Changes in the free amino and other nitrogen compounds in stored beef muscle

Abstract

Changes in the levels of 21 amino compounds, ammonium-N and urea-N. during the storage of fresh beef at various temperatures have been investigated. The meats were also subjected to bacteriological analysis. Glutathione and glutamine were found to decrease in the meats during storage, while most other aniinoacids, notably glutamic acid and tryptophan, increased. The increase in glutamic acid appeared to be related to the microbial numbers in the meats. On the other hand, the increase in tryptophan seemed directly related to the time and temperature of storage. There was an initial increase in urea-N followed by a gradual disappearance of this compound from the stored meats. Ammonium-N did not rise significantly until the stage of incipient spoilage had been reached. lntroduction Studies in the changes of individual free amino-acids in beef during storage have been the subject of numerous investigations,1-8 most of which are concerned with autolytic processes. However, Avshalumova5 examined the changes in the free amino-acids in meat during storage at 18-20' and at the same time observed the microbiological condition of the meat by a direct smear technique.The levels of ammonium N have also been evaluated as an index of microbial proteoly~is.~-~8 The most recent workers16-l* agree that it is an index of advanced rather than incipient putrefaction of flesh foods and is not a good index of spoilage. Recorded values for the ammonium N content of fresh meat show wide variations.5~ 1'J, 18 In this paper the changes in the levels of free amino-acids, ammonia, urea and the number and types of bacteria present in beef during storage have been examined to assess if any of the chemical criteria could be used as an index of incipient spoilage. Experimental Preparation of meatsExperiment 1 .-The source and preparation of the meats stored at 4", 9" and 15" has been described elsewhere by Gardner . @ Experiment 2.-The meats used in this experiment were taken from the foreleg muscles of cows within 3 h post mortem. The preparation of these was similar to that in Experiment I, except that in all cases the storage temperature was 15". Bacteriological analysisThe techniques and media employed in assessing the flora changes of the meats during storage have been previously described.lg Chemical analysisSamples were taken at the time of bacteriological analysis and stored at -20" until required. Protein and fat-free extracts of the meats were preparmed by the method of Awapara.20 +Present address : Ulster Curers' Association, 2 Greenwood Avenue, Belfast 4, N. Ireland. J. Sci. Fd Agric., 1966, Vol. 17,, NovemberAmino-acids.-Amino-acids were separated by the electrochromatographic procedure of Biserte et aL21 and quantitatively estimated by the method of Barrollier.22 Elution of the neutral amino-acids and basic amino-acids after primary separation was carried out by the method of Finkle.23 Glutamine was estimated as glutamic acid after the neutral amino-acid fraction of each sample had been hydrolysed in 2~ sulphuric acid for 60 min. a...

Effects of slaughter age on the levels of free amino acids and dipeptides in fattening cattle

“…Even proteases from microorganisms were not completely excluded in these studies of FAA changes and our present study. Large increases in glutamic acid were sometimes caused by bacterial metabolism of glutamine (Gardner & Stewart 1966). These overriding effects during storage would be larger than the effects of growth rate or breed in the present study, and such effects could be one of the main reasons for the inconsistencies in FAA data between studies.…”

Chemical and organoleptic changes in poultry meat resulting from the growth of psychrophylic spoilage bacteria at 1° C

“…Van den Berg et al (1963) and Khan and vander Berg (1964) noted appreciable increases in NPN after 5 weeks at o° C, though changes up to 10 d were negligible. Increases in ninhydrin-positive extractives (mainly amino acids) were, however, detectable after 7 d. Gardner and Stewart (1966), storing beef at 4 0 , 9 0 and 15° C, concluded that most amino acids, particularly glutamic acid and tryptophan, increased. Their data, however, show a decrease in glutamic acid up to 7-7 d at 4 0 C, although several other amino acids showed appreciable increases up to this time, some with sharp decreases later, presumably as a result of bacterial utilisation.…”

Comparison of Meat Quality Traits, Free Amino Acid and Fatty Acid on Longissimus Lumborum Muscles from Hanwoo, Holstein and Angus Steers, Fattened in Korea

“…Apart from nutritional aspect, free amino acid is very important non-volatile materials for meat taste and flavour (Gardner and Sterwart, 1966;Davey and Gilbert, 1966), free amino acids from heated meat improve meat flavour (Ockerman and Cresopo, 1982). Tseng et al (2005) classified free amino acid in food to umami (aspartic acid, glutamic acid), sweet (serine, glycine, threonine, alanine), bitter (valine, methionine, isoleucine, leucine, phenylalanine, histidine, arginine), and others (Glutamine, tyrosine, systine, lysine and proline).…”