Olive leaves are well known for their high polyphenol content and beneficial effects to human health. The two main phenolic compounds of olive leaves are oleuropein and 3-hydroxytyrosol. Use of olive leaves as beer ingredient was evaluated, to investigate their contribution to bitterness and antioxidant activity of beer. Thirteen beer samples were produced, adding olive leaves during boiling at different boiling times, in different forms and concentrations. Three different forms were used: dry crumbled leaves, infusion, and atomized extract. The effects of olive leaves addition were evaluated through following analysis: total polyphenols content, oleuropein and 3-hydroxytyrosol content, antioxidant capacity, sensory analysis, shelf-life prediction. Results confirmed that addition of olive leaves highly increased polyphenol content of beers. Boiling time favored hydrolysis of oleuropein to 3-hydroxytyrosol. Antioxidant activity was not influenced by addition of olive leaves. Higher polyphenol content of beer samples increased colloidal instability of beer. Sensory analysis results demonstrated that about 10 g/L of olive leaves imparts a sour/astringent taste and herbal aroma. A lower quantity of olive leaves (about 5 g/L) allowed to obtain a beer with a pleasant sensory profile. PRACTICAL APPLICATION: Our research was inspired by both the high interest in alternative ingredients able to add nutraceutical value to traditional food, and by the growing craft beer market, with its constant research for innovative and characterizing ingredients. This project has several aims: evaluate if olive leaves could partially substitute hops in beer bittering (reducing costs); if their addition increase beer polyphenol content; which amount and using technique gives the best results in terms of polyphenol extraction and sensory profile; how this addition influence beer stability. This work could then encourage new research about the nutraceutical value of this new type of beer.
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