Optimization of polyphenols extraction from fresh tea leavesusing box-behnken design and use of tea polyphenols forfunctional cracker production

In this study, the total phenolic contents of the tea leaves (Camellia sinensis) harvested in three different harvest periods were determined, and the extraction conditions of the green tea extract (GTE) with the highest polyphenol content were optimized using response surface methodology (RSM). In the second stage, the production of saltine crackers with increased nutritional value was carried out by using the aqueous extract of the tea leaf with the highest polyphenol content. The lyophilized tea leaf extract (at the rate of 1% of the dough weight) was replaced with a part of the flour and included in the cracker formulation. In order to reveal the physicochemical properties of the crackers and the extract, the antioxidant capacity, total phenolic content and their bioaccessibilities, total flavonoid content, individual phenolics with HPLC, texture and color values were determined. Also, the sensory analysis was also evaluated by the panel results. According to the findings, it was observed that the total phenolic content of crackers with GTE was increased approximately three times compared to the control group produced without tea extract. Although antioxidant capacity could not be determined in the control group, this value was determined as 1223,61 mmol AAE/100g DM in crackers with GTE. Compared to the control sample, approximately two times more flavonoids were detected in the enriched cracker. The bioavailability of polyphenols, antioxidants and flavonoids tended to reduce in the gastric and intestinal stages. There was a decrease in L and h values, and an increase in a, b and c color values in crackers with GTE. An increase in hardness and a decrease in crispness were detected in the same sample. As a result of the sensory evaluation carried out by ten panelists, it was determined that the cracker with GTE had higher scores in terms of hardness and crispness compared to the control sample, and was close to the control in terms of general acceptability. With this thesis, it was concluded that green tea leaves are suitable for use in cracker production and can be used in the composition of many other foods, due to the positive effects on the nutritional quality of the product and its sensory preference.