Olive leaves microencapsulated polyphenols as functional ingredient to prolong oxidative stability of biscuits

Nowadays there is a growing interest towards functional foods enriched with natural antioxidants derived from plant by-products. This trend has the double aim to prolong product shelf life, retarding oxidation, and promote health benefits for consumers. Olive by-products, such as olive leaves, are rich in biophenols, especially oleuropein, with high antioxidant activity. These molecules are very sensitive to environmental conditions such as high temperature, pH and oxygen, limiting their applications as ingredients in food formulations. Encapsulation techniques are proposed as a way to protect polyphenols from adverse conditions. In particular hydrocolloids are widely used to encapsulate sensitive compounds into „microgels“ since they are atoxic, highly biocompatible and mechanically strong. In this work olive leaves phenolic extracts were added to biscuits formulations both in a free form or encapsulated in microbeads of sodium alginate and pectin, obtained by emulsification/internal ionotropic gelation. The aim was to evaluate the effect of free or encapsulated phenols on fat biscuits oxidation, in comparison to non enriched controls. All biscuit samples were submitted to spectrophotometrical assays such as Folin- Ciocalteau and DPPH. Moreover, the oxidative stability of the biscuit itself was monitored using the Oxitest reactor (VELP Scientifica), an instrument based on accelerating fat oxidation at high temperature and oxygen pressure, which does not require any preliminary fat separation and pretreatment. Results obtained showed an increment of about 8% of the stability of the biscuits enriched with free polyphenols respect to controls, and about 35% between biscuits containing encapsulated polyphenols and controls. These data demonstrated that encapsulation can stabilize the active substances and protect them also during technological and cooking processes with the effect of enhancing the shelf-life of the food products. This study is part of the project S.O.S.-Sustainability of the olive oil system, supported by AGER 2 project (grant no. 2016-0105).