Brewer's Yeast Slurry, I. Composition as Affected by Length of Storage, Temperature, and Chemical Treatment

Abstract

A factorial design split plots in time was used to evaluate effects of temperature (4.4C, 21C, 30C) and length of storage (0, 7, 14, 21, 28, 35 days) on the composition of brewer's yeast slurry. Dry matter, pH, crude protein, true protein, ammonia, and nitrogen solubility were measured. Dry matter and true protein contents declined linearly to 35 days at 4.4C storage while at the higher temperatures these declined rapidly to 7 days then remained constant. Loss of original dry matter content amounted to 4.9%, 13.2%, and 10.4% in yeast slurry stored at 4.4C, 21C, and 30C. Crude protein content (dry basis) varied inversely with dry matter. Nitrogen solubility increased over time at the higher temperatures. These changes were accompanied by a reduction in live cell numbers. In a second storage trial lasting 6 wk, yeast slurry (stored at 21C) was treated with no chemical additive, a mixture of acetic and propionic acids, or a mixture of acetic, propionic, formic acids and formaldehyde each at 1% wt/wt. Loss of dry matter was reduced by the additives, the mixture including formic acid and formaldehyde being most effective. Increases in ammonia content, breakdown of true protein, and nitrogen solubility were not prevented by either chemical additive. Live cell numbers were reduced greatly by addition of either additive to the slurry.