Optimization and kinetic modelling of robinetin and dihydrorobinetin extraction from Robinia pseudoacacia wood

Due to its rapid growth and important biomass production abilities, black locust (Robinia pseudoacacia L.) wood could represent an interesting source of natural compounds. Here, we optimized the extraction of the two main flavonoids accumulated in this species wood (i.e.: robinetin and dihydrorobinetin) with 80:20 (w:w) ethanol:water solvent well adapted for further industrial uses such as cosmetics. Our experimental design focused on two main extraction parameters: temperature and wood/solvent volume ratio that were optimized to 27.5 °C and 177 g L−1, respectively. These conditions lead to an optimal recovery of about 3000 mg L−1 of dihydrorobinetin and 700 mg L−1 of robinetin in the extracts. Interestingly, the effect of temperature could be neglected allowing reduced energy consumptions at the industrial level. Analysis of the evolution of robinetin and dihydrorobinetin concentrations during the timespan of the experiments revealed similar behaviours for both molecules. Kinetic modelling of robinetin and dihydrorobinetin release showed that pseudo-second order rate laws described well the extraction process with r2 values over 0.91. In the end, the results of this study provided useful insights to scale-up the extractions and lead to an industrial production of black locust wood extracts enriched in both flavonoids of interest.