept behind the circular economy in agriculture is to find secondary uses for agricultural waste through valorization methods, such as waste-to-energy, which converts waste into bioenergy, as described in the next section. Detailed terminology, strategies, and methodologies are outlined in several review papers59,60,61.

Figure 7 illustrates some waste management strategies for specialty crops in California, developed within the framework of the circular economy concept. These strategies focus on minimizing crop waste, repurposing agricultural by-products, and enhancing sustainability through innovative recycling and reuse practices.

Fig. 7
Fig. 7The alternative text for this image may have been generated using AI.
Full size image

Circular economy-based waste management strategies for California specialty crops.

Innovative technologies and methods

In this section, we describe various recent technologies and methods that are developed to reduce waste and to achieve a more sustainable food production. These technologies include early defect detection methods, protective coatings, chemical and physical treatments, smart packaging, temperature management and waste recycling through waste valorization.

Early defect detection and sorting

Minimizing fruit loss during harvesting and processing is essential for maintaining quality and reducing economic waste. Advanced imaging technologies, such as Hyperspectral Imaging, VIS-IR Spectroscopy, Computer Vision, X-ray, and Terahertz Imaging, offer non-destructive and efficient defect detection and fruit sorting methods. During a sorting process, fruits are categorized based on measurable biophysical attributes (such as size, shape, weight, color, or density) to ensure uniformity and quality in the final product. Each of these technologies offers unique advantages, depending on whether they are applied in the field or at the processing plant.

Hyperspectral imaging

Hyperspectral imaging provides detailed spectral information across a wide range of wavelengths, enabling the detection of both surface and internal defects in fruits62. By capturing images across hundreds of narrow spectral bands, this technology can differentiate healthy fruits from defective ones based on subtle variations in reflectance. It is particularly effective for identifying bruises, ripeness levels, and even chemical compositions of fruits63. Hyperspectral imaging can be applied in both the field and processing plants, facilitating real-time quality assessment and sorting. Its capability to detect defects invisible to the naked eye, such as internal rot or chemical contamination, makes it invaluable for enhancing overall fruit quality64.

Visible and infrared spectroscopy

Visible and Infrared (VIS-IR) spectroscopy is a widely used technique for assessing fruit quality and detecting defects. It analyzes the reflectance or absorbance of light in the visible and infrared spectrum to measure crucial chemical characteristics such as moisture content, sugar levels, and acidity. These parameters are vital for determining ripeness and overall quality. In agricultural fields, VIS-IR spectroscopy aids in making informed harvesting decisions by early detection of qualitative factors such as percent sugar and acidity, and physiological defects like bruising and rot65. In processing plants, VIS-IR spectroscopy plays a significant role in quality control by predicting chemical constituents and identifying contamination. Despite challenges such as calibration requirements and data processing complexity, VIS-IR technology remains an effective, non-destructive method for fruit sorting and defect detection66.

Computer vision

Computer vision systems utilize advanced algorithms to automatically process and analyze fruit images, identifying surface defects such as discoloration, spots, and blemishes. Recent advances in machine learning have enabled faster techniques for object detection, making it easier to develop a machine vision system for defect detection. In field applications, UV and RGB cameras help detect ripe and healthy fruits, optimizing harvest timing. On production lines, computer vision can rapidly and accurately sort fruits based on visual features, ensuring defective fruits are removed before further processing. This technology not only reduces waste but also enhances product quality by minimizing the chances of defective fruits entering the supply chain. With its rapid image processing capabilities, computer vision is highly efficient for large-scale operations in the agricultural and food industries67.

X-ray umaging

X-ray imaging is extensively used in the food processing industry to detect internal defects that are otherwise invisible. By analyzing density differences within fruits, X-ray systems can identify foreign bodies such as stones, glass, or metals, as well as internal defects like cavities, bruising, or pest damage. This technology is particularly widely utilized in processing plants, ensuring that only high-quality fruits are processed and packaged for consumers. X-ray imaging provides real-time inspection without damaging the fruits, making it an essential tool for quality control68. In spite of its potential use in plant production, this technology is not widely utilized due to safety concerns for the operator. It is, however, expected that with the increase in new autonomous and cost-effective robotic platforms, this technology will be used at the production level as well.

Terahertz Imaging

Terahertz (THz) imaging is an emerging non-destructive technology that uses electromagnetic waves in the terahertz range to inspect the internal structure of fruits69,70. Its ability to penetrate non-conductive materials like fruit skins makes it especially useful for detecting internal defects, such as rot or insect damage71. THz imaging can also identify contaminants within fruit packages, both metallic and non-metallic, providing a high level of safety and quality control during fruit processing. Despite its advantages, such as sensitivity to moisture and high-resolution imaging, the current limitations of terahertz imaging include high equipment costs and slow data acquisition rates72.

Each of the above-mentioned technologies has unique characteristics, advantages, and disadvantages for different applications73. Depending on the need and applica tion, determining the quality of fruit may require one or more of these technologies.

Protective coatings

Fresh fruits deteriorate and lose quality due to spoilage, moisture loss, weight reduction, appearance changes, discoloration, tissue softening, or over-maturation. These processes are often the result of contamination or biochemical reactions, such as enzymatic activity or oxidative damage74. Such changes not only reduce the quality of the produce but also increase waste and decrease marketability. Coating agricultural products after harvest plays a crucial role in preserving their quality and extending shelf life. There are two main types of coatings for fresh fruits and vegetables: 1) non-edible coatings, which have been used for many years, and 2) edible coatings and waxes, which have become more prevalent in recent years.

Non-edible coatings, such as plastic-based films, are synthetic materials used to protect fruits and reduce spoilage. However, they present environmental concerns due to their non-biodegradable nature75. On the other hand, waxes can either be synthetically made or derived from natural sources. Natural waxes, such as insect-based products (e.g., beeswax and shellac) or plant-based alternatives (e.g., carnauba wax from palm trees and candelilla wax from Candelilla shrubs) are considered food additives and must meet food-grade standards to be safe for consumption. These waxes are evaluated by the Joint FAO/WHO Expert Committee on Food Additives to ensure compliance with food safety regulations28. During the waxing process, a thin layer of wax is applied to the product’s surface through methods such as manual rubbing, dippingm or submerging, or automated roller brush application76. Wax coatings are among the most widely used in the global market and are mainly used for citrus fruits, apples, and cucumbers. It has been shown that wax coatings account for about 80–90% of all fruit coating applications77. Apples, pears, plums, peaches, and citrus fruits are examples of California’s produce that are waxed to extend their shelf life and reduce their waste.

Edible coatings (made from polysaccharides, proteins, or lipids), are sustainable alternatives to plastic packaging, are used for a variety of fruits, and currently hold ~10% of the market share. This share is growing as consumers demand more natural products. During the coating process, a micro-layer of biopolymers is applied directly to the surface of fresh fruits or vegetables and forms a protective barrier. This layer prevents moisture loss, oxidation, and microbial growth75. The edible coating must be recognized as GRAS (Generally Recognized as Safe), provide protection against UV light, antimicrobial and antifungal, preserve healthy microorganisms, and transport water vapor and gases78 (Fig. 8). Various biopolymers, such as polysaccharides, proteins, and lipids, can be used for crop coatings (21 CFR175.3). Figure 9 illustrates the most common natural biopolymers used for this purpose. However, the main challenge with edible coatings lies in their limited thickness and low mechanical barrier properties74,75,76,78,79.

Fig. 8
Fig. 8The alternative text for this image may have been generated using AI.
Full size image

Key features of edible coatings.

Fig. 9
Fig. 9The alternative text for this image may have been generated using AI.
Full size image

Eco-friendly biopolymers for fresh produce coatings.

In addition to significantly extending the shelf life of produce, edible coatings reduce waste generation, lower packaging costs, and minimize the need for secondary packaging. They are biodegradable, environmentally friendly, and improve marketability by expanding market reach for agricultural crops and increasing profits80. These coatings also align with sustainability goals by lowering greenhouse gas emissions associated with food waste78,81. Studies have shown that coatings can retain the shiny appearance of tomatoes and green chilies after 10 days at room temperature and extend their shelf life by up to a month82,83. The application of coatings for protecting crops from deterioration and spoilage significantly reduces waste generation and contributes to sustainability.

Chemical and physical treatments

Physical and chemical treatments can be applied to crops at pre- and post-harvest stages to maintain the quality, extend shelf life, reduce waste generation, and ensure sustainability throughout the supply chain. These methods play a crucial role in combating losses in both quantity and quality, especially in perishable products such as fruits. In this section, we briefly discuss a few common physical treatments (such as heat treatments, ultraviolet (UV) radiation, and gamma radiation) and two significant chemical treatments (e.g., pesticides and fungicides).

Physical treatments are non-invasive, maintain product quality, and are environmentally friendly. Heat treatments (such as hot water or steam) are commonly used to control post-harvest pathogens (e.g., Salmonella in almonds) and pests (e.g., fruit flies in tomatoes)84,85,86,87. Gamma and UV irradiation also inactivate bacteria, molds, and yeasts on surfaces, preventing spoilage and extending the shelf life of perishable commodities like fruits and vegetables88,89,90,91. Since irradiation is a non-thermal process, it preserves the freshness, texture, and nutritional quality of agricultural products while extending their shelf life and reducing waste generation. The limitations of these methods include the high cost of the technology, consumer hesitation to consume irradiated food products, training requirements, and the lack of sufficient rules and regulations for irradiated products.

Simple chemical treatments, such as ethylene inhibitors, are applied to delay the processes of ripening and senescence. Consequently, these interventions mitigate post-harvest losses by reducing the likelihood of product degradation due to over-ripening92.

Pests and pathogens are serious food safety issues, and before the introduction of synthetic chemicals in 1940, all pest management strategies focused more on cultural practices93. In a comprehensive review, Tyagi et al. discussed all pre-harvest activities that influence the overall quality of fruits at the pre-harvest level94. It has been discussed that application of pesticides (synthetic and bio-pesticides), herbicides, and fungicides is essential to prevent infestations and disease at the pre-harvest stage and increase yield95,96,97 and fertilizers improve plant growth and ensure a healthier and more robust crop. An ideal pesticide or fungicide should be non-toxic, eco-friendly, and biodegradable. However, many current pesticides and fungicides are not specific to the target organism and kill beneficial ones that play a crucial role in maintaining ecosystem balance93.

To promote sustainable agriculture, the use of chemical treatments must be applied very cautiously and with careful consideration of their broader environmental impacts. Unfortunately, the excessive use of non-biodegradable chemicals (especially in developing countries) has resulted in significant pollution of soil, water, and air ecosystems. Numerous comprehensive reviews and studies have documented the entry of pesticides and fungicides into the food chain98,99,100,101 and several reports have linked both acute and chronic human diseases to pesticide exposure102,103,104,105,106. To move toward organic farming and promote sustainable agriculture, biological control methods are recommended as alternatives to synthetic pesticides and fungicides107,108,109,110,111,112.

At the post-harvest stage, fumigation and washing with chlorinated water are effective methods to reduce pest and pathogen loads, prevent contamination, and minimize waste generation. Various fumigants are used for this purpose, such as chlorine dioxide gas, hydrogen sulfide gas, ammonia, nitric oxide, and carbon dioxide. Numerous studies have reported the application of fumigation and chlorinated water washing -either alone or in combination with weak acids113,114,115,116,117,118,119,120. However, the widespread use of these methods faces limitations, primarily due to issues such as product discoloration and chemical residues. Additional concerns include worker health risks from exposure to fumigants or chlorinated water, potential corrosion of equipment, and environmental challenges related to releasing the gases into the air or disposal of wastewater containing chlorine and pathogens, which must comply with specific regulatory guidelines and rules121,122.

Green processing

This section focuses on non-chemical, residue-free methods for reducing agricultural waste in the food chain. These methods, known as green technologies, refer to innovations and practices designed to minimize environmental impact while promoting sustainability. The aim of these technologies is to reduce chemical usage, lower greenhouse gas emissions, and conserve natural ecosystems. In agriculture, adopting green technologies helps improve resource efficiency, reduce waste generation, lower carbon footprints, and ultimately create a sustainable food system that meets both current and future needs.

Green technologies such as cold plasma and ozone are mostly applied at the post-harvest stage to preserve food quality and extend shelf life. These methods effectively control microbial growth, delay ripening, reduce spoilage, and, as a result, decrease waste generation across the supply chain. Additionally, due to their non-thermal nature, these technologies maintain the nutritional and sensory qualities of agricultural products. Several comprehensive reviews have focused on the use of these technologies and their advantages and disadvantages123,124,125,126,127,128,129,130.

Ozone, a triatomic oxygen molecule, has a high oxidation/reduction potential of –2.07 V, which exceeds that of other common oxidants in the food industry, such as chlorine (–1.36 V) and hydrogen peroxide (–1.78 V). Ozone, in both its gaseous and aqueous forms, is a powerful oxidizing agent that destroys microorganisms without leaving harmful residues and reduces spoilage and waste generation. Here are some examples of green technology uses that can be applied to California’s specialty crops: ozone treatment has been shown to significantly reduce bacterial contamination, storage fungal rot, and extend the marketable life of apples131,132,133,134,135. Ozone gas reduces the volume and weight loss of fresh figs and prolongs their shelf life (doubling their typical shelf life)136, and controls bacterial contamination (E. coli and Bacillus cereus) in dried figs137. It also reduces fungal rot and waste generation in grapes138, lowers fungal spoilage in berries133,139,140,141,142, maintains freshness, lowers spoilage and extends the shelf life of plum and nectarine143, and reduces microbial load and extends the shelf life of citrus fruits144,145,146.

Cold plasma is produced by applying energy to a gas, which excites its molecules through the application of an electric field or electromagnetic waves. This process leads to gas ionization and the formation of reactive species. Due to generating reactive species (such as ions and radicals), cold plasma effectively inactivates pathogens and molds responsible for spoilage in fruits. Highly perishable fruits like berries are particularly vulnerable to microbial contamination and have a very short shelf life. Cold plasma has been shown to reduce microbial contamination, preserve the quality of strawberries over extended storage periods147,148,149, and lower spoilage rates in blueberries150,151,152. Cold plasma offers a non-thermal, chemical-free method for managing food waste, reducing losses from microbial decay, and contributing to sustainability goals in fruit production.

Smart packaging

Fruits and vegetables are highly perishable, necessitating appropriate internal packaging conditions such as temperature, gas composition, and humidity in order to maintain the quality and to preserve the shelf-life. Packaging systems aim to preserve the food for long-term storage, maintaining its freshness and structural integrity. They also serve as protective barriers against various physical, chemical, and biological hazards, allow traceability of the product while moving across the supply chain, and help ensure food safety and security153. For several decades, various packaging technologies such as modified atmosphere packaging, active packaging, and edible packaging have been widely used to enhance food preservation154,155. Recently, a novel concept known as smart packaging (described next) has emerged and received significant attention due to its potential to improve food safety and provide real-time monitoring of product conditions. We next describe this area briefly.

Currently, labels such as the “best before” and “sell by” or “use by” have become a norm in the food Industry. However, such labels fail to provide information on the state of food inside the package. Smart packaging systems involve the inclusion of electronic sensing devices to monitor conditions of packaged foods during storage and transportation, to ensure the safety of the food as it reaches the consumers, and to reduce food wastes56,156,157,158,159,160. These systems can be classified in several ways. One way that is summarized here is to classify them as: (I) data carriers; (II) indicators; (III) sensors.

I) Data carriers: They are used for traceability, automation, and theft or counterfeit protection by storing and transmitting information about storage, distribution, and other parameters. They are most frequently barcode labels and Radio Frequency Identification (RFID) tags. While RFID technology has been known for a long time, its penetration in the agriculture market has lagged behind barcodes, mainly due to cost reasons.

II) Indicators: They provide qualitative or semi-quantitative information about the existence of a compound, the extent of reaction between compounds, and the concentration of a compound or a class of compounds. They fall under three categories: (a) temperature indicators, (b) freshness indicators, (c) gas indicators.

II.a) Temperature indicators: They most commonly include simple temperature indicators and time-temperature integrators (TTIs). Temperature indicators inform the consumer whether a product has been exposed to an undesirable (critical) temperature for a sufficient time, which may signal potential physicochemical or biological reactions (e.g., irreversible textural deterioration upon defrosting of frozen products or freezing of fresh or chilled products, or growth of a pathogenic microorganism). In contrast, and given the importance of both temperature and time, time-temperature integrators monitor temperature over time. The basic operating principle ranges from diffusion-based (e.g., advance of a blue dyed ester diffusing along a wick), polymer-based (e.g., solid state polymerization reaction), and enzymatic-based (e.g., enzymatic hydrolysis of a lipid substrate), resulting in a visible response in the form of color development or color movement or mechanical deformation161. Time-temperature monitoring devices are proposed for both fresh and minimally processed fruits and vegetables162. An issue with widespread use of these indicators is how to correlate the response of specific TTIs to the quality characteristics of specific products.

II.b) Freshness indicators: Consumers often find it difficult to judge the ripeness or the freshness factor of products. To aid with this, ripeness indicators have been developed that change color by reacting with the volatile organic compounds emitted by the commodity, which enables the consumer to decide on the ripeness state. For example, methyl red-based packaging is developed to monitor the ripeness of strawberries. There is a rise in the pH due to the formation of esters during the ripening of strawberries, resulting in color change163.

II.c) Gas indicators: These indicators monitor the changes occurring inside the package due to microbial metabolism, enzymatic or chemical reactions on the food, and permeation through (or leakage in) the package. Most often, the information is displayed visually, e.g., a change in color. Since these indicators are placed inside the package, they must be non-toxic and non-water soluble. The most widely known gas indicators are used to check oxygen164,165 and carbon dioxide166,167 concentrations, given their critical roles in the degradation of many foods since they are needed for microorganisms to survive.

III) Sensors: A chemical sensor is a device that detects and measures the presence and concentration or quantity of a chemical analyte in a sample. In its simplest form, it consists of two functional units, a recognition (receptor) element and a transducer. The analyte of interest interacts and modifies the receptor. The modification is then converted by an appropriate transducer into an electrical, optical, mechanical, or acoustic output signal. Ideally the sensor must be sensitive to be able to measure often minute amounts of chemicals of interest; be selective towards the target species to avoid giving false positives; be stable so that it does not degrade through time; have fast response and recovery times; and be small and low cost. In the context of smart packaging for food products, they can be divided into (a) biosensors and (b) gas sensors.

III.a) Biosensors. The receptor element in these sensors is made of biological materials such as enzymes, antigens, hormones, or nucleic acids156,168. Depending on the measuring parameters, the transducer can be electrical, electrochemical, mechanical, optical, acoustic, etc. For example, a biosensor developed by Toxin Alert (Toxin Guard), based on antibodies integrated in plastic packaging, can detect pathogens such as Salmonella, E. coli, and Listeria. As another example, Flex Alert has developed a number of biosensors to detect E. coli O157, Listeria spp., Salmonella spp., and Aflatoxins.

III.b) Gas sensors. These sensors respond quantitatively and reversibly to gaseous analytes156,168,169,170. They include metal oxide semiconductor (MOS) or conductive polymer-based chemiresistors and field-effect transistors (MOSFETs), electrochemical (such as amperometric oxygen), quartz-crystal microbalance, and optical (such as non-dispersive IR CO2 sensors). The gas sensor technology has also evolved from a single device to an array of sensors known as an electronic nose (E-nose) to enhance the ability to differentiate between various gaseous species. In particular, because of the limited specificity of a sensor, an array of sensors utilizing different sensing materials (and hence different responses) is employed. The electrical signals from the sensors are then used to generate a pattern corresponding to the overall composition of the gas. A variety of E-nose approaches have been reported during crop production to signal infestation by insects by measuring the volatile organic compounds released by the damaged crop, e.g., tomatoes171. The E-nose technology is also used to classify the degree of ripeness of many fruits post-harvest, e.g., berries172,173, peaches174.

Of the smart packaging systems discussed above, the data carriers are widely used due to their low price and ease of use. In contrast, indicators and sensors are rarities on the market, due such factors as size, cost, temperature cross sensitivity (e.g., in electrochemical sensors), safety, and their disposal (most of the materials used are neither biodegradable nor easily recyclable).

Cooling and cold chain management

Cold chain and cooling are crucial factors in managing food loss and waste. Fresh and perishable fruits and vegetables must be kept at optimized temperatures during transportation. Controlling and monitoring temperature is very challenging during long transportation via air, sea, and land, as well as during post-harvest processing at processing sites and retail stores175. Due to inadequate access to refrigeration facilities, more than 20% of all perishable produce is wasted in the supply chain176. Temperature abuse or deviations from optimal temperature in the supply chain may lead to the over-ripening of produce or increase the growth rate of foodborne pathogens, which will contribute to food loss and waste177. In addition to ensuring the availability of cold chain systems, maintaining the integrity of the cold chain is equally important. Breaches in temperature control can occur during loading and unloading at various transit points, from farms to kitchens. Even temporary temperature breaches can result in a reduction in the quality and safety of food products178.

Agriculture waste valorization

Utilizing agricultural waste and by-products is one of the most efficient and eco-friendly approaches to preserving our current resources and protecting the environment. Agricultural wastes (Ag-wastes) are valuable forms of biomass and include any unused or unconsumed parts of fruits or vegetables, such as peels, pulps, husks, shells, stones, or seeds179. Crop wastes are rich sources of compounds with high nutritional value and can sometimes be used for pharmaceutical purposes180. Ag-wastes contribute to over 20% of the total crop waste generated181. To achieve sustainable agriculture, the primary focus must be on preserving crops and food through the implementation of GAPs, GHP, HACCP, the use of chemical, physical, and green technologies, along with reuse strategies. However, if these efforts fail, the final step is to extract valuable molecules from the Ag-waste and transform them into value-added products. This section highlights some of the valuable products derived from Ag-wastes, focusing particularly on California specialty crops.

Bioactive compounds

Bioactive compounds, such as phenolic compounds, can be extracted from plants, animals, or microorganisms. Those derived from edible plants are recognized as GRAS and are primarily used as supplements182. These bioactive molecules can interact with various components of living tissue and play significant roles in the body, including anti-cancer, anti-inflammatory, antioxidant, and antimicrobial activities. In a comprehensive review183 discussed various bioactive compounds extracted from food, highlighting their specific roles in the body, their bioavailability, and the challenges associated with their use.

Table 3 lists the potential bioactive compounds that can be extracted from some of California’s specialty crops. Despite the significant potential for extracting valuable bioactive compounds, the majority of agricultural waste or by-products are discarded. The food and agricultural industries must invest in technologies to utilize these wastes for the production of value-added products. This approach will not only benefit growers and producers but also reduce waste, protect the environment, and move us closer to achieving sustainable agriculture.

Table 3 Potential bioactive compounds from California’s specialty crops
Full size table

Bio-additives

Acids are among the most widely used ingredients in the food industry. They are utilized mainly in the beverage industry, bakery products, and as flavor enhancers in processed foods. The most common acids include acetic, citric, fumaric, lactic, malic, succinic, and tartaric acids. It is estimated that the global demand for these acids is increasing. For example, the global market for citric acid is expected to grow by more than 5.24% by 2025, reaching $3.6 billion184. The demand for lactic acid is projected to increase from 1220 kilotons in 2016 to 1960 kilotons in 2025185, and an annual growth rate of 20% is forecasted for succinic acid. In a comprehensive publication184, detailed all bio-additives extracted from food wastes, including methods of production, limitations, and future directions. Here, we focus only on the possibility of using California’s specialty crops’ agricultural wastes (e.g., pomegranate peels, grape, pear, peach, and apple pomace, and orange peels) for bio-additive production.

Pomegranate peels can be used for the production of citric acid over a period of eight days using Aspergillus niger, yielding 0.78 grams of citric acid per gram of pomegranate peel186. Fermentation of apple pomace with Rhizopus oryzae can produce fumaric acid with a yield of 52 grams per kilogram187. Apple pomace can also produce acetic acid with a production level of 52.4 g per 100 g of dry matter using Acetobacter pasteurianus188. Lactic acid can be produced from peach, pear, and apple wastes with a volumetric productivity of 1.32 g/L·h189, and from orange peels using Lactobacillus plantarum with a yield of 18.9%190. Grape and apple pomace are excellent substrates for malic acid production191. Apple, pear, and orange wastes fermented with Yarrowia lipolytica can produce succinic acid. Pure tartaric acid can be extracted from grape pomace through an alcohol extraction process192.

Fibers are widely used in the food industry. Bacterial cellulose is highly pure, has high mechanical strength, elevated water-holding capacity, and high crystallinity. Orange peels and citrus waste can be utilized for the production of bacterial cellulose through a fermentation process using Gluconacetobacter or Komagataeibacter species193,194, and pectin can be extracted from apple peels195 and citrus peels196,197.

Polyhydroxyalkanoates (PHAs) are high-value biodegradable polyesters used for food packaging and have been approved by the FDA as food-contact materials. Among California’s specialty crop wastes, grape pomace and apple pulp wastes can be used for the production of PHAs, with yields of 49% and 63% of cell dry weight, respectively198,199.

As evidenced by the cited research above, California’s agricultural waste serves as a valuable source of bio-ingredients. Utilizing this wastes for the production of bio-additives not only reduces the agricultural waste generated within the state, but also significantly boosts the state’s economy, provides high-quality and environmentally friendly ingredients, and promotes sustainability.

Bioenergy

Due to the U.S. government initiatives aimed at reducing fossil fuel dependency as well as implementing environmental protection policies, biofuel production has significantly increased since the 1980s. Over the past 15 years, the Federal Renewable Fuel Standard (RFS) program has substantially contributed to the rise in biofuel production and consumption122. Additionally, California has implemented the low-carbon fuel standard to lower the carbon intensity of its transportation fuels and promote the use of low-carbon and renewable alternatives to improve air quality200. These alternative energy sources, collectively referred to as biofuels or bioenergy, play a crucial role in these initiatives.

As a result of these regulations, over 18.7 billion gallons of biofuels were produced in 2022, and ~17.6 billion gallons were consumed201. The USDA defines biofuel/bioenergy as a renewable energy source derived from biological materials, or biomass, such as plant and organic waste. Biofuels can be utilized for heating, electricity generation, or as transportation fuels. The four major biofuel types that qualify for the federal RFS program are ethanol, biodiesel, renewable diesel, and other biofuels (such as renewable heating oil and jet fuels). In 2022, ethanol accounted for the largest share of U.S. biofuel production, comprising about 82% of production and 75% of consumption. Biodiesel ranked second with both production and consumption rates at 9%201.

Extensive research and reviews have been conducted on generation of bioenergy/biofuels from food and Ag-waste202,203,204,205,206. In this paper, we briefly describe California’s specialty crop wastes with potential for bioethanol and biodiesel production.

The following wastes are great substrates for the production of bioethanol: orange peels207, mandarin peels208,209,210, other citrus peels104,196,211,212,213 apple pomace214,215,216,217,218,219 olive pomace & mill waste220,221,222,223, berries224,225,226 and pomegranate peels227,228,229,230. Biodiesel can be generated from citrus peel231,232,233,234 and olive pomace235,236,237.

As demonstrated above, Ag-waste generated in California has significant potential for the production of bioethanol and biodiesel. Considering California’s status as one of the primary agricultural hubs in the U.S. and its large fruit production, utilizing the state’s agricultural waste for biofuel production can greatly contribute to advancing green and sustainable agriculture.

Biofertilizers

Due to the recent rise in the price and use of fertilizers, there is growing demand for employing Circular Economy in agriculture to utilize agricultural waste toward biobased fertilizers and pesticides. In addition to these factors, recent global challenges, such as greenhouse gas emissions, wars, and pandemic outbreaks (which directly or indirectly affect the supply chain of raw materials, including natural gas and potassium salts used in chemical fertilizer production) highlight the importance of valorizing agricultural waste. Recovering these valuable materials can improve soil nutritional value, reduce environmental impacts, and decrease the production and side effects of chemical fertilizers206,238.

More than 50% of edible and non-edible parts of fruits and vegetables are wasted in the field, processing plants, and retail sectors174. In addition to all food waste sources mentioned in the previous sections, the following California’s specialty crop waste can be used as a source for biofertilizer production: olive and fruit pomace after oil or juice extraction, stone fruits post-harvest processing residues, pistachio soft hull and hard shell, and almond shell and hull239,240,241. Methods of processing biofertilizer production based on the type of waste are summarized in Table 4.

Table 4 Biofertilizer production from waste and by-products of California specialty crops
Full size table

Conclusions and future directions

According to the reports of the Environmental Protection Agency, about 30 to 40% of the edible food supply is wasted every year in the U.S. The USDA’s domestic goal and UN SDG 12242 have set the goal to halve the current food loss and waste by 2030 through responsible production and consumption strategies. In this review, we have discussed the factors and challenges that contribute to the generation of food waste at various stages from farm to fork. A significant portion of the paper is devoted to current methods and potential opportunities to reduce and recycle food waste.

Ideally, our efforts should be aimed at reducing waste and loss through the use of food as food. Based on circular economy principles, the first step in reducing waste and loss should focus on utilizing new methods of harvesting specialty crops, e.g., by using the robotic harvesting system to reduce labor costs and fruit loss. Additionally, employing modern post-harvest methods, equipment, and periodic services helps reduce waste and loss caused by mechanical damage. From a food safety and hazard control perspective, there is a growing need for more robust and integrated technologies to prevent contamination and extend the shelf life of agricultural products. One of the recent and most effective ways to reduce both waste and environmental impact is through the use of biological control methods as alternatives to chemical pesticides and fungicides. Training and education also play a critical role in waste reduction. These include the agricultural workers who must gain the skills necessary to reduce crop waste and prevent contamination and damage during production, harvest, and handling. Consumer education is equally important, in that they should be informed about proper food storage techniques, food safety practices, and efforts should be made to increase their acceptance of imperfect produce.

Advances in sensor technologies can provide critical information about the state of the food at various stages of production and processing, providing opportunities to minimize waste. Edible coatings represent a sustainable method and an effective way to extend the shelf life of produce while reducing spoilage. However, the primary challenge with this method is improving the mechanical properties of these coatings to provide better protection against environmental factors. Research in this field should focus on enhancing the use of biodegradable and food-grade materials in coatings. Even with the implementation of loss and waste prevention strategies, some crops will still be unsuitable for human consumption and need to be recycled before they end up in landfills. At this stage, techniques such as using crops as animal feed, biofertilizers, bioactive compounds, and bioenergy can help reduce the current status of crop waste and loss. These strategies collectively support the transition from the current linear economy model (Make, Use, Dispose) in agriculture to a more sustainable circular economy model (Reduce, Reuse, Recycle).