Evaluation of chemical composition, gas production and digestibility of Lathyrus sativus grain treated using different heat-processing by in vitro and in situ experiments

Introduction Providing the energy and protein in the diet of livestock, due to the high cost of its sources makes the highest cost of feed. Therefore, new and cheap domestic resources should be used in order to reduce costs and independency. Lathyrus sativus as a source of protein has been used in ruminants’ diet and because of similar amino acids profile to soybean meal can be used instead of soybean meal in ruminants’ diet. The protein content of Lathyrus sativus is 25.6-35.9 % of its dray matter. It is also reported that heat-processed soybeans are used as an important source of protein and energy in ruminants because heating reduces the breakdown of protein in the rumen and the passage of essential amino acids into the intestine (5). On the other hand, the reduction of anti-nutrients due to heat treatment, especially extrusion in soybean, has been reported in several studies. There is limited information about the effect of heat-processing on the nutritional value of Lathyrus sativus. The purpose of this experiment was to investigate the chemical composition, anti-nutrients, extent and rate of gas production and protein digestibility of Lathyrus sativus treated with different heat-processing by in vitro and in situ experiments.Materials and methods The Lathyrus sativus seed were processed by 1) Autoclave at 120 ˚C, 2) Oven at 100 ˚C, 3) Extruding at 110 ˚C, 4) Roasting on direct heat, 5) Furnace at 120 ˚C and 6) Furnace at 200 ˚C. Chemical composition including dry matter, organic matter, crude protein, crude fat, calcium and phosphorus was performed using AOAC methods. Tannin and total phenolic compounds were meseared by Folin and Ciocalteu (12). Extent and rate of gas production were done based on Menk and Stingas. Mobile nylon bag technique was applied for determination of protein digestibility in the romen and intestine. Data were analyzed using GLM procedure of SAS using a completely randomized design with 5 replications.Results and Discussion Dry matter, ash, crude protein, crude energy, crude fat, calcium and phosphorus were not affected by different processing methods (P <0.05). However the amount of acid detergent fiber (ADF) and natural detergent fiber (NDF) with heat processing methods was significantly lower than non-processing method (P <0.05). Autoclaving and extrusion of Lathyrus sativus reduced the amount of phenolic compounds compared to the control (P <0.05). In addition, the furnace at 120 ° C and roasting even more than autoclaving and extrusion reduced the total phenolic compounds. The amount of gas production during various hours and its rate were significantly affected by the different processing procedures (P<0.05). At the initial hours (2 and 8 h) of incubation, the amount of gas produced in Lathyrus sativus unprocessed and processed in oven 100 ˚C was higher than autoclave 120 ˚C, furnace 120 ˚C, and roasted seeds. Extruded seeds were reduced gas production in initial hours than any other processed methods except those put in the furnace 200 ˚C. The Lathyrus sativus placed in 200 ˚C furnace severely diminished gas production of the incubation at primary hours. The extruded Lathyrus sativus showed higher gas at the 12th and 24th hours of incubation compared with primary hours. This trend continued up to the 96th hour of incubation. The results of gas production had conformity with rumen and intestine digestibility. It seems that the steam pressure in extrude and autoclave process can influence Lathyrus sativus fermentation. This effect in extrude process was higher than autoclave. The rumen and intestine dry matter and protein digestibility in extruded process was higher than the others. Lathyrus sativus with no process, at oven 100 ˚C and furnace 200 ˚C were shown equal dry matter and protein digestibility. The findings of the present research revealed that extruding, autoclaving and roasting procedures lead to increase of dry matter through decreasing water content and that it had no significant effect on other chemical composition. Also, the findings showed that place of Lathyrus sativus in furnace 200 ˚C decreased ADF and NDF Lathyrus sativus which might be due to the removal of some of the shells in this processing. Consequently, the process of extruding, autoclaving and roasting reduced the rapid part degradation of dry matter and protein of Lathyrus sativus and caused the slow part of degradation to increase, which is in consistent to other researcher about increasing of intestine protein digestibility in extruded and roasted soybean seed.Conclusion Extruded, autoclaved and roasted Lathyrus sativus with the reduction of the amount of ruminal disappearance and the increase of the post ruminal digestibility of dry matter and crude protein transferred the place of the digestion of protein from the rumen to the small intestines. In furnace 200 ˚C, due to the intense denaturation of the protein or the formation of a protein-carbohydrate complex, the digestibility of dry matter and crude protein of Lathyrus sativus in the rumen and intestine was reduced. In addition, the results of our studies in confirming the studies of others reduced the concentration of total tannin and total phenolic compounds in Lathyrus sativus.