Effects of Gamma Irradiation on Chemical Composition, Antinutritional Factors, Ruminal Degradation and In vitro Protein Digestibility of Full-fat Soybean

M. Taghinejad,A. Nikkhah,M. Chamani,A. A. Sadeghi,G. Raisali

doi:10.5713/ajas.2009.80567

Abstract

The aim of this study was to evaluate the effects of gamma irradiation (y-irradiation) at doses of 15, 30 and 45 kGy on chemical composition, anti-nutritional factors, ruminal dry matter (DM) and crude protein (CP) degradibility, in vitro CP digestibility and to monitor the fate of true proteins of full-fat soybean (SB) in the rumen. Nylon bags of untreated or γ-irradiated SB were suspended in the rumens of three ruminally-fistulated bulls for up to 48 h and resulting data were fitted to a nonlinear degradation model to calculate degradation parameters of DM and CP. Proteins of untreated and treated SB bag residues were fractionated by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). Digestibility of rumen undegraded CP was estimated using the three-step in vitro procedure. The chemical composition of raw and irradiated soybeans was similar. Results showed that phytic acid in γ-irradiated SB at dose of 30 kGy was eliminated completely. The trypsin inhibitor activity of 15, 30 and 45 kGy γ-irradiated SB was decreased (p<0.01) by 18.4, 55.5 and 63.5%, respectively. From in sacco results, γ-irradiation decreased (p<0.05) the washout fractions of DM and CP at doses of 30 and 45 kGy, but increased (p<0.05) the potentially degradable fractions. Gamma irradiation at doses of 15, 30 and 45 kGy decreased (p<0.05) effective degradability of CP at a rumen outflow rate of 0.05 h -1 by 4.4, 14.4 and 26.5%, respectively. On the contrary, digestibility of ruminally undegraded CP of irradiated SB at doses of 30 and 45 kGy was improved (p<0.05) by 12 and 28%, respectively. Electrophoretic analysis of untreated soybean proteins incubated in the rumen revealed that β-conglycinin subunits had disappeared at 2 h of incubation time, whereas the subunits of glycinin were more resistant to degradation until 16 h of incubation. From the SDS-PAGE patterns, acidic subunits of 15, 30 and 45 kGy γ-irradiated SB disappeared after 8, 8 and 16 h of incubation, respectively, while the basic subunits of glycinin were not degraded completely until 24, 48 and 48 h of incubation, respectively. It was concluded that γ-irradiated soybean proteins at doses higher than 15 kGy could be effectively protected from ruminal degradation.

Highlights

Incorporating soybeans and its byproducts into rations for dairy cattle is a fairly common practice
The results observed in this study indicate that the irradiation treatment has a substantial effect on the anti-tryptic activity naturally present in soybeans
Farag (1989) reported that the detoxification dose needed for complete inactivation of all the anti-nutritional factors naturally present in soybeans seemed to be higher than the maximal dose level of 10 kGy recommended by the JECFI in 1980

Summary

Introduction

Incorporating soybeans and its byproducts into rations for dairy cattle is a fairly common practice. They are excellent sources of essential amino acids and they fit into any type of forage-based ration. Whole soybean is used as a high energy-protein supplement for dairy cows, but the. Sci. 22(4):534541 ionizing radiations, such as gamma rays emitted from radioisotopes 60 Co and 137 Cs, or high energy electrons and X-rays produced by machine sources (Diehl, 2002). In 1981, the US Food and Drug Administration (FDA) concluded that food irradiated at 10 kGy or less can be considered safe for human consumption (FDA, 1981). Treatment of soybean meal and canola meal with gamma irradiation was successful in reducing degradation of protein by rumen microorganisms and increasing protein intestinal digestibility (Shawrang et al, 2007, 2008)

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