Optimization of apple puree fermented by mixed lactic acid bacteria and analysis of main volatile components and in vitro digestion of phenols and antioxidation

In this study, the synergistic effects of mixed-strain fermentation (Lacticaseibacillus rhamnosus GG, Lactobacillus acidophilus NCFM, and Bifidobacterium animalis subsp. lactis Bb-12) on enhancing the nutritional profile and volatile components of apple puree were investigated. Under the optimal fermentation conditions, the apple puree demonstrated significant improvements: (1) Nutritional enhancement: 62.78% and 29.48% elevation in total phenolics and total flavonoids, and antioxidant capacities improvement; (2) Sensory modification: the achievement of superior sensory score (92.44), reduced sweetness, and enhanced sourness and umami; (3) Volatile components: the identification of 91 volatile components, with increased concentrations of alcohols, esters, ketones and acids, and decreased concentration of aldehydes. Notable increases in key esters and alcohols such as 3-methyl-1-butanol (23.00%), ethyl acetate (47.17%) and γ-butyrolactone (14.67%) contributed to a fruity top note and long-lasting creamy fragrance. Decreases in acetaldehyde (10.03%), propanal (45.71%) and (E)-2-heptenal (39.08%) mitigated harsh spiciness and enhanced masked fruity for a more balanced flavor profile; (4) Simulated digestion: total phenolics remained stable in the gastric phase, but increased by 305.13% during intestinal digestion, which indicated improved bioaccessibility. Overall, this study demonstrates that mixed-strain fermentation enhances the nutritional value of apple puree and provides valuable insights into the fermented fruit and vegetable industry.