Chemical and Microbial Changes During the Natural Fermentation of Strawberry Tree (Arbutus Unedo L.) Fruits

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.

Yeast diversity in the Mediterranean strawberry tree (Arbutus unedo L.) fruits' fermentations

“…The low pH and the high concentration of sugars (°Brix 15) at the beginning of the fermentations favored the multiplication of the yeast biota. According to previously published results, the berries of A. unedo are characterized by low pH values and high soluble sugar concentrations reaching more than 20 g/l as described by Cavaco et al (2007).…”

“…The berries are also an interesting source of omega-3 polyunsaturated fatty acids (Oliveira et al, 2011). However, the fruits' main application is the production of a distilled beverage known as "Aguardente de medronho" in Portugal (Cavaco, Longuinho, Quintas, & Carvalho, 2007), "Koumaro" in Greece (Soufleros et al, 2005) and "Corbezzolo" in Italy (Versini et al, 1995). This beverage is a traditional product made in small or industrial scale units during the months of September to January and its production constitutes a agro-sustainable business which makes A. unedo an interesting shrub by social and economic reasons (Alarcão-E-Silva, Leitão, Azinheira, & Leitão, 2001;González, Agrasar, Castro, Fernández, & Guerra, 2011;Soufleros et al, 2005).…”

“…This beverage is a traditional product made in small or industrial scale units during the months of September to January and its production constitutes a agro-sustainable business which makes A. unedo an interesting shrub by social and economic reasons (Alarcão-E-Silva, Leitão, Azinheira, & Leitão, 2001;González, Agrasar, Castro, Fernández, & Guerra, 2011;Soufleros et al, 2005). Berries are mixed with small amounts of water in plastic, wood or stainless steel vessels, which are then closed and a solid state fermentation starts depending on the yeasts, present naturally on the fruits and in the environment (Cavaco et al, 2007). The duration of the processes varies between one and three months according to the producers, depending on the amount of sugars present in the fruits, the temperature, the equipment and the species/strains involved.…”

“…The duration of the processes varies between one and three months according to the producers, depending on the amount of sugars present in the fruits, the temperature, the equipment and the species/strains involved. The fermented mass, containing 16-22% ethanol (w/w), is subsequently heated and distilled, to obtain a beverage containing 45-50% ethanol (v/v) and characterized by a specific aroma profile (Cavaco et al, 2007;Galego & Almeida, 2007). However, the quality of the distilled product may be affected by off-flavors that may occur due to uncontrolled fermentations.…”

Solid-state fermentation of red raspberry (Rubus ideaus L.) and arbutus berry (Arbutus unedo, L.) and characterization of their distillates

“…In addition, these fruits have been used to treat arterial hypertension (Cavaco, Longuinho, Quintas, & Saraiva 2007) or as antiseptics, diuretics and laxatives in traditional folk medicine (Ayaz, Kucukislamoglu, & Reunanen 2000;Pabuçcuoglu, Kivçak, Bas, & Mert 2003). In the same way, raspberries (Rubus idaeus L.) have reported to contain high levels of ellagic acid (Juranic et al, 2005), which has shown to have antiviral activity (Corthout, Peiters, Claeys, Vanden Berghe, & Vleitinck 1991) and anticancer potential (Stoner & Morse 1997).…”