(P06-019-23) Assessment of Preservation Techniques for Kombucha Starter Culture

Objectives: Kombucha has gained popularity due to its purported health benefits. Production requires a culture (SCOBY) embedded with yeast and bacteria that determine the composition of the fermented beverage. Cultures self-propagate for use in sequential brewing cycles which may distort the microbial consortium resulting in inconsistencies in the beverage. There are no validated cryoprotectants/preservation techniques to maintain the quality and integrity of the cultures.

This study evaluates preservation techniques and cryoprotectants and their effects on microbial stability, recovery, and survival after storage of kombucha SCOBYs.

Methods: Three SCOBYs were obtained from commercial suppliers (n=2) or homebrewers (n=1). Each culture system was brewed following a standard recipe. Newly propagated SCOBY samples were collected at pH 3 and size-modified by blending into fine paste. Samples were preserved with cryoprotectants (20% w/v mannitol, 5% w/v glucose, combination of both). Four SCOBY sample sets, each consisting of unmodified and fine paste samples were subjected to one of each treatment group: no preservation (control), vacuum drying (40 °C), freezing (-20°C) and freeze drying (-20 °C, for 30 min/0.6mbar, for 48 hr). Cryoprotected and preserved samples were analyzed at days 1 and 30 post-treatment. Samples were enumerated for acetic acid bacteria (AAB) and yeast on selective media. Data was subjected to ANOVA and bar plots for visualization.

Results: Microbial populations were significantly affected by vacuum and freeze-drying. Overall, AAB counts were highest in the frozen, fine blended samples preserved with mannitol at day 1. Yeast counts were similar in glucose treated unpreserved versus frozen samples with no significant decrease observed with storage. Combination of glucose and mannitol failed to show a synergistic effect on yeast and AAB counts. Prolonged storage showed a significant reduction in microbial count in cultures preserved with glucose and mannitol.

Conclusions: Study showed vacuum-drying and freeze-drying of cultures adversely affects stability and viability of microbial cultures. Cryoprotection of frozen cultures increased survival of yeast and AAB cells and should be integrated into SCOBY preservation strategies.

Funding Sources: USDA-NIFA