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Relation of Protein Components and Free Amino Acids to Pork Quality¹

University of Kentucky, Lexington

Abstract

Four closely related litters of five Hampshire barrows each were raised under the same conditions and distributed among five slaughter weight groups so that each litter was represented in each group. Various quality and palatability characteristics, certain protein nitrogen components, and 16 individual free amino acids were determined on raw and cooked samples of the l. dorsi muscle. The drippings from cooking also were analyzed for the free amino acids.

The percents of soluble fibrillar protein nitrogen, sarcoplasmic protein nitrogen, non protein nitrogen, and residual connective tissue protein nitrogen decreased in the cooked product when compared to the fresh state by about 75%, 100%, 33% and 43.5% respectively. The percent total nitrogen increased about 45.4%, and the percent collagen nitrogen remained almost constant from the raw to the cooked state. Proportions of free glycine, alanine, methionine and proline decreased in the cooked product while proportions of free serine, glutamic acid, valine, isoleucine, leucine, tyrosine, phenylalanine, lysine and arginine increased. When the free amino acids in the drippings were compared with those in the raw plus cooked muscle, valine, alanine, threonine, histidine, and the total free amino acids were higher and tyrosine, phenylalanine, glycine and methionine were lower.

Significant partial correlation coefficients were found for percent of total nitrogen of raw pork with marbling ( –.44), flavor (– .51), juiciness (– .79) and over-all satisfaction (– .72). Such coefficients also were found for percent sarcoplasmic protein nitrogen of raw pork with firmness (0.58), juiciness (0.51) and over-all satisfaction (0.45); free glutamic acid of raw pork with flavor (– .52); free glutamic acid ( – .66), tyrosine (– .57), aspartic acid ( – .54), serine (.46) and glycine (0.49) of cooked pork with flavor; free glutamic acid (0.44), leucine (0.56), serine (0.50) and phenyl-alanine (0.51) of raw pork and aspartic acid (0.45) of the drippings with tenderness. Significant partial correlation coefficients also were found for free glycine (0.70), valine (–.46) and leucine ( – .46) in raw pork along with free proline (0.60), glycine (0.52), leucine ( –.44), methionine ( – .55), valine ( – .56), isoleucine ( – .59) and phenylalanine (– .66) in cooked pork and tyrosine ( – .45) and isoleucine ( – .56) in the drippings with the percent collagen nitrogen.

Various individual free amino acids in cooked pork were most frequently correlated with flavor followed by juiciness and over-all satisfaction.

¹ The investigation reported in this paper (67-5-82) is in connection with a project of the Kentucky Agricultural Experiment Station and is published with approval of the Director.

² Present address: Department of Animal Science, University of Minnesota, St. Paul.

³ The authors gratefully acknowledge the assistance of the University of Kentucky Computing Center in analyzing data.