Strawberries are not only delicious; they are a natural source of phenolic compounds with antioxidant, and anti-inflammatory properties. Overproduction of strawberries leads to food waste since they cannot be stored long-term without spoiling. To make use of berries that are otherwise unusable due to over-ripening, Álvarez-Fernández et al. used gluconic fermentation to produce a strawberry juice drink. Following this, the team measured the bioactive composition over time and determined the optimal storage conditions.
Beginning with strawberry puree, the researchers added 125 mL of inoculum of G. japonicus strain E1. Next they combined the mixture with a small proportion of an acetic fermented product. They obtained the strawberry vinegar by using a semi-continuous fermentation with Acetobacter malorum.
The researchers described the end of the fermentation process as the point at which the glucose was totally consumed. To stop fermentation, they centrifuged the drink product for 10 min at 1,500g and diluted with soda water and dimethyl dicarbonate as a preservative. Following this, they poured the drink into individual bottles, and pasteurized the samples at 90 °C for 90 s. They stored drink samples in the refrigerator at 4 °C or at room temperature at about 30 °C, until samples were taken at 0, 15, 30, 60, and 90 days.
The team used a hybrid quadrupole-Orbitrap Elite mass spectrometer (Thermo Scientific) to analyze the drink composition following the fermentation. They found sixty-four non-anthocyanin phenolic compounds including hydroxybenzoic acids and derivatives, hydrolyzed and condensed tannins, ellagic acid and derivatives, hydroxycinnamic acids, dihydroflavanols, flavanones, flavanols, flavones, chalcones, and others such as citric and quinic acid. The researchers also identified four compounds that had not been previously reported in beverages fermented from strawberry: aromadendrin hexoside, phloretin 2′-O-xylosyl glucoside, dihydroferulic acid 4-O-glucuronide, and kaempferol hexosyl hexoside.
The results of the composition testing revealed that in general, the drink composition remained unchanged until day 15 of storage at room temperature (27−30 °C) and until day 30 under refrigerated conditions (4 °C). They saw a large loss of non-anthocyanin phenolic compound content at room temperature. Another finding was a large increase (13 times initial value) in protocatechuic acid after 60 days at 30 °C, with its concentration reaching 11 times its initial value after 90 days at 4 °C. The researchers considered that this increase may be due to the degradation process of anthocyanin compounds.
The researchers also queried a panel of sensory analysts to differentiate taste. The panel perceived sensory differences from 30 days of storage at room temperature, but could not establish differences between refrigerated samples whatever the storage time was. They also could not differentiate between samples stored during 30 days at different temperatures. However, differences between samples stored at 4 or 27−30 °C for 60 days could be perceived, and even larger differences were perceived for samples stored for 90 days. The authors determined that the ideal strawberry fermented beverage storage period should not exceed 30 days at room temperature or 60 days at refrigeration conditions. As a result, Álvarez-Fernández and colleagues concluded that gluconic fermentation is a satisfactory strategy for preventing fruit waste.
Álvarez-Fernández, MA, et al. (2016) “Determination of Nonanthocyanin Phenolic Compounds Using High-Resolution Mass Spectrometry (UHPLC-Orbitrap-MS/MS) and Impact of Storage Conditions in a Beverage Made from Strawberry by Fermentation.” Journal of Agricultural and Food Chemistry. 2016 Feb 17;64(6):1367-76. doi: 10.1021/acs.jafc.5b05617. Epub 2016 Feb 4.