Effect of zein coating enriched by addition of functional constituents on the lipid oxidation of roasted hazelnuts

Abstract

This study investigates the effects of hazelnut skin extract powder (HEP) and -tocopherol addition to zein coating on lipid oxidation, texture, and moisture content of roasted hazelnuts. Total phenolic content of hazelnut skin extracted with three different solvents (acetone, ethanol, methanol) under hot (50 degrees C) and cold (29 degrees C) conditions were determined. The highest phenolic content (652.6 mg GAE/g) was achieved by using methanol as solvent at 50 degrees C. Uncoated and coated hazelnuts were subjected to accelerated shelf-life testing at 40 degrees C for 5 months. Peroxide value, free acidity, K-232, and K-270 values of oil fraction of hazelnuts were measured at each month as indicators of oxidative rancidity. All coatings significantly reduced the investigated parameters indicating that they are all effective in prevention of oxidation. -Tocopherol incorporated coating provided the lowest PV (1.21 meqO(2)/kg) and K-232 (3.03) values at the end of storage period and also it has the smoothest outer surface appearance. Hardness values and moisture contents of coated and uncoated hazelnuts remained unchanged during storage.

Practical applicationsApplication of zein coating reduced the oxidative rancidity of roasted hazelnuts without producing significant changes in its color, texture, or moisture content at ambient storage conditions. Incorporation of -tocopherol improved the coating performance while incorporation of HEP did not at the level of 0.5% (w/v). This study shows that the shelf-life of roasted hazelnuts may be enhanced by coating with zein solution containing natural antioxidant.