Thermally-driven phenolic remodeling in probiotic-fermented red-fleshed pitaya: A dual-strain comparative study via...

Red-fleshed pitaya contains phenolics providing health benefits. Lactic acid bacterial fermentation facilitates the release and transformation of the phenolics present in pitaya, thereby further enhancing their biological activity. However, heat treatment would alter the phenolics composition of fermented red-fleshed pitaya. The effects of different heat treatment temperatures (85 °C and 121 °C) on the phenolic composition of fermented red-fleshed pitaya by Bifidobacterium breve or Lactobacillus casei were investigated. The 85 °C heat treatment promoted the conversion of phenolic compounds into low-molecular-weight derivatives, exemplified by the presence of caffeic acid in Bifidobacterium breve fermented samples, and anisaldehyde and protocatechuic aldehyde in Lactobacillus casei fermentations, as determined by UPLC-ESI-QTOF-MS/MS. When the temperature was elevated to 121 °C, these compounds underwent further conversion into more complex phenolic and flavonoid compounds, including isorhamnetin-3-O-neohespeidoside and chlorogenic acid. Furthermore, heat-treated Bifidobacterium breve fermented samples revealed a heightened propensity for the production of phenolic acids, including caffeic acid and gallic acid. However, Lactobacillus casei fermented samples unveiled in the production of various flavonoids, including quercitrin, nevadensin, plantagoside, pectolinarin, and kaempferol-3-O-rutinoside, along with the generation of aromatic compounds such as cinnamic acid and 6-gingerol. Lactobacillus casei fermented red-fleshed pitaya heat treated at 121 °C resulted in the most diverse array of phenolic compounds. This enhances the quality of fermented red-fleshed pitaya products. In addition to phenolic transformations, GC-MS analysis revealed that the combination of Bifidobacterium breve fermentation and 85 °C heat treatment increased total ester content from 15.39 % to 33.20 %, contributing to brandy-like aromas such as ethyl caprylate. In contrast, Lactobacillus casei combined with 121 °C treatment enhanced ketone abundance from 10.54 % to 16.19 %, producing creamy and milky notes. These microbial-specific changes highlight the concurrent modulation of aroma and phenolic profiles by fermentation and thermal treatment.