title: Effects of Psychrotrophic Bacteria, Serratia liquefaciens and Acinetobacter genomospecies 10 on Yogurt Quality.
abstract: The aim of this study was to evaluate the effect of proteolytic (Serratia liquefaciens, match %: 99.39) or lipolytic (Acinetobacter genomospecies 10, match %: 99.90) psychrotrophic bacteria (bacterial counts, analysis of free fatty acids (FFA) and analysis of free amino acids) on the microbial and chemical properties (yogurt composition), and sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) of yogurt during storage. Yogurts were prepared with raw milk preinoculated with each psychrotrophic bacteria. The total solid, fat, and protein content were not affected by preinoculation, but the pH of yogurt preinoculated with psychrotrophic bacteria was higher than in control. There was a dramatic increase in short chain free fatty acids among FFA in yogurt with Acinetobacter genomospecies 10. For 14 d of cold storage condition, SCFFA was 25.3 mg/kg to 34.4 mg/kg (1.36 times increased), MCFFA was 20.4 mg/kg to 25.7 mg/kg (1.26 times increased), and LCFFA was 240.2 mg/kg to 322.8 mg/kg (1.34 times increased). Serratia liquefaciens (match %: 99.39) in yogurt caused a greater accumulation of free amino acids (FAA), especially bitter peptides such as leucine, valine, arginine, and tyrosine, but SDS-PAGE showed that the inoculation of Serratia liquefaciens did not affect the degree of casein degradation during storage. Taken together, the excessive peptides and FFA in yogurt generated from psychrotrophic bacteria could develop off-flavors that degrade the quality of commercial yogurt products.
authors.affiliation: Institute of Dairy Food Research, Seoul Dairy Co-op., Ansan 425-839, Korea.
authors.forename: Yong Kook
authors.initials: YK
authors.lastname: Shin
authors.affiliation: Institute of Dairy Food Research, Seoul Dairy Co-op., Ansan 425-839, Korea.
authors.forename: Nam Su
authors.initials: NS
authors.lastname: Oh
authors.affiliation: Institute of Dairy Food Research, Seoul Dairy Co-op., Ansan 425-839, Korea.
authors.forename: Hyun Ah
authors.initials: HA
authors.lastname: Lee
authors.affiliation: National Institute of Animal Science, Rural Development Administration, Suwon 441-706, Korea.
authors.forename: Jong-Woo
authors.initials: JW
authors.lastname: Choi
authors.affiliation: Department of Animal Biosystem Science, Chungnam National University, Daejeon 305-764, Korea.
authors.forename: Myoung Soo
authors.initials: MS
authors.lastname: Nam
keywords: Acinetobacter genomospecies 10; Serratia liquefaciens; free fatty acids, free amino acids; psychrotrophic bacteria