Juices citrus, flavor

Demole, E., Enggist, P., and Ohloff, G. 1982. 1 -p-Menthene-8-thiol A powerful flavor impact constituent of grapefruit juice (Citrus paraadisi Macfayden). Helv. Chim. Acta 65 1785-1794. 

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). 

We have applied a modified odor unit equation for evaluating aroma quality of the volatiles of Citrus sinensis OSBECK, ev. Shiroyanagi. Although the concept of odor units in flavor research was proposed by Rothe et al. (9) as a objective index of aroma quality, the concentration of individual components in a food (Fc in equation [1]) depends on the extraction efficiency of the essential oils. If the test sample is a solid, we can not calculate the exact concentration. Because the aroma oils, for example, may exist in different cells in the peels of citrus, we cannot take out only specified cells. It does not give a homogeneous concentration. Therefore, the odor units of individual aroma components in a food do not always give a constant value. Equation [1] should be applied to beverages such as apple juice, citrus juice, coffee, milk and so forth. The modified odor unit equation (75) for liquid and solid samples is shown as follows ... 

Beyond the health benefits, we were motivated to investigate the role of PMFs on the citrus flavor profile. Although citrus flavor is usually associated with the more volatile terpenes, esters and aldeh des, it is well known that citrus flavors based upon volatile fractions can not entirely reproduce the flavor profile of citrus juices. We were interested to determine the role that PMFs played in the citms flavor profile. 

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). 

Important to any measurement of citrus juice volatile flavor components is the presence of (i-limonene, since this compound is naturally present as the most concentrated component in all of the natural citrus oils. Also, the solubility of d-limonene in aqueous media must be considered, since after liquid phase saturation, the headspace concentration remains constant. It has long been established for d-limonene and similar nonpolar flavor compounds over water that meaningful headspace measurement techniques [e.g., solid-phase microextraction (SPME)] require equilibrium of the vapor and liquid phase concentrations. Equilibrium may take a number of hours for static (unstirred) experiments and less than 1 hr for stirred systems. These conditions have been discussed elsewhere, and solubility and activity coefficients of d-limonene in water and sucrose solutions have been determined [1,2]. More recently, the chemical and physical properties as well as citrus industry applications of d-limonene and other citrus essential oils have been compiled [3]. Although not specific to d-limonene, important relationships affecting behavior of flavor release and partitioning between the headspace and the liquid phase of a number of food systems have also been discussed [4]. 

Other methods to inactivate or inhibit PE have been identified, but violate standards of identity for 100% citrus juice (1,6), are highly variable (1), and change flavor (2). 

Grapefruit, typically, has harsher flavor notes. Similar to other citrus oils, grapefruit oil is predominately composed of terpenes. There have been 206 volatile compounds identified in grapefruit juice. However, the flavor impact compounds are more dominant. Nootkatone and l-p-methene-8-thiol are the major compo-... 

Juice Cloud. Mechanical extraction of citrus fruits yields a turbid suspension of wall fragments and cellular organelles in a serum composed primarily of cell vacuolar fluids. In most citrus juice products, such a suspension of fragments and organelles is a desirable component, since it provides most of the characteristic color and flavor (28). Essence and peel oils suspended in juice contribute desirable citrus notes to flavor, and these oils are rapidly adsorbed by juice particulate material shortly after extraction (29). 

Limonene, a terpene hydrocarbon, is the major component of orange oil (3), and it is present in orange juice at a level almost 800 times its taste threshold in water. Limonene possesses a weak, citrus-like aroma but does not by itself impart an orangelike flavor note to a bland orange juice base (5 6). Limonene and the other terpene hydrocarbons probably make a significant... 

The sugars, which contribute much to the acceptability of citrus juices, under adverse conditions can play a major role in the formation of off flavors that reduce the acceptability of the citrus juices and their products. The sugars, primarily the hexoses, can participate in "browning" reactions that cause darkening of the juice and these reactions give rise to components that are described generally as apricot-like or pineapple-like in flavor. In general,the more processed flavor that a citrus product exhibits, the less acceptable it becomes to the consumer. 

Flavor changes that occur in citrus juices are the result of heat input into the product over time i.e., they are a function of temperature and time. It is for this reason that canned and bottled juices are generally less preferred by consumers than other processed citrus juices, e.g., frozen concentrates or chilled juices. The canned juices receive more heat input during pasteurization and they remain at relatively high temperatures for extended periods of time because they are discharged from the water coolers at temperatures near 40°C to facilitate drying and to inhibit rusting of the cans. It is well known that the rate of flavor deterioration increases with temperature, so canned juices are stored at a temperature as low as is economically practical before distribution at the retail level to extend their shelf life as much as possible. 

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