[Main nutritional components and evaluation of commercially available teas in Guizhou Province]

To investigate the main nutrient components of commercially available teas in Guizhou Province and to evaluate their nutritional value.

A total of 17 kinds of tea samples(12 kinds of unfermented tea and 5 kinds of fermented tea) with local characteristics were collected in 4 different regions of Guizhou Province, and the samples were divided into 3 batches according to different varieties. According to national standards, direct drying method, Kjeldahl method, Soxhlet extraction method, high performance liquid chromatography, inductively coupled plasma mass spectrometry and other detection method were used for the determination of general nutrients, vitamins, minerals, and ash and other indexes, and the content of the detection indexes was analyzed and made into a comprehensive evaluation of the method of the affiliation function.

The differences in general nutrients and ash content among the 17 teas with different tea-making processes were not statistically significant. The differences in carotenoids(9837.52 μgRAE/100 g vs.3042.9 μgRAE/100 g) and vitamin C(206.95 mg/100 g vs.12.42 mg/100 g) between the fermented teas and the unfermented teas were statistically significant(carotenoids Z=-2.85, vitamin C Z=-2.21, P<0.05). The difference between sodium content in fermented and unfermented tea(42.65 mg/100 g vs.32.87 mg/100 g) was statistically significant(Z=-2.11, P<0.05) and there were synergistic and antagonistic effects between the elements, sodium and phosphorus(r=0.592, P<0.05), manganese and iron(r= 0.673, P<0.01) showed significant positive correlation. According to the comprehensive evaluation by membership function method, the highest nutritional quality varieties were Kaiyang selenium rich tea(X_μ= 0.5944), Zunyi Maofeng(X_μ=0.5872), Meitan Cuiya(X_μ= 0.5844) and Fanjingshan Cuifeng(X_μ= 0.5506).

Most of the nutritional values of unfermented tea in commercially available tea in Guizhou were higher than those of fermented tea, and from the nutritional point of view, green tea retained more natural components.