Process optimization, antioxidant activity and sensory characteristics of green tea made from young fragrant rice leaves cultivar damgatondam

Abstract

Green tea was made from one-month old leaves of the Thai upland black waxy rice cultivar Damgatondam (DGTD), which has a pleasant smell of jasmine.The objective was to determine the optimum process required to produce green tea that is acceptable to consumers and has health benefits.The processing conditions were steaming at 98 ± 2°C for 30, 45, 60 75, 90 or 105 sec then pan roasting at 70 ± 2°C for 5, 10, 15, 20, 25 or 30 min and finally tray drying by using electrical cabinet tray dryer at 60 ± 2°C for 30, 45, 60 or 90 min.Brewed samples were compared to brewed samples of seven commercially available Camellia sinensis tea products by descriptive analysis with 10 trained panelists.The highest quality of DGTD tea was: steaming at 98 ± 2°C for 60 sec, which completely inactivated peroxidase enzymes and preserved the green color, followed by pan roasting at 70 ± 2°C for 30 min and tray drying at 60 ± 2°C for 90 min in order to achieve a moisture content of less than 5%.The proximate analysis showed the DGTD tea prepared by the above method had: 3.77% moisture content, 7.94% ash, 22.59% crude fiber, 2.58% fat and 17.73% protein.Moreover, Ca, Mg, K, Fe, Mn and Na were 3400, 3200, 20400, 66.4, 139.1 and 113.8 mg/kg, respectively.It was found that protein, fat, crude fiber, ash, Mg, K and Na contents in DGTD tea, were higher than levels in tea from Camellia sinensis.Total phenolic content of DGTD tea was 9.53 mg GAE/g and antioxidant activity was 357.52 mM TE/g by Ferric reducing antioxidant power ( FRAP) , l34.08 mM TE/g by 2,2 diphenyl-1-picrylhydrazyl assay ( DPPH) and 108.89 mM TE/g by 2,2'-azino-bis ( 3-ethylbenzothiazo line-6-sulphonic acid) ( ABTS) .The descriptive analysis of trained panels identified 11 particular attributes of DGTD tea, consisting of yellowness, clearness, tea odor, hay odor, green odor, seaweed odor, jasmine rice odor, tea flavor, seaweed flavor, bitter taste and astringent taste.The descriptive analysis showed that the DGTD tea was less bitter and astringent than the Camellia sinensis tea and its jasmine odor was positively accepted.