Production of zinc-enriched yeast extracts

Dried zinc-containing yeasts (5 g zinc / 100 g yeast) were rehydrated at 20 % solids and subjected to autolysis at 50 degreesC for 24 h. Either of the following enzymes, glucoamylase, mannanase, beta -1, 3 glucanase, fungal acid protease, validase FP or papain was added to promote lysis. Autolysis yields, recovery of zinc in the yeast extract (YE) as well as composition of the YE (nitrogen, sugars) were determined. In the absence of added enzymes, autolysis yield with fresh Bakers' yeast was 46 %, while that with the rehydrated zinc-enriched yeasts was 21 %. All adjunct enzymes increased autolysis yields (up to 41 %) from the rehydrated zinc-enriched yeast. The fraction of the zinc that was recovered in the YE ranged from 64 to 81 % of the total amount originally present in the yeast, depending on the enzymes used (beta -1, 3 glucanase and validase FP gave best results). Yeast extracts obtained from glucanase had higher contents of glucose, but lower contents of a-amino nitrogen than those produced with the proteases. The use of enzymes to obtain YE from rehydrated zinc-containing yeasts generated YE having 15 g of zinc/100 g of yeast extract.