Lamb and mutton flavour: Contributing factors and chemical aspects

LAMB A N D M U T T O N FLAVOUR: C O N T R I B U T I N G FACTORS A N D CHEMICAL ASPECTS*

J. D. SIYK & F. CAPOm~SO

The Pennsylvania State University, University Park, Pennsylvania, 16802, USA (Recei,md: 24 June, 1976)

SUMMARY

A review of the occurrence and chemistry o f lamb/muttonflavour is presented. The low consumption of both lamb and mutton has been attributed to the flavour of these meats. There is general agreement that the flavour of meat from younger anbnals is more desirable than that from older ones. Further, the flavour intensity of meat from wethers is less than that of ewes, and ewes less than rams. Breed appears to have an effect; mutton flavour is more predominant in the fine-wool breeds and is apparently directly related to the fineness o f the wool. However, no significant sire effects within or between breeds hate been reported. Nutritional factors appear to play a major role in the flavour intensity of sheep meat. Certain foodstuffs (legumes and grains) can intensify the flavour, whereas withdrawal of sheep from grazing before slaughter can reduce it. There is"no reliable evidence to implicate slaughtering and processing factors (except heating) in flavour derelopment. Although the exact chemical compounds responsible for lamb/mutton flavour are not yet known, the)' are undoubtedly lipid soluble, with the carbonyl and/or sulphur-containing compounds as the most promising candidates. Further, there appears to be no consistent expression of a 'characteristic" lamb/mutton flavour.

INTRODUCTION

Sheep (Ovis aries) are ruminant animals that essentially do not compete directly with man either for foodstuffs or land use. These animals can utilise roughages and even waste products satisfactorily in their diets. Further, they can graze certain lands that are unsuitable for the production o f man's foodstuffs or for his habitation. * Paper No. 4989 in the journal series of the Pennsylvania Agricultural Experiment Station. 119

Meat Science (1) (1977)---© Applied Science Publishers Ltd, England, 1977 Printed in Great Britain

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Consequently, as the world food crisis becomes more acute, the use of sheep as a meat source for man should be more fully exploited. Generally, animal meat products are well balanced nutritionally in energy, protein, minerals and vitamins and their palatability makes them a desirable food source for man. However, during the past 15 years, w o r l d p e r capita consumption of sheep meat has decreased steadily whilst that of other species has increased (USDA, 1976). The characteristic flavour has been cited as one reason for the low consumption of sheep meat (only 1.2 ~ of the total red meat eaten in 1975 by the inhabitants of the USA). It would be difficult to imagine when the first objection to the flavour of sheep meat was made. It was probably some time between 6000 BC when sheep were first domesticated (Zeuner, 1963) and 1907 when the first obtainable flavour description of various differences was recorded (Anon., 1907). However, most of the literature on sheep meat flavour has been written since 1960. Thus, any research to increase lamb/mutton consumption must focus attention on its flavour. Definitions and terms The United States Department of Agriculture (USDA, 1960) officially describes lamb as being meat from ovines less than 12 months of age. Yearlings are animals of between 12 and 24 months which have cut one pair of permanent incisor teeth, and mutton is from animals over 24 months of age which have cut two pairs of permanent incisor teeth. This specific description of the types of sheep meat, based on age, has not been used by many researchers and is a source of confusion in the literature. To some researchers (Hoffman & Meijboom, 1968; Pearson et al., 1973), the term mutton means the meat of all sheep, regardless of age, while others (Ramsey, 1960; Batcher et al., 1969; Karmas, 1970; Bourjaily, 1972) have used the official USDA definitions. However, many investigators have termed the characteristic 'off flavour in sheep meat (regardless of age) as a 'mutton' flavour (Cramer & Marchello, 1962; Cramer et al., 1970; Cramer, 1974; Weller et al., 1962; Hornstein & Crowe, 1963). Although Wasserman & Talley (1968) reported that the flavour of lamb is so characteristic it can be identified by people with little previous exposure, the distinction between the 'characteristic' flavours of lamb and mutton meat has not been well defined. People apparently differ in their concept of what constitutes mutton flavour. Mutton meat may have an entirely different fiavour from that of lamb, or may merely represent a change in concentration. The ability to distinguish between lamb and mutton flavours varies among people. In preliminary studies on threshold tests, Batcher et al. (1969) found that 3 out of 14 people tested were able to detect mutton flavour in ground lamb patties containing 15 ~o mutton, 7 were able to detect the flavour in ground lamb patties containing 1 5 ~ - 3 5 ~ mutton, and the remaining 4 people required more than 35 ~ mutton in the patties before the presence of mutton flavour was detected.

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Problem statement

Consequently, it appears that the basic dilemma with regard to lamb and mutton consumption revolves around the characteristic flavour of the product (Ziegler & Daly, 1968). Much has been reported in the literature concerning this aspect of the acceptability and consumption of ovine products. The purpose of this paper is to present a review of lamb/mutton flavour and of those factors which may infuence its expression. FACTORS AFFECTING LAMB/MUTTON FLAVOUR

Chronological age as a f a c t o r

It is a generally accepted fact that meat animal flavour intensity increases with chronological age. H a m m o n d (1932) observed in sheep that muscles of older animals are more highly flavoured than those of younger ones. Since then several contradictory reports have appeared in the literature on sheep flavour and animal age. Weller et al. (I 962), using ! 7 inexperienced students and 6 faculty members as a taste panel, reported that a "natural' flavour was found in older, heavier animals whilst the younger, lighter ones were more often described as 'strong' and/or 'off. Batcher et al. (1969) found no association between animal age and flavour except in lamb broths. Panellists could not detect any differences in slices of roasted, broiled, or braised meat from lamb or yearling sheep. The authors concluded that the flavour scores of the meat slices may have been influenced by other, more dominant, palatability characteristics, such as tenderness and juiciness, which would have no effect on flavour detection in the broths. Therefore, more emphasis was placed on the flavour scores of the broths, and it was concluded that there were subtle flavour differences in lamb which were attributable to age. Both Weber & Loeffel (1932) and Paul et al. (1964) reported more intense, more pronounced and/or less desirable flavours of lean and fat with increasing age of the animal. In evaluating these investigations, it seems that there is an age effect upon the flavour of sheep meat, with older animals yielding a more intense meat flavour. Genetic f a c t o r s Sex: H a m m o n d (1932) noted that the muscles ofwethers had a more acceptable

flavour than those from rams, while those ofewes were intermediate between the two. However, Usborne et al. (1961), Batcher et al. (1962) and Wilson et al. (1970) all reported no significant differences in flavour due to sex. In another experiment, Batcher et al. (1969) found that significant differences in flavour and intensity, attributable to sex, were observed only in those lamb patties with a high fat content. As the fat content of the cooked patty increased from 13 ~ - 3 3 ~ , the flavour of patties from ram meat was rated more intense than that of patties made from wether meat.

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Reporting on practices in France, Charlet (1969) indicated little flavour difference in the meat from either wethers or rams up to about 8-12 months of age. Beyond this age, rams were not used because the farmers believed castration resulted in more tender meat with less 'sheep' flavour and that m a n y customers disliked the strong 'wool" or 'sheep" flavour of the meat from intact older males. Breed." Studies on lamb and mutton flavour indicate that a great deal of variation exists between breeds. Cramer et al. (1970) observed that mutton flavour increased with increased fineness of wool. Rambouillet lambs had the most intense flavour, Targee lambs the next most intense flavour, Columbia lambs next and Hampshire lambs had the least amount o f ' m u t t o n ' flavour. Sire: Fox et al. (1962), using 22 different sires from the Hampshire, Columbia and Targee breeds, found no major or consistent flavour differences in the meat from weaning lambs, for different sires within a breed or between breeds. In a later study, Fox et al. (1964), using Hampshire rams on Columbia and Targee ewes, found no significant flavour differences among breeds or a m o n g the sires.

Nutritional factors Douglas's Encyclopaedia (Anon., 1907) states that the exquisite flavour of English and Scotch mutton comes from the aromatic wild herbs in their pastures. Cramer et al. (1967) noted that the flavour of the fat and of the lean was more intense in whiteclover (Trifolium repens) fed lambs compared with those fed on ryegrass (Lolium perenne). They also noted that the intensity of flavour of the lean and of the whiteclover fed lambs was correlated with the amount of fat. Shorland et al. (1970) found that differences in flavour of lean between lambs fed perennial ryegrass and those fed clover developed within 3 weeks of the animals being fed these diets. In a later study, Czochanska et al. (1970) observed that the intensity of odour was greater in lambs slaughtered 1 h after feeding than in those slaughtered 24 h after feeding. They noted that the withdrawal ofsheep from grazing before slaughter did not appear to affect the flavour of the cooked meat but it did reduce the intensity of the odour. They also found, in agreement with Cramer et al. (1967), that animals fed on white-clover had a significantly greater intensity of flavour in the lean and fat and a significantly stronger odour than those fed on perennial ryegrass. Richardson & Dickson (1936) examined the eating quality of feedlot lambs given free access to lucerne hay (Medicago sativa) and fed various grains. Oats, barley, maize and wheat produced slight differences in the intensity and desirability of the a r o m a and flavour of the lean in roast leg or loin, and in the flavour of the fat; oats plus lucerne hay produced the most desirable a r o m a and flavour and barley plus lucerne hay the least desirable. Park et al. (1972a) reported significant differences in the flavour characteristics of stewed minces from lambs raised on either lucerne or phalaris (Phalaris tuberosa) pastures. The meat from lambs raised on lucerne had a more intense 'sharp' and

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'sickly' aroma and flavour and a significantly lower flavour acceptability. These characteristics were not significantly altered when the lambs were fasted for up to 3 days before slaughter. However, the flavour of meat from lambs transferred from lucerne to phalaris 7 or 14 days before slaughter was not significantly different from that of lambs grazed solely on phalaris. In another study, Park et al. (1972b) found that the flavour characteristics of meat from sheep fed rape ( Brassica napus cv. Rangi), vetch (Vicia dao, carpa L. cv. Lana), or oats (Arena sativa cv. Acacia) differed significantly from those of meat from similar sheep grazing native ryegrass-white-clover pastures. Grazing on rape often produced a meat with a nauseating aroma and flavour, and with significantly lower acceptability of flavour than the pastures. There was no significant difference in the acceptability of flavour of meat from pasture and vetch fed sheep, although vetch gave an intense meaty flavour. Meat from sheep grazing oats possessed a pungent odour and flavour, but with a flavour only slightly, but significantly, less acceptable than that of meat produced on pasture. Park & Minson (1972) described the effects of sheep grazing one of four tropical legumes on the flavour of the meat, as evaluated by a laboratory taste panel. Meat from siratro (Phaseolus atropurpureus), dolichos (Dolchos axillaris) and silverlead desmodium (Desmodium uncinatum) grazed lambs was not significantly different from grass (Panicum maximum) grazed controls in flavour acceptability. However, glycine (Glycine wightii) grazed lambs exhibited a characteristic objectionable odour and flavour in one trial and a lower intensity of this flavour in another trial, indicating a variability in the tainting properties of this legume. Barbella et al. (1936) showed that retarding the growth of lambs, by restricting dietary intake, made the meat less desirable in flavour. Jacobs et al. (1973) reported no effect of dietary stress due to reduced energy intake on flavour, juiciness, fat flavour or overall satisfaction.

CHEMICAL ASPECTS OF LAMB/MUTTON FLAVOUR

Water sohtble components Hornstein & Crowe (1963) noted that the flavour precursors in lean lamb meat are low molecular weight, water soluble compounds that produce characteristic meat aromas on heating. Subsequently, Jacobson & Koehler (1963) observed that the uniformity of the identity of amino acids among sheep breeds suggests that these water soluble components are not responsible for important differences in flavour, although they doubtless contribute to the meaty flavour. Macy et al. (1964a) reported the presence of glutathione in water extracts of lamb muscle but not in those from beef or pork. These authors (Macy et al., 1964b) also reported that the total carbohydrate content of fresh lamb muscle was about half that of beef and pork. However, after heating, the amount of carbohydrate in the muscle was quite

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similar for all three species. They emphasised the importance of sugar concentration in the production of browned products, and consequently flavour production during heating. The percentages of both amino compounds and carbohydrates lost during heating were proportional to the initial quantities present, thus implying an interaction between these constituents. Wasserman & Spinelli (1972) found that the water-wash of a chloroform:methanol extract of lamb adipose tissue gave a non-specific roast meat aroma on heating to dryness. Many amino acids and glucose were identified in the water-wash. Lipid sohlble components Hofstrand & Jacobson (1960) had noted an indication that fat may contribute to the flavour of lamb and mutton broths and that flavour components were especially prevalent in the depot fats. In a later study, Cramer et al. (1967) found no flavour differences between subcutaneous and perirenal depot fats. In 1963, Hornstein & Crowe reported that the characteristic aroma of heated lamb is obtained from the fat, particularly the carbonyl compounds. However, they indicated that these flavour compounds, or their precursors, are apparently present in only trace amounts. Lactones, as well as carbonyls, have also been found in sheep depot fats. Dimick et al. (1966) noted trace amounts of aliphatic 6-1actones and, in addition to these lactones, Watanabe & Sato (1968) observed the presence of T-lactones in small amounts. They reported that the predominant 6-1actone was the Ct4 and the predominant 7-1actone was also the C1, component. Park et al. (1974) identified 4hydroxydodec-cis-6-enoic acid lactone and trans, trans-deca-2,4-dienal as largely responsible for the 'sweet' and 'oily' odour and flavour characteristics of cooked meat from sheep fed a lipid-protected dietary supplement. In a later study, Park et al. (1975) suggest an increase in the amount of the lactone contributes to a decrease in flavour acceptability whereas an increase in decadienal levels may impart desirable flavour properties to lamb meat. In an experiment to determine the role of fat in characterising meat species, Wasserman & Talley (1968) observed that the lamb flavour factor was either a component of the fat or fat soluble. Wong et al. (1975) recently identified by gas chromatographic-mass spectrometric techniques various C6--C12 acids from the steam volatile acid fraction of cooked mutton fat. They attributed a 'sweaty-sour' odour note or 'soo' odour to the branched-chain and unsaturated Cs-10 fatty acids of this fraction. Hornstein & Crowe (1963) concluded that the major portion of the odour of heated lamb is contributed by carbonyl compounds. The literature verifying the significant role of carbonyl compounds in the flavour/odour of lipid-containing foods is voluminous (Forss, 1972; Sink, 1973). However, studies on the carbonyls of lamb have been surprisingly limited. Ellis et al. (1961) and Gaddis et al. (1961) studied carbonyl generation in various animal and vegetable fats. They reported that heating increased the amount of steam

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volatile monocarbonyls, alkanals, alk-2-enals, and alk-2,4-dienals from lamb fat. Alk-2,4-dienals increased four times in concentration, while the other fractions doubled. Nonanal, non-2-enal, dec-2-enal, and undec-2-enal were the major monocarbonyl components. Hornstein & Crowe (1963) noted that there was no change in the amount of monocarbonyls detected upon heating in air but that there was a twofold increase when heating was conducted in nitrogen. Alk-2,4-dienals were only detected in fat heated in air, while hexanal levels undetectable in fat heated in air were high in unheated fat and fat heated in nitrogen. The major monocarbonyls detected were hexadecanal and octadecanal which are not ordinarily volatile and do not contribute to aroma. Jacobson & Koehler (1963), investigating the components of the flavour of lamb, found carbonyl compounds to be important contributors to aroma. They identified various saturated monocarbonyls collected from simmering lamb: Cz-C to alkanals, C5-C~o alk-2-ones and possibly 2-methylcyclopentanone. They suggested that typical lamb flavours may be a result of variations in the carbonyl compounds present. Hoffman & Meijboom (1968) obtained an off-flavour concentrate from strongly smelling Australian mutton tallow by stripping it with a stream of nitrogen in a 10mm Hg vacuum at 160 °C for several hours. Then, mainly by chromatographic and UV spectrophotometric techniques, 4-cis- and 4-trans-heptenal (with a "green' odour, characterised in high dilution as tallowy, creamy, butterscotch-like) and 2trans, 7-cis- and 2-trans, 6-trans-nonadienal (with a 'green'-cucumber-like and a tallowy odour) were isolated from reverted mutton tallow. Park et al. (1974) identified trans, trans-2,4-decadienal as contributing the'oily' or "chicken-oily' aroma note to lipid-protected supplementally fed lamb. This compound was also isolated as a minor constituent of animals fed a conventional control diet. Riley et al. (1971) reported lamb carbonyl data from chloroform-extracted subcutaneous fat and lean (longissimus dorsi) samples. One hour fat, 10-day fat, cooked 10-day fat, and drippings from 10-day fat and lean were the samples analysed. As previously reported, no alk-2-ones were detected in any of the lamb samples. Alkanals were the major monocarbonyl component in all fat samples. Alkanal and alk-2-enal concentrations were higher in 10-day than 1 h fat samples, while alk-2,4-dienals were detectable in 1-day fat samples only. The effect of heating upon the monocarbonyl concentration of fat could not be evaluated since the drippings of both the fat and lean were pooled together.

Sulphur components Pepper & Cramer (1964), without giving any details, reported tentatively identifying certain sulphur-containing compounds obtained from the volatile fraction of heated mutton fat. Recently, Cramer (1974) reported finding copious

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b l a c k p r e c i p i t a t e s in the m e r c u r i c c y a n i d e c o l l e c t i o n t r a p s o f the v o l a t i l e f r a c t i o n o f cooking mutton, indicating that much larger amounts of hydrogen sulphide were p r e s e n t t h a n are f o u n d in b e e f fat. H e h y p o t h e s i s e d t h a t the specific m u t t o n o d o u r o f l a m b a n d m u t t o n is c a u s e d by s u l p h u r - c o n t a i n i n g c o m p o u n d s . S u p p o r t i n g these findings, K u n s m a n & R i l e y (1975) h a v e r e p o r t e d the e v o l u t i o n o f H z S f r o m l a m b a d i p o s e a n d m u s c l e tissues: m o r e H 2 S w a s l i b e r a t e d u p o n h e a t i n g the a d i p o s e tissue t h a n t h e m u s c l e . F u r t h e r , it was o b s e r v e d t h a t t h e H2S released f r o m m u s c l e o c c u r r e d e a r l i e r in the c o o k i n g p r o c e s s t h a n did t h a t f r o m the a d i p o s e tissue s a m p l e s . M e c c h i et aL (1964) have s u g g e s t e d t h a t the r a t e o f H 2 S e v o l u t i o n f r o m h e a t e d m u s c l e c a n be a p p r o x i m a t e l y p r e d i c t e d f r o m its c y s t i n e c o n t e n t . T h e w o r k o f M a c y et aL (1964b), r e p o r t i n g h i g h cystine c o n c e n t r a t i o n s in l a m b , w o u l d a p p e a r t o s u p p o r t this o b s e r v a t i o n .

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