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Application of yeast-based biocontrol agents against fruit spoilage moulds
Author(s)
Gomomo, Zukisani
Date Issued
2024
Type
Thesis
Publisher
Cape Peninsula University of Technology
Abstract
Fruits such as apples, oranges, strawberries and grapes are of commercial importance, serving
as primary sources of essential growth factors, including vitamins and minerals. However, their
production, safety, and economic contributions to the agricultural sector are severely impacted
by mould-induced spoilage. Pathogens such as Botrytis cinerea and Penicillium spp. cause
substantial losses during pre- and post-harvest stages, with over 50% of fruit losses in
developing countries attributed to these fungi. In South Africa, annual fruit losses due to mould
spoilage exceed 60%.
Synthetic chemical fungicides are widely used to manage fruit spoilage fungi, but their
prolonged application raises concerns regarding environmental safety, consumer health, and
the development of fungicide-resistant strains. Consequently, non-Saccharomyces yeasts have
emerged as promising, eco-friendly biocontrol agents. These yeasts utilise diverse mechanisms
such as nutrient competition, parasitism, and the secretion of antimicrobial compounds to
inhibit fungal growth. This study aimed to evaluate non-Saccharomyces yeasts for extracellular
enzyme production, antifungal activity against key fruit spoilage fungi, and their viability and
stability assessments on fruit surfaces under post-harvest conditions.
Among 23 yeast isolates screened for extracellular enzyme activity, five were selected
for further analysis: Aureobasidium melanogenum (Y6), Suhomyces pyralidae (Y63), Pichia
kluyveri (Y64), Meyerozyma guilliermondii (Y88) and Zygoascus hellenicus (Y89). These
yeasts were tested in vitro using radial inhibition, dual culture, and double Petri dish assays, as
well as in vivo post-harvest trials on apples, strawberries, and oranges. The yeasts were
evaluated for antagonistic effects against three B. cinerea strains (B05.10, IWBT-FF1, PPRI
30807) and three Penicillium species (Penicillium expansum PPRI 5654, P. italicum PPRI
10380 and P. digitatum PPRI 30517). Compatibility and potential synergistic effects were
assessed through yeast-yeast interaction assays. Extracellular enzyme production varied among the isolates, with Aureobasidium
melanogenum demonstrating robust activity for proteases, glucanases, chitinases, cellulases
and pectinases. This yeast achieved 55%, 52% and 40% inhibition against B. cinerea strains
B05.10, IWBT-FF1 and PPRI 30807, respectively. Pichia kluyveri and M. guilliermondii
showed 100% inhibition of B. cinerea spore germination, while S. pyralidae exhibited 100%
inhibition for two strains (B. cinerea B05.10 and IWBT-FF1), and 87% for B. cinerea PPRI
30807. Volatile organic compounds (VOCs) such as isobutanol, 2-phenylethanol, and isoamyl
acetate, identified using solid-phase microextraction coupled with gas chromatography–mass
spectrometry (SPME-GC-MS) were found to contribute to mould inhibition.
During post-harvest trials, S. pyralidae achieved the highest inhibition of B. cinerea on
apples with a mean inhibition of 43%, while M. guilliermondii was most effective against P.
digitatum and P. italicum on oranges. Commercial fungicides demonstrated higher efficacy in
some instances, though yeast treatments provided viable alternative control. Stability and
viability assays revealed varying levels of yeast survival on fruit surfaces, with a decrease in
yeast cell concentrations observed after oven drying, while stability was maintained during the
storage period. The study concludes that the selected non-Saccharomyces yeasts hold
significant potential as biological control agents against fruit spoilage moulds. While post harvest trials demonstrate promising results, further optimisation and field applications are
recommended to enhance their efficacy and adoption in agricultural practices.
as primary sources of essential growth factors, including vitamins and minerals. However, their
production, safety, and economic contributions to the agricultural sector are severely impacted
by mould-induced spoilage. Pathogens such as Botrytis cinerea and Penicillium spp. cause
substantial losses during pre- and post-harvest stages, with over 50% of fruit losses in
developing countries attributed to these fungi. In South Africa, annual fruit losses due to mould
spoilage exceed 60%.
Synthetic chemical fungicides are widely used to manage fruit spoilage fungi, but their
prolonged application raises concerns regarding environmental safety, consumer health, and
the development of fungicide-resistant strains. Consequently, non-Saccharomyces yeasts have
emerged as promising, eco-friendly biocontrol agents. These yeasts utilise diverse mechanisms
such as nutrient competition, parasitism, and the secretion of antimicrobial compounds to
inhibit fungal growth. This study aimed to evaluate non-Saccharomyces yeasts for extracellular
enzyme production, antifungal activity against key fruit spoilage fungi, and their viability and
stability assessments on fruit surfaces under post-harvest conditions.
Among 23 yeast isolates screened for extracellular enzyme activity, five were selected
for further analysis: Aureobasidium melanogenum (Y6), Suhomyces pyralidae (Y63), Pichia
kluyveri (Y64), Meyerozyma guilliermondii (Y88) and Zygoascus hellenicus (Y89). These
yeasts were tested in vitro using radial inhibition, dual culture, and double Petri dish assays, as
well as in vivo post-harvest trials on apples, strawberries, and oranges. The yeasts were
evaluated for antagonistic effects against three B. cinerea strains (B05.10, IWBT-FF1, PPRI
30807) and three Penicillium species (Penicillium expansum PPRI 5654, P. italicum PPRI
10380 and P. digitatum PPRI 30517). Compatibility and potential synergistic effects were
assessed through yeast-yeast interaction assays. Extracellular enzyme production varied among the isolates, with Aureobasidium
melanogenum demonstrating robust activity for proteases, glucanases, chitinases, cellulases
and pectinases. This yeast achieved 55%, 52% and 40% inhibition against B. cinerea strains
B05.10, IWBT-FF1 and PPRI 30807, respectively. Pichia kluyveri and M. guilliermondii
showed 100% inhibition of B. cinerea spore germination, while S. pyralidae exhibited 100%
inhibition for two strains (B. cinerea B05.10 and IWBT-FF1), and 87% for B. cinerea PPRI
30807. Volatile organic compounds (VOCs) such as isobutanol, 2-phenylethanol, and isoamyl
acetate, identified using solid-phase microextraction coupled with gas chromatography–mass
spectrometry (SPME-GC-MS) were found to contribute to mould inhibition.
During post-harvest trials, S. pyralidae achieved the highest inhibition of B. cinerea on
apples with a mean inhibition of 43%, while M. guilliermondii was most effective against P.
digitatum and P. italicum on oranges. Commercial fungicides demonstrated higher efficacy in
some instances, though yeast treatments provided viable alternative control. Stability and
viability assays revealed varying levels of yeast survival on fruit surfaces, with a decrease in
yeast cell concentrations observed after oven drying, while stability was maintained during the
storage period. The study concludes that the selected non-Saccharomyces yeasts hold
significant potential as biological control agents against fruit spoilage moulds. While post harvest trials demonstrate promising results, further optimisation and field applications are
recommended to enhance their efficacy and adoption in agricultural practices.
Additional information
Thesis (Doctor of Agriculture)--Cape Peninsula University of Technology, 2004
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