Method for improving quality of xuanwei ham and application thereof

Abstract

This invention discloses a method for improving the quality of Xuanwei ham and its application, belonging to the field of food processing. The Xuanwei ham prepared by this invention through a combination of staged salting and phased temperature and humidity fermentation with mixed fermentation of two Penicillium species, *Penicillium Rubens* W10-1 and *Penicillium fusiforme* V8, effectively increases the ham's moisture content and water activity, improves its color brightness and redness, significantly reduces lipid oxidation, alters the composition of volatile flavor compounds, enhances characteristic flavors such as fruit, wine, and cream aromas, and inhibits the accumulation of undesirable compounds.

Description

Technical Field

[0001] This invention relates to a method for improving the quality of Xuanwei ham and its application, belonging to the field of food processing. Background Technology

[0002] The flavor development of traditional ham products is a highly complex process closely related to geographical environment and processing techniques. Taking Xuanwei ham, one of the representatives of traditional Chinese dry-cured hams, as an example, its unique flavor is mainly formed by the synergistic effects of multiple factors during fermentation, including the microbial community structure (including lactic acid bacteria, staphylococci, yeast, and molds), fat degradation, and amino acid transformation. Studies have shown that during the post-ripening stage of Xuanwei ham, the dynamic changes in microbial community structure, free amino acid composition, and volatile flavor compounds are key factors determining its flavor characteristics. Furthermore, Xuanwei ham and other traditional ham products are rich in various bioactive peptides with potential physiological functions such as antioxidation, further enhancing their nutritional and functional value.

[0003] However, with changes in the production environment and diversification of consumer demand, regional specialty meat products such as Xuanwei ham face certain challenges in terms of quality stability and industrialized production. Currently, the commonly used microbial fermentation agents in ham fermentation are mainly lactic acid bacteria and yeast, but they still have certain limitations in flavor development. Lactic acid bacteria primarily metabolize lactic acid, producing a relatively limited variety of flavor compounds, and their protein and fat decomposition capabilities are limited, making it difficult to fully impart complex and rich flavor characteristics to ham. Similarly, yeast primarily metabolizes carbohydrates, with weak protein and fat degradation capabilities, making it difficult to meet the needs of dry-cured ham for deep flavor development when used alone.

[0004] Molds play a crucial role in the traditional dry-curing and fermentation of meat products. Compared to lactic acid bacteria and yeasts, they possess a stronger ability to hydrolyze proteins and fats. They can promote the formation of flavor precursors by secreting various extracellular enzymes and generate volatile compounds such as alcohols, esters, and aldehydes, which significantly contribute to the aroma of ham. Furthermore, the microbial film formed by molds on the surface of meat products not only helps regulate the surface microbial community structure but also slows down excessive moisture loss and inhibits the growth of harmful microorganisms, thereby improving the overall quality of the ham.

[0005] However, actual research has revealed that even with the inoculation of superior mold starter cultures, the overall quality of Xuanwei ham still has room for improvement. This is mainly manifested in less than ideal product texture and flavor, as well as fluctuations in flavor stability and harmony. The quality of Xuanwei ham is the result of the synergistic effect of multiple factors; relying solely on starter cultures cannot comprehensively address all quality shortcomings.

[0006] Therefore, how to further optimize the processing technology based on the inoculation of excellent mold starter culture to systematically improve the texture characteristics and flavor stability of Xuanwei ham and achieve synergistic enhancement of the overall product quality is a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0007] To address the aforementioned problems, this invention provides a method for improving the quality of Xuanwei ham and its application. This invention uses a 1:1 volume ratio mixture of two Penicillium fungi, *Penicillium Rubens* W10-1 and *Penicillium fumonis* V8, as a starter culture. Combined with an optimized multi-stage salting and phased temperature and humidity fermentation process, this method systematically enhances the moisture retention, color quality, and antioxidant properties of Xuanwei ham, and significantly optimizes its volatile flavor composition (enhancing beneficial flavors, suppressing undesirable flavors, and generating unique flavors). Ultimately, the resulting Xuanwei ham exhibits significantly superior sensory quality and overall acceptability compared to naturally fermented or single-strain fermented ham.

[0008] The first objective of this invention is to provide a method for preparing Xuanwei ham, comprising the steps of: (1) Salt the pre-treated fresh ham for 40-45 days to obtain cured ham; (2) After the ham is cured, it is washed and air-dried to obtain air-dried ham; the air-dried ham is placed in a temperature of 10~15℃ and a relative humidity of 55~65% for 60~90 days to obtain ham in the early stage of fermentation; the ham in the early stage of fermentation is placed in a temperature of 25~30℃ and a relative humidity of 70~80% for 100~120 days to obtain ham in the middle stage of fermentation; the ham in the middle stage of fermentation is coated with a mixture of fermentation agent and bacterial solution at a coating amount of 1~3 wt% of the ham weight and then fermented at a temperature of 10~20℃ and a relative humidity of 60%~70% for 120~150 days to obtain mature Xuanwei ham; In step (1), the total amount of salt applied is 5-15 wt% of the weight of the fresh leg. The salting is done in four stages, with the mass ratio between the first, second, third, and fourth salting applications being 15-20:15-20:6-10:4-6. The first salting is repeated for 5-8 days, followed by the second salting. The second salting is done 12-15 days after the second salting, and the third salting is done 7-15 days after the third salting. The fermentation agent mixture in step (2) is composed of a concentration of 10... 6 cfu / mL ~10 7 cfu / mL of Bensminoides ( Penicillium rubens W10-1 fermentation inoculum and Penicillium thuringiensis ( Penicillium fuscoglaucum V8 starter culture was prepared by mixing the cultures at a volume ratio of 1~2:1~2. The Penicillium ( Penicillium rubensW10-1 was deposited at the China Center for Type Culture Collection on August 11, 2023, with accession number CCTCC NO: M 20231436; The brown algae (Penicillium) Penicillium fuscoglaucum V8 was deposited at the China Center for Type Culture Collection on August 11, 2023, with accession number CCTCC NO: M20231437.

[0009] In one embodiment, the salting process in step (1) is carried out at a temperature of 4~8℃ and a humidity of 80%~90%.

[0010] In one embodiment, the pretreatment in step (1) involves removing the loose connective tissue, cutting off excess fat and skin from both sides of the qualified hind leg meat after aging at 4-6°C for 10-12 hours to obtain the pretreated fresh leg.

[0011] In one embodiment, the fermentation agent liquid in step (2) is obtained by inoculating the activated W10-1 and V8 surface spores into the culture medium, culturing at 27℃~29℃ and 140~160 rpm for 3~4 days, and centrifuging to obtain the fermentation agent liquid.

[0012] A second objective of this invention is to provide Xuanwei ham prepared by any of the methods described above.

[0013] The third objective of this invention is to provide a method for increasing the moisture content, volatile aldehyde content, and reducing lipid oxidation in Xuanwei ham, comprising the following steps: (1) Salt the pre-treated fresh ham for 40-45 days to obtain cured ham; (2) After the ham is cured, it is washed and air-dried to obtain air-dried ham; the air-dried ham is fermented for 60 to 90 days at a temperature of 10 to 15℃ and a relative humidity of 55 to 65% to obtain ham in the early stage of fermentation; the ham in the early stage of fermentation is fermented for 100 to 120 days at a temperature of 25 to 30℃ and a relative humidity of 70 to 80% to obtain ham in the middle stage of fermentation; the ham in the middle stage of fermentation is coated with a mixture of fermentation agent and bacterial solution at a coating amount of 1 to 3 wt% of the ham weight and then fermented for 120 to 150 days at a temperature of 10 to 20℃ and a relative humidity of 60% to 70% to obtain mature Xuanwei ham with high moisture content, high content of volatile aldehyde flavor compounds and low degree of lipid oxidation. In step (1), the total amount of salt applied is 5-15 wt% of the weight of the fresh leg. The salting is done in four stages, with the mass ratio between the first, second, third, and fourth salting applications being 15-20:15-20:6-10:4-6. The first salting is repeated for 5-8 days, followed by the second salting. The second salting is done 12-15 days after the second salting, and the third salting is done 7-15 days after the third salting. The fermentation agent mixture in step (2) is composed of a concentration of 10... 6 cfu / mL ~10 7 cfu / mL of Bensminoides ( Penicillium rubens W10-1 fermentation inoculum and Penicillium thuringiensis ( Penicillium fuscoglaucum V8 starter culture was prepared by mixing the cultures at a volume ratio of 1~2:1~2. The Penicillium ( Penicillium rubens W10-1 was deposited at the China Center for Type Culture Collection on August 11, 2023, with accession number CCTCC NO: M 20231436; The brown algae (Penicillium) Penicillium fuscoglaucum V8 was deposited at the China Center for Type Culture Collection on August 11, 2023, with accession number CCTCC NO: M20231437.

[0014] In one embodiment, the salting process in step (1) is carried out at a temperature of 4-8°C and a humidity of 80-90%.

[0015] In one embodiment, the pretreatment in step (1) involves removing the loose connective tissue and cutting off the excess fat and skin on both sides of the qualified hind leg meat after aging at 4-8°C for 10-12 hours to obtain the pretreated fresh leg.

[0016] In one embodiment, the fermentation agent liquid in step (2) is obtained by inoculating the activated W10-1 and V8 surface spores into the culture medium, culturing at 27~29℃ and 140~160 rpm for 3~4 days, and centrifuging.

[0017] The four objectives of this invention are to provide the application of any of the above-described methods in the preparation of Xuanwei ham.

[0018] Beneficial effects This invention relates to Xuanwei ham prepared through a combination of staged salting and temperature-humidity fermentation with mixed fermentation of two Penicillium species, *Penicillium Rubens* W10-1 and *Penicillium fumonis* V8. This process effectively increases the ham's moisture content and water activity, improves its color brightness and redness, significantly reduces lipid oxidation, alters the composition of volatile flavor compounds, enhances characteristic flavors such as fruit, wine, and cream aromas, and inhibits the accumulation of undesirable compounds. Ultimately, the resulting Xuanwei ham exhibits significantly superior sensory quality and overall acceptability compared to naturally fermented or single-strain fermented hams. Specifically: The Xuanwei ham prepared by this invention has a moisture content of 49.96%, significantly higher than the 42.68% of the natural group; meanwhile, its TBARS value (malondialdehyde content) is only 0.376 mg·kg. -1 It was significantly lower than the 0.443 mg·kg⁻¹ in the naturally fermented group. -1 .

[0019] Regarding flavor compounds, the total aldehyde content of Xuanwei ham prepared by this invention can reach 141.31 μg·kg. -1 The key component that imparts the fruity aroma, isovaleraldehyde, contains up to 23.94 μg·kg. -1 In addition, it can effectively reduce the content of compounds with pungent odors, such as 3-methyl-2-pentanone, thereby ensuring the purity of the ham flavor. Attached Figure Description

[0020] Figure 1 Determination of moisture content in Xuanwei ham from different fermentation groups; Figure 2 Determination of water activity of Xuanwei ham in different fermentation groups; Figure 3 TBARS determination for Xuanwei ham from different fermentation groups; Figure 4 To determine the content of volatile compounds in Xuanwei ham from different fermentation groups; Figure 5 Radar images of electronic noses for Xuanwei ham from different fermentation groups; Figure 6 PCA diagrams of electronic noses for Xuanwei ham from different fermentation groups. Detailed Implementation

[0021] The present invention will be further described below with reference to the accompanying drawings and specific embodiments. These embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Experimental methods in the following embodiments, where specific conditions are not specified, are generally performed under conventional conditions in the art. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those familiar with the art.

[0022] Raw material source: The fresh pork hind leg was purchased from Xuanwei Farmers Market.

[0023] Culture media involved in the examples: The formula for PDA medium is 300 g potato (from which extract powder is obtained), 20 g glucose, 15 g agar, and 0.1 g chloramphenicol.

[0024] The formula for PDB medium is 300 g potato (from which extract powder is obtained), 20 g glucose, and 15 g agar.

[0025] The strains involved in the examples are: A strain of Penicillium Rubens ( Penicillium rubens W10-1, taxonomically named Penicillium Rubens W10-1 Penicillium rubens W10-1 was deposited on August 11, 2023, at the China Center for Type Culture Collection (CCTCC) with accession number CCTCC NO: M 20231436 and address at Wuhan University, Wuhan, China; it has been published in patent CN117343846 A.

[0026] A strain of brown algae Penicillium ( Penicillium fuscoglaucum V8, taxonomically named Penicillium fumonis V8 Penicillium fuscoglaucum V8 was deposited on August 11, 2023, at the China Center for Type Culture Collection (CCTCC) with accession number CCTCC NO: M 20231437, located at Wuhan University, Wuhan, China; and has been published in patent CN117343846 A.

[0027] Measurements involved in the examples: 1. Determination of moisture content Based on the method of GB5009.3-2016, the moisture content of each group of samples was determined. Each group of samples was measured in parallel 6 times, and the average value was taken.

[0028] 2. Determination of water activity Place the minced meat sample (3 g) into a water activity meter, ensuring it completely covers the bottom of the chamber, and record the Aw value of the sample. Perform the experiment in 6 parallel trials and take the average value.

[0029] 3. Color Measurement The sample was sliced, and its luminance (L*), redness (a*), and yellowness (b*) were measured using a colorimeter. The colorimeter was calibrated using a standard white plate. After calibration, the measurements at different points on each sample were repeated 6 times, and the average values ​​were taken for statistical analysis.

[0030] 4. Determination of thiobarbituric acid (TBARS) Take 2 g of minced meat, add 3 mL of 4,6-dihydroxy-2-mercaptopyrimidine solution and 17 mL of trichloroacetic acid solution, and heat in a boiling water bath for 30 min. After cooling to room temperature, take 4 mL of the supernatant, mix it thoroughly with an equal volume of chloroform, and incubate at 4℃ and 3000 r·min. -1 Centrifuge for 10 min. Measure the absorbance of the supernatant at 532 nm and correct with chloroform. TBARS is expressed as milligrams of malondialdehyde per kilogram of lipid oxidation sample. The calculation formula is shown in the formula below: TBARS = (A 532 / m)×9.48 In the formula: A 532 The absorbance of the supernatant at 532 nm; m is the mass of the sample, in grams; 5. Determination of volatile flavor compounds Volatile compounds in Xuanwei ham were detected by GC-MS, and the content of volatile flavor compounds in Xuanwei ham was quantified by internal standard method. 3 g of well-mixed Xuanwei ham sample was placed in a 20 mL headspace vial, and 1 μL of a 100 mg·L⁻¹ solution was added. -1 After adding 1,2-dichlorobenzene solution (internal standard), seal the vial. Equilibrate at 45°C for 10 min. Insert the DVB / CAR / PDMS extraction head into the headspace vial at a distance of 1 cm from the sample, extract at 45°C for 30 min, and then desorb in a gas chromatograph-mass spectrometer for 5 min.

[0031] GC conditions: DB-WAX column (30 m × 0.25 mm × 0.25 μm), He carrier gas, flow rate 1.5 mL·min -1 No splitting; heating program: initial temperature 40 ℃, hold for 3 min; 5 ℃·min -1 Heat to 90 °C, then at a rate of 10 °C·min. -1 The temperature was increased to 230 °C at a rate of 100 °C and held for 7 min; the vaporization chamber temperature was 230 °C.

[0032] MS conditions: electron ionization source, electron energy 70 eV, filament emission current 200 μA, ion source temperature 200 °C, interface temperature 230 °C, detector voltage 1000 V, scan mass range 40–400 amu. Volatile compounds were identified using the NIST 2011 library combined with retention index search analysis. Odor activity value (OAV) was calculated as shown in the formula: OAV = V / T; In the formula: C is the concentration of volatile compounds, in μg·kg⁻¹. -1 ; T is the odor threshold of volatile compounds, expressed in mg·kg⁻¹. -1 .

[0033] 6. Measurement of electronic nose Place 3 g of sample in a glass bottle and heat in a 45°C water bath for 30 min. The equipment cleaning time before testing is 120 s, and the cleaning time after testing is 1800 s. For a single test, the testing time is 120 s, the cleaning time is 120 s, and the temperature is maintained at 1 L·min throughout. -1 The airflow rate was measured. Six replicates were set up for each sample group, and the average value was recorded.

[0034] 7. Sensory evaluation Sensory evaluations were conducted on Xuanwei hams processed in different ways. A sensory evaluation panel of 15 experienced personnel was selected. The five-point pleasure method was used to quantify and score the sensory characteristics of the samples (such as color, texture, taste, aroma, and overall acceptability). The scoring criteria are shown in Table 1.

[0035] Table 1 Sensory rating criteria

[0036] Example 1: A method for improving the quality of Xuanwei ham A method for improving the quality of Xuanwei ham, the steps of which are as follows: 1. Preparation of fermentation broth Remove Rubens from the -80°C freezer. Penicillium rubens W10-1 and Penicillium chrysogenum ( Penicillium fuscoglaucum V8 mold strains were thawed at 4°C to a liquid state, spread onto PDA solid medium, and subcultured three times for activation.

[0037] The activated surface spores were then inoculated into PDB liquid medium and cultured in a 29°C shaker at 150 rpm for 72 h. After liquid culture, the spores were centrifuged at 4°C at 6000 rpm for 5 min to obtain 10% concentration spores. 6 W10-1 and V8 starter cultures with cfu / mL.

[0038] 2. Preparation of Xuanwei Ham (1) Pretreatment of pork hind leg After the qualified pork hind leg meat is cooled and deacidified in a well-ventilated environment at 4℃ for 10 hours, the loose connective tissue on the meat is trimmed with a knife, and the excess fat and leg skin on both sides are removed to obtain the pre-treated fresh leg.

[0039] (2) Pickling The fresh ham is salted and cured with salt at 11 wt% of its weight in four batches, from bottom to top and from the skin to the meat. The salt is then evenly applied and rubbed onto the hind leg meat in each batch. The ham is cured for 45 days at a temperature of 4°C and a relative humidity of 80% to obtain the cured ham.

[0040] The first and second salting amounts were 36% of the total salt, the third salting amount was 18% of the total salt, and the fourth salting amount was 10% of the total salt. The second salting was carried out 7 days after the first salting. The third salting was carried out 12 days after the second salting. The fourth salting was carried out 15 days after the third salting.

[0041] (3) Fermentation After cleaning the surface of the cured ham to remove salt and dirt, hang it in a drying room to air dry. Then, place the air-dried ham in a fermentation room at 10℃ and 55% relative humidity for 60 days to obtain pre-fermentation ham. Ham in the early stage of fermentation was placed in a fermentation room at a temperature of 25℃ and a relative humidity of 70% for 100 days to obtain ham in the middle stage of fermentation. During the mid-fermentation stage, the fermentation agent mixture was applied to the ham at a rate of 1 wt% of the ham weight and fermented in a fermentation room at 10°C and 60% relative humidity for 120 days to obtain Xuanwei ham of the V8+W10-1 fermentation group. The starter culture mixture was prepared by mixing W10-1 and V8 starter cultures in a 1:1 volume ratio, with both W10-1 and V8 starter cultures having a concentration of 10. 6 cfu / mL.

[0042] Comparative Example 1: Only W10-1 fermentation agent solution was applied. The specific implementation method is the same as in Example 1, except that when applying the fermentation agent liquid, only the W10-1 fermentation agent liquid is applied, the amount of application remains unchanged, and the other steps remain the same, so as to prepare Xuanwei ham of the W10-1 fermentation group.

[0043] Comparative Example 2: Apply only V8 starter culture solution The specific implementation method is the same as in Example 1, except that when applying the fermentation agent liquid, only the V8 fermentation agent liquid is applied, the amount of application remains unchanged, and the other steps are kept the same, so as to prepare the V8 fermented Xuanwei ham.

[0044] Comparative Example 3: Natural Fermentation The specific implementation method is the same as in Example 1, except that no fermentation agent liquid is applied during the fermentation process, while the other steps remain the same, and Xuanwei ham with natural fermentation is obtained.

[0045] Example 2: Performance determination of Xuanwei ham from different fermentation groups The performance of Xuanwei hams prepared in different fermentation groups as described in Example 1 and Comparative Examples 1-3 was measured.

[0046] 1. Moisture content determination The moisture content of Xuanwei ham from different fermentation groups was determined as follows: Figure 1 As shown in the figure. The results showed that the moisture content of all mold inoculation groups was significantly higher than that of the natural fermentation group (P < 0.05). Among them, the V8+W10-1 mixed fermentation group had the highest moisture content, reaching 49.96%, which was significantly better than the V8 group and the W10-1 single-strain fermentation group, while the natural fermentation group had only 42.68%. In the traditional dry-cured ham processing, due to the high initial moisture content, coupled with the penetration of salt and air drying during the curing process, the moisture will gradually be lost as the fermentation time increases.

[0047] This is because after inoculation with the mold starter culture, especially in the V8+W10-1 mixed fermentation group, the mold grows on the surface of the ham and forms a dense and uniform mycelial protective layer, effectively inhibiting excessive moisture evaporation. Compared with the naturally fermented group, the V8+W10-1 group has the slowest rate of moisture loss, and therefore its moisture content is significantly higher than that of the other groups, demonstrating the best moisture retention capacity.

[0048] 2. Water activity determination The water activity determination results of Xuanwei ham from different fermentation groups are as follows: Figure 2 As shown, the results indicate that the water activity of the naturally fermented group was 0.740, while the water activities of different fermentation groups ranged from 0.745 to 0.770. This is basically consistent with the water activity range of traditional Chinese dry-cured ham. The water activity of Xuanwei ham inoculated with mold was higher than that of naturally fermented ham, especially the W10-1 fermentation group and the V8+W10-1 fermentation group, which were significantly higher than those of the naturally fermented group. This is because after inoculation with mold starter in the later stage of fermentation, a dominant microbial community quickly forms and a dense mycelial layer, thus forming a dense physical barrier. This barrier regulates the water exchange between the internal and external environments of the ham to a certain extent, and may even slow down excessive water evaporation at certain stages. In contrast, naturally fermented ham, due to the randomness of microorganisms, cannot form a dense mycelial layer in a short period of time. Therefore, the water inside the ham may be more easily lost due to the influence of the external environment.

[0049] 3. Color determination The color measurement results of Xuanwei ham from different fermentation groups are shown in Table 2. The results show that the brightness of Xuanwei ham prepared by mold fermentation is significantly higher than that of the naturally fermented group. Among them, the Xuanwei ham prepared by the V8+W10-1 fermentation group has the highest L* value of 32.81, while the Xuanwei ham prepared by the naturally fermented group is only 29.21. This is because mold produces abundant extracellular enzymes, especially proteases and lipases, during the fermentation process. These enzymes participate in the color and flavor generation process of the ham, thereby improving the brightness of the ham.

[0050] Table 2. Color determination of Xuanwei ham

[0051] 4. Determination of TBARS value The determination of TBARS values ​​of Xuanwei ham in different fermentation groups is as follows: Figure 3 As shown, the results indicate that the malondialdehyde content in the V8+W10-1 fermentation group was 0.376 mg·kg⁻¹. -1 The concentration was significantly lower than that of the naturally fermented group (0.443 mg·kg⁻¹). -1 The values ​​for the V8 fermentation group were 0.398 and for the W10-1 fermentation group were 0.393 mg·kg⁻¹. -1 The lipid oxidation level was slightly lower than that of the naturally fermented group, indicating that the mold has the potential to produce antioxidant compounds. The V8+W10-1 fermentation group produced Xuanwei ham with a lower degree of lipid oxidation.

[0052] 5. Analysis of flavor compounds The types and contents of volatile compounds in Xuanwei ham from different fermentation groups are as follows: Figure 4 As shown in Table 3, a total of 43 volatile compounds were detected in the naturally fermented ham. These included 6 aldehydes, 6 esters, 2 ketones, 3 aromatic compounds, 2 furans, 4 alkanes, and 1 other type. The volatile compounds detected in the ham from different fermentation groups are as follows: 37 in the V8 fermentation group, 45 in the W10-1 fermentation group, and 37 in the V8+W10-1 fermentation group. The W10-1+V8 fermentation group contained 7 aldehydes, 2 alcohols, 8 esters, 2 ketones, 1 furan, 3 pyrazines, 1 alkanes, and 1 olefin.

[0053] Table 4 shows the volatile compounds with OAV>1 in different fermentation groups of Xuanwei ham. The results indicate that 13 compounds were identified as the main flavor compounds during the fermentation process of Xuanwei ham. Among these 13 compounds, there were 6 aldehydes (2-methylbutyraldehyde, nonanal, n-octanal, isovaleraldehyde, 3-methyl-1-pentanal, and butyraldehyde) and 7 esters (methyl 2-methylbutyrate, methyl isovalerate, ethyl hexanoate, ethyl 2-methylbutyrate, methyl isovalerate, and ethyl isovalerate). These substances are likely the main factors influencing the flavor formation of ham, and the differences in their content led to variations in the sensory characteristics among the ham samples.

[0054] Aldehydes, as key flavor compounds in Xuanwei ham, primarily impart fruity and other characteristic flavors to the product, playing a crucial role in constructing the ham's flavor profile. The total aldehyde content detection results showed that the total aldehyde content in the V8+W10-1 fermentation group was 141.31 μg·kg⁻¹. -1 It was significantly higher than the 120.67 μg·kg⁻¹ in the naturally fermented group. -1 Isovaleraldehyde is a significant contributor to fruity aroma, reaching a content of 23.94 μg·kg⁻¹ in the V8+W10-1 fermentation group. -1 It was significantly higher than the 12.52 μg·kg⁻¹ in the naturally fermented group. -1 This process enhances the fruity aroma of the product. Nonanal, with its oily and citrus aromas, is present in slightly higher concentrations in the V8+W10-1 fermentation group. The lipoxygenase activity of the strains promotes the targeted oxidation of unsaturated fatty acids, enhancing the overall oiliness of the ham. Compared to the relative fluctuations in the natural group, mixed fermentation is more conducive to flavor uniformity, avoiding off-flavors caused by insufficient or excessive oxidation. The mold inoculation group, especially the V8+W10-1 mixed fermentation group, can effectively increase the total amount of aldehydes in Xuanwei ham, achieving targeted regulation and optimized synthesis of characteristic aldehydes, and enriching the complexity of the ham's flavor.

[0055] Ketones are important substances that impart characteristic flavors such as creamy and fruity aromas to Xuanwei ham, and different mold fermentation groups show significant advantages in ketone regulation. Among them, 3-hydroxy-2-butanone was detected only in the V8+W10-1 fermentation group (2.15 μg·kg⁻¹). - ¹), while it was not detected in the naturally fermented group, indicating that mixed mold fermentation can promote the synthesis of specific ketones, enriching the flavor composition of ham. In addition, 3-methyl-2-pentanone has a pungent odor, and its content in the naturally fermented group was 6.33 μg·kg⁻¹. - ¹, significantly higher than the 0.70 μg·kg in the W10-1 group. - ¹, and it was not detected in either the V8 fermentation group or the V8+W10-1 fermentation group, indicating that mold inoculation can effectively inhibit the formation of this undesirable flavor substance and ensure the purity of the ham flavor.

[0056] Alcohols are the core flavor compounds that impart a wine-like aroma to Xuanwei ham, and the total alcohol content in the mold-fermented group was significantly higher than that in the naturally fermented group. Specifically, the total alcohol content in the W10-1 fermentation group was 11.82 μg·kg⁻¹. -1 The fermentation group V8+W10-1 had a yield of 10.74 μg·kg⁻¹. -1 Both were significantly higher than the 2.61 μg·kg⁻¹ of the naturally fermented group. -1 1-Penten-3-ol imparts a grassy aroma to ham; this substance was detected only in the V8+W10-1 mixed fermentation group at a concentration of 2.90 μg·kg⁻¹. -1 The substance was not detected in the naturally fermented group, indicating that mixed fermentation with mold is beneficial for synthesizing characteristic alcohols that cannot be produced by natural fermentation, adding an extra flavor dimension to the ham. It can enhance the mellowness of the product flavor by increasing the content of core alcohols, and can also synthesize other alcohols with better aromas to enrich the flavor layers. In contrast, the overall content of alcohols in the naturally fermented group was low, which could easily lead to a single flavor expression in the product. This further illustrates the optimizing effect of mold fermentation agent on the flavor of Xuanwei ham.

[0057] Esters are the core source of the fruity and ester aromas in Xuanwei ham, but excessive accumulation can lead to an oily and heavy taste, disrupting the flavor balance. The total ester content in the naturally fermented group was 164.59 μg·kg⁻¹. -1 The concentrations were significantly higher than those in the mold fermentation group (31.85–43.52 μg·kg⁻¹). -1 The contents of methyl 2-methylbutyrate and methyl isovalerate, two highly sweet-contributing esters, in the naturally fermented group were 46.93 μg·kg⁻¹. -1 and 78.63 μg·kg -1 The values ​​were significantly higher than those of the various mold fermentation groups (4.13~16.32 μg·kg⁻¹). -1 This indicates that mold fermentation can effectively inhibit excessive ester accumulation and avoid the defects of greasy flavor; regarding the methyl hexanoate content, the V8 single-strain inoculation group was 9.36 μg·kg. -1 Compared with the naturally fermented group (8.45 μg·kg⁻¹), -1 There was no significant difference, but the content was lower in the W10-1 fermentation group and the V8+W10-1 fermentation group (3.64~4.13 μg·kg). -1 This demonstrates the precise control that mold inoculation can exert on different esters; ethyl isovalerate, as a characteristic ester aroma compound, was only found in the V8 fermentation group (6.54 μg·kg⁻¹). -1 ) and V8+W10-1 fermentation group (12.56 μg·kg -1The presence of esters in the culture medium was detected, while it was not detected in the naturally fermented group, indicating that mold inoculation can directionally synthesize unique ester aroma components that cannot be produced by natural fermentation. In summary, the mold-inoculated group achieves optimized flavor balance in ham by reducing the total amount of esters, precisely controlling the content of characteristic esters, and synthesizing unique esters. In contrast, the excessive accumulation of esters in the naturally fermented group may not only lead to flavor imbalance but also affect the flavor stability of the product.

[0058] Pyrazines originate from the Maillard reaction and contribute roasted and nutty flavors. The total amount of pyrazines in the V8+W10-1 fermentation group was 13.91 μg·kg⁻¹. -1 The naturally fermented group had a yield of 8.20 μg·kg⁻¹. -1 This indicates that mold fermentation enhances the Maillard reaction, providing richer roasted aromas and flavor complexity, thus avoiding the lack of flavor found in the natural group.

[0059] Alkanes are mostly background compounds in the ham flavor system, contributing no significant flavor themselves; in fact, excessive presence can interfere with the expression of characteristic flavors. Total alkane analysis showed that the naturally fermented group had the highest total alkane content, at 32.70 μg·kg⁻¹. -1 The total alkane content in each mold fermentation group was significantly lower (1.00~16.77 μg·kg). -1 The advantage lies in the regulation of reducing the content of key alkanes: n-dodecane and undecane were present in higher amounts in the naturally fermented group, at 14.40 μg·kg⁻¹. -1 and 10.93 μg·kg -1 In all fermentation groups, the content of these two alkanes was significantly reduced or undetectable. This indicates that mold fermentation can effectively reduce the accumulation of alkanes that do not contribute to flavor, reduce their dilution and interference with characteristic flavors, and improve the purity of ham flavor, which is an advantage that natural fermentation cannot achieve.

[0060] Among other compounds, there were significant differences in the total amount among the groups: the V8 fermentation group had the highest total amount (35.49 μg·kg⁻¹). -1 The V8+W10-1 fermentation group did not detect it, and the levels were significantly lower than those in the natural fermentation group (15.18 μg·kg⁻¹). -1 The core advantage of the fermentation group lies in the reduction and control of impurity compounds: di-tert-butyl peroxide, a potentially harmful oxide, was present in the same quantity in the V8 fermentation group as in the natural fermentation group, while it was not detected in either the W10-1 or V8+W10-1 fermentation groups, indicating that mold fermentation can effectively reduce the accumulation of impurities such as oxides. In particular, the V8+W10-1 fermentation group completely eliminated these impurity compounds, significantly improving the purity of the ham flavor system and highlighting the synergistic advantages of mixed inoculation, which is unattainable by the natural fermentation group.

[0061] Compared with the natural fermentation group, different fermentation groups enhanced the production of beneficial flavor substances (such as aldehydes and alcohols), promoted the formation of complex aromas, reduced the accumulation of certain potentially undesirable compounds (such as alkanes), improved product stability, and increased the content of specific substances, ultimately improving the overall sensory quality. Among them, the V8+W10-1 fermentation group showed the most significant improvement in flavor.

[0062] Table 3. Volatile compounds of Xuanwei ham from different fermentation groups

[0063] Note: Different superscript letters in the same line indicate significant differences, and ND indicates not found.

[0064] Table 4. Volatile compounds of Xuanwei ham with OAV>1 in different starter cultures

[0065] 6. Electronic nose analysis of Xuanwei ham The electronic nose analysis results of Xuanwei ham prepared by fermentation of different fermentation groups are as follows: Figure 5 , Figure 6 As shown. Figure 5 The image shows electronic nose radar images of Xuanwei ham prepared by different fermentation groups. As can be seen from the image, there are significant differences in the aroma profiles between the natural fermentation group and the mold fermentation group. In particular, there are significant differences in the response values ​​of the sensors at S2, S6, S9, and S18, indicating significant differences in aldehydes, alcohols, and ketones. This is consistent with the GC-MS results, indicating that the addition of the starter culture effectively enhances the flavor of the ham.

[0066] Figure 6 PCA maps of Xuanwei ham were prepared using an electronic nose for fermentation of different fermentation groups. The results showed that PC1 contributed 64.7% and PC2 contributed 26.8%, accounting for a total of 91.5% of the system variance. The V8+W10-1 group was closer to sensors 2 (alcohols, aldehydes), 9 (aromatics), and 18 (ketones), effectively reflecting the changes in the overall odor characteristics of the ham. The naturally fermented group was located in the first and second quadrants, while the V8+W10-1 group was located in the third and fourth quadrants, indicating that the electronic nose can distinguish the samples.

[0067] 7. Sensory rating The sensory evaluation results of Xuanwei hams prepared by different fermentation groups are shown in Table 5. The results indicate that there are significant differences in the quality and overall acceptability of hams inoculated with different mold starter cultures (P<0.05). Hams inoculated with mold starter cultures are significantly better than those in the naturally fermented group in terms of color and texture. This is because Penicillium has a strong protein and fat decomposition ability, which is conducive to the formation of ham flavor. Combined with electronic nose analysis, it can be seen that compared with naturally fermented hams, the mold-fermented group has a brighter color, richer aroma, higher flavor richness, better coordination and integration of various attributes, and firmer meat texture, resulting in higher overall sensory acceptability. In particular, the ham inoculated with W10-1+V8 has higher eating quality and sensory acceptability.

[0068] Table 5 Sensory scores of Xuanwei ham from different fermentation groups

[0069] Note: Different superscript letters in the same row indicate significant differences (P<0.05). 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 Xuanwei ham, characterized in that, Including the following steps: (1) Salt the pre-treated fresh ham for 40-45 days to obtain cured ham; (2) After the ham is cured, it is washed and air-dried to obtain air-dried ham; the air-dried ham is placed in a temperature of 10~15℃ and a relative humidity of 55~65% for 60~90 days to obtain ham in the early stage of fermentation; the ham in the early stage of fermentation is placed in a temperature of 25~30℃ and a relative humidity of 70~80% for 100~120 days to obtain ham in the middle stage of fermentation; the ham in the middle stage of fermentation is coated with a mixture of fermentation agent and bacterial solution at a coating amount of 1~3 wt% of the ham weight and then fermented at a temperature of 10~20℃ and a relative humidity of 60%~70% for 120~150 days to obtain mature Xuanwei ham; In step (1), the total amount of salt applied is 5-15 wt% of the weight of the fresh leg. The salting is done in four stages, with the mass ratio between the first, second, third, and fourth salting applications being 15-20:15-20:6-10:4-6. The first salting is repeated for 5-8 days, followed by the second salting. The second salting is done 12-15 days after the second salting, and the third salting is done 7-15 days after the third salting. The fermentation agent mixture in step (2) is composed of a concentration of 10... 6 cfu / mL ~10 7 cfu / mL of Bensminoides ( Penicillium rubens W10-1 fermentation inoculum and Penicillium thuringiensis ( Penicillium fuscoglaucum V8 starter culture was prepared by mixing the cultures at a volume ratio of 1~2:1~2. The Penicillium ( Penicillium rubens W10-1 was deposited at the China Center for Type Culture Collection on August 11, 2023, with accession number CCTCC NO: M 20231436; The brown algae (Penicillium) Penicillium fuscoglaucum V8 was deposited at the China Center for Type Culture Collection on August 11, 2023, with accession number CCTCC NO: M20231437.

2. The method according to claim 1, characterized in that, The salting process described in step (1) is carried out at a temperature of 4~8℃ and a humidity of 80%~90%.

3. The method according to claim 1, characterized in that, The pretreatment mentioned in step (1) involves removing the acid from qualified hind leg meat at 4-6℃ for 10-12 hours, removing loose connective tissue, and cutting off excess fat and leg skin on both sides to obtain pretreated fresh leg meat.

4. The method according to claim 1, characterized in that, The fermentation agent broth in step (2) is obtained by inoculating the activated W10-1 and V8 surface spores into the culture medium, culturing at 27℃~29℃ and 140~160 rpm for 3~4 days, and then centrifuging.

5. Xuanwei ham prepared by any of the methods shown in claims 1 to 4.

6. A method for increasing the moisture content and volatile aldehyde content of Xuanwei ham while reducing lipid oxidation, characterized in that, Including the following steps: (1) Salt the pre-treated fresh ham for 40-45 days to obtain cured ham; (2) After the ham is cured, it is washed and air-dried to obtain air-dried ham; the air-dried ham is fermented for 60 to 90 days at a temperature of 10 to 15℃ and a relative humidity of 55 to 65% to obtain ham in the early stage of fermentation; the ham in the early stage of fermentation is fermented for 100 to 120 days at a temperature of 25 to 30℃ and a relative humidity of 70 to 80% to obtain ham in the middle stage of fermentation; the ham in the middle stage of fermentation is coated with a mixture of fermentation agent and bacterial solution at a coating amount of 1 to 3 wt% of the ham weight and then fermented for 120 to 150 days at a temperature of 10 to 20℃ and a relative humidity of 60% to 70% to obtain mature Xuanwei ham with high moisture content, high content of volatile aldehyde flavor compounds and low degree of lipid oxidation. In step (1), the total amount of salt applied is 5-15 wt% of the weight of the fresh leg. The salting is done in four stages, with the mass ratio of the first, second, third, and fourth salting applications being 15-20:15-20:6-10:4-6. The first salting is repeated for 5-8 days, followed by the second salting. The second salting is done 12-15 days after the second salting, and the third salting is done 7-15 days after the third salting. The fermentation agent mixture in step (2) is composed of a concentration of 10... 6 cfu / mL ~10 7 cfu / mL of Bensminoides ( Penicillium rubens W10-1 fermentation inoculum and Penicillium thuringiensis ( Penicillium fuscoglaucum V8 starter culture was prepared by mixing the cultures at a volume ratio of 1~2:1~2. The Penicillium ( Penicillium rubens W10-1 was deposited at the China Center for Type Culture Collection on August 11, 2023, with accession number CCTCC NO: M 20231436; The brown algae (Penicillium) Penicillium fuscoglaucum V8 was deposited at the China Center for Type Culture Collection on August 11, 2023, with accession number CCTCC NO: M20231437.

7. The method according to claim 6, characterized in that, The salting process described in step (1) is carried out at a temperature of 4~8℃ and a humidity of 80%~90%.

8. The method according to claim 6, characterized in that, The pretreatment mentioned in step (1) involves removing the loose connective tissue, cutting off the excess fat and skin on both sides of the qualified hind leg meat after 10-12 hours of acid removal at 4-8℃.

9. The method according to claim 6, characterized in that, The fermentation agent broth in step (2) is obtained by inoculating the activated W10-1 and V8 surface spores into the culture medium, culturing at 27~29℃ and 140~160 rpm for 3~4 days, and then centrifuging.

10. The application of the method according to any one of claims 6 to 9 in the preparation of Xuanwei ham.

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