Phosphate rather than surfactant accounts for the main contribution to enhanced ®bre digestibility resulting from treatment with boiling neutral detergent

It is known that extraction of some grasses with neutral detergent (ND) increases the in vitro digestibility [Kennedy, P.M., Lowry, J.B., Conlan, L.L., 1999. J. Sci. Food Agric. 79, 544]. Here, we report experiments which de®ned the contribution of ND components to digestibility increases. Substrates were prepared from spear grass (Heteropogon contortus) by boiling at neutral pH in solutions of 0.05 M disodium EDTA, 0.018 M sodium borate, and 0.03 M sodium phosphate, and a mixture of the three solutions. Phosphate was the most effective single component in increasing ND ®bre (NDF) digestibility in vitro, after 120 h of fermentation, from 472 to 522 g/kg NDF, equivalent to 68% of the increase found with boiling ND. NDF digestibility of bagasse at 120 h increased from 162 to 186, 230 and 277 g/kg NDF after boiling for 1 h in water, neutral phosphate and ND, respectively. Phosphate treatment of bagasse produced a 44% increase in NDF digestibility, compared to increases of 5, 8, 14, and 16 % for rhodes grass (Chloris gayana), spear grass, angleton grass (Dicanthium aristatum) and carpet grass (Axonopus af®nis), respectively. Increases of cumulative gas production against incubation time indicated that most of the increased fermentation had occurred by 24 h of fermentation for the grasses, whereas 72 h was needed for bagasse. There were also improvements in NDF digestion with neutral phosphate treatment of spear grass at temperatures of 75, 85 or 958C, with prolonged treatment times required at lower temperatures. These treatments reduced the content of acid insoluble ash in NDF and increased the rate of production of gas during fermentation. Removal of minerals from the cell wall matrix appeared to be responsible for the increase in NDF digestibility caused by phosphate treatment. The possible commercial use of phosphate on-farm to upgrade nutritional quality of straws is discussed. # 2000 Elsevier Science B.V. All rights reserved.