Orange juice is a popular beverage worldwide, with production growing annually as consumers look to healthier breakfast alternatives. However, producers face a specific difficulty that directly affects flavor: the formation of delayed bitterness.

Researchers at Huazhong Agricultural University’s College of Food Science and Technology are investigating this process to reduce its effects on juice flavor.

Delayed bitterness is caused by limonin, a bitter, white, crystalline substance found in citrus and other plants. At a concentration of 6 ppm or above, limonin will cause an unacceptable level of bitterness in the juice.

During processing, limonoate A-ring lactone (LARL, non-bitter), a precursor substance of limonin in citrus, is released into the acidic juice medium, where it is lactonized to limonin.

Huazhong scientists analyzed the distribution of limonin in sweet oranges. Then, they evaluated the effects of heat treatment, storage temperature, clarification, homogenization, and acidity adjustment on limonin content in sweet orange juice.

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The study showed that heat treatment and the addition of an enzyme called pectinase may exacerbate the release of LARL from cells and conversion to limonin, which can increase the delayed bitterness of citrus juice. 

However, refrigeration at 39°F appeared to slow down the conversion of LARL to limonin, thus, preserving the desired sweetness.

Citrus juice is rich in bioactive components such as vitamins, carotenoids, organic acids, minerals, flavonoids, and limonoids, which have high nutritional value and support the immune system.

Global production is expected to increase to 1.5 million tons in 2023-24, according to the 2024 USDA Foreign Agricultural Service Statistical report.