Difference of taste among streaming tea soup from tea plantations under different measures against frost based on electronic tongue

Abstract: The late spring coldness is one of the natural disasters frequently occurring in recent years, which severely affects the yield and quality of tea, famous tea in particular. Because of the late spring coldness, the yield of spring tea decreases by 10%-20% every year, especially early-sprouting varieties. The tea plantation with protection measures can avoid frost and protect tea shoots from the injury of late spring cold, such as frost protection with the wind machine system, and shelterbelt planting. The electronic tongue, a kind of rapid analytical tool, has been widely used to assess the quality of food. The purpose of this research is to evaluate the difference in the steaming tea taste from 3 types of tea gardens with different measures against the frost. In this experiment, the steaming tea samples from 3 different tea gardens, i.e. tea garden installed with frost protection with the wind machine system (TGFPWMS), tea garden among shelterbelt planting (TGSP), and common tea garden without protection measures (TGWPM), were used as experimental targets. The fresh tea shoots were plucked from 3 different tea gardens in Yinchunbiya tea plantation, Danyang, Jiangsu, China in April 2015. Because the late spring coldness was coming, the plucking time was at 3 pm and 11 pm on April 2, 4 am on April 3, 2015. The plucked tea shoots were processed into the steaming tea by steamed tea processing technology, whose tea soup taste was detected by electronic tongue. The electronic tongue utilized was Astree from Alpha-MOS with 7 sensors (SRS, GPS, STS, UMS, SPS, SWS and BRS). The components and contents of the amino acids in tea soup were measured by high performance liquid chromatography (HPLC). The results showed that part of the sensors of electronic tongue could effectively analyze the variation of steaming tea taste, such as the sensor BRS, SWS, UMS and SPS. The statistic analysis results showed that both the principal component analysis (PCA) and the soft independent modeling of class analogy (SIMCA) analysis could effectively discriminate the steaming tea taste among 3 different tea gardens. The clustering analysis successfully clustered the steaming tea taste into 2 groups. The steaming tea taste from TGFPWMS and TGSP showed much closer relationship, and the steaming tea taste from TGWPM could be divided into the class separately. By means of HPLC, 18 kinds of free amino acids were detected from steaming tea samples from TGFPWMS, TGSP and TGWPM. The content of 18 kinds of free amino acids ranged from 19.691 to 30.947 mg/g. The percentage of the content of theanine occupying the content of free amino acids ranged from 55.1% to 70.5%. Accompanied with air temperature dropping, the contents of free amino acids and theanine appeared to rise. With the decreasing of the temperature, the contents of 3 kinds of delicious amino acids (asparagic acid, glutamic acid and theanine), 5 kinds of sweet amino acids (proline, alanine, glycocoll, threonine and serine) and 5 kinds of bitter amino acids (isoleucine, leucine, phenylalanine, tyrosine and valine) of steaming tea samples from TGFPWMS and TGSP respectively rose, declined and declined, while those of steaming tea samples from TGWPM varied irregularly. It was considered that the mild "late spring coldness" resulted that the steaming tea taste from TGWPM deteriorated, TGSP alleviated the cold damage, and the frost protection with the wind machine system could not only reduce the frost damage, but also avoid the decline in quality of tea taste. The research results can provide scientific basis and technical support for further researching tea quality under various protective measures.