Phenolic Characterisation of Citrus Peel Aqueous Extract: By-Products of Hydrodistillation and the Effect of Enzymatic Pretreatment.

This study aimed to characterize the phenolic composition of aqueous extracts obtained as by-products of hydrodistillation of orange, mandarin, and clementine peels and to evaluate the effect of enzymatic pretreatment on phenolic recovery. Different enzymatic pretreatments were applied prior to hydrodistillation, and the resulting extracts were analyzed by UPLC-MS/MS. Differences in the mass fractions of phenolic compounds were observed among pretreatments, with the magnitude of these changes depending on the citrus species and extraction conditions. Quercetin and kaempferol were the predominant phenolic compounds in all three citrus species. The highest sum of the mass fractions of quantified phenolic compounds was observed for mandarin peel following combined enzyme pretreatment in citrate buffer (19.73 µg/g) and for clementine peel following xylanase pretreatment in water (34.94 µg/g). For orange peel, the highest value was obtained following combined enzyme pretreatment in citrate buffer (10.88 µg/g), although no increase in the sum of the mass fractions of quantified phenolic compounds was observed compared with the corresponding control. Overall, the observed changes following enzymatic pretreatment were species-dependent, with the most pronounced increases in phenolic mass fractions found for mandarin and clementine peels.