Optimization of pretreatment and enzymatic hydrolysis conditions of tomato pomace for production of alcohols and esters by Kluyveromyces marxianus

Tomato pomace (TP) is generated as a natural by product in a significant amount in the tomato processing industry, and it is a good source of lignocelluloses to produce some high-value products from fermentable sugars (FS). The present study was performed to produce FS by using either ultrasound-assisted dilute acid (UADA) or heat-treated dilute acid (HTDA) pretreatments of TP followed by enzymatic hydrolysis (EH). When HTDA and UADA were compared in terms of FS (g/L) concentration, HTDA pretreatment generally produced more FS content than UADA. The optimum conditions for HTDA pretreatment were the application of 2.5% H2SO4, 10% (w/v) solution of TP, and heating at 121 °C for 6 min, which yielded 31 g/L FS concentration. Beside the optimized conditions for EH of HTDA, pretreated TP required 1.5% of enzyme concentration and 6 h of hydrolysis time. In conclusion, the most abundant volatile organic compounds (VOCs) produced by K. marxianus in final tomato pomace hydrolysate (TPH) were isoamyl alcohol, phenyl ethyl alcohol, ethyl acetate and phenyl ethyl acetate in a 5-L bioreactor. Nine descriptive sensory terms were developed to characterize fermented TPH. The rose and sweet floral aromas were defined as aroma characteristics for TPH fermented by K. marxianus. •Different pre-treatments and enzyme hydrolysis for tomato pomace (TP) were evaluated.•Fermentable sugar in TP increased by ultrasound-assisted dilute acid pre-treatment.•1.5% of enzyme level and 6 h of enzyme hydrolysis were optimum condition for TP.•Major volatile compounds in fermented TP were alcohols and esters.•The rose and sweet aromas were defined as descriptive sensory terms for fermented TP.