Manufacture of a beverage from cactus pear juice using tea fungus fermentation

Kombucha is a beverage that is prepared by fermenting sweetened black tea using a tea fungus, which is a symbiotic culture of acetic acid bacteria and yeasts. In the present study, cactus pear juice was used as a substrate for kombucha fermentation in order to develop a new beverage with enhanced nutritional properties. Changes in chemical and microbiological parameters of the fermented juice were determined during fermentation. The growth of microflora induced a reduction in pH from 5.1 to 3.5 and a 23 % increase in total phenol content after 6 days of fermentation. The antioxidant potential of the beverage was also improved, reaching 81 % and 65 % as determined, respectively, by 2,2-diphenyl-1-picrylhydrazyl (DPPH) and 2,2'-azino-bis (3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) radical scavenging assays. The improved antioxidant capacity was attributed to betalains and to certain metabolic products formed during the fermentation process. Furthermore, the fermented juice showed antimicrobial activity against the tested Gram-positive (Staphylococcus aureus ATCC 6538, Bacillus cereus ATCC 11778, Staphylococcus epidermidis ATCC 12228 and Enterococcus faecalis ATCC 10541) and Gram-negative bacteria (Escherichia coli ATCC 10536, Klebsiella pneumoniae ATCC 10031, and Pseudomonas aeruginosa ATCC 9027), which was attributed to its acetic acid content. Sensory evaluation of fresh juice and juice after 6 and 12 days of fermentation by a taste panel showed high acceptability of the juice after the first 6 days of fermentation, as the cactus pear juice taste qualities were still present, without the higher acidity that some panelists found unacceptable after longer fermentation.