Enemies of Citrus Fruit Juice: Formation Mechanism and State-of-the-Art Removal Techniques

Citrus fruits are among those commercially grown crops whose importance for immunoregulation has amplified recently in the post-COVID era. Unfortunately, bitterness and off-flavor development in citrus fruit juices is a key concern. Bitterness is predominantly caused by naringin and limonin, while nomilin, hesperidin, etc. are known to be the minor contributors. Although the paper describes the biological properties of these bittering compounds and their potential application, the presence of the same in juices is often not desired. Similarly, the presence of undesirable odors in stored juices is caused by compounds such as guaiacol, ethanol, acetaldehyde, 2-methyl-3-furanthiol, methional, terpinen-4-ol, and dimethyl trisulfide. This review primarily examines the bitter and undesirable flavor compounds found in citrus fruit juices that is created during the process of production and storage. It also explores the specific processes by which these compounds are formed. A range of debittering techniques has been proposed, that involves the addition of sugar, lye, β-cyclodextrin, hot water, adsorption using cellulose acetate and activated carbon, pre-treating the juice with sonication, supercritical fluid, enzymes, and microbial consortia. Similarly, strategies for averting the formation of off-flavor-related compounds can include treating the juice with electrical current, high pressure, microwave, ultrasound, and chemical inhibitors. This review is anticipated to guide the Citrus juice manufacturers in choosing one or more (amalgamated) technologies for achieving extended shelf-life.