The Nutritive Value of Pasture Proteins
VII. Digestibility of Proteins in Orchard Grass Dried by Wilting and Heating-Investigation Using Two Different Pepsin-Digestion Methods
1962 Volume 33 Issue 1 Pages 32-37
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1962 Volume 33 Issue 1 Pages 32-37
Two drying processes, wilting for 7 days in the laboratory and heating at 70°C with ventilation, were examined for effect on the digestibility of proteins in orchard grass (Dactylis glomerata).
The proteins in the grass were fractionated into 5 groups, water-, 0.3%-NaOH-, and hot-alkaline-60%-ethanol-soluble and insoluble protein, using successive extractions with these solvents.
The two digestion methods described in the previous paper were applied. In "digestion A", grass samples were ground and digested with pepsin before various forms of protein nitrogen were determined. In this case, digestibility was calculated comparing the value of protein N in each fraction before and after pepsin-digestion. In "digestion B", the fractions extracted with the solvents (and the insoluble fraction) were treated with pepsin. Digestibility was determined from a decrease in protein nitrogen.
The results obtained are as follows:
1. Although the amount of total nitrogen in the grass changed neither by wilting nor by heat-drying, the protein nitrogen (the sum of the protein N in each fraction) in the fress grass decreased to a large extent by wilting, but slightly by heat-drying (table 1).
Conspicuous changes in amount of proteins in each fraction by drying were a decrease in water-soluble protein N and an increase in water-soluble non-protein N by wilting and a decrease in water-soluble protein N and an increase in hot-alkaline-ethanol-soluble protein N by heat-drying (table 2).
2. In wilted grass, digestibility "A" was higher than digestibility "B" in water-soluble, hot-alkaline-ethanol-soluble, and insoluble protein, showing the same trend as in fresh grass.
3. Water-soluble protein showed a little change in digestibility "A" by wilting. On the other hand, the digestibity "A" of hot-alkaline-ethanol-soluble and insoluble proteins decreased remarkably by wilting.
4. After wilting, digestibility "B" decreased considerably in water-soluble and hot-alkaline-ethanol-soluble proteins, scarcely changed in NaOH-soluble protein and decreased remarkably in insoluble protein.
5. By heat-drying, digestibility "B" decreased a little in water-soluble protein, increased considerably in NaOH-soluble protein, hardly changed in hot-alkaline-ethanol-soluble protein, and decreased remarkably in insoluble protein.
6. The digestibility of protein as a whole was a little lower in wilted grass than in fresh grass by digestion "A", much lower in wilted and in heat-dried samples than in fresh grass by digestion "B".
