Effect of composition of the medium used for the inoculum cultivation, of the age and amount of the inoculum was investigated using a 3-L glass fermentor with a working volume of 1 L. The highest productivity of the culture was obtained when using a 20% (V/V) 1-d inoculum grown in the MRS medium. Yields of lactic acid were 88-97%, while the L(+)-isomer represented about 80% of the total product.
Several tens of mutants were obtained by UV irradiation of a spore suspension of Aspergillus niger. Producers yielding large amounts of citric acid were selected on a modified Czapek agar containing methyl red as pH indicator. After a submerged cultivation in flasks with baffles, a mutant characterized by yellow pigmentation on wort agar and by yields of citric acid up to 74.6% in the medium containing glucose was chosen from 130 isolates tested.
Auxotrophic strains of Aspergillus niger were obtained from citric-acid-producing strains of the fungus after irradiation with UV light. Protoplasts were isolated from young hyphae of the auxotrophic strains after treatment with snail enzyme and than treated with polyethylene glycol (30%, W/V), in a Ca2+ (10 mmol/L) solution. The pH value of the suspension was adjusted to 9.0. The frequency of the heterokaryons (related to the number of protoplasts reverting after PEG treatment) was 0.67%. Prototrophic heterozygous spores were isolated from a heterokaryon with the frequency of 1.2 x 10(-6). Citric acid production in the best heterozygous strains was about 15% higher than that of the high-production parent strain.
A considerable lowering of aeration demands occurs during diffuse growth of citric acid-producing Aspergillus niger in a submerged cultivation. However, the diffuse culture poses stricter demands on the type of aeration and agitation. The impeller frequency affects considerably the morphology of the producer fungus and the accumulation of citric acid. The effect of impeller frequency on the distribution of air in the medium and on the amount of air fed into the diffuse culture is less important.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.