Influence of organic acids on heat resistance characteristics of Talaromyces flavus ascospores.

Three strains of Talaromyces flavus were investigated for their tolerance to organic acids during and after exposure to elevated temperatures. Fumaric, sorbic and benzoic acids were clearly more lethal than acetic, malic, citric and tartaric acids, and lethality was enhanced as the pH of the heating medium was reduced from 5.0 to 2.5. The effects of sorbic and benzoic acids on viability of ascospores varied depending upon the strain and were influenced by other constituents in the heating medium. Ascospores of a T. flavus strain with greater heat tolerance were larger and less ellipsoid in shape than ascospores of a less heat-tolerant strain, as observed by scanning electron microscopy. While both strains are known to develop heat resistance with age, no external differences in shape, degree of ornamentation and size could be discerned between ascospores as influenced by age (11 and 51 day old) of cultures.