15A-1 |
Enzymatic enhancement of citric acid production from corncobs |
Y. D. HANG and E. E. Woodams. Dept. of Food Science & Technology, Cornell Univ., W. North St., NYSAES, Geneva, NY 14456 Corncobs are the large-volume solid waste that result from sweet corn processing. They are currently either used as animal feed or are returned to the harvested fied for land application. Corncobs are considerably rich in cellulose and hemicellulose (approximately 800 g/kg dry matter) that can serve as a potential source of renewable biomass for the production of a variety of value-added products (reducing sugars, ethanol, organic acids, etc.) by enzymatic and microbial fermentation processes. This research was undertaken to develop for a better process for rapid production of citric acid by a specially selected strain of Aspergillus niger from corncobs. Corncobs were chopped and blended with 0.1 N NaOH (20 g/100 ml). The pretreated corncobs were acidified to pH 5.0 and autoclaved at 121 degree C for 15 min. Fermentation studies were conducted in 500-ml Erlenmeyer flasks at 30 degree C in a New Brunswick shaker operated at 200 rpm. The enhancing effect of Rapidase Pomaliq (Gist-Brocades), a commercial apple juice processing enzyme preparation with high celulolytic and xylanolytic activities, on microbial production of citric acid under a variety of fermentation conditions were determined. Citric acid and reducing sugar were analyzed by HPLC using a Bio0Rad HPX-87H column with refractive index detector. Aspergillus niger NRRL 2001 produced less than 200 g of citric acid per kg of dry matter of corncobs without enzyme treatmen. Combined treatments of corncobs with 0.1 N NaOH and Rapidase Pomaliq significantly increased the yield of citric acid. The fermenting organism was found capable of producing up to 400 g of citric acid per kg of dry matter of corncobs with enzyme treatment after 120 h of submerged fermentation at 30 degree C. It is concluded from the results of this study that Rapidase Pomalig could serve as a low-cost biocatalyst for enzymatic enhancement of citric acid production by Aspergillus niger from chemically pretreated corncobs.
Session 15A, Biotechnology
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