Screening of a High Ethyl Hexanoate-Producing Monascus purpureus Strain and Its Application in Hexanoic Acid-Supplemented Strong-Flavor Baijiu Fermentation

Ethyl hexanoate is a dominant ester contributing to the characteristic cellar-like and fruity aroma of strong-flavor Baijiu. In this study, a high ethyl hexanoate-producing strain (H-8) was isolated from Baijiu-related fermentation sources and identified as Monascus purpureus based on morphological characteristics and internal transcribed spacer (ITS) sequence analysis. Under optimized culture conditions, strain H-8 produced 1,203.43 mg/L ethyl hexanoate in liquid fermentation, indicating its strong esterification potential. The application potential of strain H-8 was evaluated in hexanoic acid-supplemented fermentations of light-flavor and strong-flavor Baijiu. In light-flavor Baijiu, inoculation with H-8 alone increased ethyl hexanoate content by 55.05%, indicating effective esterification activity under hexanoic acid-supplemented conditions. Co-inoculation of H-8 with the ester-producing yeast F-5 further enhanced ethyl hexanoate formation, with increases of 69.57% and 64.40% in light-flavor and strong-flavor Baijiu, respectively. Gas chromatography–mass spectrometry (GC–MS) analysis showed that H-8 addition enriched the volatile profile, particularly the ester fraction. These results demonstrate that M. purpureus H-8 is a promising functional strain for enhancing ethyl hexanoate formation and improving flavor quality in hexanoic acid-supplemented Baijiu fermentation.