Effect of enzyme inactivation by microwave and oven heating
on preservation quality of green tea
Yuanyuan Huang, Jianchun Sheng, Fangmei Yang, QiuHui Hu*
Laboratory of Food Processing and Quality Control, College of Food Science and Technology, Nanjing Agricultural University, Nanjing 210095, PR China
The effects of enzyme inactivation by microwave and oven heating were determined on the quality of tea harvested and stored in the
spring and autumn tea processing season. The results indicated that both spring and autumn tea possessed by microwave heating had
significantly higher vitamin C content and less loss during storage than that by oven heating. The absorbance of extracts of spring and
autumn tea by microwave heating was higher than that by oven heating after several months’ storage, though lower for the first few
months. The chlorophyll content of spring and autumn tea by microwave heating was higher and more stable than that by oven heating
followed by storage, which indicated that microwave-heating treatment could reduce the decomposition of chlorophyll. The sensory
quality was also higher in spring and autumn tea treated by microwave heating. However, no significant difference was found in the con-
tent of tea polyphenol between microwave and oven heating in spring and autumn tea. These results indicated that the preservation qual-
ities of green tea harvested in spring and autumn were greatly enhanced by microwave heating.
Keywords: Green tea; Preservation quality; Microwave heating; Oven heating
Green tea, the favorite type consumed in Japan and
China, has also become increasingly popular in western
countries in recent years due to its potential pharmacologi-
cal properties such as antioxidative, antitumor and anticar-
cinogenic activities (Schut & Yao, 2000; Tijburg, Mattern,
Folts, Wiesgerber, & Katan, 1997; Wang, Provan, & Keith,
2000). However, green tea quality is reduced due to
oxidation of vitamin C and tea polyphenol, decomposition
of chlorophyll and browning of green tea during storage
because of the residual enzymes and moisture.
Oven heating has been widely used to inactivate
enzymes in green tea processing in China. However, this
method induces unstable quality in green tea owing to
the uncontrolled temperature during processing. Micro-
wave is an innovative tool and has been applied in the food
industry for extraction of essential oils from the leaves of
rosemary and peppermint, pasteurization of apple juice
to enhance quality, expanding the shelf life and so on
(Canumir, Celis, de Bruijn, & Vidal, 2002; Chen & Spiro,
1994). Microwave heating is widely used in the food indus-
try for its reduced processing time and costs, enhancing
product uniformity and yields, improving unique micro-
structure and protecting food from surface browning and
crusting (Anastasis, Katerina, & Michael, 1999; Domenico,
Anna, & Matteo, 2004).
It was found that the quality of tea was improved by
applying the microwave technology to enzyme inactivation
and dehydration (Gulati, Rawat, Singh, & Ravindranath,
2003; Yang, Gao, & Huang, 2002). However, these studies
have focused on the treatment of microwave to enhance the
quality of green tea in processing. Little has been reported
on whether the treatment by microwaves could enhance the
preservation quality of green tea. The contents of major
components such as tea polyphenol, chlorophyll and
*Corresponding author. Tel.: +86 25 84399086; fax: +86 25 84396431.
E-mail address: firstname.lastname@example.org (Q. Hu).
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