Orange juice ketones

Table 6.4 Orange juice ketones with aroma activity... 

Methylcyclopentenolone has a strong caramel-like, maple-like or licorice-like aroma (31j, and was found in browned, dehydrated orange juice at the 1 ppm level (43). Its synergistic flavor effect with other compounds, such as 5-methyl-2-furfural and N-ethylpyrrole- 2-carboxyaldehyde, was reported (43). Although it is present at levels five times below its threshold value, it still impacts on the heat-abused flavor of dehydrated orange juice. This ketone probably results from amine-assisted sugar degradation (45). 

The essence of citrus flavor is a complex mixture of volatile alcohols, aldehydes, esters, hydrocarbons, ketones and oxides. Alcohols are the largest class and ethanol is the main organic constituent of the essence. Esters and aldehydes are considered to contribute most to the characteristic flavor and aroma. In these two classes ethyl butyrate and acetaldehyde were shown to be important components of high quality orange juice (1). 

Ingram and Vas (1950a) studied this reaction with several compounds other than glucose which might be present in orange juice. These included other sugars, other aldehydic and ketonic compounds, and pectin. It was... 

Distillation of citrus juices yields two volatile fractions, namely, aqueous essences and essence oils that are separated from each other by condensation of the distillate (7). Aqueous essence, the bottom layer of the condensate is comprised of organic acids, alcohols, aldehydes, esters, hydrocarbons, ketones, hydrogen suthde, and oxides (10). Considering many components found in both cold-pressed peel oil and aqueous essence, essence oil has a flavor similar to that of flie combined peel oil and aqueous essence (10). However, essence oil usually contains a larger amount of aUphatic ethyl esters (e.g., ethyl butyrate in orange essence oil) compared with the peel oil (41). Thus, its aroma resembles that of the corresponding juice more than that of the peel oil (7). In general, citrus flavor results from a complex mixture of components in the appropriate proportions (42). 

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