Determination of fermentation and digestibility parameters of tomato pomace in comparison with wheat bran under in vitro conditions

Using agro-Industrial by-products in animal nutrition is an efficient way to improve low quality materials to high quality feeds. Agro-industrial by-products are wasted often and their disposal may cause environmental problems, as they are perishable and potential pollutants. Tomato pomace (TP) is the main waste of tomato factories. In Iran, about 6.9 million tons of tomatoes are produced annually, from that about 575,000 tons of TP is produced. TP, as a by-product, is a good source of vitamin B1, B2 and a reasonable source of vitamin A. Additionally, TP contains important compounds such as carotenoids such as lycopene, which their presence in animal products can be important for consumer health. TP can be used as promising protein and fiber sources in ruminant nutrition. The chemical composition of TP in different parts of the country has already been reported. There are some discrepancies among the results in term of chemical composition. Different results obtained by various studies could be due to the different analytical methods used as well as differences in processing conditions. A few experiments have examined the potential use of TP in ruminant diets. For example, TP has been used in dairy cows without any negative effect on milk production. There are also reports of a positive effect of using TP in fattening lambs. However, information about the effect of TP on ruminal fermentation and digestibility parameters is lacking. The aim of this study was to determine the chemical composition and nutritional value of dried TP and its replacement with wheat bran (WB) in vitro.

Initially the TP was prepared from Rojin Tak factory in Kermanshah. After that, TP samples have dried in the shade, and transported to the laboratory. Chemical composition and gas production parameters of TP and WB were measured using conventional methods. Dry matter (DM), ash, Ether extract (EE), neutral detergent fiber (NDF), acid detergent fiber (ADF) and crude protein (CP) of the samples were determined. In the first gas production experiment, ruminal fluid was obtained from two male Lori sheep (live weight 47 ± 0.2 kg) fitted with permanent rumen cannula. Samples (250 mg on a DM basis and particle size 1 mm) were accurately weighed into 100 ml serum bottles. Each bottle was filled with 5 mL strained rumen fluid and 20 mL buffer solution, closed with a butyl rubber stopper, sealed with aluminum crimp, shaken and placed in a water-bath at 39°C. Gas production (ml/250 mg sample) after 24 h (GP24), 48 h (GP48), 72 h (GP72) and 96 h (GP96) incubation were determined. two parameters of b (GP from the fermentable fraction (ml)) and c ( rate constant of GP (ml/h)) were calculated based on gas production at 16 h The gas volume produced was recorded at 2, 4, 6, 8, 12, 16, 24, 48, 72 and 96 h using a digital pressure transducer. Fermentation parameters were determined after 24 h of incubation. Bottles were placed in an ice bath to stop fermentation and gradually warmed up to 25°C. The gas production volume was recorded and pH determined. From each bottle, a sub sample of supernatant (5 mL) was immediately preserved with 5 mL of HCl 0.1 N and stored at -20°C for ammonia-nitrogen (NH3-N) analysis. Fermentation residues were oven dried at 60°C for 48 h to estimate the DM disappearance. Furthermore, the in vitro dry matter (IVDMD) and organic matter disappearance (IVOMD), short chain fatty acid (SCFA; mmol/g DM), microbial protein (MP; mg/g DM) and estimated metabolisable energy (ME; Mcal/kg DM) of TP were measured and compared to those of wheat barn (WB). In the second gas production experiment, the effects of 0 (control), 2.5, 5, 7.5 and 10% (dry matter basic) levels of TP substituted with WB on fattening lambs diet were investigated (on based nutrient requirements). In this section, fermentation parameters were determined only at 16 h after incubation.

The results showed that organic matter, ash, CP, NDF and ADF of TP were 940, 59, 172, 630 and 420 g/kg DM, respectively. In the present experiment, TP had more CP, EE, NDF and ADF than WB (P<0.05). TP showed lower gas production potential and gas production rate than WB (P<0.05). TP showed lower GP24, GP48, GP72 and GP96 than WB (P<0.05). The inclusion of TP in diets linearly increased partitioning factor and MP (P<0.05), but it linearly decreased IVDMD, IVOMD, SCFA and ME (P<0.05). The partitioning factor and microbial protein production of TP was higher than WB (P<0.05). It seems that low gas production for TP compared to WB was resulted due to high content of insoluble fiber in the TP, which requires more time for attachment and fermentation of microorganisms. Complete replacement of TP with WB increased partitioning factor and microbial protein production (P<0.05), with no negative effect on gas production, metabolizable energy and fermentation parameters (P>0.05). Increased microbial protein production with TP incubation is presumably related to the presence of phenolic compounds in TP. It has been shown that in low-concentration, tannins may improve microbial protein production by modulating rumen fermentation conditions. The experimental results showed that by adding TP, digestibility of dry matter and organic matter decreased. This reduction seems to be related to the higher cell wall part of the TP as compared to WB. It appears that carbohydrates in TP are digested slower than those in WB. This could be overcome by some chemical treatments. Another reason for the reduced digestibility of TP diets is probably due to higher fat content of TP.

In overall, using TP in the diets of fattening lambs had no negative effect on rumen fermentation parameters; therefore, based on chemical composition and lower price of TP compared to WB, using TP up to 10% of diets might be economically useful in lamb fattening.