The in vitro gas production technique: an investigation on its potential use with insoluble polyvinylpolypyrrolidone for the assessment of phenolics-related antinutritive factors in browse species

Abstract

Leaves of Cistus incanus (summer), Arbutus andrachnoides (winter), A. andrachnae (spring) and a summer or autumn harvest of A. unedo, Carpinus duinensis, Quercus coccifera and Fraxinus ornus were analysed for neutral and acid detergent fibre (NDF, ADF), lignin, crude protein (CP), total extractable phenols (TEPH), total extractable tannins (TETa) and total extractable condensed tannins (vanillin-HCl TECTa), and total extractable proanthocyanidins (TEPA) or total proanthocyanidins (TOPA). Gas production (in vitro) from the samples was measured during 96 h incubation with or without addition of insoluble polyvinylpolypyrrolidone (PVP). Concentrations of the phenolics and the fibre components were variable ( P < 0.05) among species. The CP content varied from 70.5 to 132.9 g kg −1 dry matter (DM), but was always decreased by 15–25% with maturity, whereas concentrations of TECTa, TEPA and TOPA increased ( P < 0.05) with maturity in A. unedo, C. duinensis and Q. coccifera, but not in F. ornus ( P > 0.05). Concentrations of phenolics were negatively related ( P > 0.05) to gas production. The correlation coefficient of the relationship was highest with TETa ( P > 0.05; r = −0.38) and TOPA ( P > 0.05; r = −0.55) at 96 h incubation. Excluding C. incanus, gas production was related ( P < 0.05) to TETa ( r = −0.63) and TOPA ( r = −0.68) at 96 h incubation. The increase in gas production on PVP treatment was highest (22%) from Q. coccifera (summer) (22%) after 24 h and C. incanus (22%) after 96 h incubation. However, despite their high content of tannins, the increase from the Arbutus species was low. On the other hand, when PVP was added to F. ornus, which had the lowest tannin content, it produced 14% more gas after 24 h incubation. In addition, the highest increase in gas production after treatment with PVP was produced at different periods of the incubation. As a result, the increase in gas production was not related ( P > 0.05) to any of the phenolic assays used, and the biological response to polyphenolic compounds depends on their nature and varies between plant species. However, although several aspects of the treatment with PVP should be further studied, the gas production technique in combination with PVP appears to have good potential for providing better insight into the effects of phenolics-related antinutritive factors in biological systems.