Method for precise quality control in processing of selenium-rich rolled tea

Abstract

This invention relates to the field of tea processing technology, and more particularly to a method for precise quality control during the processing of selenium-enriched milled tea. Using fresh leaves of Fuyun No. 6 tea, treated with 0.1 wt% glucosamine liquid organic selenium fertilizer, as raw material, the method involves three processes: fixation, first drying, second drying, stem-leaf separation, and finished product screening. By precisely controlling the temperature, time, and rotation speed parameters of the three core heat processing steps, the method identifies fixation and first drying as the core for controlling heat-sensitive components, and second drying as the core for increasing free amino acids. This invention can control the total loss rate of tea polyphenols to within 16.52%, increase the free amino acid content by 14.73% compared to fresh leaves, and maintain the selenium content stably at around 2.39 mg / kg. The final phenol-to-amino acid ratio of the milled tea product is reduced to 3.39 (the range for high-quality milled tea). This invention features a simple process, controllable parameters, and requires no additional specialized equipment, making it suitable for the industrialized and standardized production of selenium-enriched milled tea, and can significantly improve the flavor quality and nutritional function of the product.

Description

Technical Field

[0001] This invention relates to the field of tea processing technology, and in particular to a method for precise quality control during the processing of selenium-enriched tea. Background Technology

[0002] Tencha is the core raw material for matcha production, and its processing technology has a decisive impact on the color, aroma, taste, and nutritional value of the finished matcha. After harvesting, fresh tea leaves undergo key processing steps such as fixation, first drying, second drying, stem and leaf separation, and final tencha screening to form tencha. The heat treatment and physical sorting conditions involved in different steps have complex effects on the stability and transformation pathways of various chemical components in the tea leaves. Especially in the production of selenium-enriched matcha, ensuring the maximum preservation of key quality components such as selenium, chlorophyll, and catechins is a core scientific issue in achieving high-quality matcha.

[0003] Currently, research on the impact of tencha processing technology on quality components mainly focuses on single processes or individual indicators, such as the effect of fixation temperature on chlorophyll stability and the regulation of catechin degradation patterns by drying conditions. There is a lack of systematic research on the complete processing system of tencha, and a lack of analysis on the dynamic changes of multiple key chemical components at each stage. In other words, it is unclear in which processes the key chemical components change significantly, which processes do not change significantly, and the relative magnitude of changes between different processes. This, to some extent, restricts the precise control of tencha processing technology and the stable improvement of quality.

[0004] Existing research on tea processing mainly focuses on parameter optimization of single steps, lacking systematic quality control research on the entire heat processing flow, resulting in the following core deficiencies: The differential effects of fixation, first drying, and second drying on different chemical components are not clearly defined, making it impossible to achieve precise targeted regulation. This results in severe losses of heat-sensitive components such as tea polyphenols, chlorophyll, and theanine, with the total flavonoid loss rate often exceeding 70%. The unique promoting effect of the second drying stage on the formation of free amino acids was ignored, and the freshness of the ground tea was not improved through process optimization, resulting in a generally high phenol-to-amino acid ratio in the finished product (>3.8). Regarding the processing of selenium-enriched tea, the thermal stability of selenium has not been fully verified, and there is a problem of excessive protection leading to process redundancy. At the same time, there is a lack of quality synergistic control schemes that match selenium enrichment. Existing process parameters are mostly based on ordinary green tea and do not take into account the differences in the biochemical characteristics of selenium-enriched tea leaves, making it difficult to synergistically improve the selenium function and flavor quality of selenium-enriched tea.

[0005] Therefore, there is an urgent need to develop a systematic method for controlling the quality of selenium-enriched tea processing, identify key control points throughout the entire process, and minimize the loss of heat-sensitive components while preserving the function of selenium, thereby improving the overall quality of tea. Summary of the Invention

[0006] The purpose of this invention is to provide a method for precise quality control during the processing of selenium-enriched matcha (tencha) to solve the aforementioned problems. The system identifies key control points in each processing step, optimizes process parameters, minimizes the loss of heat-sensitive components, maximizes the content of free amino acids, and ensures the stable retention of selenium, ultimately yielding selenium-enriched matcha with a low phenol-to-amino acid ratio, high freshness, and excellent nutritional functions. This invention provides a method for precise quality control of selenium-enriched matcha raw materials (tencha) in key processing steps such as fixation and drying, applicable to improving the quality of tencha processed from selenium-enriched tea leaves.

[0007] This invention systematically studies the dynamic changes of major chemical components such as selenium content, total chlorophyll, and catechin compounds throughout the entire process of matcha processing. It clarifies the contribution characteristics of each processing step to the changes of different chemical components, identifies key control nodes and major rise and fall stages, and provides a theoretical basis for the scientific optimization of processing parameters of selenium-enriched matcha and the improvement of product quality stability.

[0008] The objective of this invention is achieved through the following technical solution: This invention relates to a method for precise quality control during the processing of selenium-enriched milled tea. Using fresh leaves of Fuyun No. 6 tea, treated with 0.1 wt% glucosamine liquid organic selenium fertilizer, as raw material, the method precisely controls the temperature, time, and rotation speed parameters of three core thermal processing steps: fixation, first drying, and second drying. Fixation and first drying are identified as the main stages for the loss of heat-sensitive components such as tea polyphenols, total flavonoids, chlorophyll, and theanine, while the second drying is the key stage for the formation of free amino acids. This invention can control the total loss rate of tea polyphenols to within 16.52%, increase the free amino acid content by 14.73% compared to fresh leaves, and stably maintain the selenium content at around 2.39 mg / kg, ultimately reducing the phenol-to-amino acid ratio of the finished milled tea to 3.39.

[0009] The first objective of this invention is to provide a method for precise quality control during the processing of selenium-enriched tea, comprising the following steps: S1. Raw material preparation: Select fresh leaves of Fuyun No. 6 tea that have been treated with 0.1wt% glucosamine liquid organic selenium fertilizer, pick new shoots with one bud and three leaves to one bud and six leaves that are just beginning to unfold, remove old leaves, diseased and insect-damaged leaves and mechanically damaged leaves to obtain fresh leaves; S2. Fixation: Place the fresh leaves in a drum fixation machine and treat them at a temperature of 210-230 ℃ for 55-65 minutes. The machine speed is controlled at 1000-1200 r / min to obtain the fixation-treated tea leaves. S3. First drying: The tea leaves after fixation are immediately transferred to a chain dryer and treated at 160-180 ℃ for 55-65 minutes. The equipment speed is controlled at 1100-1300 r / min to obtain the tea leaves after the first drying. S4. Second drying: The tea leaves after the first drying are transferred to a chain dryer and processed at 160-170 ℃ for 55-65 minutes. The speed of the equipment is controlled at 1100-1300 r / min to obtain the tea leaves after the second drying. S5. Stem and Leaf Separation: After the second drying, the tea leaves are naturally cooled to 20-25℃, and the stems and leaves are separated using an air separation sieve to obtain the tea after stem and leaf separation. S6. Finished product screening: The tea leaves after stem and leaf separation are sieved through an 80-mesh sieve to remove coarse particles and impurities, resulting in selenium-enriched tea finished product.

[0010] Furthermore, in step S1, the total amount of selenium applied by the 0.1wt% glucosamine liquid organic selenium fertilizer is 900 mg / mu, and it is applied by foliar spraying in 3 applications, with each application 10 days apart; Furthermore, in step S1, the selenium content of the fresh leaves is ≥2.30mg / kg, and the weight of 100 buds is ≥480g.

[0011] Furthermore, in step S2, the blanching temperature is 220℃, the processing time is 60 minutes, and the equipment rotation speed is 1100 r / min.

[0012] Furthermore, the moisture content of the tea leaves after processing should be controlled at 70%-75%.

[0013] Furthermore, in step S3, the drying temperature is 170℃, the processing time is 60 minutes, and the equipment rotation speed is 1200 r / min.

[0014] Furthermore, the moisture content of the tea leaves after the first drying is controlled at 30%-35%.

[0015] Furthermore, in step S4, the secondary drying temperature is 165℃, the processing time is 60 minutes, and the equipment rotation speed is 1200 r / min.

[0016] Furthermore, the moisture content of the tea leaves after the second drying is controlled at 3%-5%.

[0017] Furthermore, in step S5, the wind speed of the air separation and screening equipment is controlled at 3-5 m / s to remove the tea stems and leaf veins, while retaining ≥95% of the leaf parts.

[0018] Furthermore, the total loss rate of tea polyphenols in the selenium-enriched tea product obtained by the method is controlled within 20% compared to fresh leaves, and the content of free amino acids is increased by more than 10% compared to fresh leaves.

[0019] More preferably, the total loss rate of tea polyphenols in the selenium-enriched tea product obtained by the method is controlled within 16.52% compared with fresh leaves, and the content of free amino acids is increased by 14.73% compared with fresh leaves.

[0020] The second objective of this invention is to provide a selenium-enriched tencha product obtained by the above-mentioned method for precise quality control during the processing of selenium-enriched tencha, wherein the selenium content of the selenium-enriched tencha product is stable at 2.35-2.43 mg / kg, the proportion of organic selenium is ≥80%, the phenol-to-amino acid ratio is ≤3.4, the free amino acid content is ≥3.8%, the tea polyphenol content is 13.5%-14.0%, and the total chlorophyll content is ≥0.58 mg / g.

[0021] The third objective of this invention is to provide an application of the selenium-enriched tencha product obtained by the above-mentioned method for precise quality control during the processing of selenium-enriched tencha in the preparation of selenium-enriched matcha products.

[0022] Compared with the prior art, the beneficial effects of the present invention are reflected in the following aspects: 1) The system quantifies the impact of each process in the entire selenium-enriched tea-making process on 10 core chemical components (tea polyphenols, free amino acids, theanine, soluble total sugars, total flavonoids, soluble proteins, caffeine, selenium, chlorophyll, and catechin compounds), and clarifies that fixation and first drying are the core for controlling heat-sensitive components, and second drying is the core for enhancing flavor, thus solving the problem of blind adjustment in existing processes.

[0023] 2) Through parameter optimization, the final phenol-to-amino acid ratio of the finished tencha product was reduced to 3.39 (the range of high-quality tencha), the free amino acid content reached 4.05%, the tea polyphenol content was 13.71%, the selenium content was stabilized at 2.39 mg / kg and the proportion of organic selenium was ≥80%.

[0024] 3) No new special equipment is required. It can be achieved simply by optimizing the temperature, time and speed parameters of the existing hot processing steps. The parameters are highly controllable and suitable for large-scale industrial production.

[0025] 4) The high thermal stability of selenium in the processing of tencha was verified. The selenium loss during the processing was negligible, ensuring the selenium supplementation function of selenium-enriched tencha, while retaining the activity of antioxidant components such as tea polyphenols and total flavonoids.

[0026] 5) Based on the biochemical characteristics of the fresh leaves of selenium-enriched Fuyun No. 6 tea, process parameters were formulated to achieve synergistic improvement of selenium function and flavor quality, and to solve the problem of unstable quality when processing selenium-enriched tea using ordinary processes. Attached Figure Description

[0027] Figure 1 The images show the state of tea after different processing steps. (A) is the state of the initial fresh leaves, (B) is the state of the tea after fixation, (C) is the state of the tea after the first drying, (D) is the state of the tea after the second drying, (E) is the state of the tea after the stems and leaves are separated, and (F) is the state of the finished selenium-enriched tea after screening.

[0028] Figure 2 The changes in tea polyphenol content in ground tea during different processing steps.

[0029] Figure 3 The changes in the free amino acid content of tea during different processing steps.

[0030] Figure 4 The changes in the ammonia-to-tearate ratio during different processing steps.

[0031] Figure 5 The variation of theanine content in ground tea during different processing steps.

[0032] Figure 6 This shows the changes in total soluble sugar content of milled tea during different processing steps.

[0033] Figure 7 The changes in total flavonoid content in tea leaves after different processing steps.

[0034] Figure 8 This shows the changes in soluble protein content in tea leaves after different processing steps.

[0035] Figure 9 This shows the variation in caffeine content of ground tea during different processing steps.

[0036] Figure 10 This shows the changes in selenium content in tea leaves during different processing steps.

[0037] Figure 11 The changes in chlorophyll a (A), chlorophyll b (B), and total chlorophyll (C) content of tea leaves after different processing steps.

[0038] Figures 2-11 In the diagram, a, b, c, and d represent significant differences between different processing steps at the same sampling time. p <0.05. Detailed Implementation

[0039] The present invention will now be described in detail with reference to specific embodiments, but this is by no means a limitation thereof. Any preparation methods, materials, structures, or compositional ratios not explicitly described in this technical solution are considered common technical features disclosed in the prior art.

[0040] In the following examples, the 0.1wt% glucosamine liquid organic selenium fertilizer used was manufactured by Jiangsu Shuanglin Marine Biological Pharmaceutical Co., Ltd.

[0041] Example This embodiment provides a method for precise quality control during the processing of selenium-enriched tea, including the following steps: S1. Raw material preparation: Select fresh leaves of Fuyun No. 6 tea that have been treated with 0.1wt% glucosamine liquid organic selenium fertilizer. Pick new shoots with one bud and three leaves to one bud and six leaves that are just beginning to unfold. Remove old leaves, diseased leaves, and mechanically damaged leaves to obtain fresh leaves. The total amount of selenium applied with the 0.1wt% glucosamine liquid organic selenium fertilizer is 900mg / mu. It is applied by foliar spraying in 3 applications, with an interval of 10 days between each application. The selenium content of the fresh leaves is ≥2.30mg / kg, and the weight of 100 buds is ≥480g. Specifically, in this embodiment, the weight of 100 buds reaches 500.05g, and the selenium content is 2.39mg / kg. S2. Fixation: Place the fresh leaves in a drum fixation machine and treat them at 2200 ℃ for 60 minutes. The machine speed is controlled at 1100 r / min to obtain the fixated tea leaves. S3, First drying: The tea leaves after fixation are immediately transferred to a chain dryer and treated at 170 ℃ for 60 minutes. The speed of the equipment is controlled at 1200 r / min to obtain the tea leaves after the first drying. S4. Second drying: The tea leaves after the first drying are transferred to a chain dryer (the same model as the dryer in step S3) and processed at 165 ℃ for 60 minutes. The equipment speed is controlled at 1200 r / min to obtain the tea leaves after the second drying. S5. Stem and leaf separation: After the second drying, the tea leaves are naturally cooled to 25 ℃. The stems and leaves are separated using an air separation sieve. The air speed of the air separation sieve is controlled at 4m / s. The tea stems and leaf veins are removed, and the leaf part is retained in ≥95% to obtain the tea after stem and leaf separation. S6. Finished product screening: The tea leaves after stem and leaf separation are sieved through an 80-mesh sieve to remove coarse particles and impurities, resulting in selenium-enriched tea finished product.

[0042] In this embodiment, the moisture content of the tea leaves after fixation is 74.20±3.08%, the moisture content of the tea leaves after the first drying is 33.69±2.55%, and the moisture content of the tea leaves after the second drying is 4.50±0.33%.

[0043] (1) Conditions for tea grinding process The process conditions for precise quality control during the processing of selenium-enriched tea are shown in Table 1.

[0044] Table 1. Processing steps and conditions for each step of the tea-making process. (2) Processing of tea samples Samples were taken immediately after each step of fixing, first drying, second drying, stem and leaf separation, and screening of finished tea. These samples corresponded to tea leaves after fixing, tea leaves after first drying, tea leaves after second drying, tea leaves after stem and leaf separation, and finished selenium-enriched tea. In addition, samples of the initial fresh leaves were taken and centrifuged at a ratio of 1:50 (w / w) for both sample / pure water and sample / 70% methanol. The resulting water extracts (sample:pure water = 1:50) and alcohol extracts (sample:70% methanol (methanol aqueous solution) = 1:50) were obtained from different experimental groups. The samples were numbered and stored in a refrigerator at 4 ℃ for later testing.

[0045] (3) Results and Discussion Changes in the state of tea during different processing steps, such as Figure 1 As shown, Figure 1 (A), (B), (C), (D), (E), and (F) represent the states of the initial fresh leaves, the leaves after fixation (after fixation), the leaves after the first drying (after the first drying), the leaves after the second drying (after the second drying), the leaves after stem-leaf separation (after stem-leaf separation and grinding), and the finished tea product after screening (selenium-enriched finished tea). As can be seen from the diagrams, as the processing progresses, the fresh tea leaves gradually shrink, curl, darken, and soften, changing from their initial whole, bright green, and soft texture. After stem-leaf separation and final tea product screening, they become fine, powdery particles.

[0046] 1. Changes in tea polyphenol content in milled tea produced through different processing steps like Figure 2 As shown, during the tea processing, the tea polyphenol content generally showed a trend of first decreasing and then stabilizing. The initial tea polyphenol content in fresh leaves was 16.43%, which decreased to 14.75% after fixation, a decrease of 10.23%; after the first drying, the tea polyphenol content decreased to 14.11%, a decrease of 4.34%; and after the second drying, the tea polyphenol content decreased to 13.72%, a decrease of 2.76%. The decrease in tea polyphenol content showed a decreasing trend throughout the three steps of heat processing, and only the fixation and the first drying processes showed a significant difference in the reduction of tea polyphenols. p <0.05), there was no significant difference in tea polyphenol content during the second drying process. p >0.05). This is because the short-term high-temperature treatment during the fixation stage induces oxidation, polymerization, isomerization, or condensation reactions in tea polyphenols. Simultaneously, the high temperature damages cell structure, allowing polyphenol oxidase (PPO) to significantly accelerate the oxidation and consumption rate of tea polyphenols in a short time after sufficient contact with the substrate. In contrast, during the first and second drying stages, PPO activity is inhibited, and the entire leaf is in a low water activity environment, with most readily reactive active polyphenols already largely consumed; therefore, the decrease is smaller compared to the fixation stage. The tea polyphenol content in stem-leaf separation and finished tea product screening was 13.71%, with no significant difference.p >0.05). In summary, to control the loss of tea polyphenols during the production of rolled tea, the temperature and other conditions of the fixation and drying steps should be strictly controlled to minimize the loss of tea polyphenol content.

[0047] 2. Changes in the content of free amino acids in tea leaves after different processing steps During the processing of ground tea, the content of free amino acids generally showed a trend of first increasing significantly and then slightly increasing. For example... Figure 3 As shown, the free amino acid content of fresh leaves in the initial state was 3.53%, which increased to 3.68% after fixation, an increase of 4.25%. During the first drying stage, the free amino acid content increased to 3.80%, an increase of 3.26%, which was smaller than the increase during fixation. However, during the second drying stage, the free amino acid content increased to 4.02%, an increase of 5.79%, the highest increase during the heat processing stage. The free amino acid content in the subsequent stem-leaf separation and finished tea product was 4.03% and 4.05%, respectively. In summary, the free amino acid content increased significantly during fixation, the first drying, and the second drying processes. p <0.05), while the content increase was not significant during the stem and leaf separation and tea product screening stages ( p The increase was only slightly higher than 0.05%. This is attributed to the high-temperature treatment during the initial drying stage, which releases bound amino acids into a free state. Simultaneously, the moderate heating activates endogenous proteases, accelerating protein hydrolysis and increasing the free amino acid content. In the later first drying stage, partial degradation of free amino acids slightly reduced the increase, while the second drying stage further increased the rate of free amino acid formation and decreased the degradation rate, resulting in the maximum increase in free amino acids during processing. During the stem-leaf separation and finished tea product screening stages, residual heat caused a slight increase in free amino acid content, but the magnitude was minimal. Overall, the processing significantly increased the free amino acid content (…). p <0.05), with a total increase of 14.73%. The second drying stage had the greatest impact on the increase in free amino acid content, and special attention should be paid to this during processing.

[0048] 3. Changes in the ammonia-to-tearate ratio during different processing steps The phenol-to-amino acid ratio is an important indicator for evaluating the overall quality of tencha (a type of green tea). A lower phenol-to-amino acid ratio during processing is more beneficial for improving tea quality, reducing bitterness and astringency while increasing freshness. For example... Figure 4 As shown, the phenol-to-amino acid ratio in fresh leaves was 4.65, which decreased to 4.01 after fixation, a reduction of 13.76%. After the first and second drying processes, the phenol-to-amino acid ratio decreased to 3.71 and 3.41, respectively, with reductions of 7.48% and 8.09%. The cumulative reduction in phenol-to-amino acid ratio after heat processing reached 26.67%, while the phenol-to-amino acid ratios during stem-leaf separation and finished tea screening were 3.40 and 3.39, respectively, with a reduction of only 0.59%. This indicates that heat processing is a key step that significantly affects the reduction of the phenol-to-amino acid ratio.p <0.05), and in terms of the decrease, the fixation and secondary drying processes had a relatively large impact on the decrease in the phenol-amino acid ratio of the tea; while the room temperature physical screening process had no significant impact on the phenol-amino acid ratio. p >0.05). The final phenol-to-amino acid ratio of the finished tencha product was 3.39, which, according to previous studies, falls within the low phenol-to-amino acid ratio range and exhibits the characteristics of high-quality tencha.

[0049] 4. Changes in theanine content of ground tea during different processing steps Theanine is the main flavor compound contributing to the freshness and sweetness of tea. The changes in theanine content during the processing of ground tea are shown below. Figure 5 As shown, the initial theanine content in fresh leaves was 16.26 mg / g, which decreased to 13.21 mg / g after fixation, a decrease of 18.76%; after the first drying, the theanine content was 11.48 mg / g, a decrease of 13.09%; and after the second drying, the theanine content was 10.63 mg / g, a decrease of 7.40%. Significant differences were observed in the decrease of theanine content among each heat processing step. p <0.05), but according to the above data, the fixation step has the most significant impact on the decrease in theanine content, followed by the first drying, while the second drying shows a smaller decrease compared to the fixation and first drying. This is because the fixation process accelerates the hydrolysis and Maillard reactions of theanine under the instantaneous high temperature of 220 ℃, resulting in a significant loss; in the first drying stage, theanine participates in the non-enzymatic browning reaction under continuous high temperature conditions and condenses with polyphenols to form N-ethyl-2-pyrrolidone-substituted flavanol derivatives (EPSFs), leading to a further decrease in content; in the second drying stage, the thermal reaction rate is significantly slowed down due to the limited cell water activity. For the two room-temperature physical operations of stem and leaf separation and tea product screening, the theanine content remains almost unchanged, at 10.63 mg / g and 10.62 mg / g respectively, with no significant change. p >0.05). In summary, the processing steps cause significant changes in theanine content ( p <0.05), in order to minimize the loss of theanine during processing, special attention should be paid to controlling the processing conditions during the fixation and drying processes.

[0050] 5. Changes in total soluble sugar content of milled tea during different processing steps like Figure 6 As shown, the initial total soluble sugar content was 4.45%. With the gradual advancement of processing steps, the total soluble sugar content generally showed a trend of first decreasing and then stabilizing. During the blanching process, the high temperature caused thermal degradation of polysaccharides, and the participation of polysaccharides in the Maillard reaction and caramelization reaction led to a significant decrease in the total soluble sugar content to 3.78%. p<0.05%, a decrease of 15.06%; subsequently, in the first drying process, the total soluble sugar content further decreased to 3.21%, a decrease of 15.08%; in the second drying process, due to the relatively stable structure of the remaining total soluble sugars, they were less likely to participate in thermal degradation reactions, and the content decreased to 2.84%, with a significant difference compared to the first drying process. p <0.05), but the decrease was 11.53%, slightly lower than the decrease during the blanching and drying processes. Final processes such as stem-leaf separation and finished product screening only caused a negligible and very small decrease ( p >0.05), the final product's total soluble sugar content is 2.80%. In summary, the processing steps significantly reduce the total soluble sugar content of the tencha (a type of tea). p <0.05), among which the decrease in total soluble sugar content was greater in the blanching and first drying processes, while the decrease in the second drying process was less than that in the blanching and first drying processes.

[0051] 6. Changes in total flavonoid content in tea leaves processed through different steps Changes in total flavonoid content during the processing of tencha (a type of tea) are as follows: Figure 7 As shown, the total flavonoid content in the initial fresh leaf state was 0.81%. After the heat processing steps of blanching, first drying, and second drying, the total flavonoid content was 0.56%, 0.37%, and 0.27%, respectively, with decreases of 30.86%, 33.93%, and 27.03%, respectively. The content decreased significantly in each step. p <0.05%, with the largest decrease in the first drying stage, and a smaller decrease in the second drying stage compared to the initial drying and the first drying stage; while the total flavonoid content of stem and leaf separation and finished tea product screening were 0.27% and 0.26% respectively, with relatively stable content and no significant difference. p >0.05). The heat processing step resulted in a 66.67% decrease in total flavonoid content. This is due to two main reasons: firstly, high temperatures facilitate the hydrolysis of flavonoid glycosidic bonds, leading to the release of flavonoid aglycones and further oxidative degradation; secondly, high temperatures accelerate the oxidation reaction rate, causing flavonoid molecules to break down, polymerize, or rearrange their structures. Therefore, the continuous decrease in total flavonoids during the fixation, first drying, and second drying stages indicates that heat processing is the main driving factor for the loss of total flavonoids in tencha. Special attention should be paid to controlling processing conditions during the fixation and first drying stages, which result in a significant decrease in total flavonoid content.

[0052] 7. Changes in soluble protein content of tea leaves after different processing steps Soluble protein levels generally show a trend of first decreasing and then stabilizing during processing. For example... Figure 8 As shown, the soluble protein content of the initial fresh leaves before processing was 3.07%. During the blanching process, the hydrogen bonds and hydrophobic bonds that maintain the spatial structure of the protein were destroyed, causing the protein molecules to denature. The denatured protein molecules aggregated and combined with other components to form insoluble precipitates, resulting in a significant decrease in the soluble protein content to 2.11%.p <0.05%, a decrease of 31.27%; subsequently, during the first and second drying processes, the soluble protein content decreased to 1.55% and 1.12% respectively due to the Maillard reaction and the continued denaturation of some proteins, representing decreases of 26.54% and 27.74% respectively. The soluble protein content remained stable and almost unchanged during the stem-leaf separation and finished tea screening processes, ultimately reaching 1.10% in the finished tea product. Therefore, it can be concluded that the soluble protein content significantly decreased during the fixation, first drying, and second drying processes. p <0.05%, the decrease in soluble protein content during the fixation step was slightly higher than that during the first and second drying steps; however, there was no significant decreasing trend in soluble protein content during the stem and leaf separation and tea product screening processes. p >0.05).

[0053] 8. Changes in caffeine content of ground tea during different processing steps like Figure 9 As shown, the overall change in caffeine content during the tea-making process was relatively small, and the decrease in content at each stage did not show significant differences. p >0.05). The initial caffeine content of fresh leaves was 33.22 mg / g, and the final caffeine content in the finished tea product screening stage was 32.95 mg / g, with a decrease of only 0.81% throughout the process. This is closely related to the stable molecular structure, strong heat resistance, and moderate water solubility of caffeine during processing.

[0054] 9. Changes in selenium content in tea leaves processed through different steps Selenium exists primarily in tea in an organically bound state, exhibiting high thermal and structural stability, and is not easily volatilized, migrated, or degraded under conventional processing conditions. For example... Figure 10 As shown, the selenium content remained stable at 2.39 mg / kg throughout the entire processing procedure. Overall, the tea processing steps did not significantly affect the total selenium content. p >0.05), the amount of selenium lost during processing is negligible, indicating that selenium is relatively stable in tea tissue.

[0055] 10. Changes in chlorophyll content of tea leaves after different processing steps With the advancement of tea-making processes, such as Figure 11 (A) Chlorophyll a content showed a significant decreasing trend. p<0.05). The initial chlorophyll a content in fresh leaves was 1.83 mg / g. After fixation, the chlorophyll a content decreased to 1.15 mg / g, a decrease of 37.16%. During the first and second drying stages, the chlorophyll a content further decreased to 0.72 mg / g and 0.45 mg / g, respectively, with decreases of 37.39% and 37.50%, indicating that high-temperature treatment had a significant impact on the stability of chlorophyll structure, and the decrease in chlorophyll a content was roughly the same across the three stages. In contrast, the chlorophyll a content did not change significantly during the stem-leaf separation and finished tea product screening stages. p The concentration of chlorophyll a was greater than 0.05, meaning that the physical sorting process had little impact on the chlorophyll a content. The chlorophyll a content in the finished product was 0.43 mg / g. Overall, the total degradation rate of chlorophyll a during the processing of rolled tea was 76.50%, and its degradation process was mainly regulated by the three thermal processing stages of fixation, first drying, and second drying.

[0056] like Figure 11 As shown in (B), the chlorophyll b content showed a significant decreasing trend during the tea processing. p <0.05). The initial chlorophyll b content in fresh leaves was 0.60 mg / g. After fixation, the chlorophyll b content decreased to 0.41 mg / g, a decrease of 31.67%. During the first and second drying stages, the chlorophyll b content further decreased to 0.26 mg / g and 0.18 mg / g, respectively, with decreases of 36.59% and 30.77%, similar to chlorophyll a. This indicates that the three high-temperature processing steps of fixation, first drying, and second drying are also the main stages of chlorophyll b content degradation. The chlorophyll b content during stem-leaf separation and tea product screening stages were 0.18 mg / g and 0.17 mg / g, respectively, with no significant difference. p >0.05), and there was almost no change in the decrease. Overall, the total degradation rate of chlorophyll b during the tea processing was 71.67%, and its change pattern was almost the same as that of chlorophyll a, but its heat sensitivity was slightly lower than that of chlorophyll a.

[0057] The changes in total chlorophyll content during the processing of tea are as follows: Figure 11 As shown in (C), the total chlorophyll content of the initial fresh leaves was 2.43 mg / g. After blanching, the total chlorophyll content decreased to 1.57 mg / g, a decrease of 35.39%. During the first drying stage, it further decreased to 0.99 mg / g, a decrease of 36.94%. During the second drying stage, it decreased to 0.63 mg / g, a decrease of 36.36%. The figure shows a significant difference in total chlorophyll content among the three heat treatment steps. p<0.05), studies have shown that under heat treatment conditions, chlorophyll undergoes a demagnesiation reaction to form pheophytin, leading to a decrease in color development ability. Simultaneously, under sustained high temperatures, the chlorophyll porphyrin ring structure undergoes thermal decomposition and oxidative ring-opening reactions, resulting in the destruction of the conjugated system and accelerating chlorophyll degradation. In contrast, the total chlorophyll content did not change significantly after stem-leaf separation and screening of the finished tea product. p The total chlorophyll content in the finished product was 0.60 mg / g (>0.05%), a decrease of only 4.76% compared to the end of the second drying process, indicating that the physical screening process had little impact on the total chlorophyll content. Therefore, the total chlorophyll content during the processing of rolled tea is mainly affected by the three thermal processing stages of fixation, first drying, and second drying, while the stem-leaf separation and rolled tea screening processes have almost no impact on the total chlorophyll content.

[0058] 11. Changes in catechin content during different processing steps The changes in catechin content at different processing steps are shown in Table 2.

[0059] Table 2. Changes in the composition and content of catechin compounds in tea leaves processed through different steps (mg / g) Note: Different letters in the same column indicate that the difference reached a significant level. p <0.05) As shown in Table 2, the content of each catechin monomer showed a significant overall decreasing trend as the tea processing progressed. p <0.05), of which EGCG, EGC, ECG and GC are the main degradation components.

[0060] The highest EGCG content was found in fresh leaves, reaching 58.41 mg / g, making it the main component of catechins. After fixation, the EGCG content decreased to 57.78 mg / g, a reduction of 1.08%. During the first and second drying stages, the EGCG content further decreased to 57.20 mg / g and 56.62 mg / g, respectively, with reductions of 1.00% and 1.02%. Overall, the overall reduction in EGCG was only 3.05%, although there were significant differences between the various processing steps (…). p The value was <0.05), but the decrease was relatively small at each step, indicating that EGCG exhibits high stability during the tea processing and has strong tolerance to heat processing.

[0061] In contrast, non-ester catechins such as EGC, ECG, EC, and GC, and some ester catechins, are more sensitive to processing conditions. Among them, the content of EGC decreased significantly from 16.25 mg / g in the initial fresh leaves to 4.75 mg / g in the finished product, a decrease of 70.77%, the most significant drop; ECG content decreased from 43.46 mg / g to 13.22 mg / g, a total decrease of 69.58%; EC decreased from 5.12 mg / g to 2.81 mg / g, a decrease of 45.12%; and GC decreased from 9.01 mg / g to 4.79 mg / g, a decrease of 46.84%. Furthermore, as shown in Table 2, except for EGCG, the content changes of the other seven catechin monomers were not significant during the stem-leaf separation and finished tea screening stages. p >0.05), indicating that non-ester catechins and some ester catechins are more sensitive to thermal processing and are the main source of catechin loss during the processing of milled tea.

[0062] This invention systematically studies the dynamic changes of major quality components throughout the entire tea processing process, clarifying the degree of influence of each processing step (fixing, first drying, second drying, stem and leaf separation, and finished tea product screening) on ​​different chemical components and the key control points. The main conclusions are as follows: The separation of stems and leaves and the screening of finished tea products have almost no effect on the changes in chemical composition. Except for EGCG, the content of all other chemical components does not change significantly in these two steps. p >0.05).

[0063] The content of tea polyphenols decreased significantly during the fixation stage (10.23%), with the decrease decreasing progressively between the first and second drying stages (4.34% and 2.76%, respectively), resulting in a total decrease of 16.52%. Losses were concentrated during the fixation stage. The content of free amino acids increased during processing, with a total increase of 14.73%, with the largest increase occurring during the second drying stage (5.79%), making it a key step in free amino acid formation. The phenol-to-amino acid ratio continued to decrease during the heat processing stage, with a cumulative decrease of 26.67%. Considering the combined effects of tea polyphenols, free amino acids, and the phenol-to-amino acid ratio, the fixation and second drying stages contributed significantly to the decrease in the phenol-to-amino acid ratio. The final finished milled tea had a phenol-to-amino acid ratio of 3.39, falling within the range of high-quality milled tea. Among catechin compounds, the content of each catechin monomer showed a significant overall decreasing trend (…). p <0.05), among which non-ester catechins such as EGC, ECG, EC, and GC, as well as some ester catechins, are more sensitive to heat processing, with reductions of 70.77%, 69.58%, 45.12%, and 46.84%, respectively, which are the main sources of catechin loss during processing; although EGCG showed significant differences between different processes, the overall reduction was small (3.05%), and its thermal stability was relatively high.

[0064] Among other major chemical components, theanine content decreased the most during the fixation stage (18.76%), followed by the first drying stage (13.09%), with the decrease slowing down in the second drying stage (7.40%); total soluble sugars decreased significantly during the fixation and first drying stages (both around 15.00%), with a slight slowing down in the second drying stage (11.53%); total flavonoids showed a continuous and significant decrease during the heat processing stage (…). p <0.05), the first drying stage saw the largest decrease (33.93%), which is the key control point for total flavonoid loss; soluble protein saw the largest decrease (31.27%) in the blanching stage, and although the first and second drying stages continued to decrease, the decrease was smaller than that in the blanching stage; chlorophyll a, chlorophyll b and total chlorophyll content all showed a significant decreasing trend in the heat processing stage, and the decrease was basically the same in the three heat processing stages, which is the key control process for chlorophyll degradation.

[0065] The caffeine and selenium content did not change significantly at any stage of the processing. p >0.05), the caffeine content decreased by only 0.81% throughout the process, demonstrating high thermal stability; the selenium content remained stable at 2.39 mg / kg, with no significant differences between the various processes. p >0.05), indicating that selenium exists mainly in the tea tissue in an organically bound state with high thermal stability, and the processing loss is negligible.

[0066] In summary, the heat processing steps (fixing, first drying, and second drying) in the processing of tencha are the key stages affecting the changes in various quality components. Among them, fixing and the first drying have the most significant impact on most components; although the second drying has a significant impact on some components, its overall impact is not as great as that of fixing and the first drying; physical processes such as stem and leaf separation and screening of finished tencha have a relatively small impact on chemical components. Therefore, the heat processing parameters for fixing and the first drying should be optimized to minimize the loss of the main chemical components in tencha, thereby effectively improving the color, flavor harmony, and nutritional value of tencha.

[0067] The above description of the embodiments is provided to enable those skilled in the art to understand and use the invention. It will be apparent to those skilled in the art that various modifications can be made to these embodiments, and the general principles described herein can be applied to other embodiments without inventive effort. Therefore, the present invention is not limited to the above embodiments, and any improvements and modifications made by those skilled in the art based on the disclosure of the present invention without departing from the scope of the invention should be within the protection scope of the present invention.

Claims

1. A method for precise quality control in the processing of selenium-enriched rolled tea, characterized by, Includes the following steps: S1. Raw material preparation: Select fresh leaves of Fuyun No. 6 tea that have been treated with 0.1wt% glucosamine liquid organic selenium fertilizer, pick new shoots with one bud and three leaves to one bud and six leaves that are just beginning to unfold, remove old leaves, diseased and insect-damaged leaves and mechanically damaged leaves to obtain fresh leaves; S2. Fixation: Place the fresh leaves in a drum fixation machine and treat them at a temperature of 210-230 ℃ for 55-65 minutes. The machine speed is controlled at 1000-1200 r / min to obtain the fixation-treated tea leaves. S3, First drying: The tea leaves after fixation are immediately transferred to a chain dryer and treated at 160-180 ℃ for 55-65 minutes. The speed of the equipment is controlled at 1100-1300 r / min to obtain the tea leaves after the first drying. S4. Second drying: The tea leaves after the first drying are transferred to a chain dryer and processed at 160-170 ℃ for 55-65 minutes. The speed of the equipment is controlled at 1100-1300 r / min to obtain the tea leaves after the second drying. S5. Stem and Leaf Separation: After the second drying, the tea leaves are naturally cooled to 20-25℃, and the stems and leaves are separated using an air separation sieve to obtain the tea after stem and leaf separation. S6. Finished product screening: The tea leaves after stem and leaf separation are sieved through an 80-mesh sieve to remove coarse particles and impurities, resulting in selenium-enriched tea finished product.

2. The method for precise quality control of selenium-enriched rolled tea processing according to claim 1, characterized in that, In step S1, the total amount of selenium applied by the 0.1wt% glucosamine liquid organic selenium fertilizer is 900mg / mu, and it is applied by foliar spraying in 3 applications, with an interval of 10 days between each application.

3. The method for quality precision regulation of selenium-enriched rolled tea processing according to claim 1, characterized in that, In step S1, the selenium content of the fresh leaves is ≥2.30mg / kg, and the weight of 100 buds is ≥480g.

4. The method for quality precision regulation of selenium-enriched rolled tea processing according to claim 1, characterized in that, In step S2, the blanching temperature is 220℃, the processing time is 60 minutes, and the equipment rotation speed is 1100 r / min; The moisture content of tea leaves after processing should be controlled at 70%-75%.

5. The method for precise quality control during the processing of selenium-enriched tea as described in claim 1, characterized in that, In step S3, the drying temperature is 170℃, the processing time is 60 minutes, and the equipment speed is 1200r / min; The moisture content of the tea leaves after the first drying is controlled at 30%-35%.

6. The method for precise quality control during the processing of selenium-enriched tea as described in claim 1, characterized in that, In step S4, the secondary drying temperature is 165℃, the processing time is 60 minutes, and the equipment rotation speed is 1200 r / min; The moisture content of the tea leaves after the second drying should be controlled at 3%-5%.

7. The method for precise quality control during the processing of selenium-enriched tea as described in claim 1, characterized in that, In step S5, the wind speed of the air separation and screening equipment is controlled at 3-5 m / s to remove the tea stems and leaf veins, while retaining ≥95% of the leaf parts.

8. The method for precise quality control during the processing of selenium-enriched tea as described in claim 1, characterized in that, The total loss rate of tea polyphenols in the selenium-enriched tea product obtained by the method is controlled within 20% compared with that of fresh leaves, and the content of free amino acids is increased by more than 10% compared with fresh leaves.

9. A finished selenium-enriched tea product obtained by the method of precise quality control during the processing of selenium-enriched tea as described in any one of claims 1-8, characterized in that, The selenium content of the finished selenium-enriched tea is stable at 2.35-2.43 mg / kg, with organic selenium accounting for ≥80%; the phenol-to-amino acid ratio is ≤3.4, the free amino acid content is ≥3.8%, the tea polyphenol content is 13.5%-14.0%, and the total chlorophyll content is ≥0.58 mg / g.

10. The application of a selenium-enriched tencha product obtained by the method of precise quality control during the processing of selenium-enriched tencha as described in any one of claims 1-8 in the preparation of selenium-enriched matcha products.

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