Biovalorization of spent Konacha tea leaves via single-culture fermentation involving wine yeasts and lactic acid bacteria

The objective of this study was to explore the potential of fermentation as a biovalorization strategy for spent tea leaves (STL), a major agrifood waste generated from the tea extraction industry. Fermentation by wine yeasts or lactic acid bacteria (LAB) has shown promising results in previous studies across various substrates.Konacha (green tea) STL slurries were inoculated with single strains of wine yeasts or LAB respectively. After a 48-h fermentation, changes in selected nonvolatile and volatile compositions were evaluated. Fermentation by LAB increased organic acid content by 5- to 7-fold (except Lactobacillus fermentum) and modulated the composition of major tea catechins, whereas wine yeast fermentation resulted in a 30% increase in amino acid content. Strain-specific production of specific volatile compounds was also observed such as butanoic acid (L. fermentum), isoamyl acetate (Pichia kluyveri) and 4-ethylphenol (L. plantarum).Both volatile and nonvolatile compound compositions of Konacha STL were successfully modified via wine yeast and LAB fermentation.Our findings indicate that Konacha STL is a suitable medium for biovalorization by wine yeasts or LAB via the generation of commercially useful volatile and nonvolatile compounds. Future optimizations could further render fermentation an economically viable strategy for the upcycling of STL.