Submitted to: Journal of Dairy Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/21/2010
Publication Date: 4/25/2011
Citation: Hoffman, P.C., Esser, N.M., Shaver, R.D., Coblentz, W.K., Scott, M.P., Bodnar, A.L., Schmidt, R.J., Charley, B.C. 2011. Influence of ensiling time and inoculation on alteration of the starch-protein matrix in high-moisture corn. Journal of Dairy Science. 94:2465-2474. Interpretive Summary: Currently, ruminal digestion of starch from high-moisture corn is believed to be limited by zein proteins that are insoluble in both water and rumen fluid. A logical addition to this hypothesis is that rumen bacteria have greater access to starch granules when these zein proteins are degraded during the fermentation process in the silo. In this study we evaluated these hypotheses with two random corns and found both hypotheses to be essentially correct. Two random high-moisture corns were ground, and ensiled for up to 240 d. Ensiling time (0 vs. 240 d) reduced most zein-protein subunits. Ensiling reduced 27-kDa ' zein by 42 to 73%, which is important because this subunit cross-links starch granules together. Degradation of zein proteins during the ensiling process appears to be best explained by proteolytic activity because inoculation with a bacterial culture (fermentation aid) yielded greater concentrations of fermentation acids, but had no effect on the degradation of zein proteins in fermented high-moisture corns. Pictures from a scanning electron microscope confirmed that starch-granule clusters disassociated during fermentation in the silo; this should logically allow greater access to starch granules by rumen bacteria when fermented high-moisture corn is consumed by dairy cows. This knowledge should help lead to more efficient feed utilization by dairy cows.
Technical Abstract: The fates of hydrophobic zein proteins, which encapsulate corn starch creating vitreous endosperm, have not been investigated in high moisture corn (HMC). To assess influences of ensiling time and inoculation on hydrophobic zein proteins in HMC, quadruplicate samples of two random corns (A and B) containing 25.7 and 29.3 % moisture were ground, inoculated (I) with or without 600,000 cfu/g of Lactobacillus buchneri 40788 (Lallemand Inc., Milwaukee, WI) and ensiled for 0, 15, 30, 60, 120 and 240 d. Nutrient composition (CP, starch, ADF, NDF), fermentation (pH, lactate, acetate) and protein degradation markers (buffer-soluble CP, isopropanol-soluble CP, NH3-N) were evaluated. At 0 and 240 d, a, ', d and ß zein subunits were profiled using HPLC. Data were evaluated as a split-split plot using the PROC MIXED procedures of SAS. Ensiling time and inoculation reduced pH, and altered lactate and acetate contents of HMC. Lactate and acetate contents of A, AI, B and BI at 240 d were 0.40, 0.32, 1.11, 0.73 and 0, 0.35, 0.30 and 0.87 % of DM, respectively. Buffer-soluble CP in HMC increased from 1.5-2.0 % of DM at 0 d to > 4.0 % of DM at 240 d. Inoculation had no effect on buffer-soluble CP but increased NH3-N content of HMC. Corn A contained more isopropanol soluble CP (5.8 vs 4.6 g/100 g starch) than corn B. Peak areas for 6 a, and all ' and d zein regions were greater for corn A, and ensiling (0 vs 240 d) reduced all zein subunits with the exception of 2 a and 1 d subunits. Ensiling reduced (42.2-73.2%) 27 kDa ' zein, that is primarily responsible for cross linking in the starch-protein matrix. Despite altering lactate and acetate contents, inoculation had no effect on degrading hydrophobic zein proteins in HMC. Data suggest hydrophobic zein proteins in the starch-protein matrix of HMC are degraded by proteolytic activity over an extended ensiling time.