article · International Journal of Microbiology
Acid proteases are valuable industrial enzymes used widely across food and beverage processing, where performance under low pH conditions is essential. Fungal strains isolated from grape and dairy farm soils were screened for protease activity, leading to the selection of a high-performing isolate identified morphologically as belonging to the genus Aspergillus. Enzyme production was optimised using solid-state fermentation on a wheat bran substrate. The optimal conditions required a moisture content of 50 percent, a pH of 4.5, and an incubation period of 120 hours at 30 degrees Celsius. Following partial purification through acetone precipitation, the resulting enzyme demonstrated peak activity at 50 degrees Celsius and pH 5. The enzyme also showed operational stability across temperatures between 40 and 60 degrees Celsius and pH levels from 4 to 6.
Industrial processing in the food and beverage sectors often requires enzymes that remain active and stable under acidic conditions and moderate heat. Finding resilient fungal sources that can be cultivated on inexpensive agricultural by-products, such as wheat bran, helps support cost-effective enzyme production methods for commercial manufacturing processes.
This research is at an early experimental stage, focusing on laboratory optimisation and partial purification. The acid protease is targeted at food and beverage industry processors seeking biocatalysts that function reliably at lower pH levels. Full commercialisation would require further purification, scaled-up fermentation trials, and formal testing in specific industrial processing streams.
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Acid proteases represent an important group of enzymes, extensively used in food and beverage industries. There is an increased demand for acid proteases adapting to the industrial extreme environment, especially lower pH. Thus, this necessitates the search for a better acid protease from fungi that best performs in industrial conditions. The fungal isolates were isolated from grape and dairy farm soil using potato dextrose agar and further screened for protease production based on the hydrolysis of clear zone on skim milk agar. The potential fungi were then subjected to secondary screening under solid-state fermentation (SSF). After the secondary screening, the potential fungus was identified to the genus level by the macroscopic and microscopic methods. The growth conditions and media composition for the potential fungus were further optimized under SSF. The crude enzyme produced by the potential isolate was characterized after partial purification by acetone and ammonium sulfate precipitation. A total of 9 fungal isolates showed protease production in primary and secondary screening; however, one potential isolate (Z1BL1) was selected for further study based on its protease activity. The isolate was identified to the genus Aspergillus based on their morphological features. The maximum acid protease from the isolate Z1BL1 was obtained using fermentation media containing wheat bran as a solid substrate, 1 mL of 3.2 <a:math xmlns:a="http://www.w3.org/1998/Math/MathML" id="M1"> <a:mi>×</a:mi> </a:math> 106 inoculum size, 50% moisture content, and pH 4.5 upon 120-h incubation at 30°C. The acetone-precipitated enzyme exhibited the maximum activity at 50°C and pH 5 with stability at pH 4–6 and temperature 40–60°C. Thus, the acid protease produced from Aspergillus showed suitable enzyme characteristics required in the industry and could be a candidate for application in the food industry after further purification.
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DOI: 10.1155/2021/6685963
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