Production of pectinases from Rhizopus sp. in solid substrates

Rhizopus sp. 26R that was isolated in Thailand and has the efficiency in hydrolyzing raw cassava starch was also found to have high pectinase activity. The pectinase from Rhizopus sp. 26R showed high potential in enhancing the digestion of raw starch from whole cassava tuber when used together with glucoamylase from an isolated Aspergillus niger J8. Production of the fungal enzymes was carried out by solid substrate fermentation composting of agricultural wastes in plastic bag in order to lower the cost of production. On the 20 gram of solid substrates composing of wheat bran and rice husk in a ratio of 18:2 Rhizopus sp. 26R gave high activity in 2 days and remained constant for 4 days. Addition of either 1 g raw cassava starch or 1 g pectin to a 20 g substrates increased the enzyme activity to 1.7 and 2.4 times, respectively. Addition of rice bran to the mixture of wheat bran and rice husk was the best substrates for the fungal pectinase production. Addition of pectin to the solid substrates that composed of rice bran could not increase the enzyme production but even inhibit the production. The highest activity obtained when the strain was grown on substrates containing a mixture of wheat bran, rice bran and rice husk in a ratio of 9:9:2 or 6:12:2 with 58% initial moisture content, pH adjusted to 5.7 and incubation temperature was at 32 degrees C. Under these conditions, Rhizopus sp. 26R produced ca. 700 units of enzyme activity per gram of solid substrates. Cost of the enzyme production in solid substrates was also estimated.