Preparation Of Bioactive Peptides From Yeast Protein By Enzymatic Hydrolysis

The yeast protein is a kind of single cell protein with protein content high up to50%andhas a complete profile of amino acids. Especially the contents of essential amino acids forhuman (such as lysine) are very high. It also has many other advantages including wildsources, high production efficiency, easy industrialization, etc. Therefore, the preparation ofbioactive peptides from yeast protein is not only a full development of high quality proteinresource, but also of significant economic and social benefits. In this study, the peptides wereprepared from yeast protein by enzymatic hydrolysis, and then separated by ultrafiltrationtechnology. The bioactivities of the peptides in vitro were measured, and its chemicalcompositions, properties and stabilities were also evaluated. The main research results are asfollows:1. The peptides were prepared from yeast protein using yeast hydrolytic enzyme. Theoptimal hydrolytic conditions for degree of hydrolysis (DH) were determined by theorthogonal test based on single-factor experiments. The results showed that the optimalhydrolytic conditions were: temperature60℃, pH6.5, the ratio of enzyme/substrate3.5%andsolid-liquid ratio1:15. Under the optimum conditions, the influence of time on DH wasinvestigated. It was found that DH increased gradually as the extension of hydrolytic time,and approached to stable after6h (DH=25.31%) hydrolysis, and the peptides yield from6hhydrolysates based on100g yeast was42.57±0.11g. Isoelectric point method and ethanolprecipitaiton method were made a comparative study for impurity removal effect. The resultsindicated that ethanol precipitation method had better removal rates and less loss of peptides.When ethanol-hydrolysates volume ratio was1:1, the removal rate of nucleic acid andpolysaccharide were87.93%and53.43%respectively, and the loss rate of peptides was only13.79%. The bioactivity of yeast peptides after impurity removal (YP1) was detected in vitro.The results showed that it had certain superoxide anion scavenging activity, DPPH radicalscavenging activity, α-glucosidase inhibitory activity and ACE inhibitory activity, with IC50values were3.98mg/mL、0.61mg/mL、21.13mg/mL and55.39μg/mL, respectively.2. MWCO-5kDa ultrafiltration membrane was employed to separate the yeast proteinhydrolysates, and the influences of ultrafiltration conditions on membrane flux were examined. The optimal ultrafiltration conditions were: peptides concentration15mg/mL,pH7.0, operation pressure0.21MPa, and temperature35℃. After ultrafiltered for1h,23.44±0.27g peptides was obtained from100g yeast. Equally, the bioactivity of yeast peptidesafter ultrafiltration (YP2) was detected in vitro. The results showed that after ultrafiltration,bioactive components were enriched and YP2had better activities than YP1. The IC50valuesof superoxide anion scavenging, DPPH radical scavenging activity, α-glucosidase inhibitoryand ACE inhibitory activity were2.60mg/mL,0.59mg/mL,10.62mg/mL and29.32μg/mL,respectively.3. Basic compositions of YP2were determined and the main component was peptideswith content of74.73%while the content of amino acids was2.77%. Results of molecularweight distribution measured by FPLC indicated that, the content of peptides lower than1kDawas80.41%, with MW1kDa-3kDa was about18.36%, while others were withMW3kDa-5kDa. Compared with YP1, YP2had better solubility, water absorption, while theemulsification and emulsion stability even decreased. The study on chemical stability andbiological stability illuminated that YP2components showed good acid-base stability, thermalstability and resistance to digestion stability.