the effect of tannins available in different parts of raisin co-products on their nutritional value

in an experiment, chemical composition, phenolics and fermentation parameters of different parts of raisin co-products (rc) were determined using in vitro gas production with or without polyethylene glycol (peg). different parts of rc included rejected raisins, pedicle, rachis, mixture of raisins, pedicle and rachis, and shekarak (a powder product obtained following sorting of raisins for packing). also, the effect of bound tannin on gas production was evaluated. the chemical composition and phenolic content of different parts of rc were varied. the highest crude protein content, neutral detergent fiber and ash were recorded for rachis, while rejected raisins contained the lowest levels of these parameters. pedicle bore the greatest total phenolics (12.68% of dm) and condensed tannins (3.96% of dm). addition of peg enhanced gas production, in vitro apparent dry matter digestibility, organic matter digestibility as well as metabolizable energy in rc. bound tannins indicated biological activity and somehow decreased gas production in all the treatments, except for shekarak. overall, the results revealed that different parts of rc contain varying levels of phenolics which influence the nutritional value thereof. further research is needed to more accurately assess the influence of rc and their phenolics upon performance of faltening as well as dairy cattle.