Debittering Techniques for Citrus Juice Processing

Bitterness in citrus juices arises primarily from flavonoid glycosides such as naringin and limonoid aglycones such as limonin. These compounds confer astringency and off-flavours that can limit consumer acceptance and the commercial value of juice products. Debittering strategies fall into three broad categories: physical removal, biochemical conversion and integrated approaches. Physical methods include adsorption on activated carbons or functionalised supports and membrane filtration to selectively remove bitter molecules while retaining desirable nutrients. Biochemical techniques exploit naringinase and related enzymes to hydrolyse glycosidic bonds, transforming bitter glycosides into non-bitter monomers. Microbial fermentation and ultrasound-assisted processes can accelerate enzymatic activity and improve mass transfer. Recent advances have focused on immobilised biocatalysts for reuse and on hybrid processes combining adsorption and hydrolysis to achieve simultaneous removal of multiple bitter components. These innovations aim to balance efficient bitterness reduction with the preservation of antioxidants, vitamins and volatile aroma compounds, meeting industry demands for high-quality, health-promoting citrus beverages.

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Technical terms

Naringin: A bitter flavonoid glycoside abundant in grapefruit and related citrus, responsible for immediate astringency.

Limonin: A non-volatile limonoid aglycone imparting persistent bitterness in citrus juices.

Naringinase: An enzyme complex (β-glucosidase/α-rhamnosidase) that hydrolyses naringin into non-bitter prunin and naringenin.

Immobilisation: The attachment of enzymes to solid supports to enhance stability and enable repeated use.

Adsorption: The removal of target molecules from solution by binding to a solid surface, often driven by hydrophobic or ionic interactions.

Ultrasonication: The application of high-frequency sound waves to intensify mixing, enhance mass transfer and accelerate biochemical reactions.

Nanofibrous membrane: A filtration medium composed of nanoscale fibres offering high surface area and selective permeation of molecules by size or affinity.

References

1. Grapefruit Debittering by Simultaneous Naringin Hydrolysis and Limonin Adsorption Using Naringinase Immobilized in Agarose Supports. Molecules (2022).
2. A Comparative Study on the Debittering of Kinnow (Citrus reticulate L.) Peels: Microbial, Chemical, and Ultrasound-Assisted Microbial Treatment. Fermentation (2022).
3. Debittering of Grape Juice by Electrospun Nylon Nanofibrous Membranes: Impact of Filtration on Physicochemical, Functional, and Sensory Properties. Polymers (2022).