Citrus flavor, components

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). 

In this chapter, we present some specific evidence on certain components important to citrus flavor. The interrelationship of certain volatile components to orange flavor is described and the flavor of grapefruit and the importance of specific compounds to the flavor of mandarin and tangerine are related to recent taste panel studies at our laboratory. 

SHAW and Wilson Volatile Components and Citrus Flavor... 

The flavor of most citrus cultivars is complex, and compounding citrus flavors requires the blending of several components in specific proportions to obtain the unique flavor of each citrus cultivar (3). Studies on Sicilian mandarin oil suggest the distinct flavor and aroma of mandarins is mainly due to 2 compounds, thymol and methyl-N-methyl anthranilate (dimethyl anthranilate) but no evidence to support this claim has been presented (42). Thymol has been identified in Dancy tangerine peel oil, and both thymol and dimethyl anthranilate have been identified in Sicilian mandarin oil (3). The reported quantities of thymol in mandarin oil varied from 0.04-0.2% of the oil, whereas only one value (0.9%) was reported for dimethyl anthranilate. 

One pragmatic approach to the problem is the flavorese concept (i). A crude enzyme preparation from the fresh food or a closely related species is added to the processed food in the hope that the nonvolatile flavor precursors are still present and will yield the full range of fresh flavor components upon enzymatic treatment. This approach has been applied with some success to watercress (1,2), cabbage 1,2, 3, 4), horseradish 2, 3), onions 2, 3), carrots 2, 3, 5), peas, beans 2,3,6), citrus juice (2, 7), raspberries (8), tomato juice (2, 3, 9), bananas (JO), and various flower fragrances 11). This would seem to be a desirable approach since the products of different enzymatic reactions are probably necessary for full flavor. However the flavor-forming activity of the enzyme preparations was variable (5, 6, 7, 9), and the flavors were not always like that of the fresh vegetable (3). The several enzymes and flavor precursors may not have been present in the normal ratios. Also, to be practical, the enzyme preparation must be inexpensive to prepare and store, the substrates must persist in the processed food, and they must be available to enzyme action. One also wonders how processed foods can be enzymatically treated under sterile conditions. 

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). 

Flavor components such as apple, citrus fruits, and plums, and spices such as allspice, cinnamon, garlic, or ginger, and herbs such as peppermint and basil, included into CyDs are available on the market and have a good reputation for the high stability they exhibit when they are heated during industrial food processing. 

Fukumoto, S., Sawasaki, E., Okuyama, S., Miyake, Y and Yokogoshi. H. 2003. Flavor components of mono-terpenes in citrus essential oils enhance the release of monoamines from rat brain slices. Neuroscience 9(l-2) 73-80. 

Citral is well-known as the most characteristic component of lemon flavor. The value of citrus drinks containing lemon flavor is dependent on the stability of citral (/). However, citral is deteriorated through acid-catalyzed or oxidation mechanisms (2-7). The potent off-flavor components formed from citral under acidic and heated conditions have been clarified by aroma extract dilution analysis (AEDA) (8). In recent years, longer storage times and displays using transparent containers under fluorescent lamps in stores have significantly increased and citral is easily deteriorated by UV light from fluorescent lamps. 

Aliphatic aldehydes having 8 to 10 carbon atoms, particularly decanal, belong to the odoriferous principle of citrus oils, although they are present only at low concentrations (190). Besides aldehyde (19), (Z)-4-decenal (31) was identified in cooked chicken (212). In the C-10 series the two 2,4-decadienals (33) and (34) are important as flavor components and have been found in a wide variety of foods (389), to... 

These are made by adding bromine to the unsaturated fatty acid component of the vegetable oil. The major use of bromi-nated vegetable oils is the production of stable flavor emulsions for use in citrus-flavored soft drinks. They are considered a food additive, and the Food and Drug Administration (FDA) allows citrus and other fruit-flavored beverages to contain only 15 parts per million (ppm). 

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). 

Faulhaber et al. [30,31] analyzed mandarin essential oils by measuring 8 C ratios of characteristic flavor compounds of this product. Mandarin oils, which are obtained by cold-pressing the peel of the fruits of Citrus reticulata Blanco, are used in the food industry and in perfume compositions. The main constituents of mandarin essential oil are limonene (approximately 69%) and y-terpinene (ap proximately 20%), even though the fragrance of this oil is mostly determined by minor components such as methyl A-methylanthranilate (approximately 0.4%) and a-sinensal (approximately 0.3%). Evaluation of genuineness of this product is of special interest, since synthetic analogs of the essential oil components are commercially available. In this context, measurements of 8 C and 8 N of methyl -methylanthranilate [30] and of 5 C of characteristic flavor components in this oil proved helpful in the authenticity assessment of cold-pressed mandarin oil [31]. The characteristic profile of mandarin essential oil so established could be applied to the authenticity control of commercially available mandarin oils. 

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]. 

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