Ultrasound-assisted enzymatic extraction of proteins from Gracilaria dura: Investigation of antioxidant activity and techno-functional properties

In this study, ultrasound-assisted enzymatic extraction was performed to extract proteins from Gracilaria dura for the first time. The ultrasonic applying time (30-300 s), enzyme/substrate (E/S, 0.5-2.5), and extraction time (20-28 h) on protein content (PC), total phenolic content (TPC), and antioxidant activity (AOA) was optimized using response surface methodology. Techno-functional properties of protein extracts obtained under optimum conditions were determined. At optimum conditions (ultrasonic applying time: 257.57 s, E/S: 2.5, extraction time: 22.61 h), PC, TPC, AOA(CUPRAC) and AOA(ABTS) were found as 189.59 mg/g, 60.52 mg GAE/g and 55.66 mg TE/g and 478.50 mg TE/g dw, respectively. The water/oil absorption capacity, foaming capacity/stability, emulsifying activity/stability of the protein extracts were 195 +/- 0.08%, 568 +/- 0.10%, 12.5 +/- 0.00%, 0%, 44 +/- 0.00%, and 75 +/- 2.50%, respectively. In conclusion, G. dura protein extracts may have an important potential to improve antioxidant activity and functional properties of various food products due to high antioxidant activity and a good level of water/oil absorption capacity. Novelty impact statement Macroalgae Gracilaria dura proteins were successfully extracted with high extraction efficiency by extraction process performed with ultrasonication application and enzyme usage. The protein extracts from G. dura can be used to improve the techno-functional and antioxidative properties of various food products due to their acceptable water/oil absorption capacity and emulsifying properties and high antioxidant activity.