Available at: https://digitalcommons.calpoly.edu/theses/3235
Date of Award
3-2026
Degree Name
MS in Agriculture - Food Science and Nutrition
Department/Program
Food Science and Nutrition
College
College of Agriculture, Food, and Environmental Sciences
Advisor
Milena M. Ramirez Rodriguez
Advisor Department
Food Science and Nutrition
Advisor College
College of Agriculture, Food, and Environmental Sciences
Abstract
This study evaluated the impact of hibiscus and whey as alternative fermentation substrates on the physicochemical, phytochemical, and microbial properties of kombucha. A 2 × 2 full factorial design was used to compare four treatments: black tea + water (BW), black tea + whey (BH), hibiscus + water (HW), and hibiscus + whey (HH). The fermentation solvents (water or whey) were heated to 88 °C, infused with 0.6% (w/v) black tea or hibiscus for 10 minutes, sweetened with 10% (w/v) sucrose, cooled to 22 °C, and inoculated with 20% (v/v) kombucha starter culture. Fermentations were carried out at 22 °C for 25 days in triplicate, with analyses conducted at 5-day intervals.
The addition of whey significantly influenced (p < 0.05) pH, °Brix, alcohol concentration, organic acid profile, color density, hue tint, total phenolic content, polyphenolic composition, antioxidant capacity (ORAC and DPPH), total protein concentration, and amino acid profile. Whey-based kombucha treatments (BH and HH) exhibited higher alcohol concentrations (0.59–0.83% v/v and 0.04–1.62% v/v, respectively), gallic acid concentration (0.07 mg/L in HH), malic acid (199 mg/L and 99.4 mg/L), lactic acid (110 mg/L and 123 mg/L), citric acid (2,705 mg/L and 2,947 mg/L), succinic acid (156 mg/L and 231 mg/L), antioxidant capacity (ORAC: 239.31–468.28 µM TE and 253.60–326.20 µM TE), total protein concentrations (0.27–0.32 mg/mL and 0.36–0.41 mg/mL), and a higher amount of amino acids compared to water-based treatments throughout fermentation. Although the use of whey and hibiscus in kombucha increased the lactic acid, antioxidant capacity, total protein, and amino acid profile, more research needs to be performed to assess the mitigation of alcohol, ideal fermentation duration, and ratio of whey to maximize extraction of substrate polyphenols.