Sensory improvement of fermented apple juice diluted from concentrate by lactic acid bacteria

To evaluate the fermentation potential of diluted concentrated apple juice (CAJ) and identify suitable strains, seven lactic acid bacteria (LAB) strains, including Lactiplantibacillus plantarum (TM3-23), Pediococcus acidilactici (G1-14), Lacticaseibacillus paracasei (TH4-4), Limosilactobacillus fermentum (LX4-19), Lactobacillus acidophilus (G3-2), Lactobacillus helveticus (G3-4), and Lactobacillus delbrueckii (SJ2-10), were employed for diluted CAJ fermentation. The identification of volatile compounds was conducted using gas chromatography-mass spectrometry (GC-MS), while sensory quality of fermented products was evaluated using electronic tongue analysis and sensory evaluation. Results indicated that TM3-23, TH4-4, G1-14, and G3-4 adapted well to diluted CAJ and demonstrated a robust ability to metabolize malic acid, with TM3-23 achieving 8.27 Log CFU/mL. TM3-23 and LX4-19 enhanced the diversity of phenolic compounds. LAB fermentation enhanced the aroma by reducing aldehyde content and increasing the diversity of alcohols and other volatile compounds. Fermentation increased L* values and reduced a* values significantly (p < 0.05). CAJ fermented by TM3-23 received the highest sensory scores for taste (22.67) and flavor (22.48). G1-14 demonstrated significant DPPH radical scavenging activity and FRAP (p < 0.05). A comparison of the physicochemical properties of fresh squeezed apple juice and diluted CAJ after fermentation revealed that diluted CAJ serves as a suitable substrate for LAB fermentation, with Lactiplantibacillus plantarum TM3-23 being the dominant strain for the development of fermented apple juice. This study demonstrates the feasibility of using diluted CAJ for fermentation, supporting its high-value application in the food industry.