Adsorption of olive leaf antioxidants on silk fibroin

Abstract

This study focused on producing protein based functional food with antioxidative and antimicrobial properties by adsorption of olive leaf antioxidants on silk fibroin. In accordance with this aim, extraction and adsorption of two most abundant polyphenols in olive leaves, oleuropein and rutin were studied. Furthermore, desorption studies were performed to increase the purity of polyphenols.In this study, effect of various parameters on extraction and adsorption were investigated by HPLC and antioxidant analyses. The adsorption isotherms of oleuropein and rutin were plotted at different temperatures, pH values and solid-liquid ratios. After adsorption, the adsorbed polyphenols on silk fibroin was subjected to SEM, FTIR, color, antioxidant and antimicrobial analyses to observe the changes in the silk fibroin.The experimental data of adsorption isotherms were well-fitted to Langmuir model. The maximum adsorption capacity was determined as 108 mg oleuropein/g silk fibroin and 21 mg rutin/g silk fibroin. In desorption process, 81% of rutin and 85 % of oleuropein were removed from the adsorbent surface in 70 % aqueous ethanol solution.After adsorption of oleuropein and rutin, the antioxidant capacity of silk fibroin increased from 1.93 mmol TEAC/g to 3.61 mmol TEAC/g. Silk fibroin also gained antimicrobial activity against Staphylococcus aureus and Klebsiella pneumoniae after adsorption of olive leaf antioxidants. Desorbed polyphenols exhibited higher antioxidant capacity than the same amount of olive leaf extract due to the increase in the purity of oleuropein and rutin after desorption.Consequently, silk fibroin is a promising protein for the production of functional food or dietary supplements and for the purification of oleuropein and rutin.