Optimization of fermentation conditions for better growth of Aspergillus niger on toasted guar meal

An in-vitro trial was conducted to optimize the fermentation conditions using Aspergillus niger on toasted guar meal (TGM) by varying the substrate with three different ratios of TGM and water i.e. 30:70, 50:50, and 70:30 each for three incubation periods of 48, 60 and 72 h at 37°C by using complete randomized design. The lyophilized culture of Aspergillus niger was reconstituted and subculture was made by agar plating technique using potato dextrose agar. Spore suspension was inoculated at the rate of one lac spore per kg of substrate. Thus, nine different conditions were evaluated in triplicate for growth of Aspergillus niger and its effect on various chemical constituents of TGM to get best suitable combination for solid substrate fermentation of TGM. Maximum growth of Aspergillus niger with increased crude protein from 41.48 to 59.28%, total phosphorus from 0.42 to 0.53% and decreased urease activity from 0.023 to 0.011 mg and NFE (mostly NSP gum) 39.67 to19.51% was recorded in the group with TGM and water ratio of 50:50 for incubation period of 60 h at 37°C. Results of aflatoxin and urease activity showed that all treatment groups had aflatoxin less than 0.08 ppm and urease activity less than 0.011 mg N/g/minute at 30°C which are reported to be safe for poultry ration. Thus, the results indicated that optimum condition for better growth of Aspergilus niger and economic fermentation was found to be TGM and water ratio of 50:50 for incubation period of 60 h at 37°C for enhancement of the nutritional value of TGM.