Optimization and component identification of ultrasound‐assisted extraction of functional compounds from waste blackberry (Rubus fruticosus Pollich) seeds

Abstract BACKGROUND Blackberry seeds, as a by‐product of processing, have potential bioactive substances and activities. A response surface method was used to determine the optimal conditions of blackberry seed extracts (BSEs) with high 2,2‐diphenyl‐1‐picrylhydrazyl (DPPH) scavenging activity by ultrasound‐assisted extraction (UAE). The composition and antioxidant capacity of BSEs were further analyzed. RESULTS The optimal conditions were material‐to‐liquid ratio of 0.07 g mL −1 , ethanol concentration of 56%, extraction temperature of 39 °C and ultrasonic power of 260 W. Using these conditions, the extraction yield and total polysaccharide, phenolic and anthocyanin contents in BSEs were 0.062 g g −1 and 633.91, 36.21 and 3.07 mg g −1 , respectively. The Fourier transform infrared spectra of BSEs exhibited characteristic peaks associated with polysaccharide absorption. The antioxidant capacity, DPPH and 2,2'‐azino‐bis(3‐ethylbenzothiazoline‐6‐sulfonic acid) radical scavenging activity, and ferric reducing antioxidant power of BSEs were 1533.19, 1021.93 and 1093.38 mmol Trolox equivalent g −1 , respectively. The delphinidin‐3‐ O ‐glucoside, paeoniflorin‐3‐ O ‐glucoside and cyanidin‐3‐ O ‐arabinoside contents in BSEs were 3.05,12.76 and 1895.90 ± 3.45 μg g −1 . Five polyphenols including gallic acid, coumaric acid, ferulic acid, catechin and caffeic acid were identified and quantified in BSEs with its contents at 8850.43, 5053.26, 4984.65, 1846.91 and 192.40 μg g −1 . CONCLUSION These results provide a method for preparing BSE containing functional components such as polysaccharides, phenols and anthocyanins through UAE, and BSEs have potential application in food industries. © 2024 Society of Chemical Industry.