Optimization of dilute acid-based pretreatment and application of laccase on apple pomace

The present study was aimed to optimize acid-based pretreatment of apple pomace in relation to acid concentration, temperature and reaction time using response surface method with glucose as response variable. In addition, laccase (EC. 1.10.3.2) from Trametes versicolor was applied for degradation of polyphenols in apple pomace that could inhibit the further bioconversion steps involving enzymes and fermenting micro-organisms. The optimized conditions were: 1.5 g/100mL acid concentration, 16 min reaction time and 91°C reaction temperature, producing 13.9 g glucose/100g on a dry matter basis. Subsequent application of laccase to hydrolyzates degraded most of the phenolic compounds in apple pomace by more than 85%. The optimized pretreatment conditions resulted in lower concentrations of other inhibitors such as furan compounds and acetic acid. Therefore, dilute acid pretreatment in combination with laccase application can be used for enhancing subsequent hydrolysis of polysaccharides and fermentation of apple pomace.