Some Microbiological and Biochemical Aspects of Starch Byconversion by Amylolytic Yeasts

Abstract

Although a relatively large number of starch-assimilating yeast species were studied previously in different laboratorie~~'~~ ~.~~.~~ for SCP production, only a limited amount of information was available on the extent of starch degradation and of amylase production by most of these strains. Moreover, these data are difficult to compare due to the use of different culture conditions and various assay methods. Therefore, a comprehensive comparative study of a large number of amylolytic yeasts was carried out in our laboratory. A. Starch Degradation When the assimilation and the extent of degradation of two soluble starch preparations was omp pa red,^^.^^ essentially three groups could be distinguished, as shown in Table 1. Soluble starch was only partially assimilated by most yeasts (groups I and 11). Clearly the most interesting species were those of group 111, since they extensively degraded both starch preparations. Amylolysis by several of these yeasts was reported in the literature: Lipomyces spp. ,30.43.49 Pichia b~rtonii,3O,~~ Saccharomycopsis sp~.,'.~~.~~ Schwanniomyces spp.,32.36 and Torulopsis ingeniosa.4' However, several species which were not described previously were equally capable of good starch conversion, namely Candida homilentoma, C. silvanorum, C. tsukubaensis, Cryptococcus flavus, Filobasidium capsuligenum, and Trichosporon pullulans.