The effects  of irradiation from gamma, electron beam, microwave and infrared sources on ruminal degradability and in vitro digestibility of soybean meal

In the past four decades, a vast knowledge has been accumulated on the chemical and biological effects of ionizing irradiation, which has contributed to promote its utilization. The chemical changes resulting from the irradiation of proteins food have been the subject of considerable study. These studies demonstrated both fragmentation and aggregation of food proteins. Application of ionizing radiation treatment of foods on an industrial scale started at the beginning of the 1980s after the joint FAO/IAEA/WHO expert committee accepted the application of a 10 kGy overall average dose for foods. Also in 1981, the U.S. Food and Drug Administration concluded that food irradiated at 50 kGy or less can be considered safe for human consumption. However, gamma irradiation of most human foods is prohibited in many countries. Most other countries that permit food irradiation also require labeling (Shawrang et al 2007). There has always been an interest in food and feed industrial applications of microwaves to improve conventional processes, with the intent of taking advantage of its rapid heating characteristics to reduce energy costs. Since it is cost competitive compared to other methods of heating, it has been used for cereal drying on a large scale. Microwave irradiation seems applicable to cereals, especially for starch, but it has not been used on a commercial scale (Sadeghi and Shawrang 2006). Soybean meal is a commonly used protein supplement for ruminants. Proteins of this supplement are extensively degraded in the rumen. Several feed processing methods (physical and chemical methods) are known to protect soybean meal proteins from ruminal fermentation. However, most of these treatments adversely affect the nutritional characteristics of the final product. No information is available concerning the comparison of gamma, electron beam, infrared and microwave irradiations on ruminal crude protein degradation Cornell Net Carbohydrate and Protein System (CNCPS). This study was conducted to compare the effects of gamma, electron beam, infrared and microwave irradiations on the ruminal protein degradability, intestinal digestibility and nitrogen fractionation of soybean meal based on CNCPS method.
Material and The Soy meal samples were obtained from the Jahan oilseed manufactory located 40 kmwest of Tehran (Iran). The CP, Ether extract (EE), and ash content were 456, 62.1 and 75 g/kg DM, respectively.Treatments were included: 1: raw meal, 2: gamma irradiated meal, 3: electron irradiated meal, 4: microwave irradiated meal, 5: infrared irradiated meal. Gamma irradiation was carried out in a cobalt-60 irradiator equipped with 3.7 PBq (100 kCi) activity at 20°C. The dose rate determined by Fricke dosimetry was 3.7 kGy/h. Three polyethylene packages of samples were irradiated in a gamma cell (Co-60) at doses of 50 kGy in the presence of air (Shawrang et al 2007). For electron beam irradiation, samples were packed in 30 cm × 40 cm × 5 cm nylon bags (0.5 mm thickness) and exposed to electron beam irradiation at the Yazd radiation processing center to dose 45 kGy at room temperature by a Rhodotron accelerator model TT200. All samples were irradiated at fixed beam energy of 10 MeV and the required irradiation doses were obtained by adjusting the electron beam parameters (electron beam current, Conveyor speed and etc.). Double side irradiation (exposure to both sides) was performed for uniform dose delivery. The dose was determined with cellulose triacetate films. Similarly, packed seed samples without irradiation served as control. Microwave irradiation was done at dose of 800 W for 4 min (sadeghi et al 2005) and infrared dose was set at 1000 W for 30 seconds. For chemical analysis, 10 g were ground to pass a 1mm screen and stored at −18 ◦C. Four adult male Moghani wethers with ruminal fistula were used for determination of ruminal degradability of dry matter and protein by nylon bag technique (Ørskov and McDonald 1979). Intestinal digestibility was measured with a three step enzymatic procedure. Proximate chemical analysis and nitrogen fractions were determined according to AOAC (AOAC 2000). Data were analyzed using the general linear models procedure of SAS (SAS 1996). Experimental data were submitted to a Duncan analysis to determine whether the different treatments yielded significantly different results.
There were no significant differences in dry matter, ether extract, protein and ash between the irradiated and non-irradiated or raw grains. The highest and the lowest rapidly degradable fraction (a) of dry matter was found in raw meal and electron beam irradiation, respectively. There were no significant differences among gamma, electron and microwave irradiation for rapidly degradable fraction (a) of dry matter. The lowest and the highest constant rate of dry matter degradability (c) was found in processed meal and raw meal, respectively (P0.05). Effect of different treatments on B1, B2 and B3 fractions was significant compared to raw meal (P0.05). The highest and the lowest intestinal digestibility of crude protein were found in processed meals and raw meal, respectively.
This study indicates that the degradation characteristics of soybean meal proteins could be altered by processing method especially infrared and electron beam irradiation. Irradiation processing of soybean meal resulted in decrease of effective protein degradation in the rumen and increase of intestinal crude protein digestibility by creating the cross-linking and aggregation of the polypeptide chains. Based upon these results, the best irradiation methods for soybean meal were suggested to be infrared and electron beam, respectively.