Optimization of Steam Treatment Conditions for Improving the Nutritive Value of Date Leaves

Abstract

The aim of this study was to investigate the effect of steam treatment on nutritive value of date (Phoenix dactylifera) leaves. Date leaves were chopped and mixed with water or sulfuric acid solution to contain 50% moisture with or without 1% sulfuric acid. Steam treatment of the date leaves was carried out using three levels of steam pressure (14, 17 and 20 bar), three reaction times (120, 180, and 240 seconds) and two levels of acid (0 and 1 percent). The treated samples were analyzed for chemical composition including: cell wall components, ash, total extractable phenolics, water soluble sugars, and reducing sugars. Dry matter loss (DML), enzymic hydrolysis, and in vitro gas production of the samples were also measured. Results showed that steam treatment significantly affected (P< 0.05) cell wall components. An increasing trend was observed in DML by increasing harshness of treatment conditions. The lowest DML (12.7 g kg-1) was observed in the autohydrolyzed (steam treatment without addition of exogenous acid) sample treated at 14 bar pressure and 120 seconds reaction time and the highest DML (78.8 g kg-1) was observed in the acid-hydrolyzed (addition of 10 g kg-1acid prior to treatment) samples treated at 20 bar pressure and 180 and 240 seconds reaction times. Steam treatment significantly (P< 0.05) decreased neutral detergent fiber (NDF) content but increased acid detergent lignin (ADL). Maximum changes in hemicellulose and water soluble sugars were observed in acid-hydrolyzed samples, in which hemicellulose decreased from 264.6 g kg-1 in control to 72.2 g kg-1 in the sample treated at 20 bar and 240 seconds and water soluble sugars increased from 14.0 g kg-1 in the control to 101.8 g kg-1 in the sample treated at 17 bar and 240 seconds. Enzymic hydrolysis of date leaves was improved after steam treatment and higher improvement was observed in acid-hydrolyzed samples. Gas production was significantly increased (P< 0.05) in all incubation times after steam treatment. The maximum increase in metabolizable energy (ME) estimated by gas production was from acid-hydrolyzed sample treated at 20 bar and 240 seconds. In auto-hydrolyzed samples, the biggest increase in ME was observed in the sample treated at 20 bar and 180 seconds. The results suggest that steam treatment could be used for upgrading the nutritive value of date leaves in the regions where date is grown and animals are encountered with severe feed shortage. Keywords: Chemical composition, Hemicellulose solubilization, Lignin depolymerization, Enzymic hydrolysis, in vitro gas production.