Optimization of olive stone powder tea production: infusion conditions, bioactive compounds, and sensory evaluation using response surface method

Abstract Olive stones, a by-product of olive processing, are now valued for their potential as a food ingredient due to their high levels of phenolic compounds and antioxidants. The innovative use of olive stones in tea production offers a unique approach to the reusing of agricultural waste in beverage production. In this study, the optimum infusion conditions of olive stone powder tea were determined using the surface response method. As a result of studies on four response variables; the total phenolic content and the L*, a*, b* values of certain ranges were determined for infusion time, infusion temperature and amount of olive stone powder. As a result of the optimization, the ideal values for infusion conditions were found to be 5 min, 95.5 °C and 2.29% of olive stone powder, respectively. The total phenolic compound content of the olive stone powder tea sample infused under optimum conditions was determined as being 0.095 mg GAE/100 g, antioxidant activity as 134.76 mg Trolox/100 g, and tannin content as 1.02 mgTAE/100 g. These results show that olive stone powder tea contains the bioactive compounds important for health. Color analysis showed that olive stone powder tea exhibited greenness and yellowness similar to herbal teas, though its brightness was lower, likely due to the lignin, cellulose, and hemicellulose content. Furthermore, the infusion temperature and the amount of olive stone powder affected the parameters of brightness, greenness and yellowness. As a result, olive stone powder tea is seen to exhibit citrus, floral, and partially fruity and green aromas, and a bitter, astringent, persistent taste. The study found that olive stone, rich in bioactive compounds and fiber, can be used to produce herbal tea, providing environmental benefits, diversifying products, and increasing the economic value of olive processing waste.