Effect of steam explosion on solid‐state fermentation of maize stalk by Penicillium decumbens and Phanerochaete chrysosporium for animal feed production

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Maize stalk is one of the most promising renewable feedstocks consisting of nearly 50% cellulose on a dry weight basis while hemicellulose and lignin account for the balance on a nearly equal basis (Chang et al., 2012). Although lignocellulosic wastes have been used as sources of energy (e g., heat and electric), it is believed that considerable additional value may be achieved using these wastes for animal feed (Graminha et al., 2008). Unfortunately, the utilization of lignocellulose in animal feed is constrained by low content of protein, vitamins and other nutrients and limited digestibility and palatability. Lots of efforts have been made to improve its nutritive value through physical, chemical and biological treatments (Chang et al., 2012; Ugwuanyi, McNeil, & Harvey, 2009; Wan & Li, 2010).
Solid‐state fermentation (SSF) is a predominant method for the protein enrichment of lignocellulose wastes used for ruminant feed. The palatability, acceptability and digestibility were also improved during lignocellulose wastes fermentation (Ugwuanyi et al., 2009; Chang et al., 2012). The common microbes used to convert lignocellusic materials to animal feed in SSF include two types: (i) producing lignocellulose and degrading enzymes; (ii) enriching protein. Duru and Uma (2003) have demonstrated that the protein content of cocoyam cormel was enriched over 50% through SSF using Aspergillus oryzae. The low technology and reduced reactor volume employed in the SSF process (Nigam & Singh, 1996) makes the process easy using in small animal farms. However, the recalcitrance of lignocellulose makes a longer SSF cycle even reaching longer than 30 days (ds) (Das & Karim, 1995).
Steam explosion (SE) is a promising method for lignocellulose materials pre‐treatment and has been used to release digestible materials from cell wall and suitable to improve lignocellulose materials for saccharification processes (Chang et al., 2012). Particle size was reduced and micropores expanded during the steam explosion, which increase sites for bacterial attachment and accessibility to free enzymes (Grous, Converse, & Grethlein, 1986). Breakdown of hemicellulose and delignification of cell wall have been suggested as the main chemical reactions, which increase availability of cellulose (Alvira, Tomas, Ballesteros, & Negro, 2010). These changes during steam explosion treatment enable rumen microbes to utilize the carbohydrate content more efficiently (Viola et al., 2008). However, it is difficult to increase the nitrogen content through SE. An acute treatment condition can inhibit micro‐organism growth or influence material digestion (Oliva et al., 2003). Therefore, the steam explosion condition (pressure, temperature, time) should be optimized according to the processing purposes to reduce the nutrients loss.
In this study, the SE and SSF were combined to an efficient method to improve the nutritive value of maize stalk. To evaluate the effects of SE on SSF, the maize stalk was steam exploded at different conditions and fermented with Penicillium decumbens NO.1 with high cellulase production and Phanerochate chrysporium ME‐446 with strong lignin degradation ability. The composition and enzyme activity of the fermented products were measured. The conversion and utilizability of maize straw in animal feedstuff was discussed.
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