Date of Award

Winter 12-16-2022

Level of Access Assigned by Author

Campus-Only Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Food and Nutrition Sciences

Advisor

Jennifer Jean Perry

Second Committee Member

Mary E Camire

Third Committee Member

L. Brian Perkins

Additional Committee Members

Suzanne Ishaq

Robson Machado

Abstract

Kombucha and water kefir are non-dairy low alcohol fermented beverages (NDLAFB) that have gained acceptance among consumers. Production of these beverages requires starter cultures that are reused in the next production cycle via backslopping ad infinitum unless subjectively discontinued by the producer. A better understanding of the effects of repeated culture usage and culture preservation on the stability, viability, and reproducibility of these beverages will aid in standardizing production and homogeneity in the final products.

This study aimed at (1) evaluating the relationship among culture composition and physicochemical composition of finished beverages; (2) determining the diversity and stability of microbial communities present in mixed culture systems and finished beverages; and (3) exploring preservation techniques and their effects on microbial stability, recovery, and survival rate after storage.

For objective 1, kombucha and water kefir cultures were obtained from commercial and homebrewers and fermented. Samples of the finished beverages underwent microbial and physicochemical assays at 2 week increments for 12 weeks under refrigerated storage. For both beverages, microbial counts were relatively stable for lactic acid bacteria (LAB) and yeast across repeated cultures. However, the high microbial count did not directly correlate with the amount of metabolites produced. During storage time microbial counts declined. The physicochemical components had the highest variation across batches of repeated brewing.

For objective 2, DNA of culture and beverage samples were subjected to Illumina amplicon sequencing of bacterial 16S rRNA and fungal ITS regions. The data suggested that the cultures were composed of higher microbial abundance and diversity relative to the beverage. Stability, diversity, and abundance changed with repeated culture usage in both culture and beverage.

For objective 3, cultures with or without cryoprotectants were preserved by freezing, vacuum-drying, and freeze-drying. Samples were enumerated for LAB, yeast, and acetic acid bacteria (AAB) on day 1 and day 30 of storage. Unpreserved cultures had the highest count in both cultures. Freezing with cryoprotectant application resulted in a relatively similar microbial count as was observed in the unpreserved cultures

This study serves as foundational knowledge to optimize the production and preservation of these fermented beverage products to improve human health.

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