Since recent years, NIR spectroscopy is being applied in the prediction of tea composition 23. Because various organic substances contain different groups, and various groups have different absorption wavelengths for NIR light in different chemical environments, the NIR spectrum can be utilized to perform qualitative and quantitative analyses in food component analysis 22. The NIR spectral region is mainly the frequency-doubled and combined-frequency absorption regions of the hydrogen-containing group X–H (X being an element such as O, N, S, or C). Near-infrared (NIR) spectroscopy is particularly attractive for this purpose. Therefore, optical spectroscopic techniques are increasingly used for the rapid, nondestructive assessment of food products 21. Although techniques based on sizable equipment provide various reliable protocols with good accuracy and sensitivity, they usually suffer from shortcomings such as complicated pretreatment procedures, time-consuming operations, high cost, and a need for professional operators 20. Tea polysaccharides can weaken the bitter taste and astringency and alleviate the stimulating effect of tea 15.Ĭurrently, the conventional physical and chemical methods for determining the levels of moisture, caffeine, tea polyphenols, and tea polysaccharides in instant tea mainly involve oven drying, spectrophotometry, and high-performance liquid chromatography (HPLC) 16, 17, 18, 19. Tea polysaccharides, which are acidic, have health benefits, such as lowering blood sugar, blood lipids, and blood pressure they also enhance the immune system and resistance to hypoxia 14. The astringent and bitter taste of tea mainly results from tea polyphenols 13. They have a variety of physiological effects, such as antioxidation, antiradiation, antiaging, hypoglycemic, and bacteriostatic effects 12. Tea polyphenols consist of four major groups: catechins, phenolic acids, flavonoids, and anthocyanins 11. Additionally, caffeine contributes a bitter taste to instant tea 10. Caffeine is an alkaloid with therapeutic effects on many diseases, including metabolic syndrome, type 2 diabetes, liver diseases, and cardiovascular and cerebrovascular diseases 8, 9. Therefore, a specific moisture content limit should be maintained during the processing and storage of instant tea to ensure the stability of its quality 7. If the moisture content is too high, the instant tea can produce mildew, and consequently, its nutrition and flavor may change. These compounds not only give the tea a unique taste, but also provide a variety of health benefits 6. The quality of instant tea is determined by several main compounds, specifically moisture, caffeine, tea polyphenols, and tea polysaccharides 5. As consumers pay increasing attention to the quality of instant tea, its quality control has also become increasingly important 4. Consequently, it is popular among consumers and has a broad market prospect 3. In addition, instant tea offers drinking convenience, has low amounts of pesticide residues, and is easy to transport. Instant tea maintains the nutritional characteristics and flavor of traditional tea. The manufacturing process of instant tea primarily comprises extraction, filtration, vacuum concentration, and drying 2. Instant tea utilizes the highest quantity of tea raw materials worldwide, and its consumption has increased rapidly in recent years 1.
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