Sulfur-free illicium verum processing method based on endogenous metabolism precursor regulation and application

Abstract

The invention discloses a sulfur-free big red star anise processing method based on endogenous metabolism precursor regulation and application, mature star anise fresh fruits with yellow peels and full seeds are used as raw materials, and the processing method sequentially comprises three links of ultraviolet stress pretreatment, short-time hot water fixation and segmented drying. Through ultraviolet treatment, red precursor metabolites such as reduced glutathione, phenolic acid, flavone, stilbenes and sugar phosphoric acid are enriched in the fruits; the polyphenol oxidase is rapidly inactivated through short-time hot water fixation, the precursor pool is stabilized, and the quality loss is controlled; in the drying stage, the precursor is promoted to be gradually converted into phenolic acid oxidation products, aromatic aldehyde, aromatic amino acid-containing small peptides and terpenoid aroma substances in a sulfur-free environment, and stable bright red color and typical aroma are formed. Compared with a traditional sulfur fumigation process, the method has the advantages that the bright red star anise with high red brightness, low fruit cracking rate, natural flavor and remarkably reduced sulfur residue risk can be obtained under the condition that sulfur is not used, and the method is suitable for green and safe processing and standardized production of the star anise industry.

Description

Technical Field

[0001] This invention relates to the fields of deep processing of agricultural and forestry resources and food engineering technology, specifically to post-harvest processing and quality control technology for spices and specialty forestry agricultural products. More specifically, this invention relates to a processing method and application for preparing commercially viable "large red star anise" by regulating endogenous metabolic precursors in star anise fruit without sulfur fumigation. This method can be used for the industrial production of dried star anise products and the development of related supporting products. Background Technology

[0002] Star anise (Illicium verum) is the dried fruit of an evergreen tree belonging to the Magnoliopsida class. It is one of the important understory economic crops in southern my country and a major spice used in condiments and traditional Chinese medicine. In the market, high-grade star anise is mainly evaluated based on its appearance: "bright red, uniform, with few cracks, and strong aroma." The brightness and uniformity of the peel color are important criteria for trade grading and pricing. In recent years, with the rapid development of industries such as snail rice noodles and hot pot base, the market demand for bright red star anise has continued to increase.

[0003] In current production practices, to obtain bright red star anise with a uniform color, grassroots enterprises commonly use sulfur fumigation or burning sulfur-containing fuels to treat star anise after blanching or preliminary drying. This process can significantly increase the redness of the peel and inhibit browning in a short time, and also has a certain anti-mold and color-preserving effect, thus it has been widely used in long-term production. However, sulfur fumigation carries the risk of sulfur dioxide residue, easily causing products to exceed standards or hover near the limit, affecting not only product exports and brand image but also raising consumer concerns about food safety. Furthermore, excessive sulfur fumigation may destroy some volatile aroma components, resulting in a "dull" or "pungent" flavor in the star anise, differing from the fresh aroma of naturally sun-dried star anise.

[0004] To reduce sulfur usage, some producers have experimented with combined processes such as natural sun drying, hot air drying, microwave drying, or "blanching + sun drying," hoping to achieve a near-bright red appearance with reduced or no sulfur. However, in practice, relying solely on traditional sun drying or simply adjusting drying temperature and time often results in star anise peels that are yellowish-brown or dark brown, with significant color variations between batches and a high rate of fruit cracking, making it difficult to consistently achieve the "bright red" grade required by the market. Some companies use added pigments or other additives to improve color, which introduces new safety and compliance issues.

[0005] On the other hand, the color formation of star anise is essentially governed by the transformation of endogenous metabolites such as polyphenols, phenolic acids, flavonoids, amino acids, and sugars in the fruit. Current technologies rely more on empirical adjustments to process parameters such as blanching time and drying temperature, lacking a systematic understanding of the intrinsic metabolic basis of color formation under non-sulfur conditions, and have not yet developed a process design approach centered on "endogenous metabolic precursor regulation." While there are reports in the literature of using ultraviolet light and hot air drying to improve the color of some agricultural products, a systematic and mature technical solution has yet to be found for sulfur-free star anise processing, specifically for this raw material: how to use controllable pretreatment methods to enrich key precursor substances and naturally transform them into stable red polymers during subsequent drying, while simultaneously controlling fruit cracking and preserving aroma. Summary of the Invention

[0006] The purpose of this invention is to overcome the shortcomings of existing technologies for producing large red star anise, which heavily rely on sulfur fumigation, natural sun drying, and conventional hot air drying, making it difficult to consistently achieve a bright red color and resulting in a high rate of fruit cracking. This invention proposes a sulfur-free processing method for large red star anise based on the regulation of endogenous metabolic precursors, and its application. By subjecting fresh star anise to specific ultraviolet stress and short-term hot water blanching, combined with a segmented drying process, a group of endogenous metabolic precursors beneficial to coloring are induced and enriched without sulfur fumigation. These precursors are then naturally converted into red polymers and characteristic aroma substances during subsequent drying, resulting in large red star anise products with a bright red color, natural aroma, and low fruit cracking rate.

[0007] To achieve the above objectives, the present invention adopts the following technical solution:

[0008] A sulfur-free processing method for star anise based on endogenous metabolic precursor regulation includes the following steps:

[0009] (1) Raw material selection: Harvest mature star anise fruits with yellow peel, plump seeds, no diseases or pests and no obvious mechanical damage as raw materials for processing.

[0010] (2) UV stress pretreatment: The mature star anise fruits are spread out in a single layer and irradiated under a UV light source with a wavelength of 320-400 nm for 20-100 minutes to obtain UV-treated star anise;

[0011] (3) Hot water blanching: Put the UV-treated star anise into hot water at 90-100℃ for blanching for 1-5 minutes, remove and drain to obtain blanched star anise;

[0012] (4) Drying treatment: The blanched star anise is dried in stages, including at least:

[0013] (4-1) Dry at 30-45℃ or under natural sunlight to reduce the moisture content of star anise to 20-35%;

[0014] (4-2) Continue drying under hot air conditions of 45-65℃ until the moisture content is no higher than 12%, to obtain dried star anise;

[0015] The processing does not involve sulfur fumigation, nor does it add sulfites or other sulfur-containing bleaching agents.

[0016] Furthermore, in step (3), the hot water blanching temperature is 92-98℃ and the blanching time is 2-4 min, so that the mass loss rate during the blanching process is controlled at 2-4%.

[0017] Furthermore, in step (4-1), the star anise is dried in natural sunlight or in hot air at 30-40℃ to reduce its moisture content from the level of fresh fruit to 25-30%; in step (4-2), it is dried in hot air at 50-60℃ for 6-12 hours until the moisture content is ≤12%.

[0018] Furthermore, at the end of steps (2) and (3), by metabolomics analysis, the total relative peak area of ​​a group of red precursor metabolites (hereinafter referred to as red precursor metabolite combination A) in the star anise sample is increased by at least 1.5 times compared with the untreated fresh sample after harvest; the red precursor metabolite combination A includes at least three of the following endogenous substances: reduced glutathione, α-ketoglutarate, 3-phosphoglyceric acid, D-fructose-6-phosphate, apigenin-8-C-arabinoside, isothavirtoside, kaempferol-3-O-(2”-acetyl)glucuronide, kaempferol-3-O-(2”-galactoyl)galactoside, pinostigmine, 4-hydroxymandelinnitriles and eugenol.

[0019] Furthermore, in the dried star anise obtained in step (4), by metabolomics analysis, the total relative peak area of ​​a group of red and aroma co-accumulating metabolites (hereinafter referred to as red and aroma co-accumulating metabolite combination B) is at least 3 times higher than that of the untreated fresh sample after harvest; the red and aroma co-accumulating metabolite combination B includes at least five of the following substances: 3,4-dihydroxyphenylacetic acid, 3-(4-hydroxyphenyl)propionic acid, 4-hydroxybenzaldehyde, p-coumaraldehyde, senna aldehyde, syringic acid, 4-hydroxyphenyllactic acid, small peptides containing tyrosine residues, small peptides containing tryptophan residues, histidine-serine-valine-glutamic acid tetrapeptide, asparagine-tyrosine-arginine-aspartic acid tetrapeptide, serine-glutamic acid-tyrosine-glutamic acid tetrapeptide, and terpenoids or terpenoid oxidation products such as citronellol, virginone, and 2-methylisoborneol.

[0020] Furthermore, at the end of pretreatment, the relative peak areas of at least six metabolites in red precursor metabolite combination A were 1.5 to 10 times that of the fresh post-harvest sample; in the sulfur-free star anise product, the relative peak areas of at least eight metabolites in red and aroma co-accumulation metabolite combination B were 3 to 10 times that of the fresh post-harvest sample. 4 times.

[0021] Furthermore, the surface color of the dried star anise obtained in step (4) is measured using a colorimeter, and its CIEL*a*b* colorimetric parameters meet the following requirements: a* value not less than 15, L* value 30-55, b* value 20-45, and the color difference ΔE between it and the star anise sample obtained by traditional sulfur fumigation is not greater than 5; the cracking rate of the dried star anise is not higher than 10%.

[0022] Furthermore, during the processing, the star anise does not come into direct contact with burning sulfur or sulfur-containing fuels, and no sodium bisulfite, dithionite or other sulfur-containing bleaching agents are added; the residual sulfur dioxide in the dried star anise obtained in step (4) is less than 50% of the limit value of sulfur-fumigated dried fruit in the relevant national standards.

[0023] This invention also provides a sulfur-free dried star anise product, characterized by the following features: in full-spectrum metabolomics analysis, the total relative peak area of ​​its red precursor metabolite combination is 10-60% lower than that of the corresponding pretreated sample, and the total relative peak area of ​​the red and aroma co-accumulated metabolite combination is 3-10% of that of the fresh sample after harvest. 5 times;

[0024] The CIEL*a*b* parameters of the dried product meet the following requirements: a* value not less than 15, L* value 30-55, b* value 20-45, fruit cracking rate not higher than 10%, and no sulfur fumigation was used throughout the processing.

[0025] The present invention also provides the use of sulfur-free dried star anise in the preparation of seasonings, compound seasonings, ready-to-eat foods or traditional Chinese medicine slices.

[0026] Technical principle of the invention:

[0027] First, raw material control. This invention selects mature star anise fruits with yellowing peels, plump seeds, and no diseases, pests, or obvious mechanical damage as raw materials to ensure the initial metabolic basis and appearance consistency, providing the prerequisite for subsequent endogenous metabolic regulation.

[0028] Secondly, ultraviolet stress pretreatment. In this invention, fresh fruit is spread out in a single layer and irradiated for a certain period of time under an ultraviolet light source with a wavelength of 320–400 nm, preferably 60–90 minutes. Ultraviolet stress, on the one hand, stimulates the accumulation of metabolites such as polyphenols, phenolic acids, flavonoids, stilbenesides, and sugar phosphates in star anise fruit, forming a "red precursor metabolite combination" represented by reduced glutathione, α-ketoglutarate, 3-phosphoglyceric acid, D-fructose-6-phosphate, apigenin-8-C-arabinoside, isothavirtoside, and eugenol; on the other hand, it initiates a stress response at the metabolic level in advance, laying the foundation for color formation during subsequent heat treatment and drying processes.

[0029] Thirdly, short-time hot water blanching is used. In this invention, UV-treated star anise is immersed in hot water at 90–100°C for 1–5 minutes, preferably 2–4 minutes. Rapid heating quickly inactivates polyphenol oxidase and related enzyme systems, slowing down uncontrolled enzymatic browning while maintaining a high level of the aforementioned precursor metabolites. Experiments have shown that quality loss at this stage can be controlled within a low range, which is beneficial for balancing yield and quality.

[0030] Fourthly, segmented drying. This invention employs a segmented drying strategy of "mild dehydration in the early stage + medium-temperature color fixing in the later stage": first, slow drying is carried out at 30-45℃ or under natural sunlight to reduce the moisture content of star anise to about 20-35%, thereby reducing severe fruit cracking caused by rapid surface water loss; then, drying continues under hot air conditions at 45-65℃ until the moisture content is no higher than 12%, promoting the conversion of precursor metabolites into red polymers and characteristic aroma products in a sulfur-free environment. During this process, the relative content of some metabolites in the precursor combination decreases significantly, while generating a "red and aroma co-accumulation metabolite combination" represented by 3,4-dihydroxyphenylacetic acid, 3-(4-hydroxyphenyl)propionic acid, 4-hydroxybenzaldehyde, p-coumaraldehyde, sennapialdehyde, syringic acid, 4-hydroxyphenyllactic acid, small peptides containing tyrosine / tryptophan residues, and terpene oxidation products such as citronellal, virginone, and 2-methylisoborneol, which metabolically support the formation of the bright red color and the unique aroma of star anise.

[0031] Fifth, the entire process is sulfur-free. The processing flow of this invention does not include a sulfur fumigation process, does not allow star anise to come into direct contact with burning sulfur or sulfur-containing fuels, and does not add sulfites or other sulfur-containing bleaching agents. The sulfur dioxide residue in the finished product can be controlled at a low level or even far below the national limit for sulfur-fumigated dried fruits, achieving a balance between safety and marketability.

[0032] Compared with the prior art, the present invention has the following technical advantages:

[0033] (1) This invention starts from the endogenous metabolic precursors of star anise fruit and uses a combination of ultraviolet stress and short-time hot water blanching to selectively enrich metabolic precursors that are conducive to coloring. In the subsequent drying process, natural reddening is achieved, and star anise with high redness and uniform color can be obtained without relying on sulfur fumigation. This solves the technical bottleneck of relying on sulfur fumigation for color fixation for a long time.

[0034] (2) The present invention adopts a segmented drying process, with mild dehydration in the early stage and medium-temperature color fixation in the later stage. On the one hand, it reduces the severe fruit cracking caused by rapid fruit dehydration, reduces the fruit cracking rate, and improves the appearance of the product. On the other hand, it promotes the gradual conversion of precursors into red polymers and aromatic components at a suitable temperature, which can maintain good brightness and yellowness while significantly improving the color difference parameter a*. The finished product has stable color and small batch-to-batch differences.

[0035] (3) Through full-spectrum metabolomics analysis, this invention clarifies the dynamic change law of the combination of red precursor metabolites and the combination of red and aroma co-accumulated metabolites on the basis of process optimization, providing a quantifiable metabolomics basis for setting process parameters, which is conducive to establishing a replicable and scalable standardized production process of sulfur-free star anise and reducing the uncertainty of "color adjustment based on experience".

[0036] (4) Under the premise of ensuring color and aroma quality, this invention avoids or significantly reduces the use of sulfur and sulfur-containing additives, reduces the risk of sulfur dioxide residue in finished products, meets the regulatory requirements of green, safe and export trade for spice processing, and is suitable for promotion and application in existing star anise processing enterprises. Attached Figure Description

[0037] Figure 1 Photographs of the appearance of star anise samples after treatment with different hot water blanching times, among which... Figure 1 'a' represents post-harvest raw materials. Figure 1 b~ Figure 1 e represents the samples after blanching for 2 min, 4 min, 6 min, and 8 min, respectively.

[0038] Figure 2 Photographs of star anise samples under different UV treatment times and 2-minute hot water blanching conditions are shown. Figure 2 a~ Figure 2 d represents the samples obtained after UV pretreatment for 20 min, 40 min, 60 min, and 80 min, respectively.

[0039] Figure 3 These are comparative photographs showing the appearance of the sulfur-free star anise sample of this invention, the traditional sulfur-fumigated star anise sample, and the naturally sun-dried sample. Figure 3 a is a sample after the raw material has been directly dried. Figure 3 b is the sample after the raw material has undergone a 2-minute blanching process followed by sun drying. Figure 3 c is the sample after UV sterilization for 20 minutes + blanching for 2 minutes + sun drying. Figure 3 d is the sample after the raw material has undergone 2 minutes of blanching, sulfur fumigation, and sun drying. Detailed Implementation

[0040] The present invention is further illustrated by the following examples, but these are not intended to limit the invention. Specific experimental conditions and methods not specified in the following examples are generally conventional methods well known to those skilled in the art.

[0041] Example 1: Preparation process of sulfur-free star anise

[0042] Raw material selection: 8.6 kg of mature star anise fruits harvested from a base in Guangxi were selected. The fruits were required to have yellow peels and plump seeds. Moldy, rotten, diseased, insect-infested, and mechanically damaged fruits were removed. All pre-processing operations were completed within 24 hours after harvesting to ensure a relatively consistent endogenous metabolic baseline.

[0043] UV stress pretreatment: The fresh star anise fruits were laid flat on a stainless steel mesh tray, with a single layer thickness, ensuring the fruit segments did not overlap. The tray was then placed in a treatment chamber equipped with a UVA light source. Stress treatment was performed under UV light with a wavelength of 320–400 nm for 80 minutes. The distance between the light source and the fruit surface was approximately 30 cm. During treatment, the fruit was gently turned every 20 minutes to ensure even light exposure. After treatment, the fruit was allowed to cool naturally for 10 minutes, and this sample was recorded as the UV-treated star anise sample (UVS).

[0044] Hot water blanching: Add water to a jacketed kettle and heat to boiling, then stabilize the temperature at 95±2℃. Add the UV-treated star anise in batches to the boiling water, stirring gently to ensure even heating. After 2 minutes, remove the star anise and place it on a stainless steel sieve to drain excess water. Weigh the samples before and after blanching; the calculated mass loss rate is approximately 3%. Take a portion of the sample and quickly freeze it in liquid nitrogen for WRT (Waste Metabolomics Research and Development). The remaining sample proceeds to the next drying step.

[0045] Segmented drying:

[0046] (1) First stage: Gentle dehydration

[0047] After blanching, spread the star anise on bamboo mats or stainless steel mesh trays, controlling the thickness to 1-2 layers, and air-dry under natural sunlight for 1-2 days on sunny days. Maintain ventilation during the drying process, turning the star anise 2-3 times daily to prevent localized accumulation. The first stage ends when the moisture content of the sample drops to 25-30%, determined by moisture content testing.

[0048] (2) Second stage: medium temperature color fixation

[0049] After the first stage of sun-drying, the star anise was transferred to a hot air drying oven, set at 55℃ and with a relative humidity of 40-50%, for 8-10 hours. During this time, the star anise was gently turned every 2 hours to ensure even contact with the hot air. At the end of drying, the moisture content of the sample was reduced to no more than 12%, yielding a bright red dried star anise product with plump segments (SDT-UV).

[0050] Metabolomics and Quality Determination: A combined liquid chromatography-tandem mass spectrometry (LC-MS / GC-MS) and gas chromatography-mass spectrometry (GC-MS) full-spectrum metabolomics technique was used to detect and quantify post-harvest fresh (RW), ultraviolet-treated (UVS), hot water blanching (WRT) samples, and the sulfur-free star anise product obtained in this embodiment (SDT-UV). Detection conditions employed commonly used plant metabolomics analysis methods in this field, such as standard methods provided by commercial non-targeted metabolomics analysis platforms. Specific instrument models and chromatographic gradients were set according to the recommended parameters of the testing institution. The results showed that, during the UV treatment and hot water blanching stages, compared with the fresh samples after harvest, the relative peak areas of precursor metabolites such as reduced glutathione, α-ketoglutarate, 3-phosphoglyceric acid, D-fructose-6-phosphate, apigenin-8-C-arabinoside, isothavirtoside, kaempferol-3-O-(2”-acetyl)glucuronide, pinassidol, 4-hydroxymandelinnitrile, and eugenol increased by 1.5 to 8 times, forming a significantly enhanced red precursor metabolite combination (combination A).

[0051] In the final dried product, the relative peak areas of some metabolites in the above-mentioned precursor combination decreased by 40-90% compared with the WRT stage. Meanwhile, the relative peak areas of metabolites such as 3,4-dihydroxyphenylacetic acid, 3-(4-hydroxyphenyl)propionic acid, 4-hydroxybenzaldehyde, p-coumaraldehyde, sennapialdehyde, syringic acid, 4-hydroxyphenyllactic acid, small peptides containing tyrosine or tryptophan residues, as well as citronellal, virginone, and 2-methylisoborneol increased by more than one order of magnitude compared with the fresh samples after harvest, forming a combination of red and aroma-accumulating metabolites (combination B). The surface color of the large red star anise obtained in this example was measured using a colorimeter. Among its CIEL*a*b* colorimetric parameters, the a* value was significantly higher than that of the naturally sun-dried, unsulfur-fumigated control, exceeding 15. L* and b* were within the appropriate range, and the sensory observation showed a bright red color. The cracking rate of all three batches of samples was less than 10%. The entire processing flow did not employ sulfur fumigation, and the sulfur dioxide residue detection value of the finished product was significantly lower than the relevant national limits. Table 1 shows representative red precursor metabolites and their changes at each treatment stage, and Table 2 shows representative red and aroma co-accumulation metabolites and their changes in the finished product.

[0052] Table 1. Representative metabolites and trends of red precursor metabolite combination A

[0053]

[0054] Table 2. Representative metabolites and trends of red and aroma co-accumulation metabolites group B.

[0055]

[0056] Example 2: Effect of different hot water blanching times on the effects of eight-cornered oyster sauce (corresponding to...) Figure 1 )

[0057] This embodiment aims to investigate the effect of hot water blanching time on the appearance and color of star anise. The resulting appearance photographs are shown below. Figure 1 ,in Figure 1 a~ Figure 1 The meaning of 'e' is as described in the accompanying illustration.

[0058] Experimental Design: Mature star anise fruits harvested from the same base as in Example 1 were selected. After removing diseased, pest-infested, and mechanically damaged fruits, they were randomly divided into 5 groups, with approximately 1.0 kg in each group. All samples underwent no UV pretreatment and were directly subjected to a hot water blanching time gradient experiment.

[0059] Group RW: No blanching, used only as a post-harvest raw material control (corresponding to...) Figure 1 a) Group W2: Blanching in hot water at 95±2℃ for 2 minutes (corresponding to...) Figure 1 b); Group W4: Blanching in hot water at 95±2℃ for 4 minutes (corresponding to...) Figure 1 c); Group W6: Blanching in hot water at 95±2℃ for 6 minutes (corresponding to...) Figure 1 d); Group W8: Blanching in hot water at 95±2℃ for 8 minutes (corresponding to Figure 1 e). The blanching procedure is the same as in Example 1: Heat water in a jacketed kettle to boiling, then adjust the temperature to 95±2℃. Add the samples in batches to the hot water, stirring gently. At the end of the set time, quickly remove the samples and drain off the surface moisture.

[0060] Drying Process: To highlight the impact of the fixation time, this embodiment uniformly adopts a natural sun-drying process: The drained star anise from each group is spread on bamboo mats, 1-2 layers thick, and sun-dried under natural sunlight on a sunny day until the moisture content does not exceed 12%, turning it occasionally to ensure even sun exposure. After sun-drying, the dried products of each fixation time group are obtained, and their appearance comparison photos are shown below. Figure 1 As shown.

[0061] Results and Analysis: Visual observation and colorimeter measurement results showed that compared with the raw material without blanching ( Figure 1 Compared to a), moderate blanching (2-4 min) can significantly inhibit uneven browning, resulting in a brighter red peel color; excessive blanching (6-8 min) can easily lead to darkening of the fruit segments, excessive water loss in some tissues, and an increased rate of fruit cracking. Considering both appearance and cracking, hot water blanching within the 2-4 min range provides a reasonable time range for subsequent sulfur-free star anise processing.

[0062] Example 3: Effect of different UV treatment times combined with 2 min hot water blanching (corresponding to...) Figure 2 )

[0063] This embodiment investigates the effect of UV treatment time on the appearance color of star anise under the condition of a fixed hot water blanching time of 2 minutes. The resulting appearance photographs are shown below. Figure 2 ,in Figure 2 a~ Figure 2 The meaning of d is subject to the "Figure Description".

[0064] Experimental Design: Mature star anise fruits from the same batch as in Example 1 were selected. After removing defective fruits, they were randomly divided into 4 groups, each approximately 1.0 kg. Each group's sample was laid flat in a single layer on a stainless steel mesh tray and placed in a UVA light source chamber. Treatment was performed under wavelengths of 320–400 nm, as follows: Group UV20: UV irradiation for 20 min (corresponding to…) Figure 2 a) Group UV40: UV irradiation for 40 min (corresponding to Figure 2 b); Group UV60: UV irradiation for 60 min (corresponding to Figure 2 c); Group UV80: 80 min of ultraviolet irradiation (corresponding to Figure 2 d). The distance between the light source and the fruit surface was approximately 30 cm. During the treatment, the fruit was slightly turned over every 20 minutes to ensure uniform light exposure. After the UV treatment, each group of samples was allowed to cool naturally for 10 minutes, and then uniformly subjected to hot water blanching at 95±2℃ for 2 minutes, in the same manner as in Example 1.

[0065] Drying treatment: This embodiment is for... Figure 2 The appearance photos were kept consistent throughout, and a natural sun-drying process was used uniformly: After blanching, each group of samples was spread out on bamboo mats and naturally sun-dried until the moisture content did not exceed 12%. After drying, the appearance of each group was photographed and recorded, as shown in the following figures. Figure 2 As shown.

[0066] Results and Analysis: The results showed that appropriately extending the UV treatment time was beneficial for the transition of star anise peel from yellowish-green to reddish-brown. Samples treated with UV for 20 min (…) Figure 2 a) The original yellowish-brown color was basically maintained, with limited improvement in redness; UV 40-60min treatment group ( Figure 2 b、 Figure 2 c) The redness of the peel increased significantly and the color became more uniform; the UV 80min treatment group ( Figure 2 d) The redness was further enhanced, but slight "scorch spots" or local dark spots appeared on the surface of some fruit segments. Considering both the uniformity of color and the improvement in redness, the 60-80 min range is the optimal UV treatment time range, and the 80 min condition selected in Example 1 was determined based on this.

[0067] Example 4: Appearance comparison between sulfur-free star anise and samples treated with traditional sulfur fumigation and natural sun drying (corresponding to...) Figure 3 )

[0068] This embodiment sets up different processing routes under the same raw material conditions to compare the appearance differences of star anise products obtained by sulfur-free process, natural sun drying, conventional blanching and sun drying, and sulfur fumigation process. Appearance photos are available in the attached images. Figure 3The meaning of each sub-figure is subject to the "Figure Description".

[0069] Experimental Design and Treatment Route: Random samples were taken from the same batch of ripe star anise and divided into 4 groups, each group containing approximately 1.0 kg.

[0070] 1) Naturally sun-dried group ( Figure 3 a)

[0071] Without blanching or ultraviolet treatment, the harvested raw materials are directly spread on bamboo mats and naturally sun-dried until the moisture content is no more than 12%, thus obtaining naturally sun-dried samples.

[0072] 2) Blanching + Sun-drying group ( Figure 3 b)

[0073] Without ultraviolet treatment, the raw material was blanched in hot water at 95±2℃ for 2 minutes, drained, and then sun-dried until the moisture content was no more than 12%, thus obtaining a sample consisting of "raw material + 2 minutes blanching + sun-drying".

[0074] 3) UV 20min + fixation + sun drying group ( Figure 3 c)

[0075] The raw materials were first subjected to ultraviolet (UV20) treatment at 320-400nm for 20min, and then cooled naturally for 10min. After that, they were blanched in hot water at 95±2℃ for 2min. Then, they were naturally sun-dried until the moisture content was no more than 12%, resulting in a sample of “UV20min+2min blanching+sun-drying”.

[0076] 4) Blanching + Sulfur Fumigation + Sun Drying Group ( Figure 3 d)

[0077] Without UV treatment, first blanch in hot water at 95±2℃ for 2 minutes, drain, and then place in a traditional sulfur fumigation environment, following existing enterprise practices (e.g., 1.5~2.0kg sulfur / m³). 3 The sample was treated with sulfur fumigation for 8-12 hours. After the sulfur fumigation was completed, the sample was taken out and dried in the sun until the moisture content was no more than 12%, thus obtaining a sample of "raw material + 2 min blanching + sulfur fumigation + sun drying".

[0078] Results and Analysis

[0079] like Figure 3 As shown, naturally sun-dried samples ( Figure 3 a) The peel is generally yellowish-brown or dark brown, lacking redness and showing significant batch-to-batch variation; samples that were simply blanched and sun-dried ( Figure 3 b) The color is slightly improved compared to naturally sun-dried samples, but it is still yellowish-brown, with irregular brown spots appearing on some fruit segments; sulfur-fumigated samples ( Figure 3d) The peel is a strong bright red or orange-red with a uniform color, but there is a risk of excessive sulfur dioxide residue, and some volatile aroma components are damaged, resulting in a slightly pungent smell.

[0080] In comparison, the sample was subjected to UV sterilization for 20 minutes followed by sun drying. Figure 3 c) Without the use of sulfur, the redness of the peel is significantly improved, the color is more uniform than that of natural sun-drying and simple blanching and sun-drying, the cracking rate is controlled at a low level, and the aroma is preserved more naturally. Combined with the color difference and metabolome results of the samples obtained using the optimized UV time and segmented drying process in Example 1, it is evident that the sulfur-free star anise processing method of this invention is superior to the traditional sulfur fumigation process in terms of color, cracking control, and safety, providing the star anise industry with a standardized and scalable green processing technology route.

Claims

1. A method for processing sulfur-free star anise based on endogenous metabolic precursor regulation, characterized in that, Includes the following steps: (1) Raw material selection: Harvest mature star anise fruits with yellow peel, plump seeds, no diseases or pests and no obvious mechanical damage as raw materials for processing. (2) UV stress pretreatment: The mature star anise fruits are spread out in a single layer and irradiated under a UV light source with a wavelength of 320-400 nm for 20-100 minutes to obtain UV-treated star anise; (3) Hot water blanching: Put the UV-treated star anise into hot water at 90-100℃ for blanching for 1-5 minutes, remove and drain to obtain blanched star anise; (4) Drying treatment: The blanched star anise is dried in stages, including at least: (4-1) Dry at 30-45℃ or under natural sunlight to reduce the moisture content of star anise to 20-35%; (4-2) Continue drying under hot air conditions of 45-65℃ until the moisture content is no higher than 12%, to obtain dried star anise; The processing does not involve sulfur fumigation, nor does it add sulfites or other sulfur-containing bleaching agents.

2. The sulfur-free star anise processing method based on endogenous metabolic precursor regulation according to claim 1, characterized in that, In step (3), the hot water blanching temperature is 92-98℃ and the blanching time is 2-4 min, so that the mass loss rate during the blanching process is controlled at 2-4%.

3. The sulfur-free star anise processing method based on endogenous metabolic precursor regulation according to claim 1, characterized in that, Step (4-1) involves sun-drying under natural sunlight or drying with hot air at 30-40℃ to reduce the moisture content of star anise from the level of fresh fruit to 25-30%; Step (4-2) involves drying with hot air at 50-60℃ for 6-12 hours until the moisture content is ≤12%.

4. The sulfur-free star anise processing method based on endogenous metabolic precursor regulation according to claim 1, characterized in that, At the end of steps (2) and (3), by metabolomics analysis, the total relative peak area of ​​a group of red precursor metabolites A in the star anise sample increased by at least 1.5 times compared with the untreated fresh sample after harvest; the red precursor metabolite group A includes at least three of the following endogenous substances: reduced glutathione, α-ketoglutarate, 3-phosphoglyceric acid, D-fructose-6-phosphate, apigenin-8-C-arabinoside, isothavirtoside, kaempferol-3-O-(2”-acetyl)glucuronide, kaempferol-3-O-(2”-galactoyl)galactoside, pinostigmine, 4-hydroxymandelinnitriles and eugenol.

5. The sulfur-free star anise processing method based on endogenous metabolic precursor regulation according to claim 1, characterized in that, In the dried star anise obtained in step (4), the total relative peak area of ​​a group of red and aroma co-accumulated metabolites B was increased by at least 3 times compared with the untreated fresh sample after harvest, by metabolomics detection; the red and aroma co-accumulated metabolite group B includes at least five of the following substances: 3,4-dihydroxyphenylacetic acid, 3-(4-hydroxyphenyl)propionic acid, 4-hydroxybenzaldehyde, p-coumaraldehyde, senna aldehyde, syringic acid, 4-hydroxyphenyllactic acid, small peptides containing tyrosine residues, small peptides containing tryptophan residues, histidine-serine-valine-glutamic acid tetrapeptide, asparagine-tyrosine-arginine-aspartic acid tetrapeptide, serine-glutamic acid-tyrosine-glutamic acid tetrapeptide, and terpenoids or terpene oxidation products such as citronellal, virginone, and 2-methylisoborneol.

6. The sulfur-free star anise processing method based on endogenous metabolic precursor regulation according to claim 4 or 5, characterized in that, At the end of pretreatment, the relative peak areas of at least 6 metabolites in red precursor metabolite combination A were 1.5 to 10 times that of the post-harvest fresh sample; in the sulfur-free star anise product, the relative peak areas of at least 8 metabolites in red and aroma co-accumulation metabolite combination B were 3 to 10 times that of the post-harvest fresh sample. 4 times.

7. The sulfur-free star anise processing method based on endogenous metabolic precursor regulation according to claim 1, characterized in that, The surface color of the dried star anise obtained in step (4) was measured using a colorimeter. Its CIEL*a*b* colorimetric parameters met the following requirements: a* value not less than 15, L* value 30-55, b* value 20-45, and the color difference ΔE between it and the star anise sample obtained by traditional sulfur fumigation was not greater than 5; the cracking rate of the dried star anise was not higher than 10%.

8. The sulfur-free star anise processing method based on endogenous metabolic precursor regulation according to claim 1, characterized in that, During the processing, star anise does not come into direct contact with burning sulfur or sulfur-containing fuels, and no sodium bisulfite, dithionite or other sulfur-containing bleaching agents are added; the sulfur dioxide residue in the dried star anise obtained in step (4) is less than 50% of the limit value of sulfur-fumigated dried fruit in the relevant national standards.

9. A sulfur-free dried star anise, characterized in that, Prepared by the method according to any one of claims 1 to 8, it has the following characteristics: in full-spectrum metabolomics detection, the total relative peak area of ​​its red precursor metabolite combination is lower than that of the corresponding pretreated sample by 10 to 60%, and the total relative peak area of ​​the red and aroma co-accumulated metabolite combination is 3 to 10 times that of the post-harvest fresh sample. 5 times; The CIEL*a*b* parameters of the dried product meet the following requirements: a* value not less than 15, L* value 30-55, b* value 20-45, fruit cracking rate not higher than 10%, and no sulfur fumigation was used throughout the processing.

10. The use of the sulfur-free dried star anise according to claim 9 in the preparation of seasonings, compound seasonings, ready-to-eat foods or traditional Chinese medicine slices.

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