Olive leaf protein: Extraction optimization, in vitro digestibility, structural and techno-functional properties.

Olive leaf, as an important by-product of olive farming, is generated from the pruning and harvesting of olive trees and represents >10 % of the total olive weight. The present study was conducted to evaluate the composition, functional and structural characterizations, as well as the in vitro digestibility of olive leaf proteins isolated from ultrasonic-assisted extraction, comparing to classical and industrial techniques. The ultrasound-assisted extraction of olive leaf protein was optimized by the simultaneous maximization of the yield and purity of protein using a Box-Behnken design (BBD) of response surface methodology (RSM). The results indicated that the optimal extraction conditions were as follows: pH of 10.99, temperature of 40.48 °C, sonication time of 47.25 min, and solvent/solid ratio of 24.08 mL/g. Under these conditions, the extraction yield and protein content were 11.67 and 51.2 %, respectively, which were significantly higher than those obtained by the conventional techniques. Regarding the functionality of protein, extraction technique had significant impacts on the structural and functional properties of proteins. In general, ultrasound assisted extraction had higher solubility, and better foaming and thermal properties and in vitro digestibility but lower emulsifying stability and fluid binding capacity compared to conventional ones. Ultrasound-assisted alkaline extraction has great potential to produce edible olive leaf protein with modified functional properties that can be used for various aims in the food applications.