Thermal Processing of Low-Moisture Foods

Low-moisture foods, defined by reduced water activity, encompass products such as nuts, spices, flours and powdered ingredients. Thermal processing of these matrices is employed primarily to inactivate pathogens and spoilage organisms, enhance shelf life and ensure consumer safety without compromising sensory qualities. Unlike high-moisture systems, heat transfer in low-moisture foods is affected by the matrix’s thermal conductivity and limited water content, which often confers increased microbial heat resistance. Uniform heating, precise control of time–temperature profiles and validation of microbial inactivation are therefore critical. Innovations in process design—from controlled heating ramps to batch and continuous equipment modifications—have sought to balance microbial lethality with maintenance of nutritional and organoleptic attributes. Globally, effective thermal interventions underpin safety standards for products that may be stored for months or years under ambient conditions, thereby reducing the burden of food-borne outbreaks associated with low-moisture commodities.

Research from Nature Portfolio

A recently described heating block system enables precise regulation of heating rates in liquid, semi-solid and solid foods. By achieving controlled ramps of 1, 5 and 10 °C per minute in representative matrices (such as almond powder and mashed potato), this platform delivers uniform thermal profiles and accurate central temperatures. Experimental and simulated data confirm that variations in heating rate significantly influence bacterial thermal resistance, offering a robust tool for rapid and reproducible assessment of microbial inactivation kinetics. Such insights facilitate optimisation of industrial time–temperature regimens and support the development of predictive models for process validation in low-moisture food manufacturing.

Thermal Processing of Low-Moisture Foods publication trend

The graph below shows the total number of articles in thermal processing of low-moisture foods across all publications each year (not limited to Nature Index journals).

Technical terms

Low-moisture food: A product whose water activity is sufficiently low to limit microbial growth and enzymatic reactions.

Water activity (aw): The ratio of vapour pressure of water in a food to that of pure water, indicating free water availability.

D-value: The time required at a specified temperature to achieve a one-logarithm (90 %) reduction in microbial population.

δ-value: The scale parameter in the Weibull model representing the time required to reduce the surviving population by a given fraction.

Heating rate: The speed at which a food sample’s temperature increases, usually expressed in °C per minute.

Thermal death kinetics: The study of the rate and extent of microbial inactivation as a function of temperature and time.

References

1. Performance of a Heating Block System Designed for Studying the Heat Resistance of Bacteria in Foods. Scientific Reports (2016).
2. Practice and Progress: Updates on Outbreaks, Advances in Research, and Processing Technologies for Low-moisture Food Safety. Journal of Food Protection (2022).
3. Salmonella and Enterohemorrhagic Escherichia coli Serogroups O45, O121, O145 in Wheat Flour: Effects of Long-Term Storage and Thermal Treatments. Frontiers in Microbiology (2019).
4. Hot water treatment as a kill-step to inactivate Escherichia coli O157:H7, Salmonella enterica, Listeria monocytogenes and Enterococcus faecium on in-shell pecans. LWT (2018).