Xiaoyang Pang

Comparative proteomics of milk fat globule membrane in different species reveals variations in lactation and nutrition

In present study, 312, 554, 175 and 143 proteins were identified and quantified by label-free quantitative proteomics in human, cow, goat and yak milk fat globule membrane (MFGM), respectively. Fifty proteins involved in vesicle mediate transport and milk fat globule secretion were conserved among species. Moreover, proteins involved in lipid synthesis and secretion (xanthine dehydrogenase/oxidase, stomatin and CD36), showed different expression pattern and the host defense proteins exhibited various profiles within species. Notably, the content and activity of lipid catabolic enzymes were significantly higher in human MFGM, which could be indicative of the superior fat utilization in breast fed infants. Our findings unraveled the significant differences in protein composition of human milk and conventionally used substitutes of it. The in-depth study of lipid metabolic enzymes in human MFGM will probably contribute to the improvement of the fat utilization through modulation of lipid catabolic enzymes in infant formula.

Comparative proteomics of milk fat globule membrane in goat colostrum and mature milk

As an important nutrient source in large area of world, the composition and nutritional value of goat milk are not well deliberated. Detailed annotation of protein composition is essential to address the physiological and nutritional value of goat milk. In the present study, 423 colostrum and mature goat milk fat globule membrane (MFGM) proteins were identified. The abundance of 189 proteins was significantly different between colostrums and mature milk MFGM. The acute phase proteins were higher in colostrums MFGM than those in mature milk MFGM which protected newborns at the beginning of life. Proteins related to synthesis and secretion were conserved through lactation to ensure the milk production. Of note, long term depression (LTD) proteins were observed in colostrum and mature milk MFGM. Milk LTD proteins could be potential biomarkers for diagnosis of lactation related depressive syndromes and should be taken into considerations of their effects on newborns.

Gene Knockout and Overexpression Analysis Revealed the Role of N-Acetylmuramidase in Autolysis of Lactobacillus delbrueckii subsp. bulgaricus Ljj-6

Autolysis of lactic acid bacteria (LAB) plays a vital role in dairy processing. During cheese making, autolysis of LAB affects cheese flavor development through release of intracellular enzymes and restricts the proliferation of cells in yogurt fermentation and probiotics production. In order to explore the mechanism of autolysis, the gene for the autolytic enzymes of L. bulgaricus, N-acetylmuramidase (mur), was cloned and sequenced (GenBank accession number: KF157911). Mur gene overexpression and gene knockout vectors were constructed based on pMG76e and pUC19 vectors. Recombinant plasmids were transformed into L. bulgaricus ljj-6 by electroporation, then three engineered strains with pMG76e-mur vector and fifteen engineered strains with pUC19-mur::EryBII were screened. The autolysis of the mur knockout strain was significantly lower and autolysis of the mur overexpressed strain was significantly higher compared with that of the wild type strain ljj-6. This result suggested that the mur gene played an important role in autolysis of L. bulgaricus. On the other hand, autolytic activity in a low degree was still observed in the mur knockout strain, which implied that other enzymes but autolysin encoded by mur were also involved in autolysis of L. bulgaricus.

Comparative proteomics analysis of human and ruminant milk serum reveals variation in protection and nutrition

In present study, 198, 169, 213 and 128 proteins were identified and quantified in human, cow, goat and yak milk serum respectively by using proteomics techniques. Large variations were observed between human and ruminant milk proteins. Human milk contained higher concentration of mucosal immune response, complement proteins and regulators. The concentration of bactericidal proteins were relatively higher in ruminants milk. Human milk exclusively expressed proteins important for delivery or utilization of nutrients. Peptidase inhibitors prevent the bioactive proteins/peptides in human milk from gastral-intestinal digestion. Protein composition among ruminants milk was similar but with variations. Goat milk contained high level of complement proteins but low level of corresponding regulators. In addition, the acute phase proteins were significantly higher in goat milk. Of note, osteopontin in yak milk was enriched, which could offer an alternative source for producing osteopontin and revealed possible nutritional value of yak milk.

Effect of high intensity ultrasound pretreatment on functional and structural properties of micellar casein concentrates

This work investigated the impact of high intensity ultrasound (HIUS) pretreatment on the functional properties and structural characteristics of micellar casein concentrate (MCC). Microfiltered casein protein retentates were treated with HIUS for 0.5, 1, 2, and 5 min prior to spray drying. The results showed that conductivity, solubility, emulsifying, gelling increased significantly as the ultrasonic time prolonged, but the change of pH value were insignificant. In addition, the structural characteristics of MCC for all samples were studied. There was an increase in surface hydrophobicity (Ho) and a reduction in particle size compared with the control (without HIUS pretreatment). The secondary structure of HIUS pretreated MCC samples changed significantly with an increase in β-sheets and random coils and a reduction in α-helix and β-turn. It can be speculated that HIUS pretreatment facilitate the change of functional properties of MCC and these changes would promote its application in food industry.

Differences in the Triacylglycerol and Fatty Acid Compositions of Human Colostrum and Mature Milk

Human colostrum is important for immune system development and plays a protective role for infants. However, the comprehensive exploration of lipids, which account for 3-5% of milk, and their biological functions in human colostrum was limited. In present study, the triacylglycerol (TAG) and fatty acid (FA) compositions of human colostrum and mature milk were analyzed and compared. Variations were observed in both the TAG and FA compositions. The concentrations of 18:1/18:1/16:0 TAG, high-molecular-weight and unsaturated TAGs were significantly higher in colostrum, whereas mature milk contained more low/medium-molecular-weight TAGs and medium-chain FAs. Furthermore, there were also specific TAGs in both colostrum and mature milk. Our data highlighted targets for further investigation to elucidate the biological function of lipids in colostrum milk. In addition, the comprehensive analysis of TAGs in Chinese colostrum might help in designing infant formula for Chinese babies, especially the preterm ones.

Identification and Functional Validation of Autolysis—Associated Genes in Lactobacillus bulgaricus ATCC BAA-365

Lactic acid bacteria (LAB) are important organisms in food production. Indeed, LAB autolysis is very critical in dairy processing. For example, it influences the development of cheese flavor by releasing intracellular enzymes, and controls cell growth in yogurts and probiotic products. Two component systems (TCS) constitute essential environmental sensors and effectors of signal transduction in most bacteria. In the present work, mutants of one TCS (LBUL_RS00115/LBUL_RS00110) were generated to assess the relationship between TCS and cell autolysis. The mutants displayed decreased autolysis in comparison with wild type; meanwhile, complementation reversed this effect. The interaction between LBUL_RS00115 and LBUL_RS00110 was confirmed by yeast two-hybrid analysis. These observations suggested that the TCS (LBUL_RS00115/LBUL_RS00110) was involved in autolysis in Lactobacillus delbrueckii subsp. bulgaricus.