Natural yeasts inhibit the formation of molds in the fruit

 Fresh fruit is a living being that, after being pulled from the tree, continues its physiological and ripening action. During this process, the fruit undergoes mold activity that eventually causes rot. The fight against molds is a major challenge for the fruit sector due to the losses it causes in fruit production.

To respond to this problem, researchers from the Food Quality and Microbiology group (CAMIALI) of the University of Extremadura in collaboration with the Center for Scientific and Technological Research of Extremadura (CICYTEX), are developing biocontrol techniques to extend shelf life of the fruit and its commercialization. In the case of fruit, biocontrol involves the use of antagonistic microorganisms, yeasts that are naturally present in fruit, and that are capable of inhibiting or reducing the growth of unwanted molds.

Preliminary in vitro studies have managed to identify two yeast strains present in fig with excellent results, Hanseniaspora opuntiae L479 and Metschnikowia pulcherrima L672. "After testing 50 yeast strains present in fruit, we have verified at the cultivation level the ability of these two strains to inhibit the growth of pathogenic molds," says Alejandro Hernández , researcher of the CAMIALI group.

In addition, a first live study in nectarines and apples confirms these results, with a reduction in growth and germination of spores greater than 50%. "Preliminary studies show that these strains work very well both at room temperature and in refrigeration," adds Hernández. Thus, in the nectarines and apples studied, these two strains, thanks to their antagonistic action, were able to control the development of common pathogenic molds in these fruits: Penicillium expansum, Botrytis cinerea, Monilia laxa and Cladosporium cladosporioides .

Biocontrol has many advantages. First, it provides a natural defense against microorganisms and an alternative to the use of synthetic pesticides in the control of mold spoilage in fruits. These chemicals, despite being effective, generate toxic waste for human health and the environment. Secondly, these yeasts are already naturally present in the fruit, and their safety for man can be demonstrated, in accordance with the protocols of the Agency for Food Safety in Europe, while preserving the sensory properties of the fruit.

Yeasts and molds compete for space and nutrients

These yeast strains act against the proliferation of molds of exogenous origin, that is, by the germination of spores that come into contact with the skin of the fruit through insects, small wounds or environmental contamination, which occurs during their commercialization and in our homes, according to the UEx researcher.

Yeasts and mushrooms compete for space and nutrients. "We give the fruit a bath in a yeast solution, in this way, when the spores of the fungi arrive they do not find a place to germinate because all the space is already taken up by the yeasts", explains Hernández.

In addition to this lack of space, it is added that yeasts are faster than molds in consuming nutrients, with which, although mold spores settle, they will not have enough food. And it is in relation to nutrients, where one of the yeasts, Metschnikowia pulcherrima L672, has shown great effectiveness because it sequesters iron, a fundamental element for the development of molds.

The ripening process of the fruit does not stop, but the development of molds is delayed, both due to lack of nutrients and space. Everything, in addition, without altering the sensory properties of the fruit, in terms of its smell, aroma and flavor.