Enhanced sensory quality and functional properties of fermented goji berry juices by low-acid-producing probiotic Limosilactobacillus fermentum WXZ2-1

Goji berries (Lycium spp.) are valued for their health-promoting potential. However, their juices often exhibit excessive acidity and unbalanced flavor, particularly after fermentation, which limits consumer acceptance and product development. This study aimed to improve both sensory quality and functional properties of red and black goji berry juices through probiotic fermentation using a low-acid-producing strain. Four probiotic strains were screened for their fermentation performance in red and black goji berry juices. Among them, Limosilactobacillus fermentum WXZ2-1 exhibited the most balanced fermentation profile; its moderate acid accumulation effectively preserved the sugar-acid balance, leading to a 29.12% increase in overall sensory acceptability scores compared to the average of other strains. L. fermentum WXZ2-1 exhibited superior growth performance in black goji juice, reaching 1.2 × 108 CFU/mL at 18 h, and produced a significantly higher sugar-to-acid ratio than other strains (SAR 27.25 in red and 23.33 in black at 24 h). Moreover, fermentation with L. fermentum WXZ2-1 significantly increased the antioxidant activity (DPPH radical scavenging capacity) and total phenolic content by 16.16% and 56.01%, respectively; in red goji berry juice, and by 15.57% and 77.63%, respectively, in black goji berry juice. Metabolomic and volatile analyses revealed enhanced sugar metabolism, moderated acid formation, and enriched aromatic profiles, particularly in black goji juice. Overall, L. fermentum WXZ2-1 is a promising starter for producing fermented goji beverages with improved sensory quality and functional benefits.