An ecological study of yeasts associated with fruits and vegetables

[摘要] English: Currently, fruits and vegetables suffer significant losses from fungal diseases afterharvest. The use of synthetic fungicides which pose a risk to human health and theenvironment, have resulted in an intensive search for safer control of postharvest diseasesby the use of microorganisms, particularly yeasts, occurring naturally on the surfaces offruits and vegetables.An ecological survey was preformed on five different fruit and vegetable commodities todetermine the diversity of yeast species associated with these commodities and the causeof spoilage at different temperatures.A. THE INCIDENCE OF YEASTS ASSOCIA TED WITH FRUITS ANDVEGETABLES.Different fruits and vegetables were surveyed to determine the diversity of yeasts and todifferentiate between yeasts found on the surface and inner layer of the different fruit andvegetable commodities. Bacterial growth dominated on the surface of vegetables due tofactors such as higher water content, more neutral pH and close proximity to the soilfacilitating their growth.Yeasts represented the major component of the microflora on the surface of fruits due toa lower pH and higher carbohydrate content that encouraged their growth. The inner layerof both fruits and vegetables yielded lower microbial counts. Schizosaccharomycespombe and Debaryomyces hansenii were the predominant species isolated on both fruitsand vegetables. Spoilage of fresh fruits usually results from the fermentative activity ofyeasts, but no such species were isolated during this study.B. THE GROWTH AND SURVIVAL OF YEASTS IN FRUITS AND VEGETABLESSTORED AT DIFFERENT TEMPERATURES.The growth and survival of yeasts were carried out at different temperatures over a 30-day period to determine an epiphytic yeast population developing on the surfaces of fruitsand vegetables. The chemical and physical composition were monitored over a 30-dayperiod to determine if the changes in pH and organic acids contributed to the developingyeast population on the surface of fruits and vegetables.A total of 119 yeast strains were isolated from fruits and vegetables with bacteriadominating on the surface of vegetables and yeasts on the surface of fruits. The mostpredominating species isolated were S. pombe and D. hansenii. A new yeast species,showing cellulase activity, was isolated from potatoes on day 20 at 25°C.C. THE IDENTIFICATION OF A NEW BASIDIOMYCETOUS YEAST SPECIESISOLATED FROM POTATOES.The new basidiomycetous related species showed interesting characteristics inassimilating lactose as a carbon source. Its sexual reproduction by teliospores verifies thecharacteristically difference compared to Cryptococcus and Rhodotorula spp. where nosexual reproduction is noted. Accordingly, the new species was described.

[发布机构] University of the Free State