Chemical composition, antioxidant potential and phenolic profile of oil mill waste water from Tunisian olive varieties (Chetoui and Chemlali)

Abstract

Oil mill waste water (OMWW) is of great interest due to the presence of valuable resources such as biophenols that can be recovered as food additives and pharmaceuticals. The aim of this study is to investigate the variation of physicochemical composition of OMWW from Chetoui and Chemlali varieties, to evaluate phenolic composition, antioxidant potential and phenolic profile of OMWW extracts under native and acidified conditions. Liquid-liquid extraction was performed for the extraction of polyphenols. Antioxidant activity was investigated by DPPH^•, ABTS^•+ and FRAP tests. Phenolic compounds content was determined by HPLC-DAD method. OMWW from Chetoui variety has been shown to contain an important amount of K, Ca and Na whereas Chemlali cultivar was rich in Mg. Phenolic extract from Chetoui fruit (COCt) has been  shown to contain the highest amount of polyphenols (2.48 ± 0.21 g L^-1) as well as an appreciable content of flavonoids (9.39 ± 0.32 g L^-1). However, phenolic extract from Chemlali fruit (COCm) has been shown to have the highest content of proanthocyanidins (0.39 ± 0.00 g L^-1). Acidification treatment improved polyphenol recovery of extracts from both varieties. COCt was more active using DPPH (EC₅₀ of 7.5 mg L^-1) and FRAP tests. However, COCt and COCm exhibited the same activity using ABTS test. In general, acidification treatment decreased antioxidant activity of extracts. COCt has been shown to contain higher amount of hydroxytyrosol when compared to COCm (157.16 ± 0.820 and 23.440 ± 0.440 mg g^-1 D.W. of extract, respectively) as revealed by HPLC-DAD analysis.