Determination of some physical, chemical and sensory properties of oolong teas have different degree of oxidation produced from turkish tea

In addition to its pleasing taste, tea has become a popular beverage due to its beneficial effects on health since it contains bioactive substances. Both the effective components on the flavour and the functional components of tea change depending on many factors, and the main factor in the formation of this change is the process differences in its production. After black and green tea, oolong tea has started to be recognized all over the world with its unique colour, taste and aroma properties, and the increasing interest of consumers has also attracted the attention of researchers and it has been seen that studies on oolong tea have increased rapidly in recent years. In our country, which has an important position in the production and consumption of tea in the world, mostly black tea is produced, and it is known that green tea and white tea are also produced. Within the scope of this thesis, it is aimed to produce oolong tea from Turkish tea by closely following the developments in Turkish tea and to determine some physical, chemical and sensory properties of the teas produced. The fresh tea product used within the scope of the research was harvested from the Ali Rıza ERTEN clone in the garden of Atatürk Tea and Horticultural Research Institute (Rize) in the 1st shooting period of 2019 and these teas were processed into green, oolong and black tea in the pilot scale facility within the institute. Oolong teas are produced by applying two different methods to have 5 different oxidation degrees. Moisture and water activity, total ash and water-soluble ash, water extract, total phenolic substance and total flavonoid substance, total antioxidant activity (using DPPH and ABTS methods), polyphenolic composition (C, CG, GC, GCG, EC, ECG, EGC, EGCG, TF, TF33'DG), gallic acid and caffeine, color analysis (L*, a*, b*, hue angle, chroma), theaflavin, thearubigin and theabrownin were analyzed. In addition, volatile component analysis and sensory analysis were performed in the samples. The determined characteristics of tea varieties (green, 10 different oolong and black tea) were compared with each other. In the study, moisture content, water activity and water-soluble ash content, water extract, total phenolic substance content, total antioxidant activity (DPPH and ABTS) values of the tea variety and TKM, C, CG, GC, EC, ECG, EGC and EGCG, P<0.001 effect on GA, K, TF and TF33'DG, L*, a*, b*, hue angle, chroma, TF, TR, TB values at P<0.001 level, on total ash, total flavonoid substance amount at P<0.01 significance level has been determined. Total phenolic content of tea varieties 8.81-15.40 g/GAE 100 g DW, total flavonoid content 2.49-3.53 g KE/100 g DW, ABTS values 8.97-20.38 mM TEAC/g DW, DPPH values 16.55-33.09 g TEAA/100 g DW, L* value 20.81-68.99, a* value 11.03-43.08, b* value 35.59-84.93, tone angle value 39.56-82.62, chroma value 52.38-85.65. EGCG was noted as the catechin with the highest amount (0.93-6.48 g/100 g DW) in all tea varieties. Examples of other catechins are EGC 0.69-5.88, ECG 0.52-1.54, C 0.79-1.00, EC 0.53-1.57, CG 0.47-0.51, GC 0.44-0.70, GCG 0.37-0.69, GA 0.5.-0.63, K 2.67-3.37, TF 0.48-0.67 and TF33'DG were determined as 0.35-1.13 g/100 g DW. In these three types of tea analysed, TF varied between 0.20-0.84%, TR between 4.47-7.29% and TB between 4.61-9.30%. Hexanal as the major volatile component in all green, oolong and black tea varieties; furan, 2-pentyl; 6-methyl-5-hepten-2-one; 3,5-octadiene-2-one; (E,E)-2,4-heptadienal; heptanal was detected. According to the results of sensory analysis, oolong tea varieties with different oxidation degrees produced by applying two different methods; although no statistically significant difference could be detected on the appearance, astringency, fullness, brew flavour and total appreciation of the dry tea, the highest total appreciation value was 79.26 points, with the 1st and 3rd kinds of oolong teas (O1.1 and O1.3), that is, oolong teas that have been fermented for a short and medium time and shaped with orthodox curling and have partially close properties to green tea have been more appreciated.