Modulation of phenolic compounds in murta (Ugni molinae Turcz) juice by lactic fermentation in monoculture and coculture: identification and quantification of extractable and non-extractable fractions by HPLC-QTOF-MS

Controlled lactic acid fermentation may be a strategy for valorization of plant matrices such as murta (Ugni molinae Turcz), a Chilean berry rich in phenolic compounds. This study evaluated the effect of fermentation in monoculture with Lactobacillus acidophilus and Lactiplantibacillus plantarum, as well as in coculture, under two optimized conditions (SAW and GDF) on the content, structural profile, and antioxidant capacity of extractable (EP) and hydrolysable (HP) polyphenols in murta juice. High Performance Liquid Chromatography coupled to Quadrupole Time-of-Flight Mass Spectrometry (HPLC-QTOF-MS) analysis identified 59 EP compounds, including methylated and glycosylated derivatives not previously reported in murta, evidencing a fermentation-induced structural reconfiguration. Additionally, 13 compounds (not present in unfermented samples) were identified in the hydrolysable polyphenol fraction, demonstrating the contribution of this constituent to a comprehensive assessment of the murta phenolic profile. The results showed significant increases in extractable polyphenols and their antioxidant activity (FRAP and ABTS) in GDF conditions, highlighting the coculture as the most effective. These findings confirm that using optimized fermentative conditions, particularly in coculture, not only increases the concentration and diversity of phenolic compounds but also underscores the importance of integrating extractable and hydrolysable polyphenol fractions to broaden the utilization of murta juice in developing fermented beverages with enhanced functional properties.