Evaluation of Extracts Prepared from Olive Oil By-Products Using Microwave-Assisted Enzymatic Extraction: Effect of Encapsulation on the Stability of Final Products

Abstract

The feasibility of microwave-assisted extraction (MAE) and microwave-assisted enzymatic extraction (MAEE) for the polyphenols recovery from olive kernel and leaves was examined. The study revealed that applying MAE at 60 °C for 30 min, the extracts obtained from olive kernel had phenolic content 10.61 mg GAE/g raw material (dw) and antioxidant activity 10.40 mg Trolox/g raw material (dw) and the extracts obtained from olive leaves had phenolic content 28.00 mg GAE/g raw material (dw) and antioxidant activity 23.40 mg Trolox/g raw material (dw), respectively. By applying MAEE at 60 °C for 30 min, the extracts obtained from olive kernel had phenolic content 10.37 mg GAE/g raw material (dw) and antioxidant activity 15.93 mg Trolox/g raw material (dw) and the extracts obtained from olive leaves had phenolic content 29.52 mg GAE/g raw material (dw) and antioxidant activity 26.20 mg Trolox/g raw material (dw), respectively. Similarly, applying conventional extraction at 60 °C for 1 h, extracts with phenolic content 11.41 mg GAE/g raw material (dw) and antioxidant activity 9.69 mg Trolox/g raw material (dw) were obtained from olive kernel and extracts with 34.53 mg GAE/g raw material (dw) and antioxidant activity 27.94 mg Trolox/g raw material (dw) were obtained from olive leaves, respectively. HPLC analyses of phenolic compounds of extracts proved that the use of enzyme on extraction process leaded to valuable recovery of phenolic compounds. The predominant phenolic compounds in olive kernel and leaves extracts were oleuropein, hydroxytyrosol and rutin. Moreover, in order to protect the phenolic compounds’ properties, the extracts of olive kernel and leaves with high antioxidant activity were encapsulated in maltodextrin by freeze-drying technique. The final encapsulated polyphenolics’ products were evaluated in terms of hygroscopicity, solubility, moisture content and microencapsulation efficiency (MEE%). The MEE% varied from 82.39 to 92.12 % and from 87.98 to 91.06 % for olive kernel and leaves formulations, respectively. The encapsulation improved the moisture content, solubility and hygroscopicity of the encapsulated products. Concluding, the MAEE method being environment-friendly was efficient for the polyphenols recovery, while the polyphenols having significant antioxidant activity can be used as a source of potential antioxidant. Importantly, the use of olive kernel and leaves for such polyphenolic products reduces the impact of olive oil production on the environment.