ABSTRACT
Summary Prevention of proteolysis during ensiling is important in preserving the nutritive value of silage. Hence, the mechanism by which silage protein is protected against degradation was studied in wilted annual ryegrass (Lolium multiflorium Lam.) silage pretreated with formic acid, formaldehyde, and a formic acid-formaldehyde mixture.
637Raw-wilted ryegrass, control ryegrass silage, and treated ryegrass silage were extracted and fractionated under conditions previously found to maximize yield of nitrogenous constituents and minimize proteolysis during the extraction of fresh grass. Extractions were by boric acid-borate buffer at pH 8.0 with and without detergent (1% sodium dodecyl sulfate). Sodium metabisulfite, an antioxidant, was included in all extractions. The fractions, obtained by differences in extractability, solubility, and molecular size, were analyzed for nitrogen content; in the case of the soluble fractions, first moment apparent molecular weights were determined by a specially designed automated gel filtration apparatus. For the forage extracted without detergent, the percentages of total nitrogen as nonextractable-insoluble residue were 72.5% for formic-formaldehyde-treated silage, 65.8% for the wilted control, 63.4% for formaldehyde-treated, 49.7% for formic acid-treated, and 41.0% for the untreated silage. The percentages of total nitrogen as extractable insoluble nitrogen were 17.1% for wilted control, 12.9% for formic-formaldehyde-treated silage, 7.6% for formaldehyde-treated silage, 5.8% for formic acid-treated silage, and 2.7% for the untreated control silage. The wilted control contained 21.7% soluble “protein,” whereas the untreated control silage contained 47.8% soluble “protein.” The formic acid-, formaldehyde-, and formic acid-formaldehyde-treated silages contained 38.1%, 28.1%, and 18.6% soluble nitrogen, respectively. Also, as was determined by gel chromatography, the treated silages had a higher relative concentration of high-molecular-weight polypeptides than the control silage. With the addition of detergent to the buffer 5%-14% more nitrogen was extracted and an additional 3%-5% nitrogen was solubilized. Neither formic acid nor formaldehyde protects proteins normally soluble in the plant cell or eliminates anaerobic activity. Both treatments reduce the extractability and therefore the degradability of polypeptides associated with cell membranes and the plant matrix. At the levels employed, formaldehyde is about twice as effective as formic acid in protecting proteins, but because of the complementary nature of their mechanisms of protection, the effect on protection of combining both chemicals in one treatment is that of additivity.
