The Role of Blackberry Grades and Fermentation Methods on Blackberry Kombucha Quality and Aroma Characteristics from Small-Scale Fermentation

Abstract

Most blackberry farms in Virginia are small operations and seek ways to profit from quality-compromised produce that do not meet the cosmetic guidelines of retail buyers and consumers. U.S. No.1 and U.S. No.2 blackberries differ in physical characteristics like size, color, or insect damage but both are still safe to consume. Utilization of the quality-compromised U.S. No.2 blackberries in innovative ways, like in a kombucha product, could help these growers reduce produce waste as well as increase their revenue. However, the production of kombucha, especially on the commercial scale, requires complex, expensive materials and equipment. Therefore, this study aims to develop a simple, small-scale fermentation strategy for blackberry kombucha to determine if and how blackberry grades and fermentation methods impact the final kombucha quality. First, the physicochemical parameters of U.S. No.1 and U.S. No.2 blackberries were analyzed, including pH, titratable acidity (TA), and total soluble solids (TSS), followed by aroma analysis using headspace-solid phase microextraction (HS-SPME) and gas chromatography-mass spectrometry-olfactometry (GC-MS-O). Then, a blackberry kombucha product was made, in biological triplicates, with either U.S. No.1 or U.S. No.2 blackberries using two different fermentation techniques, involving the addition of blackberries either at the start of fermentation (method 1) or after a week of initial fermentation (method 2). Physicochemical parameters, including pH, TA, sucrose, glucose, and fructose contents, and total phenolic content (TPC), were measured at several time points throughout the fermentation. Additionally, aroma-active compounds were extracted using liquid-liquid extraction (LLE) followed by solvent assisted flavor evaporation (SAFE) and characterized by use of GC-MS-O in the final products. The results showed significant differences (p<0.05) in the pH, TA, sugars contents, and TPC between fermented kombucha from method 1 and method 2. The method 2 fermentation technique yielded a more acidic product with fewer phenolic compounds, more residual sugar, and higher concentrations of notable aroma compounds on the last day (day 14) of fermentation. On the other hand, there were few significant differences (p>0.05) in physicochemical parameters or aroma compounds between U.S. No.1 and U.S. No.2 blackberries or between kombucha fermented from either blackberry grade. These findings suggest that compromised quality of blackberry fruit does not necessarily compromise final quality of kombucha, as well as that the method 2 fermentation lends to a more aromatic product. This small-scale kombucha fermentation approach seems to be a feasible way to increase Virginia growers' revenue by repurposing compromised berry fruits for value-added beverages.