Abstract

The growth and production of ©¿-amylase and amyloglucosidase by Aspergillus awamori NRRL 3112 and A. niger CBS 26265 were investigated, with a view to obtaining optimal levels of both these enzymes in shake flask culture, and subsequently on the large scale. The effect of various parameters, such as carbon source, nitrogen source, presence/absence of buffering agents, carbon:nitrogen ratio , pH values, and time were examined. Following the screening of ten strains of Aspergilli, A. awamori NRRL 3112 was found to be the superior amyloglucosidase producing strain , while A. niger CBS 26265, produced higher levels of o i-amylase. The favoured nitrogen source for amylolytic enzyme production was corn steep powder, which had a strong buffering effecton the medium. Starch or its breakdown products stimulated ©¿»amylase and amylolucosidase expression'as well as secretion. oC-Amylase production was more sensitive to pH than amyloglucosidase. The former showed peak production after 24-48 hours while the rate of amyloglucosidase synthesis was linear for 6-7 days. The fermentation was scaled up to 5 and 10 1 laboratory scale fermenters. The effects of various agitation and aeration rates were examined. Oxygen transferrate (OTR) or oxygen transfercoefficient (K\. a) was found to have a large effect on biomass and enzyme yield s , with the conditions for maximal amylase production corresponding to suboptimal conditions for Aspergillus growth. Controlling pH a t 4.5 or 5-5 increased oo-amylase production, but had little effect on amyloglucosidase yield s . The average doubling time of A. awamori NRRL 3112 varied with the medium pH. Minimum values were recorded a t pHi 4.1. The specific growth rate of this filamentous organism reached a maximum at 12 - 16 hours, a t 0.085-0.377 h"1. This corresponded with the period of greatest change in pH. It is concluded that A. awamori NRRL 3112 is a superior producer of amyloglucosidase, and is most suitab le for large scale production of amylolytic enzymes.