Control of mould spoilage on apples using yeast-based biological agents

Abstract

In orchards, storage and processing facilities, considerable quantities of fresh products are lost due to mould spoilage thus threatening the economic growth, food safety and security. Twenty five percent of the total fruits produced in industrialised countries is lost due to mould and more than 50% in developing countries. Fresh fruit and those used for beverage production must meet stringent quality and regulatory requirements in order to reach consumers in good quality. Currently, preservation can be achieved by application of synthetic chemicals to control the growth of mould. However, chemical fungicides pose serious health concerns to consumers such as skin and eyesight damage, as well as cardiovascular diseases. Synthetic fungicides can also have a negative impact on the environment, which results in the search for alternative methods of preservation. Biological control is a promising alternative to reduce or eliminate the use of synthetic chemicals, since it is more environmentally friendly and cost-effective. Yeasts can be used as alternative to synthetic chemicals because of their ability to compete for nutrients and produce inhibitory growth compounds The aim of this study was to screen yeasts for growth inhibition activity against fruit spoilage mould, Botrytis cinerea, Penicillium expansum and Alternaria alstroemeriae under in vitro and in vivo conditions. Yeasts were screened against Botrytis cinerea, Penicillium expansum and Alternaria alstroeneriae using radial fungal plug inhibition assay, dual inhibition assay and the mouth-to-mouth plate inhibition assay. Three yeast strains were also evaluated for growth inhibition activity against the mould during post-harvest apple trials. Out of 104 yeasts screened, 67 showed growth inhibition activity against Penicillium expansum, 36 yeasts inhibited Botrytis cinerea, 47 yeasts inhibited Alternaria alstroemeriae and 22 yeasts showed inhibition against all three moulds. Candida pyralidae, Meyerozyma guilliermondii and Zygoascus hellenicus yeast strains showed highest inhibition activity against P. expansum (38%, 42% and 35%), B. cinerea (62%, 63% and 58%) and A. alstroemeriae (34%, 40% and 35%), respectively. Volatile organic compounds produced by Pichia kluyveri, showed 81%, 91% and 76% growth inhibition activity against P. expansum B. cinerea and A. alstroemeriae respectively. While, C. pyralidae showed 57% and 68% against B. cinerea and A. alstroemeriae respectively, and two M guilliermondii yeast strains were effective in inhibiting the growth of all three mould with percentage inhibition ranging from 57% to 70%. On apples, a commercial fungicide showed 100%, 51% and 24% growth inhibition activity against A. alstroemeriae, B. cinerea and P. expansum, respectively. While the selected P. kluyveri strain showed 100%, 57% and 26% inhibition against A. alstroemeriae, B. cinerea and P. expansum, respectively, and M. guillermondii showed 100%, 60% and 18% inhibition against A. alstroemeriae, B. cinerea and P. expansum, respectively. C. pyralidae showed least inhibition activity by showing 36%, 47% and 13% inhibition against A. alstroemeriae, B. cinerea and P. expansum, respectively. The P. kluyveri and M. guilliermondii strains showed good potential as biocontrol agents against spoilage moulds and needs further investigation. Yeast can be used to control the growth of mould, but the level of inhibition is species dependent. The bio-control yeasts that were used in this study were comparable to a commercial fungicide, therefore they can potentially be considered as alternatives to chemical fungicides. Future research should investigate the application of these yeasts as biofungicides during pre- and post-harvest trials of different fruit.