Lactic acid fermentation of papaya and mint: physicochemical parameters and bioactive compounds

Papaya (Carica papaya) is a nutrient-rich fruit with significant bioactive compounds, presenting substantial potential for the development of functional beverages. This study explores the impact of lactic acid fermentation on the physicochemical parameters, bioactive compounds, and color stability of papaya and mint (Mentha piperita) smoothies. An optimal mixing ratio of 64:1 (w/w) for papaya to mint was established through preliminary experiments. Fermentation was conducted using Lactiplantibacillus plantarum and Bifidobacterium bifidum at 37°C, with a smoothie-to-water ratio of 2:1 (w/w).

The results showed that both strains proliferated rapidly in the smoothies, with colony counts increasing from approximately 6 × 10⁴ CFU/g to 8 × 10⁷CFU/g within 24 hours, followed by a stationary phase and slight decrease by 48 hours due to pH inhibition. Lactic acid fermentation significantly decreased the pH and titratable acidity (TA) of the smoothies, with the pH dropping to 3.51-3.56 and TA reaching 0.559%-0.553% after 24 h. After 48 h, TA increased further to 0.799%-0.743%. The otal soluble solids (TSS) also decreased significantly, falling to 5.58-5.53°Bx after 48 h of fermentation.

Furthermore, lactic acid fermentation preserved the total phenolic content (TPC) and ferric reducing antioxidant power (FRAP) in both papaya and papaya–mint smoothies, while enhancing the DPPH (2,2-Diphenyl-1-picrylhydrazyl) radical scavenging activity in the papaya–mint smoothie. Color analysis indicated that fermentation maintained or improved the color stability of the smoothies, with lightness (L*), chroma (C*), and hue (H*) parameters being preserved or slightly enhanced, contributing to the visual appeal of the final product. This study underscores the potential of lactic acid fermentation in creating functional beverages from papaya and mint, promoting health benefits, enhancing color stability, and extending shelf life. The findings suggest that fermenting papaya smoothies with L. plantarum for 48 h offers optimal results, providing a novel beverage option that preserves nutritional content, improves visual attributes, and reduces food waste.