Sodium sulphite effects on recovery and composition of detergent fibre andlignin from forage legumes varying in levels of proanthocyanidins

Alfalfa (Medicago sativa L), red clover (Trifolium pratense L), birdsfoot t refoil (Lotus corniculatus L), sainfoin (Onobrychis viciifolia Scop), crown vetch (Coronilla varia L), cicer milkvetch (Astragrlus cicer L), sericea le spedeza (Lespedeza cuneata (Dum-Cours) G Don) and kura clover (Trifolium am biguum M Bieb) were subjected to sequential detergent fibre analysis to inv estigate the effects that the addition of sodium sulphite to neutral deterg ent has on the recovery and composition of fibre and lignin from forage leg umes that vary in levels of proanthocyanidin (PA). Soluble, insoluble and n eutral detergent insoluble PA (NDIPA) concentrations were highest in serice a, moderate in crownvetch, sainfoin and birdsfoot trefoil and absent in alf alfa, cicer milkvetch, red clover and kura clover. Addition of sodium sulph ite reduced levels of neutral detergent fibre (NDF), acid detergent fibre ( ADF), acid detergent lignin (ADL), neutral detergent insoluble nitrogen (ND IN) and acid detergent insoluble nitrogen (ADIN) recovered from most forage s tested. The addition of sodium sulphite effectively eliminated NDIPA from NDF. The difference between fibre fractions prepared without and with the addition of sodium sulphite during the neutral detergent procedure was rela ted to PA concentration. Neutral detergent fibre difference was positively correlated with soluble PA (r=0.730, p=0.0001), insoluble PA (r=0.905, p=0. 0001) and NDIPA (r=0.913, p=0.0001). Acid detergent fibre difference was po sitively correlated with soluble PA (r =0.796, p =0.0001), insoluble PA (r = 0.976, p = 0.0001) and NDIPA (r = 0.974, p = 0.0001). Acid detergent lign in difference was positively correlated with soluble PA (r=0.846, p=0.0001) , insoluble PA (r=0.992, p=0.0001) and NDIPA (r = 0.972, p = 0.0001). Neutr al detergent insoluble nitrogen difference was positively correlated with s oluble PA (r = 0.475, p = 0.0255), insoluble PA (r =0.579, p = 0.0047) and NDIPA (r =0.570, P =0.0056). Acid detergent insoluble nitrogen difference w as positively correlated with soluble PA (r=0.798, p =0.0001), insoluble PA (r = 0.969, P = 0.0001) and NDIPA (r = 0.979, p = 0.0001). Sodium sulphite has large effects on fibre values of PA-containing species. Our results su ggest that the difference between fibre fractions prepared with and without the addition of sulphite to neutral detergent may be used to determine the effects of PA on protein solubility in detergents. (C) 1999 Society of Che mical Industry.