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

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 ۵۰% moisture with or without ۱% sulfuric acid. Steam treatment of the date leaves was carried out using three levels of steam pressure (۱۴, ۱۷ and ۲۰ bar), three reaction times (۱۲۰, ۱۸۰, and ۲۴۰ seconds) and two levels of acid (۰ and ۱ 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< ۰.۰۵) cell wall components. An increasing trend was observed in DML by increasing harshness of treatment conditions. The lowest DML (۱۲.۷ g kg-۱) was observed in the auto-hydrolyzed (steam treatment without addition of exogenous acid) sample treated at ۱۴ bar pressure and ۱۲۰ seconds reaction time and the highest DML (۷۸.۸ g kg-۱) was observed in the acid-hydrolyzed (addition of ۱۰ g kg-۱acid prior to treatment) samples treated at ۲۰ bar pressure and ۱۸۰ and ۲۴۰ seconds reaction times. Steam treatment significantly (P< ۰.۰۵) 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 ۲۶۴.۶ g kg-۱ in control to ۷۲.۲ g kg-۱ in the sample treated at ۲۰ bar and ۲۴۰ seconds and water soluble sugars increased from ۱۴.۰ g kg-۱ in the control to ۱۰۱.۸ g kg-۱ in the sample treated at ۱۷ bar and ۲۴۰ 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< ۰.۰۵) 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 ۲۰ bar and ۲۴۰ seconds. In auto-hydrolyzed samples, the biggest increase in ME was observed in the sample treated at ۲۰ bar and ۱۸۰ 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.

کلیدواژه ها:

Chemical composition ، Hemicellulose solubilization ، Lignin depolymerization ، Enzymic hydrolysis ، in vitro gas production