CHEMICAL AND MICROBIAL CHANGES DURING THE NATURAL FERMENTATION OF STRAWBERRY TREE (ARBUTUS UNEDO L.) FRUITS

Abstract

ABSTRACT Aguardente de medronho is the name given in Portugal to a spirit made from the fermented fruit of Arbutus unedo (strawberry tree), a plant grown in the Mediterranean region. In order to gain a better understanding of the fermentation process, as it is performed in the farms, a natural fermentation with wild microbiota was carried out during 36 days, and some physicochemical and microbiological parameters were studied. The microbial parameters analyzed were total viable, lactic and acetic acids bacteria, and yeast counts. The physicochemical parameters monitored were sugars, minerals, ethanol, organic acids and pH. Yeasts were the main responsible for the fermentation of the fruits, as the lactic and acetic acids bacteria are absent. As the fermentation progressed, the sugars increased during the first 2 days and gradually decreased along the fermentation period. Maintaining the good quality of the product could contribute to the preservation and valorization of traditional resources that are of great importance to prevent their disappearance. PRACTICAL APPLICATION Aguardente de Medronho is a distillate in which its preservation, of great importance in the south of Portugal, is associated with its certification as a traditional product that is well defined and characterized. The information gathered during this study contributes to the understanding of the fermentation phase of this spirit's production in order to improve its fermentation and produce a consistent and high-quality final product. Now it is possible to suggest changes in the existing production process to enhance product quality and make it more competitive. This study aims in the first place to evaluate the microbiology and biochemistry of the fermentation process; second, it attempts to replace the natural fermentation with fermentations conducted with a well-defined cocktail containing several yeasts species.