Optimization of steam treatment as a method for upgrading rice straw as feeds

The objective of the present study was to study the effects of different co nditions of steam treatment on nutritional value of rice straw (RS). The st eam treatment was accomplished in a high pressure vessel at pressures 15, 1 7 and 19 kg/cm(2) for a range of treatment time (0, 5 and 10 min) at a wate r-to-straw ratio of 1:1. The effect was also studied of the amount of water added (0:100-50:50 (w/w)) on the nutritive value of treated RS, where trea tment was conducted at 15 bar pressure for 5 min. The effects of steam trea tment were evaluated in terms of dry matter loss, fibrous portions, sugar p rofiles and in vitro gas production (GP). Steam treatment increased water s olubility of RS. There was no significant effect of steam pressure on dry m atter loss, pH, fibrous fractions (NDF, ADF and hemicellulose), and sugar p rofiles (total and individual) in either water extracts or insoluble residu es. Dry matter loss was however, significantly greater in longer treatment time (10 min) than in shorter time condition (0 and 5 min). In the water in soluble residues of the steam-treated straw, hexoses were dominantly higher than pentoses, indicative of the hemicellulose hydrolysis during treatment . Steam treatment of RS also resulted in an increased soluble carbohydrate content, which decreased with the increasing pressure and prolonged One. Co mpared with the untreated RS, the treated straw had a higher 24 h GP, and a faster rate of GP but the potential GP was similar. All these GP parameter s tended to be higher at lower steam pressure and shorter time of treatment , though the effect was not significant (P>0.05). Significant differences ( P<0.01) were found in all parameters between lower and higher amount of wat er added. Compared to the lower water-to-straw ratio (below 2:8), the treat ed straw at the high moisture had a lower dry matter loss (P<0.01), higher water soluble carbohydrates (P<0.01) and higher GP (P<0.01). From these res ults and considerations of energy economy, it is inferred that the optimal treatment condition is likely at a steam pressure of 15 bar for 5 min, and that water-to-straw of above 3:7 seem to be needed to obtain optimal treatm ent results. (C) 1999 Elsevier Science B.V.