Probiotic Enrichment of Jamun Juice With Streptococcus thermophilus: Effects on Antioxidant Activity and Quality

Abstract

The increasing demand for functional beverages has driven interest in incorporating probiotics into fruit juices. This study investigates the functionalization of jamun juice with Streptococcus thermophilus (S. thermophilus), a thermophilic probiotic bacterium, to enhance its probiotic properties and assess storage stability under varying temperature conditions. S. thermophilus was isolated from commercial yogurt and identified through colony morphology, Gram staining, and catalase and oxidase tests. The probiotic culture was cultivated in nutrient broth and inoculated into 250 mL of pasteurized jamun juice using 1 mL of bacterial suspension at a concentration of 1.5 × 10⁸ CFU/mL, resulting in a final concentration of 6.0 × 10⁵ CFU/mL in the juice. The functionalized juice was stored at 37°C (incubation), 25°C (room temperature), and 4°C (refrigeration) for 28 days, during which microbial load, pH, sugar content, antioxidant activity, and sensory acceptability were monitored. Results showed a significant increase in microbial load at 37°C, peaking at 10⁹ CFU/mL by Day 14. At room temperature and refrigeration, microbial growth remained minimal, with levels around 10⁸ to 10⁶ CFU/mL. The pH declined most rapidly at 37°C, and at the same temperature, sugar content decreased to 2.2 mg/mL by Day 21. Antioxidant activity, measured using the DPPH assay, was highest (82.35%) at 37°C, indicating enhanced probiotic metabolic activity. Sensory evaluations revealed improved acceptability with lower temperature storage, particularly at refrigeration temperatures, while higher temperatures led to a decrease in sensory quality. Functionalizing jamun juice with S. thermophilus improved its probiotic properties, with temperature playing a key role in maintaining these benefits. Refrigeration preserved both quality and probiotic stability, suggesting the potential of this probiotic jamun juice as a functional beverage. Future research could investigate its long-term stability, sensory characteristics, and nutritional profile, including the presence of bioactive compounds.

Keywords: Streptococcus thermophilus; antioxidant activity; functional beverage; jamun juice; probiotics.

FIGURE 1

Colony morphology of predominant isolates on a nutrient agar plate.

FIGURE 2

Appearance of gram‐stained presumptive S. thermophilus isolates under light microscopic observation (×100).

FIGURE 3

Catalase test for selected S. thermophilus isolates.

FIGURE 4

Oxidase test for selected S. thermophilus isolates.

FIGURE 5

Fresh pasteurized jamun juice packed in a 250 mL bottle.

FIGURE 6

A 250 mL bottle containing functionalized probiotic jamun juice.

FIGURE 7

Microbial load in functionalized probiotic jamun juice stored at different temperature conditions: (A) incubator at 37°C (yellow solid line), (B) room temperature (blue solid line), and (C) refrigeration (green solid line), along with (D–F) respective control samples (dash dot lines).

FIGURE 8

Standard calibration curve for total sugar determination using the phenol–sulfuric acid method. A series of glucose standards (0–0.10 mg/mL) were reacted with 5% phenol and concentrated sulfuric acid, and absorbance was measured at 490 nm. The absorbance values showed a linear relationship with glucose concentration (R ² = 0.956).