Effects of plant enzyme inactivation or sterilization on lipolysis and proteolysis in alfalfa silage

Abstract

This experiment studied the contribution of plant enzymes and microbial activity on lipolysis and proteolysis in ensiled alfalfa. Before ensiling, the wilted alfalfa was treated with plant enzyme inactivation by autoclaving or with sterilization by γ-ray irradiation. The treated alfalfa was then inoculated with commercial lactic acid bacteria inoculants and ensiled for 40 d. Alfalfa without treatment was ensiled as the control. The content of total fatty acid (FA) after ensiling decreased 43% in the control silage and 28% in the γ-ray-treated silage, but did not change in the autoclave-treated silage. Among the major FA (C16:0, C18:2n-6, C18:3n-3), a considerable increase was observed in proportion of C16:0 in the control silage as compared with fresh alfalfa; conversely, decreases in proportions of C18:2n-6 and C18:3n-3 occurred during ensilage. Silage treated with γ-ray radiation at ensiling had a smaller proportion of C16:0 and greater proportions of C18:2n-6 and C18:3n-3 than control silage. Autoclave treatment further decreased proportions of C16:0 and most of the other FA, and increased C18:2n-6 and C18:3n-3 proportions in comparison with γ-ray treatment. Proportions of C16:0, C18:2n-6, C18:3n-3 and other detected FA (except for the proportion of C15:0) did not differ between fresh forage and autoclave-treated silage. Remarkably, smaller nonprotein nitrogen content was observed in the autoclave-treated silage compared with the γ ray-treated silage or the control silage. These results indicated that an extensive lipolysis occurred during ensiling of alfalfa, and plant enzymes played a major role in lipolysis and proteolysis.

Chemical composition and in vitro fermentation characteristics of high sugar forage sorghum as an alternative to forage maize for silage making in Tarim Basin, China

“…It is interesting to note that the ensiling process had little impact on the CP of MZ and HS (<5% change), but it reduced the CP concentration by 23% from 64 g CP per kg of DM in FS to 49 g CP per kg of DM in FSS. This may be related to the proteolysis reaction during ensiling of the forages (Heron et al 1989;Ding et al 2013). Merry et al (2006) observed more active proteolysis reaction when pH is higher in silage, due to low WSC and starch in forage before ensiling.…”

Effects of addition of malic or citric acids on fermentation quality and chemical characteristics of alfalfa silage

“…The pH was measured immediately; then, one part of the filtrate was acidulated with 7.14 M H 2 SO 4 and filtered with a 0.45-µm dialyzer. Lactic acid, acetic acid, propionic acid, and butyric acid were analyzed by HPLC (Shodex KC-811 column; Shimadzu, Kyoto, Japan; oven temperature: 50°C; flow rate: 1 mL/min; SPD-10Avp, Shimadzu: 210 nm) as described previously (Ding et al, 2013). A total of 1 mL of 250 g/L (wt/vol) trichloroacetic acid was added to 4 mL of the second part of the filtrate from each bag.…”

“…Following this, 1 g of NaHSO 4 was added and, after vortexing for a further 2 min, the samples were centrifuged at 1,400 × g for 5 min at 4°C. The upper liquid layer was used for the determination of FAME by GC with attached MS (model 6890N-5975C, Agilent Technologies, Santa Clara, CA) fitted with a fused-silica capillary column (30 m × 0.25 mm × 0.50 µm; DB-FFAP, Agilent) as described previously (Ding et al, 2013).…”

“…Because including malic or citric acids provided additional substrates to the silage fermentation, the DM and WSC content in ensiled alfalfa increased with the increased application of malic or citric acids. Reduction in proteolysis during ensilage is a conventional but prevalent concern of ensiled legume forage because extensive proteolysis in silage, mainly caused by plant proteases (Ding et al, 2013), normally results in a low efficiency of N utilization by ruminants (Givens and Rulquin, 2004). Lowering pH value in ensiled forage can effectively inhibit proteolysis because plant enzymes are quickly inactivated with a decrease in pH (Kung and Bedrosian, 2010).…”

“…Additionally, the FA composition in ensiled forages has been of interest. Generally, linoleic acid (C18: 2n -6) and α-linolenic acid (C18: 3n -3) make up a major proportion of the FA composition of fresh and ensiled forage (Clapham et al, 2005;Ding et al, 2013). It was reported that a high intake of PUFA could increase the concentration of PUFA in ruminant products (Wood and Enser, 1997;Kalač and Samková, 2010) and consequently be beneficial to human health (Simopoulos, 2001).…”