EFFECTS OF FOUR SPECIES OF BACTERIA ON PORCINE MUSCLE. 1. Protein Solubility and Emulsifying Capacity

Abstract

SUMMARY– A technique was used to obtain aseptic porcine muscle, portions of which were inoculated with cultures of Pediococcus cerevisiae, Micrococcus luteus, Leuconostoc mesenteroides and Pseudomonas fragi. The inoculated samples were compared with aseptic controls throughout a 20‐day storage period at temperatures of 2 and 10°C. All 4 organisms grew at 10°C, but only P. fragi and L. mesenteroides grew at 2°C. The solubilities of the various protein fractions were affected by inoculation treatment. This was exemplified by correlation coefficients ranging from —.37—0.50. The coefficients indicated the interrelationships affected by storage conditions and bacterial growth. Protein solubility studies revealed a loss in the water‐soluble fraction during storage of the controls and the M. luteus‐ and L. mesenteroides‐treated samples. Samples inoculated with P. fragi evidenced an initial loss, followed by an increase. The solubility of meat proteins in a salt solution increased during the first 8 days of storage, then decreased or remained relatively constant for all samples. In comparison with controls, samples inoculated with P. fragi increased in salt‐soluble protein solubility during the first 8 days, whereas those inoculated with L. mesenteroides decreased during the latter part of storage. Insoluble protein generally increased except for P. fragi‐inoculated samples, which decreased. Nonprotein nitrogen (NPN) increased for all treatments and controls during the 20‐day storage period. NPN extracted from the samples inoculated with P. fragi increased greatly. The pH increased with growth of M. luteus and P. fragi and decreased with growth of P. cerevisiae and L. mesenteroides. The emulsifying capacity was not influenced by the growth of M. luteus or P. cerevisiae. However, the emulsifying capacity of samples inoculated with L. mesenteroides decreased, whereas that of samples inoculated with P. fragi increased.