Protection of cottonseed meal protein from rumen degradation using dextrin to create Maillard-type reactions

Abstract Text:  

Various methods of heat processing are used to reduce ruminal protein degradation. Reduction in protein degradability occurs because of Maillard-type reactions between reducing carbohydrates and amino groups. We hypothesized that addition of dextrin followed by heat treatment would decrease cottonseed meal (CSM) ruminal protein degradation rate. Treatments were control CSM (C), CSM plus dextrin without heat (D), and CSM plus dextrin heated at 140°C for 120 minutes (DH). Dextrin was included at 3 times the molar concentration of reactive amino groups. Batch culture in vitro experiments were conducted to compare degradation rates. Treatments (n=3/treatment/time period) were weighed into tubes, inoculated with a 1:4 mixture of strained rumen fluid and McDougall’s buffer, and closed with stoppers fitted with one-way valves. After inoculation, half of the tubes were immediately frozen while the remaining were fermented for 48 h in a shaking water bath at 39°C. Tubes were thawed, centrifuged to remove supernatant and bacteria, and dried at 55°C. Dry matter and CP disappearance and AA profile of the residues were analyzed at 0 and 48 h. pH was measured at 0, 4, 8, 12, 24, and 48 hours of fermentation, at which times supernatant subsamples were taken for ammonia analysis. Ammonia production was used as a measure of CP degradation and >88% of feed N was recovered in NH₃ by 48 h. Data were analyzed as a completely randomized design using the GLM procedure of SAS and Fisher’s LSD for means comparison. Rank transformations were used to normalize pH data. Quadratic equations best fit the rates of NH₃ degradation, and linear and quadratic coefficients were calculated and compared among treatments. Crude protein disappearance was greater (P ≤ 0.05) at 0 h in C than D and DH treatments, but treatments did not differ at 48 h. pH was not different (P > 0.05) among treatments at any time point. Linear slope of NH₃ production was greatest for C, and different among all treatments (P ≤ 0.001). The quadratic coefficient was similar between C and D and both were greater than DH (P ≤ 0.001). There were no differences in AA profiles among treatments at 0 or 48 h, although concentrations of individual AA changed due to fermentation. We concluded that addition of dextrin to CSM slowed ruminal CP degradation but did not selectively protect AA.

Keywords: CP degradation; Maillard reaction; Rumen fermentation