Nuclear techniques in the improvement of the quality of cassava traditionally fermented in Indonesia

Microflora of 25 samples of ''ragi tape'' (microbial starter using for the production of ''tape ketela'' - Indonesian traditional cassava fermented food) was studied and 161 microbial strains including 75 moulds, 47 yeasts and 39 bacteria were isolated from these samples. Two mould strains, which have the highest amylase ability and two yeast strains producing high ethanol were selected for improvement of their fermentative characteristics with the help of the gamma-radiation treatment. LD50 of two mould strains (RBM3 and RSM2) were determined as 97,5 krad and 182,5 krad respectively, whereas selected yeast strains (RCrgy2 and RBdgy2) had LD50 of 35 krad and 37 krad respectively. Using the appropriate LD50, mould strain RBM3 and yeast strain RCrgy2 were irradiated and as a result of this treatment 47 and 226 irradiation surviving mutants have been obtained respectively. Among the mould survivors, two mutants were very promising in amylase ability and the glucose production of these has been found to be increased 4 times when compared with the wild strain. However, only one of the yeast mutants showed a slight increase in the ethanol production than in the wild strain (about 55%). Further study is required to obtain stable mutants with a high ability to convert/assimilate the cassava starch. (author). 11 refs