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The aim of this study was to investigate diversity of the αS1-casein gene in Maiwa yak. A polymorphism of αS1-casein gene has been identified in Chinese Maiwa yak by PCR single-strand conformation polymorphism protocol. Comparing the X59856 sequence, some non-coding and coding DNA variants of yak CSN1S1 gene were detected in this present study, including KJ397913 (promoter region, 9969A/G, 9984 A/G, 10153 C/T, 10175 A/C, 10261 G/C), KJ397914 (promoter region 10261 G/C), KJ397896 (intron III, 14862 T/C), KJ397897 (intron III, 14862 T/C, and deleted 14944-14946 CTT), KJ397899 (intron IV, 15297 A/C), KJ397901 (intron VIII, 17503 A/C, 17666 A/C), KJ397902 (exon IX, 18901C/A, intron IX, 18970 T/G, 19088 add A, 19120 add A, 19202 add T, 19296 G/T), KJ397903 (intron IX, 18970 T/G, 19088 add A, 19120 add A, 19202 add T, 19296 G/T), KJ397904 (intron IX, 19537 T/G, 19539T/G, 19599G/A, 19638 C/T), KJ397905 (intron XIV, 23402 T/G, 23417 C/T, 23480 T/C, 23511 G/A), and KJ397907 (intron XVI, 25976 G/T; exon XVII, 26181A/G). The polymorphism of αS1-casein gene may be helpful for future studies on genetic variation within and between yak populations or on associated traits. [ABSTRACT FROM AUTHOR]

Most psychrotrophic bacteria have the ability to produce thermoresistant proteases that can destroy the quality of milk and dairy products. To investigate the population dynamics of psychrotrophic bacteria during refrigeration, three raw cows' milk samples (sample A comprising milk from 10 farms in Beijing, sample B comprising milk from 5 farms in Heihe, and sample C comprising milk from 7 farms in Harbin) were refrigerated at 0–5 °C and 5–10 °C. PCR-DGGE (Polymerase chain reaction-denaturing gradient gel electrophoresis) analysis revealed that the bacterial community profiles varied from geographical site to site, and with refrigeration temperature. The dominant psychrotrophic bacteria among the samples after storage were affiliated with the order Pseudomonadales . Following isolation and identification, 8 psychrotrophic isolates were selected as stronger protease producers and their growth and proteolytic activities were assessed. The results indicate that the composition of psychrotrophic bacteria play an important role in the determination of the quality of milk and dairy products. [ABSTRACT FROM AUTHOR]