SYMPOSIUM ON MEAT FLAVOR OFF-FLAVORS IN MEAT AND FISH - A Review G. A. REINECCIUS ABSTRACT Current literature on the off-flavors in meats due to genetics (mut- ton odor and swine sex odor), the animal’s diet and environment, processing (irradiation and retorting), bacterial spoilage and oxida- tion are reviewed. Emphasis is placed on discussing chemical mecha- nisms, compounds responsible for and means of inhibiting these off-flavors. INTRODUCTION FLAVOR is one of the most important palatability charac- teristics of foods. While food must look good enough to be tasted, flavor primarily determines whether the meal will be a pleasant experience. The importance of flavor must also be considered in nutrition. Food which is not palatable due to off-flavors and therefore not consumed, certainly has no nutritional value: Foods can be made to look very appeal- ing, nutritious and have a suitable texture but still not be consumed if they have an off-flavor. In this symposium, my task was to review some of the more common sources of off-flavors in meats. Therefore, an attempt was made to present some of the research that defines the nature, the source, chemical compounds re- sponsible for and factors influencing the occurrence of each off-flavor. OFF-FLAVORS DUE TO GENETIC FACTORS Mutton flavor Lamb’and mutton constitute a very small proportion of the meat consumed in the United States. The limited U.S. consumption of ovine meat is partially due to the characteristic odor which occurs during and following cooking (Batcher et al., 1969; Weidenhamer et al., 1969). This odor is considered to be unpleasant by a large pro- portion of the population in the United States. This objectionable odor has been described by Wong (1975) as being sweaty-sour in nature. Species differences in meat flavor have often been attributed to the fat portion of the meat (Hornstein and Crowe, 1963). The lean portion is believed to contribute a basic meaty flavor while the fat portion contributes the characteristic speciesflavor. It is logical then that most studies have looked for mutton odor in the fat portion of the meat. Hornstein and Crowe (1963) reported on the role of free fatty acids and carbonyls to lamb flavor. They noted that the char- acteristic mutton odor could be generated in lamb fat by heating. If rendered lamb fat was extracted with hexane and reacted with DNPH prior to heating, the typical mutton odor could not be gen- erated. Therefore, it was assumed that the precursors of mutton odor were either carbonyl in nature or not soluble in hexane. Car- bonyls were found to increase significantly during heating and were considered to be primarily responsible for the typical mutton aroma. The chemical source of mutton odor eluded detection until 1975 (Wang et al., 1975). Wong et al. (1975) using a combination of Author Reineccius is with the Dept. of Food Science & Nutrition, University of Minnesota, 1334 Eckles Ave., St. Paul, MN 55108. 0022-1147/79/0001-0012$02.25/O 0 1979 Institute of Food Technologists 12-JOURNAL OF FOOD SCIENCE-Vol. 44, No. 1 (1979) Table l-Incidence of sex odor in SOW and boars Author s0vb5.a Boarsa Williams et al. (1963) 95.0 35.6 USDA (1968) 81 .O 25.0 Self (1957) 82.3 74.2 a % of samples withour sex odor steam distillation and solvent extraction, fractionated the distillate into acidic and nonacidic fractions. They found that the character- istic mutton aroma was primarily associated with the volatile acidic components. The bulk (80-90%) of these acids were found to be even-numbered normal fatty acids containing 6-12 carbons (0.01% of the fat). The remaining fatty acids were branched and/or unsatur- ated in nature. Sniffing of the GLC effluent determined the fatty acids responsible for the typical mutton odor. These fatty acids were identified by mass spectrometry to be 4-methyl octanoic and 4-methyl nonanoic acids. Synthesis and organoleptic evaluation con- firmed the role of. these fatty acids as being responsible for the typical mutton odor. ,The influence of such factors as sex, age and fatness on the occurrence of mutton odor has been studied by many workers (Weber and Loeffel, 1932; Cline and Eckblad, 1937; Weber et al., 1931; Barbella et al., 1936; Jones, 1952; Hofstrand and Jacobson, 1960; Weller et al., 1962; Batcher et al., 1962; Paul et al., 1964; Batcher et al., 1969). These reports are often contradictory, and clear conclusions are difficult to draw. The most recent work by Batcher et al., (1969) reported that their panel could detect differ- ences in odor of broth due to age and sex of animal. Broth from the lean meat of lamb (7-8 month) was preferred over broth from 15-16 month mutton carcasses.The panel could not detect any influence of age or sex on the flavor of sIiced roasted, broiled or braised meats. Swine sex odor Lerche (1936) reported on the occurrence of an objectionable aroma which is found in swine. This off-aroma was described as being perspiration or onion-like in character. It was found to occur in sexually. mature uncastrated hogs but was absent from castrated hogs. This odor was celled “boar odor” until Self (1957) reported that it occurred in barrows, gilts and sows as well as in boars and therefore, suggested the name of “sex odor” for this off-aroma. The occurrence of sex odor in gilt and sow carcasseswas further sup ported by Williams et al., (1963) and the USDA (1968). The actual frequency of objectionable odor appearing in sows and boars varied wi’ilely in the literature. Table 1 illustrates the variation in data. The validity of data which showed a high frequency of sex odor in hogs other than boars has been questioned by Pearson et al. (1969) who felt that methodogy used by Self (1957) did not yield representative data. The primary criticisms were incorrect choice of muscle for odor evaluation, too low sample heating temperature to bring out off-aroma for sensory evaluation and a panel selection basis which was not ideal. The choice of examining diaphragm mus- cle as an indicator of sex odor was not desirable since this muscle is very lean and the sex odor was found to be concentrated in the fat portion of the meat. The samples were heated to 95”C, while Craig et al. (1962) showed that a temperature of 100°C was necessaryto volatilize the components responsible for sex odor. Criticism of Sells (1957) use of an untrained, unselected panel related to the fact that people differ in their ability to detect sex odor, and other odors are (or may be) present in the meat which might be confused with sex odor by the untrained panelist. In fact, Griffiths and Pat- teison (1970) later found a difference in ability to detect sex odor based on sex of the panel member. They found that only 46% of the