The effect of microwave irradiation at different times on in vitro nutritional value components of red grape pomace

The grapevine (Vitis vinifera L.) is a woody vine cultivated worldwide for its edible berries (grapes) that are eaten fresh or pressed to make juices. Grape processing generates a large number of by-products that can be broadly classified as follows: solid by-products (leaves, stems, seeds, skins, and pulp), highly viscous by-products (lees), and low-viscosity by-products (wastewater). The seeds (pips) are sometimes extracted to make oil. This datasheet deals with grape pomace (grape marc), which is the main solid residue of grape processing. Grape pomace always includes the pressed skins and the disrupted cells of grape pulp, which depends on process, stems, and seeds. Grape leaves , grape seeds, and oil meal are presented in their own datasheets. Condensed tannins were considered as a main limiting factor in some of the agricultural byproducts. So many research data are available about the effects of different chemical and physical treatments on condensed tannins levels and activity in tanniferous plants. Due to its high content of fiber (and particularly lignin) and the presence of phenolic compounds, grape pomace has low digestibility (Provenza and Launchbaugh, 1999). It can be used to feed ruminants, horses and rabbits, in association with feeds, which have a better nutritive value, but it is not recommended for pigs and poultry as a source of energy and protein. Grape pomace can be fed fresh, but as it is highly perishable and produced seasonally, it must be dried or ensiled before storage. Red grape pomace is one of the main agro-industrial byproducts with medium to high levels of condensed tannins. High concentration of condensed tannins limits their use in the feeding of farm animals (Abarghuei and Ruzbehan, 2013). Along with tannin, soluble and structural carbohydrates is expected to play a role in determining the extent of digestion and resultant fermentation products. Both tannins and carbohydrate sections had been reported to change as grape pomace is processed. Condensed tannin and carbohydrates are diverse in different grape pomace components (e.g. skin, seed, stalk) or from different cultivars. Processing with irradiation-based techniques can be served as green processing methods without negative environmental effects. However, reports about the effects of these processing methods on anti-nutritional factor are so scares. On the other hand, condensed tannins (proanthocyanidins) have been proved to be effective in reducing methane emissions both in vitro and in vivo. The main objective of this study was to determine the effects of microwave irradiation on in vitro and in situ chemical composition, levels of anti-nutrients, and nutritive value parameters of grape pomace.

Shade- air dried grape pomace was irradiated in a microwave oven at 2, 4, and 6 minutes and effects of irradiation were examined on chemical composition measures as well as phenolic compounds. Three ruminally fistulated male Holstein steers were used to prepare rumen fluid and to incubate the in-situ samples within the rumen according to a completely randomized block design in two separate stages. In order to determine the effect of processing on the gas production potential and inactivation of phenolic compounds and tannins, in vitro gas production was measured according to the method of Menke and Steingass (1988) in three separate runs and three replications in each run. Rumen fluid was prepared from the same three fistulated Holstein steers prior to morning meal. The degradability coefficients of dry matter and crude protein were also determined. Two bags for each sample were incubated in the rumen of each cow for 2, 4, 8, 12, 24, 48, 72, and 96 hours. To estimate the amount of disappearance at time zero, the bags containing the feed sample were washed with only cold tap water. Rumen incubated nylon bags were washed and rinsed until the effluent was clearو using a washing machine. The bags were oven dried at 60 °C for 48 hours. quantifying The NLIN procedure of SAS (statistical software, version 9.1) and Ørskov and McDonald (1979) proposed model were used to determine the degradability parameters of dry matter and crude protein.

Irradiation with microwave increased the amount of crude protein, dry matter, ash and insoluble fiber in neutral detergent. Significant decrease was observed in the total amount of phenolic compounds, total tannin, free condensed tannin and protein and fiber bound condensed tannins. In addition, the biological activity of phenolic compounds in protein deposition was also reduced. The highest reduction was seen in treatment of 6 minutes. The highest reduction was seen in 6-min treated samples. Irradiation with microwave irradiation increased the degradability of dry matter of red grapes and the quantities of produced gas at all incubation times in 4 minutes, but reduced the dry matter degradability in the treatment of 6 minutes compared with the control group. Irradiation reduced the protein degradation in all treatments compared with the control group. Irradiation also increased gas production. The highest gas production was observed in 2 minutes treatment with 120 h incubation (71.98 vs. 55.07 mL per 500 mg of dry matter). Also, section b showed a significant increase compared with control in treatments 2 and 6 minutes. The results of this study showed that microwave irradiation increases the nutritional value of red grape pomace by disabling a large part of the anti-nutrient contents and their activities. The effect of microwaves irradiation on the kinetics of crude protein degradability was significant at all of the processing times (P <0.05). Microwave irradiation significantly increased potentially degradable rotein, so it can be expected to change protein degradation in the rumen (NRC, 2001). Decreased protein degradation can be explained by cross-linking, breaking of hydrogen bonds and other weak non-covalent bonds, changing the position of amino acids, and ultimately increasing hydrophobicity of protein levels (Mora et al., 2003, VanSoet, 1994). Based on the results, it can be concluded that microwave irradiation can improve the nutritional value of red grape pomace, due to inactivation of condensed tannins.