Biological Activities of Steamed Miang (Camellia sinensis (L.) Kuntze var. assamica (J.W. Mast.) Kitam) Juice Extracts

Miang (Camellia sinensis (L.) Kuntze var. assamica (J.W. Mast.) Kitam.) is an Assam tea which is mainly found in northern Thailand. Fermented Miang is made from young and semi-mature Miang leaves by the local wisdom. Briefly, Miang leaves are harvested and steamed for approximately 2 hours prior to cooling down and subsequently packed into a container with close lid. Fermentation process will take place and run for 1-3 months normally. Steaming step renders a high quantity of steamed Miang juices (SMJ) which will be discarded afterwards. Evaluation of this biological waste will bring about ways of making value-added products. The purpose of this study aims to investigate the effects of steaming time and ages of Miang leaves on biological activities of SMJ obtained. Fresh, young and semi-mature, Miang leaves were collected and steamed for 30 minutes, 1, 2 and 3 hours. Meanwhile, young and old Miang leaves were steamed for 2 hours as compared with the conventional method. All SMJ were further evaporated and lyophilized to obtain SMJ crude extracts (CE). The 3-hour SMJ-CE had the highest antioxidant activity and total phenolic content (p<0.05), 548.4±13 μg GAE/ g extract and 460.24±11.8 μg GAE/g extract, respectively. Comparing between SMJ-CE of young and old Miang leaves, the antioxidant activity and total phenolic content of the young leaves SMJ-CE was significantly higher than the old leaves SMJ-CE (p<0.05). Moreover, all SMJ-CE had antibacterial activities to inhibit growth of some gastrointestinal pathogenic bacteria including Bacillus cereus, Escherichia coli, Escherichia coli O157:H7, Salmonella Typhi, Shigella dysenteriae, Staphylococcus aureus, Methicillin-resistant Staphylococcus aureus (MRSA) and Vibrio cholerae with the young leaves SMJ-CE showed the highest activities. The information obtained will be further used as a guideline in food and cosmetic application using SMJ-CE as a raw material.