Differential production and degradation of 1-hydroxyoctan-3-one and octane-1,3-diol in Penicillium digitatum or Botrytis cinerea infected apple puree

The “old apple taste” off-flavor is a spoilage described for apple-derived products such as puree and juice. It appears as a significant challenge to the fruit transformation industry. The two C8 linear compounds 1-hydroxyoctan-3-one and octane-1,3-diol were recently associated with this defect. These compounds, characterized by a mushroom-like aroma, have been linked to pre-harvest fungal contamination and post-harvest colonization, but yet their metabolic origins and fates remain poorly understood. In this study, we investigated the biochemical pathways underlying the production and degradation of these off-flavor markers in apple product artificially contaminated with Penicillium digitatum or Botrytis cinerea . Using stable isotope dilution assay (SIDA) LC-MS/MS, we quantified 1-hydroxyoctan-3-one and octane-1,3-diol in fungal inoculated puree with linoleic acid or exogenous glycosidase addition. Our findings revealed a divergence in fungal metabolism. P. digitatum robustly synthesized 1-hydroxyoctan-3-one via a lipoxygenase-dependent pathway, stimulated in the presence of linoleic acid. In contrast, B. cinerea neither produced nor accumulated this compound, instead metabolizing it when co-inoculated. Glycosidase treatment has highlighted a glycosylated reservoir of octane-1,3-diol in apple matrix, but not for 1-hydroxyoctan-3-one, pointing to distinct precursor pools for these compounds. In purees, octane-1,3-diol levels rose when contaminated by P. digitatum , but declined in those infected by B. cinerea , suggesting a species-specific ability to bind this compound. These results not only improve our understanding of fungal-mediated off-flavor development but also underline the major role of matrix composition and microbial interactions in shaping the sensory quality of apple derived-products. By identifying key metabolic pathways and fungal contributions, this work paves the way for targeted strategies to limit off-flavor formation in apple-derived products.