Effect of different chemical and enzymatic treatments on nutritional value, gas production and digestibility of tomato Waste by in vitro techniques

Considering water and land limitation in agriculture, providing some year-round feedstuffs for livestock animals is a challenge for producers. Agro-industrial co-products, which are not in completion with human food resources, can be effectively consumed by ruminant species. Tomato waste (TW) is a by-product obtained after production of tomato sauce, paste and juices in manufactures. Using some physical and chemical processing of by-products can improve their nutritive value for feeding ruminants. Autoclave and exogenous fibrolytic enzymes are of those physical and chemical processing, which have been applied for several agro-industrial co-products. This study aimed to evaluate nutritive value, nutrient digestibilities and gas production parameters of chemically (autoclave and urea treating) and enzymatically (Natuzyme®) treated TW. Material and Fresh TW were sun-dried and were stored in cold temperature until the beginning of the experiments. Experimental treatments included: control (untreated), autoclaved (120 psi for 30 min), urea (3% urea added DM basis and anaerobically stored for 28 days in room temperature), and autoclave+urea (combination of previously mentioned treatments, 0. 5% enzyme and 1% enzyme). One day before the starting of experiment, aqueous solutions of enzymes were added to the samples. For the rest of experiments, samples were ground to pass 1 mm sieve size. Chemical composition of samples (i. e. , DM, NDF, ADF, CP and ash) was determined. For in vitro gas production tests (GP), the rumen fluid was taken from three ruminally fistulated Mehraban male mature lambs. For measuring kinetic parameters of gas production, 200 mg of samples were incubated in glass syringes containing 30 ml buffered-ruminal fluid for 144 hours. The cumulative produced gas was recorded at different times of incubation. The gas production data were fitted to exponential equation of GP= A (1-e-c(t-L) ); where GP is gas production at different times of incubation, A is asymptotic gas production (ml/200 mg DM), c is rate of gas production (/h), t is time of incubation and L is lag time (h). For measuring digestibility parameters, 500 mg of samples in glass syringes contained 40 ml buffered ruminal fluid were incubated at 39 °C for 24 hours. Volume of GP, metabolizable energy (ME), organic matter digestibility, partitioning factor (PF) and microbial biomass were determined after termination of incubation. All the in vitro gas production trials were carried out in three runs. Data were analyzed based on a completely randomized design using Proc GLM of SAS software. The differences among treatments were evaluated using Duncan's multiple range test. The highest amount of NDF, ADF and ash were observed in control treatment, while the highest CP was recorded with the treatment of 3% urea. The lower cell wall content in treated TW could be due to the role of urea and enzymes in breaking the links between cellulose and lignin. The treatment of 1% urea had the highest increment in comparison with control which is likely because of the activity of added enzymes in increasing fermentation of TW cell wall. The lower GP of 3% urea and autoclave+urea among all treatments can be due to the negative effect of ammonia on both direct GP from microorganisms activities and indirect GP from buffering of produced volatile fatty acids during fermentation. Also, the highest values of L were observed in 3% urea and autoclave+urea groups. The treatments were significantly different in dry matter  digestibility and OMD of which control had the lowest value. This could be due to the higher percentage of cell wall in control TW and the negative relation of cell wall with digestibility. The treatment of 1% enzyme and control showed the highest and lowest MB, respectively (P<0. 05). The higher MB in treated TW shows that processing had increased the availability of growth required factors for microorganisms. The PF were higher in urea, autoclave+urea and 1% enzyme groups (P<0. 05). The higher value for this parameter shows that degraded organic matter is more directed towards microbial biomass production rather than production of volatile fatty acids. The treatment of 1% enzyme had the highest value of ME, while control showed the lowest value (9. 57 vs. 9. 30 MJ/kg DM, respectively). Considering the obtained data related to dry matter digestibility, NDF, PF and chemical compositions of different treatments, it is concluded that the administration of 3% urea and using Natuzyme® at the level of 1% of DM improved the nutritive value of TW. Further research is needed to study the effect of using TW in performance of productive ruminants.