Proteolytic effect of starter cultures on dry fermented Chinese-style sausage

The proteolytic effect of three different starter cultures (Lactobm:acillus casei subsp.casei-1.001, Pediococcus pentosaceus-ATCC 33316 and Staphylococcus xylosus-12) on dry fermented Chinese-style sausages has been investigated. The increment in non protein nitrogen (NPN) was significantly highest (p < 0.05) (6.8mg/g dm) in sausage inoculated with S. xylosus-12, while lowest (4.8mg/g dm) in control. Moreover, free amino acids such as Glu, Gly, Thr, Arg, Val, Trp, Phe, Leu, Lys and Pro were predominantly found (above 30mg/100g dm), summing up over 80% of the total. The sausage added with starter Sx-12 showed the highest content of total free amino acid (1287.9 mg/100g dm) and lowest in control. The essential free amino acids were increased approximately by 2.5 times in ripened products as compared to initial minced mix. SDS-PAGE showed that the intensity of myosin heavy chain (HMC) in myofibrillar muscle became thinner due to proteolysis action of starter cultures and producing a lower molecular weight protein (~116kDa). Likewise, the actin degradation was observed more intensive in starter added sausages. Other protein bands like troponin-T (37kDa), myosin light chain-1 (25kDa), myosin light chain-2 (18kDa), and myosin light chain-3 (15kDa) noticeably degraded during ripening of products inoculated with starter cultures. In other hand, the protein bands with molecular weight ~26, 43, 50, 97, and 150 kDa have been totally disappeared after ripening process, while no effect on protein band particularly with molecular weight ~40kDa was observed, meanwhile the intensity of polypeptide with a molecular weight of ~13, and 21kDa were increased in ripening due to degradation of higher polypeptide bands caused by bacterial proteolysis and protein denaturation due to high acid or salt concentration in products. Therefore, the starter cultures S. xylosus-12 and P.pentosaceus- ATCC 33316 were more capable in protein degradation forming several free amino acids and lower molecular weight peptides during fermentation and ripening of dry fermented Chinese-style sausage, which could improve the flavour and textural properties of such meat products.