Effects of ensiling, air-drying and addition of polyethylene glycol on in vitro gas production of pistachio by-products

The objective of this study was to determine effects of freeze-drying, sun-drying, ensiling and addition of polyethylene glycol (PEG) on deactivation of tannins in pistachio by-products (PB) by assessing changes in the chemical composition and phenolics levels of freeze-dried, sun-dried and ensiled PB for 30 or 60 days. In vitro gas production for 24 h (IVGP), estimated organic matter digestibility (OMD) and metabolisable energy, with or without PEG addition, were determined. Ensiling decreased the content of water soluble carbohydrates (WSC), neutral detergent fiber (NDFom) and acid detergent fiber (ADFom) as well as condensed tannins, hydrolysable tannins, protein-precipitable phenolics, IVGP and OMD (P<0.05). Adding PEG to freeze-dried, sun-dried and ensiled PB increased (P<0.05) IVGP and OMD demonstrating the positive influence of PEG, but not sun-drying or ensiling, on inactivation of tannins in PB.