Flavor undesirable citrus

Various chemical processes of limonene, which lead to the obtainment of useful chemicals and some analytical methods, are based on these reactions. Many flavor chemicals are synthesized from limonene by reaction with water, sulfur and halogens, or hydrolysis, hydrogenation, boration, oxidation and epoxide formation (Thomas and Bessiere, 1989). Hydroperoxides have also been studied and isolated because of their effect on off-flavor development in products containing citrus oil flavoring agents (Clark et al., 1981 Schieberle et al., 1987). Hydration of d-limonene produces alpha-terpineol, a compound that gives off an undesirable aroma in citrus-flavored products. It is also possible to produce alpha-terpineol and other useful value-added compounds... 

Bitterness is a generally undesirable flavor component and is usually detrimental to the quality of citrus products. Any bitterness in orange or tangerine products reduces their quality, whereas, a little bitterness is actually desirable for grapefruit products. However, it has been shown (35) that as the concentration of bitter materials increase, flavor scores and overall product acceptability decrease. Thus, excessive bitterness is usually considered objectionable and the Florida Department of Citrus has enacted regulations which limit the amount of naringin which may be present during the early weeks of the season (36). 

Excessive pressure used in hand-reaming of citrus fruit can also result in juice containing high peel oil content and perhaps significant amounts of undesirable flavor constituents (primarily of a bitter nature) as well. Since high peel oil and undesirable flavor constituents would seriously affect sensory evaluation results in a negative way, care should be taken in hand-reaming citrus fruit to apply only as much pressure as necessary to extract most but not all of the juice. In this way the amounts of peel oil and undesirable flavor factors will be held to normal levels. 

Limonin and naringen, which can give citrus juices an undesirable bitter flavor, can be removed selectively by passing juice through a crosslinked polymer of (3-cyclodextrin.87,88 Only the bitter components are removed. The polymer can be regenerated for reuse by washing the polymer with a 1-2% solution of sodium hydroxide. 

Essential Oils Essential oils are produced by distillation of flowers, leaves, stems, wood, herbs, roots, etc. Distillations can be done directly or with steam. The technique used depends mostly on the desired constituents of the starting material. Particular care must be taken in such operations so that undesired odors are not introduced as a result of pyrolytic reactions. This is a unique aspect of distillation processing in the flavor and fragrance industry. In some cases, essential oils are obtained by direct expression of certain fruits, particular of the citrus family. These materials may be used as such or as distillation fractions from them (see Chapter 9). 

Although terpene hydrocarbons, especially monoterpenes, are the most abundant constituents of citrus peels oil, they serve only as a flavor carrier and contribute little to flavor on their own (23). These terpenoid hydrocarbons are usually removed by deterpenation in order to increase the concentration of flavor and fragrance compounds. Furthermore, unsaturated hydrocarbons (terpenes) are unstable to heat and light, and may oxidize rapidly to produce undesirable off-flavor compounds that adversely affect the desirable aroma of products (24). Therefore, concentrated and deterpenated oils have become popular in the citrus oil market. 

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