Physico-chemical characteristics and quality improvement of machine picking green tea by automatic production line

Abstract: The green tea primary processing has important effects on the quality, color, taste and other flavor quality of green tea. In order to enhance the quality and capacity of tea processing production, the curl-shape green tea processed by electromagnetism technology and the traditional roasted green tea were analysed. At the same time, mechanically-harvested fresh tea leaves consisted of mixed shoots and leaves, varied in sized, are obviously coarse and heterogeneous compared to the hand picking fresh tea leaves, which has negative effects on the green tea enzyme deactivation, second drying, shaping, hot rolling drying and raising fragrant processing, and it is hard to get the high quality green tea with mechanically-harvested fresh tea leaves. At present, the green tea primary processing of mechanically-harvested fresh tea leaves were traditional methods, for example, hot roller enzyme deactivation, hot air second-drying, hot roller drying and hot air raising fragrant technologies. Although the existing technologies can enhance the flavor and taste quality of tea by experienced workers, they usually have low production and thermal efficiency, inaccurate temperature controlling, uneven heat distribution and unstable quality, and other issues. For these reasons, based on the electromagnetic roller-hot air fixation, second drying with electromagnetic heating and raising fragrant with fluidized bed drying technologies, the automatic tea production line used in the article combine the advantages different equipments and manners in tea processing, in addition, electromagnetic roller-hot air fixation is heated by electromagnetic heat technology, which significantly improvements of energy efficiency and heating stability. The thermal efficiency of the machine was improved, and could easily be controlled accurately. While the heat pipe technology were applied into the tea processing line, the results indicated the thermal efficiency was increased and the effect of energy conservation was remarkable; vibration fluidized bed had good drying effect, energy conservation and so on, which was begin to be used in tea drying industry. Finally, with the technologies above and the other matching equipments, this paper had integrated a new automatic tea production line, in order to enhance the tea flavor and taste quality, obtain stable and high-quality tea, at the same time the thermal efficiency and production efficiency were enhanced. According to the results of sensory evaluation quality and biochemical composition, the production capacity of automatic production line was 1 750 kg leaves one day, and the thermal efficiency increased 100% compared to traditional roasted green tea process. The sensory quality score of curl-shape green tea made of leaves harvested by machines was 88.8, which was 2 point higher than the traditional roasted green tea, and the hue of color (a/b) of tea, tea brew and infused tea leaves were be better (P<0.01) and the ratio of polyphenols to amino acids were the lower (P<0.01). The capacity production was increased 37.5%, the number of labor was reduced by 50% by automatic production line, the sensory quality of curl-shape green tea made of leaves harvested by machines also significantly improved, which could be used for green tea production harvested by machines.