Previously identified fungal pectinase producers of the species Aspergillus sojae were used for optimization of polygalacturonase production in solid-state fermentation applying Design of Experiment. The effects of media composition and several process parameters, like inoculum size, moisture level, incubation time and temperature on polygalacturonase activity were studied in screening and optimization investigations. Utilization of agricultural and agro-industrial by-products provided the establishment of a cost-efficient and sustainable process for enzyme production. Comparison of pectinase production by A. sojae ATCC 20235 and A. sojae CBS 100928 under optimized conditions yielded 6.9 times higher polygalacturonase activity by A. sojae ATCC 20235. Highest enzyme yield (909.5 ± 2.7 U/g) was obtained by A. sojae ATCC 20235 after 8 days at 30°C applying 30% sugar beet pulp as inducer substrate in combination with wheat bran as medium wetted at 160% with 0.2 M HCl. Furthermore, an overview of pectinolytic enzyme activities present in the extracts of both strains is provided. Protein profiles of both strains are given by SDS-PAGE electrophoresis, as well as zymograms for pectinolytic enzymes in comparison to commercial pectinase preparations.Electronic supplementary materialThe online version of this article (doi:10.1186/2193-1801-3-742) contains supplementary material, which is available to authorized users.

No abstract

Calf rennet has been traditionally used for cheese making all over the world since ancient times. It is primarily a type of aspartic protease. Calf rennet, also known as chymosin, is considered the best milk coagulant in cheese manufacturing. Its usage and demand are increasing day by day in the food industry; however, some ethical issues are also related since it is naturally present in the calf's stomach and obtained by the slaughtering of young animals. Therefore, researchers are trying to introduce some new and better alternatives for chymosin in the food industry. Mucor racemosus f. racemosus CBS 381, Mucor racemosus DSM 62760, and Aspergillus oryzae were cultivated by solid substrate fermentation using the design of experiment (DoE) (MODDE; Umetrics, Sweden) to optimize and analyze the various combinations of different factors and responses (milk-clotting activity, proteolytic activity, specific activity). Based on the analysis of the screening and optimization results, Mucor racemosus CBS 381 was found to be the potential strain in terms of high production of aspartic protease, as well as had high milk-clotting activity under a solid-state fermentation system. However, molasses and casein were determined to be significant carbon and nitrogen sources, respectively, under conditions such as 70% moisture content and 25 • C temperature. The molecular weight of the enzyme (Mucor CBS 381) is ∼30 KDa and it exhibits maximum activity at pH 4.8 at 45 • C. The investigated enzyme was pronounced as thermal-sensitive and lost activity completely after 10 min incubation at 55 • C. The remarkable qualities of the studied enzyme, such as cost-effective production, milk-clotting and proteolytic activity make Mucor racemosus CBS 381 a promising alternate to calf chymosin in the cheese-making industry.

No abstract