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With the semi-finished and finished products of pickled and dried mustard in Ningbo as experimental materials, the dominant bacteria strains were isolated by ten-fold dilution method. The results showed that seven and three bacteria were obtained from the semi-finished and finished products, respectively, which were named as strain MGCB1~MGCB7 and strain MGC1~MGC3. The ten strains were identified by morphological observation, physiological and biochemical tests, and 16S rRNA sequence analysis. They were likely belong to Bacillus subtilis (MGCB1), Bacillus aerius (MGCB2), Bacillus altitudinis (MGCB3), Bacillus pumilus (MGCB4), Staphylococcus succinus (MGCB5), Staphylococcus succinus (MGCB6) and Bacillus amyloliquefaciens (MGCB7), Bacillus sp. (MGC1), Virgibacillus halodenitrificans (MGC2), and Cytobacillus gottheilii (MGC3), respectively. The protease activities of MGCB1 and MGCB7 were 16.39±0.79 and 13.45±0.46 U/mL, and the cellulase activities of MGCB1 and MGCB7 were 3.27±0.13 and 1.60±0.02 U/mL, respectively, after cultured at 37 ℃ for 96 h. These findings provide a useful reference for developing appropriate starter cultures to improve the quality of traditional pickled and dried mustard.

Casein was hydrolyzed by neutral protease, alkaline protease and trypsin to determine the best protease for preparation of cholesterol-lowering peptide. The effects of hydrolysis pH value, hydrolysis temperature, enzyme to substrate ratio, substrate concentration and hydrolysis time on casein hydrolysis degree and cholesterol micelle solubility inhibition rate were investigated by single factor and response surface experiments, and the optimal hydrolysis conditions were determined. Then the separation process of cholesterol-lowering peptide was determined by ultrafiltration and gel filtration chromatography. The results showed that the optimal enzyme was neutral protease, and the optimal hydrolysis conditions were as follows: Reaction temperature 51.3 ℃, enzyme to substrate concentration ratio 6.47%, pH6.34, substrate concentration 5 g/100 mL, reaction time 3.5 h , and cholesterol inhibition rate 58.25%±0.59%; The separation conditions of casein cholesterol-lowering peptide by Sephadex G-10 were as follows: Loading concentration 80 mg/mL, loading volume 2.5 mL, elution rate 3.5 mL/min; The inhibition rates of cholesterol solubility of peak 1 and peak 2 samples were 24.2%±0.24% and 4.3%±0.16% at 100 µg/mL after ultrafiltration and chromatography.

In order to improve the stability and water solubility of astaxanthin, the snailase was used for the wall-breaking extraction of astaxanthin from Haematococcus pluvialis, and gum arabic and whey protein powder (rich in milk fat globule membrane) were used as wall materials to prepare astaxanthin nanoparticles using a complex coacervation method, in addition, the stability of the nanoparticles was investigated. The results showed that the optimum conditions for the preparation of astaxanthin nanoparticles were pH4.0, protein/gum arabic mass ratio of 2:1 and astaxanthin concentration of 60 μmol/L. The encapsulation rate of astaxanthin under these conditions was 92.93%±0.19%. The average particle size was 265.71±0.55 nm and the Zeta potential was −13.44±0.14 mV. The nanoparticles showed good storage stability with only 6.1% increased in size, 90.78%±0.25% retention of astaxanthin and 79.31%±0.18% clearance of DPPH after 15 d storage at 4 ℃. This study would improve the stability and water solubility of astaxanthin and provide technical support for the efficient utilization of astaxanthin.

In order to develop and utilize the milk polar lipids, the chloroform-methanol extraction method was used to extract the polar lipids from buttermilk. The phosphorus content as an index, the condition of chloroform-methanol volume ratio, liquid-to-methanol ratio, extraction temperature and time were optimized by single-factor experiment and the analysis of response surface methodology determined the optimum extraction conditions. The obtained samples were analyzed and identified by thin-layer chromatography(TLC). The results indicated that the optimal extraction conditions for polar lipids were: Chloroform-methanol volume ratio 2:1(v/v, %), 1:4(v/v, %) for the ratio of material to liquid, 20 ℃ for extraction temperature, and 10 min for extraction time. The phospholipid contents in the sample under this extracted condition was (1.647±0.010) mg/g, and there were polar lipids such as phosphatidylcholine, phosphatidylethanolamine, phosphatidylserine, and sphingomyelin. This process aims to provide a research basis for the extraction and development of milk polar lipids.