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.

中文翻译：

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橄榄（Olea europaea L.）叶作为啤酒原料的应用及其对啤酒化学成分和抗氧化活性的影响

橄榄叶以其高多酚含量和对人类健康的有益作用而闻名。橄榄叶的两种主要酚类化合物是橄榄苦苷和 3-羟基酪醇。评估了橄榄叶作为啤酒成分的使用，以研究它们对啤酒的苦味和抗氧化活性的贡献。生产了 13 种啤酒样品，在不同煮沸时间、不同形式和浓度的煮沸过程中加入橄榄叶。使用了三种不同的形式：干碎叶、浸液和雾化提取物。通过以下分析评估添加橄榄叶的效果：总多酚含量、橄榄苦苷和 3-羟基酪醇含量、抗氧化能力、感官分析、保质期预测。结果证实，添加橄榄叶大大增加了啤酒的多酚含量。沸腾时间有利于橄榄苦苷水解为 3-羟基酪醇。抗氧化活性不受添加橄榄叶的影响。啤酒样品中较高的多酚含量增加了啤酒的胶体不稳定性。感官分析结果表明，约 10 g/L 的橄榄叶赋予酸/涩味和草本香气。较少量的橄榄叶（约 5 克/升）可以获得具有愉悦感官特征的啤酒。实际应用：我们的研究受到对能够为传统食品增加营养价值的替代成分的高度兴趣，以及不断增长的精酿啤酒市场对创新和特色成分的不断研究的启发。该项目有几个目标：评估橄榄叶是否可以部分替代啤酒苦味中的啤酒花（降低成本）；如果它们的添加增加了啤酒多酚含量；在多酚提取和感官特征方面，哪种用量和使用技术可提供最佳结果；这种添加如何影响啤酒的稳定性。这项工作可以鼓励有关这种新型啤酒的营养价值的新研究。