Nutritive Value of Distillers’ Dried Solubles as a Source of Protein

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Abstract
The nutritive value of distillers' dried solubles as a source of protein was evaluated by means of biological tests with rats and by chemical analyses. It was found to be inadequate as the sole source of protein and as a protein supplement because of deficiencies of lysine and tryptophane. Since the proteins of solubles are derived from the protein of yeast and cereal grains, a study was made of the nutritive value of dried brewers' yeast and various combinations of yeast and solubles for the purpose of determining the value of yeast in the fortification of solubles. It was found that yeast was of greater nutritive value than dried solubles as the sole source of protein and effectively supplemented solubles, corn and combinations of these products. Chemical studies revealed that solubles contain considerably less lysine and tryptophane than yeast. Furthermore, digestion experiments with proteolytic enzymes indicated that these amino acids are less available in solubles than in yeast. Since it was found that the addition of small amounts of yeast to dried solubles definitely increased its nutritive value, production of dried solubles with a higher yeast content would be desirable.