Influence of ensiling time, inoculation on zein proteins in HMC

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The fates of hydrophobic zein proteins, which encapsulate corn starch to create vitreous endosperm, have not been investigated in high-moisture corn (HMC).

To assess influences of ensiling time and inoculation on zein proteins in HMC, quadruplicate samples of 2 random corn hybrids (A and B), containing 25.7 percent and 29.3 percent moisture, were ground, inoculated with or without 600,000 cfu/g of Lactobacillus buchneri 40788 (Lallemand Animal Nutrition, Milwaukee, Wis.), and ensiled for 0, 15, 30, 60, 120 and 240 d. Nutrient composition [crude protein (CP), starch, acid detergent fiber, and neutral detergent fiber], fermentation (pH, lactate, and acetate), and protein degradation markers (buffer-soluble CP, isopropanol-soluble CP, and NH3-N) were evaluated. At 0 and 240 d, 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 decreased 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 percent of DM, respectively. Buffer-soluble CP in HMC increased from 1.5 percent to 2.0 percent of DM at 0 d to >4.0 percent 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 than did corn B and peak areas for (varians) zein regions were greater for corn A. Ensiling (0 vs. 240 d) decreased all zein subunits with the exception of 2 α and 1 δ subunit. Ensiling decreased (42.2 percent –73.2 percent) γ zeins, which are 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 that hydrophobic zein proteins in the starch-protein matrix of HMC are degraded by proteolytic activity over an extended ensiling time.



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