Preparation method of a citron-based postbiotic coffee

Abstract

The application discloses a preparation method of a carambola-based postbiotic coffee and belongs to the technical field of food. The carambola is used as a substrate, is inactivated after being fermented by lactobacillus plantarum HNU531, 10% to 40% (w / w) of beta-cyclodextrin and malt dextrin are added as drying aids, vacuum freeze-drying is carried out, postbiotic freeze-dried powder is prepared, and the postbiotic freeze-dried powder is compounded with coffee at a mass ratio of 1:10, so that the original flavor base of the coffee can be completely retained, the bitterness of the coffee can be effectively reduced, the sour and sweet taste of the coffee can be improved, the flavor of the beverage is more coordinated and palatable, and the sensory evaluation score of the product is significantly improved.

Description

Technical Field

[0001] This invention discloses a method for preparing starfruit-based post-biotic coffee, belonging to the field of food processing technology. Background Technology

[0002] Coffee is a globally popular non-alcoholic beverage, its flavor comprised of multiple taste characteristics including bitterness, acidity, and sweetness. Consumers increasingly favor coffee products that are low in stimulants, have a harmonious flavor, and offer health benefits. Therefore, preserving coffee's unique flavor characteristics while reducing bitterness and enriching its sweet and sour layers has become a key technological challenge for the entire coffee industry chain. Currently, most methods for improving coffee flavor rely on coffee bean variety selection, roasting process control, extraction parameter optimization, and the blending of exogenous ingredients. Among these, microbial fermentation technology is recognized by the industry as having the greatest potential for flavor improvement. This technology can regulate the ratio of organic acids and flavor glycoside precursors, optimizing the coffee's taste system. However, current coffee fermentation processes are mostly applied to the processing of fresh coffee cherries and green beans, resulting in significant batch-to-batch flavor variations and poor process controllability, making it difficult to precisely achieve targeted flavor improvements in the finished coffee, such as reducing bitterness and increasing acidity and sweetness.

[0003] To impart health benefits to coffee, current research often involves adding live probiotics to the coffee system. However, probiotic cells have extremely poor tolerance to high-temperature processing, acidic environments, and high-pressure extraction conditions, resulting in significant fluctuations in cell survival rates. Furthermore, probiotic metabolic byproducts easily damage the original aroma of coffee, leading to unstable flavor in the finished product. Postbiotics, on the other hand, are complexes of microbial cell lysates and metabolically active substances remaining after microbial fermentation. They possess characteristics such as resistance to high temperatures, acids, alkalis, and mechanical shearing, making them suitable for all food processing steps and exhibiting excellent quality stability. However, current research and application of postbiotics largely rely on dairy products and fruit and vegetable juices as fermentation carriers, with very few applications in the deep processing of coffee. There is also a lack of integrated application solutions that simultaneously improve coffee flavor and enhance its nutritional functions.

[0004] Star fruit is rich in soluble sugars, fermentable polysaccharides, and other fermentable substrates, possessing a refreshing sweet and sour fruity aroma and a mild, mellow flavor. It is well-suited for lactic acid bacteria fermentation and metabolism, making it a high-quality fermentation raw material for preparing specialized flavor enhancers. However, current applications of star fruit in the food industry are limited to simple processing methods such as fresh fruit juicing and physical flavor enhancement. Microbial fermentation technology has not been utilized to transform the star fruit substrate into functional fermented components that can regulate beverage flavor, nor has a standardized processing technique for blending star fruit fermentation products with coffee been established. Based on these industry pain points, a new process has been developed to use star fruit juice as a fermentation substrate to prepare highly stable enhancers for blending with coffee. This process can precisely optimize the taste of coffee, reduce bitterness, and impart beneficial functional values ​​to coffee, effectively addressing the shortcomings of existing coffee flavor improvement and functional processing technologies. Summary of the Invention

[0005] To address the shortcomings of existing coffee flavor enhancement and functional ingredient processing technologies, this invention aims to provide a starfruit-based post-biotic coffee preparation process: starfruit juice is fermented using a specific strain of *Lactobacillus plantarum*. After fermentation, the juice is inactivated at high temperatures to prepare post-biotic raw materials. These post-biotics are then added to coffee powder to reduce bitterness and enhance acidity, umami, and sweetness, thereby comprehensively optimizing the sensory quality of the coffee. To achieve the above research objectives, this invention adopts the following technical solution: This invention provides a method for preparing star fruit-based post-biotic coffee, which involves inoculating star fruit juice with Lactobacillus plantarum HNU531 for fermentation, drying the fermentation product, and then mixing it with coffee powder. The Lactobacillus plantarum HNU531 has been disclosed in patent CN 121852279 A, ​​with accession number GDMCC No: 67494.

[0006] In one embodiment, the method includes the following operational steps: The activated Lactobacillus plantarum HNU531 third-generation strain was inoculated into star fruit juice for constant temperature fermentation. After the fermentation process was completed, the fermentation broth was inactivated to obtain the star fruit-based post-biotic fermentation substrate.

[0007] As a preferred technical solution: First, *Lactobacillus plantarum* HNU531 was inoculated into MRS liquid medium and cultured statically at 37°C for 24 hours. Two generations of the primary bacterial culture were then passaged, with each generation cultured at 37°C for 24 hours, to obtain the third-generation activated strain. The third-generation bacterial culture was centrifuged at 4000 rpm for 5 minutes, the supernatant was removed, and the precipitated bacterial cells were resuspended in sterile physiological saline. The culture was then inoculated into a star fruit juice system and fermented at 37°C for 24 hours. After fermentation, a compound drying agent (β-cyclodextrin combined with maltodextrin) at a mass ratio of 10%–40% was added to the fermentation system. The mixture was then freeze-dried under vacuum to obtain powdered star fruit-based post-biotic.

[0008] As a preferred technical solution, the star fruit fermentation liquid is inactivated and sterilized by maintaining a constant temperature of 90℃ for 10 minutes. This invention also discloses the application of the above-mentioned starfruit-based post-gene in coffee processing products. As a preferred technical solution: Starfruit-based post-biotic powder is thoroughly mixed with coffee powder at an addition ratio of 5% to 20% to obtain starfruit-based post-biotic compound coffee.

[0009] This blended coffee retains the original aroma and flavor of coffee while effectively reducing bitterness and enhancing the acidity, umami, and sweetness of the beverage, significantly improving the overall sensory quality of the product. The present invention also provides the application of Lactobacillus plantarum HNU531 in the preparation of starfruit-based post-biotic coffee, wherein the preservation number of Lactobacillus plantarum HNU531 is: GDMCC 67494.

[0010] This invention also provides the application of Lactobacillus plantarum HNU531 in improving coffee flavor.

[0011] In one embodiment, the improvement in coffee flavor is to reduce coffee bitterness and increase umami, acidity, and sweetness.

[0012] Beneficial effects: 1. This invention uses star fruit juice as the substrate for lactic acid bacteria fermentation. Fresh star fruit is rich in reducing sugars, free flavor amino acids, and trace elements such as potassium and magnesium, which can provide natural nutrients for the growth and metabolism of Lactobacillus plantarum and ensure the stability and controllability of the composition of post-fermentation products.

[0013] 2. This invention uses postbiotics to replace active probiotics in the coffee system, which completely solves the problem that active probiotics are easily deactivated and ineffective during coffee roasting, extraction, processing, and room temperature storage. Relying on the high temperature resistance and adaptability of postbiotics to various processing conditions, the quality of different batches of coffee products is guaranteed to be consistent.

[0014] 3. Adding the starfruit-based post-biotic prepared in this invention to coffee at a ratio of 10% can completely preserve the original flavor base of coffee, effectively reduce the bitterness of coffee, enhance the acidity and sweetness of coffee, make the beverage flavor more harmonious and palatable, and significantly improve the sensory evaluation score of the product. Attached Figure Description

[0015] Figure 1 The reducing sugar (A), pH (B), and total sugar (C) of coffee and starfruit-based post-biotic coffee.

[0016] Figure 2 Electronic tongue images of coffee and starfruit-based post-biotic coffee.

[0017] Figure 3 Volcano diagram of differential metabolites in coffee and starfruit-based post-biotic coffee (A), volatile component analysis diagram during fermentation (B), and LC-VIP (C).

[0018] Figure 4 GC-VIP image for coffee and Yangtaoji Post-Growth Coffee. Detailed Implementation

[0019] The listed embodiments are only for assisting in understanding the technical solutions of the present invention and are not intended to limit the preferred embodiments of the present invention, nor do they limit the technical content and scope of protection of the present invention. Any identical or similar products prepared by those skilled in the art based on the technical ideas provided in this invention, or by combining the technical features of this invention with existing technologies, are all within the scope of protection of this invention.

[0020] The coffee powder used in this embodiment was purchased from Hainan Nongken Mushan Coffee Co., Ltd. Other commercially available finished coffee powders, or coffee powders made from commercially available coffee beans, can achieve the technical effects of this invention.

[0021] The present invention relates to Lactobacillus plantarum ( Lactiplantibacillus plantarum HNU531 has been published in patent CN 121852279 A, ​​with accession number GDMCC No: 67494.

[0022] The star fruit juice involved in this invention was purchased from Baixianyuan Company (NFC standard).

[0023] Example 1: Preparation of Starfruit-Based Post-Activated Coffee The activated and amplified third-generation strain of Lactobacillus plantarum HNU531 was inoculated into the star fruit juice system for liquid fermentation. After the fermentation process, the fermentation mixture was subjected to high-temperature inactivation treatment to finally obtain the star fruit matrix post-biotic fermentation raw material. Lactobacillus plantarum strain HNU531 was inoculated into MRS liquid medium and incubated at 37°C for 24 hours to obtain the primary bacterial culture. 200 μL of the primary culture was precisely transferred to fresh, sterile MRS liquid medium and incubated at 37°C for 24 hours to obtain the second-generation bacterial culture. Another 200 μL of the second-generation culture was transferred to fresh MRS liquid medium and incubated at the same 37°C for 24 hours to obtain the third-generation activated bacterial culture, which was then stored for later use. Ripe, fresh star fruit was crushed and pulped. The pulp residue and coarse fiber impurities were removed using sterile gauze to obtain clear star fruit juice. The activated Lactobacillus plantarum HNU531 third-generation bacterial culture was centrifuged at 4000 rpm for 5 minutes. The supernatant was discarded, and the bottom bacterial precipitate was resuspended and reconstituted using sterile physiological saline.

[0024] The prepared third-generation bacterial culture medium was placed in a centrifuge and centrifuged at 4000 rpm for 5 minutes. After removing the supernatant, the bacterial cells were resuspended in sterile physiological saline and then inoculated into sterilized star fruit juice. The initial concentration of *Lactobacillus plantarum* HNU531 in the system was adjusted to 10. 9CFU / mL, fermented at a constant 37℃ for 24 hours. After the fermentation cycle, the star fruit fermentation broth was placed in a water bath and heat-treated at 90℃ for 10 minutes to inactivate the live bacteria in the system, thus obtaining the star fruit matrix post-biotic broth. 10%–40% by weight of β-cyclodextrin or maltodextrin was added to the post-biotic broth as a drying agent, mixed thoroughly, and then freeze-dried under vacuum to prepare powdered star fruit-based post-biotic product. The star fruit-based post-biotic powder was then thoroughly mixed with pure coffee powder at a ratio of 5%–20% by weight to prepare a composite star fruit-based post-biotic coffee powder.

[0025] Example 2: Screening of Starfruit-based Desiccant Drying Agents For the specific implementation method, refer to Example 1. The difference is that the content of the drying aid added to the post-biotic stock solution is adjusted. 10% to 40% by mass of maltodextrin and 10% to 40% by mass of β-cyclodextrin are added separately to the post-biotic stock solution, mixed well, and then subjected to vacuum freeze-drying. The moisture content and solubility of the resulting freeze-dried powder are then tested.

[0026] Table 1. Moisture content and solubility of star fruit after adding maltodextrin and β-cyclodextrin (10%-40%) respectively

[0027] Table 1 shows the changes in moisture content and solubility of freeze-dried star fruit products prepared using maltodextrin and β-cyclodextrin at different addition ratios (10%~40%). (Note: Star fruit does not form powder when 10% maltodextrin is added as a drying aid, therefore, relevant moisture content and solubility data are not available.) Overall, regarding moisture content: as the addition of β-cyclodextrin increases from 10% to 40%, the residual moisture content of the resulting star fruit product decreases; however, there is no uniform trend in moisture content when the addition of maltodextrin increases from 10% to 40%. Specifically, the solubility of the maltodextrin group increases with increasing addition, while the solubility of the β-cyclodextrin group decreases with increasing addition. In summary, the lowest moisture content (4.25%) is found with 40% maltodextrin, while the highest solubility (100.00%) is found with both 30% and 40% maltodextrin. Considering both moisture content and solubility, subsequent experiments were conducted on star fruit supplemented with 10% β-cyclodextrin and 20% maltodextrin.

[0028] Example 3: Analysis of Starfruit-Based Post-Activated Coffee The starfruit post-biotic compound coffee was prepared according to the process described in Example 2: 10% β-cyclodextrin was added to the starfruit post-biotic stock solution, and the mixture was freeze-dried to obtain starfruit post-biotic dry powder. The starfruit post-biotic dry powder and coffee raw materials were thoroughly mixed at a mass ratio of 1:10 to prepare a compound coffee powder, which was designated as Starfruit Post-biotic Coffee (β-10%). Separately, 20% maltodextrin was mixed into the starfruit post-biotic stock solution, freeze-dried, and then mixed with coffee powder at a 1:10 ratio to prepare starfruit post-biotic coffee powder, which was labeled as Starfruit Post-biotic Coffee (Malt-20%). Pure coffee powder without any added additives was used as a blank control, referred to as pure coffee. All coffee samples were uniformly brewed with hot water at 90-95℃, and sensory quality testing was conducted after brewing. The tasting panel consisted of 15 researchers aged 20-30. The evaluation criteria included mouthfeel, aroma, body, finish, powder texture, and acidity. Five samples of each type of coffee were prepared for blind tasting, in accordance with the SCAA professional coffee tasting standards.

[0029] Table 2 Sensory Evaluation Scoring Table

[0030] Table 2 shows the sensory quality scoring record, and Table 3 shows the corresponding sensory evaluation. The evaluation included five dimensions: acidity, aroma, powder form, richness, and aftertaste. Higher scores for each dimension indicate better sensory performance. Blank pure coffee sample: Total score 54.50, with the aftertaste and texture branches achieving the highest scores, indicating that pure coffee maintains a good aftertaste. Starfruit-based post-biotic blended coffee (β-10%): The sample has a prominent flavor, but its richness is lower than pure coffee, and the aftertaste is moderate. Starfruit-based post-biotic blended coffee (maltodextrin-20%): It has the best mouthfeel and body, with similar scores for powder form and richness. Overall comparison results: The overall drinking quality of pure coffee is inferior to the two samples with added starfruit post-biotics; the sensory differences between the two starfruit-modified samples with 20% maltodextrin and 10% β-cyclodextrin are slight. Based on the data analysis results of powder moisture and solubility mentioned above, and combined with the conclusions of this sensory evaluation, Yangtao-based post-natal coffee (Mai-20%) was finally selected for subsequent physicochemical parameter testing experiments.

[0031] Table 3 Comparison of Coffee Flavors

[0032] Example 4: Analysis of Starfruit-Based Post-Activated Coffee Starfruit-based post-generic coffee (Mc-20%, M20%-Coca) was prepared according to the method in Example 3, and coffee prepared from pure coffee powder was used as a control for subsequent analysis.

[0033] This experiment used the 3,5-dinitrosalicylic acid colorimetric method to determine the reducing sugar content in brewed coffee samples, such as... Figure 1 As shown in Figure A, this method can specifically quantify reducing monosaccharides and oligosaccharides within a system, directly reflecting the level of sugars in the sample that can directly participate in the Maillard reaction and provide a sweet flavor. The bar chart data shows that the reducing sugar content in the pure coffee group was approximately 23 mg / mL, while the reducing sugar content in the 20% maltodextrin-starfruit-based post-generic coffee (M20%-Coca) group was close to 38 mg / mL. The reducing sugar content in the experimental groups was significantly higher, and the difference between the two groups was extremely significant (P < 0.001). The addition of a post-generic compound containing starfruit fermentation matrix and maltodextrin significantly increased the accumulation of reducing sugars in the system. On the one hand, this enhances the mellow natural sweetness of coffee and reduces the dependence on added white sugar in the finished product. On the other hand, the higher concentration of reducing sugars allows for a full Maillard reaction during roasting and hot brewing, enriching the caramel and nutty flavor compounds in the coffee and optimizing the overall aroma profile of the beverage.

[0034] Use a pH meter to measure the pH value of coffee, such as Figure 1 As shown in Figure B, pH is a key physicochemical indicator affecting the balance of coffee's flavor, the stability of polyphenols, and its compatibility with intestinal digestion. Both groups of samples were in the slightly acidic range, consistent with the inherent acidity characteristics of coffee beverages. The pure coffee group had a pH of 5.29, while the 20% maltodextrin-starfruit-based post-biotic coffee group had a pH of approximately 5.22. The experimental group showed a slight decrease in pH, and the difference between the two groups was statistically significant (P < 0.001). The post-biotic base of starfruit fermentation contains organic acids, which slightly lower the pH of the system. Although the magnitude of the change was small to the naked eye, the statistical distinction was significant. A moderately low acidic environment can stabilize the antioxidant polyphenol components in coffee, while the slight fruit acidity can neutralize the bitterness of coffee, improve the smoothness of the mouthfeel, and prevent drastic changes in acidity from damaging the original flavor base of the coffee.

[0035] ABTS determination method: ABTS powder and K2S2O8 were dissolved in purified water at a volume ratio of 1:1 and mixed thoroughly. The mixture was then allowed to stand at room temperature for 16 hours in the dark. Subsequently, the mixture was diluted with purified water until the absorbance at 734 nm reached 0.70 ± 0.02, thus obtaining the ABTS stock solution. For measurement, 0.3 mL of the sample solution was taken, and 2 mL of the ABTS stock solution was added. After thorough mixing, the mixture was reacted at room temperature in the dark for 30 minutes, and then the absorbance was measured at 734 nm. The ABTS free radical scavenging rate was calculated using the following formula. The results showed that the ABTS value of starfruit-based post-biotic coffee was higher than that of ordinary coffee. This indicates that the antioxidant activity of coffee was enhanced after the starfruit-based post-biotic compounding treatment. The introduction of starfruit-based post-biotics not only did not weaken the antioxidant properties of coffee but also significantly improved its ABTS free radical scavenging ability, giving the product stronger functional attributes and having positive significance in the development of health-oriented coffee products.

[0036] This experiment used the sulfuric acid-phenol method to determine the total sugar content of coffee samples, such as... Figure 1 As shown in Figure C. The sulfuric acid-phenol method can detect all carbohydrates in the sample, including reducing sugars and non-reducing polysaccharides and oligosaccharides, fully reflecting the total carbohydrate content of the beverage. The column results show that the total sugar content of the pure coffee group was only 0.5 mg / mL, while the total sugar content of the 20% maltodextrin-starfruit-based post-biotic coffee (M20%-Coca) group reached 2.2 mg / mL. The total sugar content of the experimental group was approximately 4.4 times that of the control group. The difference between the two groups was statistically significant (P < 0.001). Maltodextrin and starfruit endogenous polysaccharides together significantly increased the total sugar level of the system. Sufficient carbohydrates can continuously release a mellow sweetness, improve the sharp bitterness of black coffee, and provide sufficient substrates for the Maillard reaction in the coffee system, giving the product a richer roasted sweet aroma. At the same time, the polysaccharide post-biotic matrix can act as a prebiotic, regulating the intestinal flora. Based on optimizing sensory flavor, this further enhances the functional value of coffee, making it suitable for the development of new coffee products that combine flavor and health benefits.

[0037] Electronic tongue analysis of coffee. Figure 2This is an electronic tongue radar map, which includes seven taste response dimensions: AHS, PKS, CTS, NMS, CPS, ANS, and SCS. AHS: Acidity sensor, detects acidity; PKS: Bitterness sensor, detects bitterness; CTS: Saltiness sensor, detects saltiness; NMS: Umami sensor, responds to umami substances; SCS: Bitterness sensor, specifically for bitterness detection; ANS: Sweetness sensor, detects sweetness; CPS: General sensor, used to synthesize taste information. Comparing pure coffee and M20%-Coca, M20%-Coca showed significantly higher response values ​​in AHS, CPS, NMS, and ANS dimensions, indicating more prominent aroma, sweetness, body, and fruity characteristics. Coffee, on the other hand, had higher values ​​in SCS and PKS, indicating a stronger bitter and burnt flavor in pure coffee. The significant differences in the response profiles of the two groups across each taste dimension demonstrate that the post-modification of coffee with starfruit extract has significantly altered its taste characteristics.

[0038] Using metabolomics analysis, such as Figure 3 As shown in Figure A, this volcano plot presents the differential metabolite analysis results between pure coffee (Coffee) and starfruit-based post-biotic coffee (Cca). The horizontal axis, Log2FC, represents the fold change in metabolites, and the vertical axis reflects the significance of the difference. The size of the dots corresponds to the VIP value; the larger the VIP, the higher the contribution of the substance to distinguishing the two groups of samples. In the figure, there are 295 red dots, representing metabolites that are significantly upregulated in starfruit-based post-biotic coffee; 192 blue dots, representing metabolites that are significantly downregulated; and 2478 gray dots, representing metabolites with no significant difference. Overall, a total of 2965 metabolites were detected in the two groups of samples, of which only 487 showed significant differences. The majority of metabolites showed no significant difference, indicating that the basic metabolic composition of the two groups is highly similar. Furthermore, the number of significantly upregulated metabolites in the post-biotic coffee group is greater than that of downregulated metabolites, indicating that the addition of starfruit-based post-biotics leads to the enrichment of more small metabolic molecules, while the content of some original coffee characteristic metabolites is significantly reduced.

[0039] like Figure 3 In Figure B, PC1 and PC2 in this PCA diagram explain 57.10% and 16.20% of the total metabolite variation, respectively. The model has R=1 and P=0.001, showing significant differentiation. Pure coffee samples are concentrated in the area to the right of PC1, while M20%-Coca starfruit-based post-biotic coffee samples are clustered in the lower left of the origin. The two groups of samples are far apart in space and do not overlap, indicating that there is a significant difference in the overall metabolite composition between the two groups. The metabolic profile of coffee changed significantly after the addition of starfruit-based post-biotic.

[0040] Figure 3The cluster heatmap comparison between pure coffee (Coffee) and M20%-Coca starfruit-based post-fermented coffee shows that polyphenolic metabolites such as chlorogenic acid, erythritol, and 4-O-caffeoylquinic acid are highly abundant (red) in the Coffee group, but significantly reduced and appear blue in the M20%-Coca group. Conversely, sugars and sugar alcohols such as L-sorbose, D-glucose, D-mannose, sucrose, mannitol, and L-glucan are significantly enriched and more abundant in the M20%-Coca group. The abundance of various characteristic metabolites in the two groups shows completely opposite trends, directly reflecting that starfruit-based post-fermented fermentation treatment significantly alters the metabolic accumulation levels of organic acids, polyphenols, and carbohydrates in coffee. Coffee made with starfruit-based post-fermented fermentation exhibits a clear distinction from conventional coffee in terms of aroma intensity, sweet flavor, and full-bodied taste, creating an innovative coffee beverage with a unique sensory profile, blending the refreshing fruity aroma of starfruit with a sweet and full-bodied texture.

[0041] like Figure 4 The VIP plot shows the differential metabolites between pure coffee (Coffee) and starfruit-based post-biotic coffee (Cca). The horizontal axis represents the VIP value. All metabolites in the plot have a VIP value greater than 1, which are key differential markers that can distinguish between the two groups. In the legend, black dots represent substances that are upregulated and enriched in pure coffee, and gray dots represent substances that are upregulated and enriched in starfruit-based post-biotic coffee. Combined with the abundance scale bar on the right, it can be seen that, except for L-sorbose which is significantly increased only in starfruit-based post-biotic coffee, the abundance of the other 17 differential metabolites, such as chlorogenic acid, 4-O-caffeoylquinic acid, 3-O-feruloylquinic acid, malic acid, and nicotinic acid, is higher in pure coffee. This indicates that after adding starfruit-based post-biotic, the content of most of the original characteristic metabolites in the coffee system decreased significantly, and only L-sorbose was significantly increased due to the fermentation of starfruit matrix. The metabolic profiles of the two types of samples are clearly distinguishable.

[0042] Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Anyone skilled in the art can make various modifications and alterations without departing from the spirit and scope of the present invention. Therefore, the scope of protection of the present invention should be determined by the claims.

Claims

1. A method for preparing starfruit-based post-biotic coffee, characterized in that, Lactobacillus plantarum HNU531 was inoculated into star fruit juice for fermentation. The fermentation product was dried and then mixed with coffee powder. The preservation number of Lactobacillus plantarum HNU531 is GDMCC No: 67494.

2. The application according to claim 1, characterized in that, The amount of *Lactobacillus plantarum* HNU531 inoculated into the star fruit juice is at least 10. 9 CFU / mL.

3. The application according to claim 2, characterized in that, The fermentation conditions are 37°C for 18-36 hours.

4. The application according to claim 3, characterized in that, After fermentation, the fermentation product is inactivated and a drying aid is added; the drying aid includes β-cyclodextrin or maltodextrin; the amount of the drying aid added is 10%~40% w / w of the fermentation product.

5. The application according to claim 4, characterized in that, The drying process includes freeze drying.

6. The application according to claim 5, characterized in that, The dried fermentation products are mixed with coffee powder at a mass ratio of 5% to 20%.

7. Starfruit-based post-biotic coffee prepared by any one of the methods described in claims 1 to 6.

8. Lactobacillus plantarum ( Lactiplantibacillus plantarum The application of HNU531 in the preparation of starfruit-based post-biotic coffee is characterized by, The preservation number of the Lactobacillus plantarum HNU531 is: GDMCC 67494.

9. Lactobacillus plantarum ( Lactiplantibacillus plantarum Application of HNU531 in improving coffee flavor.

10. The application according to claim 9, characterized in that, The improvement of coffee flavor refers to reducing bitterness and increasing umami, acidity, and sweetness.

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