Study On Improvement Yield And Quality Of Yeast Extract

Production of yeast extract with waste brewer's yeast was investigated, and emphasis of this thesis was to improve yield and quality of yeast extract. The result indicated:1. Hops could be decomposed when waste brewer's yeast was treated with 0.5% NaHCO3(w/w). The time of treatment with NaHCO3 was 1 hour.2. The optimum autolysis conditions adding salt as autolysis promoter were that pH was adjusted to 5.0, at 50 C, 3% salt, and 10% brewer's yeast suspension for 40 hours. Yield, the content of amino acid nitrogen in supernatant was 47.50%, 0.498g/100mL, respectively.3. The mechanical cell breaking could obviously increase the rate of autolysis and improve yield and the content of amino acid nitrogen in supernatant. The effect of high pressure homogenization was better than the effect of supersonic wave cell breaking. The optimum condition of high pressure homogenization was that 10% brewer's yeast suspension was homogenized under 35MPa for two times.4. Adding papain could decrease the time of autolysis and improve yield and the content of amino acid nitrogen in supernatant. After the high pressure homogenization, the optimum autolysis conditions of adding papain were that papain was added by 0.8% (according to the dry weight of brewer's yeast) at 4 hours after autolysis beginning, pH was adjusted to 5.5, then autoylzed at 55 C for 28 hours. The content of amino acid nitrogen in supernatant, yield was 0.714g/100mL, 69.47%, respectively. The content of amino acid nitrogen in supernatant was increased by 42.97%, and net growth rate of yield was 21.97%.5. The optimum conditions of extracting 5'-phosphodiesterase from malt roots were that fresh malt roots were kept in nine times of water at 5 C for 24 hours. The extracting solution was filtered, which was the raw 5'-phosphodiesterase solution. The activity of this enzyme came to 143.5U/mL.6. Adding raw 5'-phosphodiesterase solution to autolyzed solution could improve thecontent of 5'-mononucleotides in supernatant. The optimum hydrolysis conditions were that 5'-phosphodiesterase was added by 5% (v/w), pH7.0 at 60 C, for 2 hours. The content of 5'-mononucleotides in supernatant came to 8.06mg/mL.7. The optimum technology conditions of yeast extract production: waste brewer's yeast -cleaning, filtration, centrifugation-treating with NaHCO3-centrifugation-yeast slurry -yeast suspension (10%)-high pressure homogenization-autolyzing-heating-cooling -5'-phosphodiesterase hydrolyzing-deactivating enzyme-cooling-centrifugation -supernatant-spray drying-powdered yeast extract.8. 100g dry brewer's yeast could produce 73.8g powdered yeast extract. Total nitrogen content, a-amino acid nitrogen content, 5'-GMP and 5'-IMP content of product was 9.23%, 5.28%, 1.45%, 0.37%, respectively.