Method for realizing ham quality grading based on non-volatile flavor substance analysis

Abstract

The invention discloses a method for realizing ham quality grading based on non-volatile flavor substance analysis, and relates to the field of ham quality grading methods. The invention solves the problems that the existing Xuanwei ham fermentation process is not standard, and the fermentation process cannot be adjusted according to the content of non-volatile compounds and the change rule of the whole taste. The method comprises the following steps: 1, taking naturally fermented mature Xuanwei ham, cutting off an oxide layer, and rapidly separating biceps femoris muscle from semimembranous muscle; and 2, respectively carrying out amino acid determination on the separated biceps femoris muscle and the separated semi-membranous muscle, and grading the quality of the ham according to test data. Through amino acid analysis, accurate evaluation of the quality of the Xuanwei ham is realized. The method is used for Xuanwei ham quality grading.

Description

Technical Field

[0001] The present invention relates to the field of methods for grading the quality of ham. Background Art

[0002] Xuanwei ham is a traditional and famous meat product in Xuanwei City, Yunnan Province, China. Due to its special sensory characteristics, such as flavor and texture, it has won high recognition among consumers. Xuanwei ham, together with Rugao ham in Jiangsu and Jinhua ham in Zhejiang, is known as the "Three Major Hams in China". The flavor substances of dry-cured ham refer to the compounds or components that help enhance and improve the taste and aroma. Some reports show that many non-volatile metabolites belong to the taste compounds in meat products. The taste substances of ham mainly include oligopeptides, free amino acids, organic acids, and mineral ions produced by protein hydrolysis. The taste of ham is not a simple superposition and accumulation of these taste substances, but a combination of these substances in a certain proportion. It has been clearly studied that free amino acids are closely related to the formation of the taste of dry-cured ham, and are one of the main components of the taste substances of dry-cured ham, and are also important precursor substances for the umami, sweet, sour, and bitter tastes of dry-cured ham. Organic acids are an important component of the taste compounds in ham. Organic acid substances can not only make the taste of dry-cured ham more rich, but also make dry-cured ham show an obvious sour taste when the content is high. However, their taste characteristics in dry-cured ham depend on the change of their concentration. Biogenic amines, that is, nitrogen-containing organic compounds, are often detected in fermented foods with relatively rich protein content. The production of biogenic amines in fermented meat products is attributed to the action of decarboxylases of several microorganisms. These enzymes promote the decarboxylation of free amino acids, and because the microbial community dominates in ham fermentation, they are more likely to undergo amine decarboxylation.

[0003] Chen et al. used high-throughput sequencing technology to explore the physicochemical properties, biogenic amine concentration, and microbial diversity during the processing of Sanchuan ham, and analyzed the dynamic correlation of physicochemical properties, free amino acid content, biogenic amine concentration, and microbial diversity during the fermentation of Sanchuan ham. Landeta et al. found that tyramine and putrescine are the most abundant components of biogenic amines in Italian dry-cured ham. WANG et al. studied the microbial community and volatile compounds in the biceps femoris (BF) and semimembranosus (SM) of normal and spoiled Xuanwei ham, analyzed the correlation between microorganisms and volatile compounds, and clarified the relationship between the microbial community of Xuanwei ham and the formation of off-flavors. Alfaia et al. evaluated the characteristics of biogenic amines in Portuguese dry-cured ham and found that spermine and cadaverine tend to be present in large amounts, while the contents of histamine and spermidine are usually low. However, the existing research lacks the monitoring of the quality of different grades of Xuanwei ham through non-volatile compounds.

[0004] Mature Xuanwei ham is divided into four grades by the "three - stick" method, that is, the intensity of the smell is evaluated by smelling bamboo sticks. Ham that shows a strong meaty aroma in all 3 designated areas is classified as high - quality product (Grade A). Ham that shows a strong meaty aroma in 2 designated areas and has no abnormal smell in the remaining areas is classified as first - grade product (Grade B). Ham that shows a strong meaty aroma in the designated area and has no abnormal smell in the other 2 areas is classified as qualified product (Grade C). Finally, the ham called spoiled product (Grade D) is identified by the presence of a strong stench in 1 of the 3 designated areas. However, traditional sensory evaluation is highly subjective and it is difficult to accurately grade. Summary of the Invention

[0005] The present invention provides a method for grading the quality of ham based on the analysis of non - volatile flavor substances, aiming to solve the problems that the fermentation process of existing Xuanwei ham is not standardized and the fermentation process cannot be adjusted according to the content of non - volatile compounds and the change law of the overall taste.

[0006] A method for grading the quality of ham based on the analysis of non - volatile flavor substances is specifically carried out according to the following steps:

[0007] I. Take a naturally fermented and mature Xuanwei ham, cut off the oxidized layer, and quickly separate the biceps femoris and semimembranosus muscles.

[0008] II. Respectively measure the amino acids in the biceps femoris and semimembranosus muscles separated in step I. Let the biceps femoris be represented by BF and the semimembranosus be represented by SM. Grade the quality of the ham according to the total amino acid content or the content of umami amino acids, and divide it into Grade A, Grade B, Grade C, and Grade D from high to low.

[0009] Furthermore, for Grade A quality in step II: the total amino acid content in the BF part ≥ 4650 mg / 100 g, and the total amino acid content in the SM part ≥ 4437 mg / 100 g;

[0010] For Grade B quality: the total amino acid content in the BF part ≥ 3997 mg / 100 g and < 4650 mg / 100 g, and the total amino acid content in the SM part ≥ 3856 mg / 100 g and < 4437 mg / 100 g;

[0011] For Grade C quality: the total amino acid content in the BF part ≥ 3023 mg / 100 g and < 3997 mg / 100 g, and the total amino acid content in the SM part ≥ 2726 mg / 100 g and < 3856 mg / 100 g;

[0012] For Grade D quality: the total amino acid content in the BF part < 3023 mg / 100 g, and the total amino acid content in the SM part < 2726 mg / 100 g.

[0013] Further, the A - level quality described in Step 2: the content of umami amino acids in the BF part ≥ 798 mg / 100 g, and the content of umami amino acids in the SM part ≥ 749 mg / 100 g;

[0014] The B - level quality: the content of umami amino acids in the BF part ≥ 677 mg / 100 g and < 798 mg / 100 g, and the content of umami amino acids in the SM part ≥ 625 mg / 100 g and < 749 mg / 100 g;

[0015] The C - level quality: the content of umami amino acids in the BF part ≥ 480 mg / 100 g and < 677 mg / 100 g, and the content of umami amino acids in the SM part ≥ 438 mg / 100 g and < 625 mg / 100 g;

[0016] The D - level quality: the content of umami amino acids in the BF part < 480 mg / 100 g, and the content of umami amino acids in the SM part < 438 mg / 100 g.

[0017] Further, if the measured values of the BF part and the SM part fall into different grades, the lower grade shall prevail.

[0018] Further, total amino acids include bitter amino acids, umami amino acids, sweet amino acids and tasteless amino acids.

[0019] Further, umami amino acids include aspartic acid and glutamic acid.

[0020] Further, bitter amino acids include histidine, arginine, tyrosine, valine, methionine, phenylalanine, isoleucine and leucine.

[0021] Further, sweet amino acids include serine, glycine, threonine, alanine, proline and lysine; the tasteless amino acid is cysteine.

[0022] Further, the Xuanwei ham is processed according to the following steps:

[0023] S1. Remove blood stains and dirt from fresh pig leg meat, then cut and shape it to obtain a leg embryo.

[0024] S2. Salt - cure the leg embryo obtained in S1 four times. After each salting, stack and press the salt - cured leg embryo, and control the total salt amount to be 9 - 14% of the mass of the leg embryo, and the total curing time is two months.

[0025] S3. Rinse the salt - cured leg embryo obtained in S2 to remove the surface salt, then air - dry it until there is no moisture on the surface, and then hang it in the fermentation chamber for natural fermentation to obtain a naturally fermented and mature Xuanwei ham.

[0026] Further, the natural fermentation in S3 is 360 - 380 days.

[0027] The biceps femoris (BF) and semimembranosus (SM) muscles also exhibit differences under the same conditions during dry-cured ham processing. The internal muscle BF shows higher water content and proteolytic activity during production compared to SM. This leads to differences in the amounts of non-volatile compounds in BF and SM.

[0028] During ham ripening, one of the most important biochemical reactions is protein degradation caused by the activity of endogenous muscle proteases, mainly including calpains, cathepsins, dipeptidases, and aminopeptidases. According to their cleavage sites on proteins and polypeptides, these enzymes are classified into endopeptidases and exopeptidases. Endopeptidases, mainly calpains and cathepsins, participate in the initial decomposition of sarcoplasmic and myofibrillar proteins by cleaving myofibrillar proteins, while exopeptidases (dipeptidases and aminopeptidases) continue to degrade proteins, mainly producing small peptides and free amino acids. The change in the content of free amino acids depends on their formation and degradation during the production of dry-cured ham. Some free amino acids directly enhance the ham flavor, while other free amino acids participate in the formation of key aroma compounds as precursor substances for dry-cured meat products. The umami taste of cured ham is highly related to the glutamic acid and aspartic acid it contains, while leucine, phenylalanine, isoleucine, valine, and methionine are considered closely related to bitterness. However, excessive accumulation of free amino acids may lead to unpleasant bitterness and sourness.

[0029] By detecting and analyzing the biceps femoris and semimembranosus muscles in Xuanwei ham, the present invention can accurately grade the quality of Xuanwei ham, establish an internal correlation between the principal component analysis and product quality, provide theoretical support for the quality control of Xuanwei ham, and lay a certain foundation for the industrialization and industrial development of Xuanwei ham.

[0030] Advantages of the present invention:

[0031] 1. Through amino acid analysis, the present invention realizes the accurate evaluation of the quality of Xuanwei ham. Compared with traditional single-index detection methods, it can more comprehensively reflect the flavor characteristics, safety, and processing maturity of ham, effectively avoiding misjudgment caused by the limitations of indicators.

[0032] 2. Precise grading and spoilage warning: Based on amino acid analysis, it can quickly distinguish grade A (superior), grade B (first-class), grade C (qualified), and grade D (spoiled ham), especially significantly improving the recognition sensitivity for spoiled products (such as grade D).

[0033] 3. High-efficiency and convenient potential for industrial application: The present invention adopts standardized detection technology, with good repeatability and convenient operation of the method, which can be connected to the quality control link of the production line. By monitoring the dynamic changes of key indicators (such as moisture content, salt gradient), it guides enterprises to adjust the pickling and drying process parameters, shortening the production cycle and reducing energy consumption.

[0034] 4. Scientific support for quality improvement and standardization: Establish a quality evaluation system based on the content index of non-volatile compounds, providing an objective and quantitative standard for the grade classification of Xuanwei ham and promoting the standardization process of the industry.

[0035] The present invention is used to realize the quality grading of Xuanwei ham. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 It is the electronic tongue analysis diagram of different muscle parts of Xuanwei ham with different grades;

[0037] Figure 2 It is the PCA diagram of the electronic tongue of different muscle parts of Xuanwei ham with different grades;

[0038] Figure 3 It is the correlation PCA diagram of different muscle parts of Xuanwei ham with different grades. DETAILED DESCRIPTION OF THE INVENTION

[0039] DETAILED DESCRIPTION OF THE INVENTION 1: This embodiment is a method for realizing the quality grading of ham based on the analysis of non-volatile flavor substances, which is specifically carried out according to the following steps:

[0040] 1. Take the naturally fermented and mature Xuanwei ham, cut off the oxidized layer, and quickly separate the biceps femoris and semimembranosus muscles;

[0041] 2. Respectively measure the amino acids of the biceps femoris and semimembranosus muscles separated in step 1. Set the biceps femoris to be represented by BF and the semimembranosus to be represented by SM. Grade the quality of the ham according to the total amino acid content or the content of umami amino acids, which are divided into grade A, grade B, grade C, and grade D from high to low.

[0042] DETAILED DESCRIPTION OF THE INVENTION 2: The difference between this embodiment and DETAILED DESCRIPTION OF THE INVENTION 1 is that for the quality of grade A in step 2: the total amino acid content of the BF part ≥ 4650 mg / 100 g, and the total amino acid content of the SM part ≥ 4437 mg / 100 g;

[0043] For the quality of grade B: the total amino acid content of the BF part ≥ 3997 mg / 100 g and < 4650 mg / 100 g, and the total amino acid content of the SM part ≥ 3856 mg / 100 g and < 4437 mg / 100 g;

[0044] Grade C quality: The total amino acid content in the BF part is ≥3023 mg / 100 g and <3997 mg / 100 g, and the total amino acid content in the SM part is ≥2726 mg / 100 g and <3856 mg / 100 g;

[0045] Grade D quality: The total amino acid content in the BF part is <3023 mg / 100 g, and the total amino acid content in the SM part is <2726 mg / 100 g. Others are the same as in the first specific implementation manner.

[0046] Specific implementation manner three: The difference between this implementation manner and the first or second specific implementation manner is: For the grade A quality described in step two: The umami amino acid content in the BF part is ≥798 mg / 100 g, and the umami amino acid content in the SM part is ≥749 mg / 100 g;

[0047] Grade B quality: The umami amino acid content in the BF part is ≥677 mg / 100 g and <798 mg / 100 g, and the umami amino acid content in the SM part is ≥625 mg / 100 g and <749 mg / 100 g;

[0048] Grade C quality: The umami amino acid content in the BF part is ≥480 mg / 100 g and <677 mg / 100 g, and the umami amino acid content in the SM part is ≥438 mg / 100 g and <625 mg / 100 g;

[0049] Grade D quality: The umami amino acid content in the BF part is <480 mg / 100 g, and the umami amino acid content in the SM part is <438 mg / 100 g. Others are the same as in the first or second specific implementation manner.

[0050] Specific implementation manner four: The difference between this implementation manner and one of the first to third specific implementation manners is: If the measured values of the BF part and the SM part fall into different grades, the lower grade shall prevail. Others are the same as in one of the first to third specific implementation manners.

[0051] Specific implementation manner five: The difference between this implementation manner and one of the first to fourth specific implementation manners is: The total amino acids include bitter amino acids, umami amino acids, sweet amino acids, and tasteless amino acids. Others are the same as in one of the first to fourth specific implementation manners.

[0052] Specific implementation manner six: The difference between this implementation manner and one of the first to fifth specific implementation manners is: The umami amino acids include aspartic acid and glutamic acid. Others are the same as in one of the first to fifth specific implementation manners.

[0053] Specific implementation manner seven: The difference between this implementation manner and one of the first to sixth specific implementation manners is: The bitter amino acids include histidine, arginine, tyrosine, valine, methionine, phenylalanine, isoleucine, and leucine. Others are the same as in one of the first to sixth specific implementation manners.

[0054] Embodiment VIII: The difference between this embodiment and any one of Embodiments I - VII is that the sweet amino acids include serine, glycine, threonine, alanine, proline, and lysine; the tasteless amino acid is cysteine. Others are the same as any one of Embodiments I - VII.

[0055] Embodiment IX: The difference between this embodiment and any one of Embodiments I - VIII is that the Xuanwei ham is prepared according to the following steps:

[0056] S1. Remove blood stains and dirt from fresh pork legs, then cut and shape them to obtain leg embryos.

[0057] S2. Salt - cure the leg embryos obtained in S1 four times. After each salting, stack and press the salt - cured leg embryos, and control the total salt amount to be 9 - 14% of the mass of the leg embryos, with the total curing time being two months.

[0058] S3. Rinse the salt - cured leg embryos obtained in S2 to remove the surface salt, then air - dry and sun - dry them until there is no moisture on the surface, and then hang them in the fermentation chamber for natural fermentation to obtain naturally fermented and mature Xuanwei ham. Others are the same as any one of Embodiments I - VIII.

[0059] Embodiment X: The difference between this embodiment and any one of Embodiments I - IX is that the natural fermentation in S3 is 360 - 380 days. Others are the same as any one of Embodiments I - IX.

[0060] The content of the present invention is not limited to the content of the above - mentioned embodiments. The combination of one or several specific embodiments can also achieve the purpose of the invention.

[0061] Example 1:

[0062] The Xuanwei ham used in the method for grading the quality of ham based on the analysis of non - volatile flavor substances in this example is prepared according to the following steps:

[0063] S1. Remove blood stains and dirt from fresh pork legs, then cut and shape them to obtain leg embryos.

[0064] S2. Salt - cure the leg embryos obtained in S1 four times. After each salting, stack and press the salt - cured leg embryos, and control the total salt amount to be 11% of the mass of the leg embryos, with the total curing time being two months.

[0065] S3. Rinse the salt - cured leg embryos obtained in S2 to remove the surface salt, then air - dry and sun - dry them until there is no moisture on the surface, and then hang them in the fermentation chamber for natural fermentation to obtain naturally fermented and mature Xuanwei ham, which takes about 12 months to fully ferment.

[0066] Example 1 All processes were completed at Dehe Co., Ltd., Xuanwei City, Yunnan Province.

[0067] Example 2:

[0068] A method for grading the quality of ham based on the analysis of non-volatile flavor substances in this example includes the following steps:

[0069] I. Take a naturally fermented and mature Xuanwei ham, cut off the oxidized layer, and quickly separate the biceps femoris and semimembranosus muscles.

[0070] II. Measure the amino acids of the biceps femoris and semimembranosus muscles separated in step I respectively. Let the biceps femoris be represented by BF and the semimembranosus muscle be represented by SM. Grade the quality of the ham according to the total amino acid content or the content of umami amino acids, which are divided into grade A, grade B, grade C, and grade D from high to low.

[0071] Example 3:

[0072] Randomly select 6 pieces from the same batch of Xuanwei hams (superior grade A, first grade B, qualified grade C, and deteriorated product D) that have been graded by the "three-signature" method, and cut off the oxidized layer (about 0.5 cm) of the Xuanwei ham. Subsequently, quickly separate the biceps femoris (BF) and semimembranosus muscle (SM) to prepare samples for amino acid, nucleotide, organic acid, and electronic tongue detection and analysis.

[0073] Among them, amino acids include but are not limited to 8 bitter amino acids (histidine, arginine, tyrosine, valine, methionine, phenylalanine, isoleucine, leucine) such as tartaric acid, malic acid, lactic acid, glacial acetic acid, citric acid, and succinic acid; 2 umami amino acids (aspartic acid, glutamic acid); 6 sweet amino acids (serine, glycine, threonine, alanine, proline, lysine); and 1 non-tasting amino acid (cysteine).

[0074] Nucleotides include but are not limited to AMP, GMP, IMP.

[0075] Organic acids include but are not limited to tartaric acid, malic acid, lactic acid, glacial acetic acid, citric acid, and succinic acid.

[0076] Electronic tongue detection includes but is not limited to saltiness, umami, bitterness, astringency, sourness, and richness.

[0077] Materials and Reagents

[0078] Trichloroacetic acid; Standard products: Chemical reagents such as lactic acid, tartaric acid, malic acid, citric acid, succinic acid, acetic acid, mixed amino acid standard solution, 17 single amino acid standard products, and 9 kinds of biogenic amine mixed standards were all purchased from Beijing Solarbio Science & Technology Co., Ltd.; Nucleotide standard products, Shanghai Yuanye Bio-Technology Co., Ltd.

[0079] Instruments and Equipment

[0080] Electronic balance (AL204), Mettler Toledo Instruments Co., Ltd.; Homogenizer (XHF-DY), Ningbo Xinzhi Biotechnology Co., Ltd.; High performance liquid chromatography (1260 Infinity), Agilent Technologies, Inc., USA.

[0081] Experimental Methods

[0082] 1. Electronic tongue determination: Take 5 g of the sample, chop it up and mix it with 100 mL of ultrapure water, and homogenize it in an ice bath at 10000 r / min for 30 s (10 s each time, for a total of 3 times), let it stand for 30 min, filter the suspension with filter paper, and then centrifuge the collected filtrate at 4 °C and 8000 r / min for 10 min. After centrifugation, the supernatant is filtered again with filter paper, and then the umami, saltiness, sourness, richness and bitterness of the sample are analyzed with an electronic tongue; 2 parallels are set for each treatment, and each parallel is measured 6 times, and three times are selected as the original data for analysis.

[0083] 2. Determination method of organic acids: Homogenize 5.0 g of the ham sample in 25 mL of purified water for 5 min; then centrifuge at 10000 g at 4 °C for 20 min, and filter the supernatant through a 0.45 μm water membrane before injection. Agilent high performance liquid chromatography and Agilent ZORBAX SB-C18 analytical column. Use 0.1% phosphoric acid as phase A and methanol (phase B) as the main body, with their proportions being 97.5% and 2.5% respectively, and all operate according to the following HPLC parameters: The sampling volume is set to 20 μL; the flow rate is set to 1.0 mL / min; the working temperature is set to 30 °C, and at the same time, 210 nm is selected as the wavelength range of the detector. By comparing the retention time and peak area of each organic acid standard product, the presence and content of various organic acids are confirmed and determined. The organic acid content is expressed as mg / g dry matter.

[0084] 3. Method for amino acid determination: First, mix 1.0000 g of minced ham sample with 25 mL of 5% trichloroacetic acid. If it exceeds the scale line, make up the volume to 50 mL and record the made-up volume. After mixing evenly, sonicate for 30 minutes at room temperature. After standing for 2 hours, filter the solution using double-layer filter paper, and centrifuge 1 mL of the clarified filtrate in a 1.5 mL centrifuge tube at 15,000 rpm for 30 min. Take 400 μL of the supernatant and transfer it to a liquid phase bottle; filter it again through a 0.22 μm water membrane. Gas chromatography analysis conditions: Chromatographic column CP WAX (30 m × 0.32 mm × 0.25 μm); injection port 250 °C, detector 250 °C, programmed temperature rise: hold at 120 °C for 3 min, rise to 190 °C at a rate of 10 °C / min, then rise to 220 °C at a rate of 2 °C / min and hold for 15 min, carrier gas N2 flow rate 3 mL / min, fuel gas H2 flow rate 47 mL / min, combustion-supporting gas (air) flow rate 400 mL / min, split ratio 10:1.

[0085] 4. Nucleotide determination: Accurately weigh 4 g of minced ham sample, add 20 mL of 5% (volume fraction) pre-cooled perchloric acid, homogenize the mixture in an ice bath at 10,000 r / min for 30 s (10 s each time, for a total of 3 times), centrifuge at 8,000 r / min for 10 min at 4 °C, and collect the supernatant, filtering it with double-layer filter paper. Add 10 mL of pre-cooled 5% perchloric acid to the precipitate, mix evenly, and then centrifuge again under the same conditions. Combine the supernatants collected from the two centrifugations, and adjust the pH value of the solution to 6.5 with 1 mol / L potassium hydroxide. Then, make up the volume to 50 mL with ultrapure water and filter it through a 0.22 μm water-based filter membrane before measurement. Determine it using a high-performance liquid chromatograph equipped with a 2487 ultraviolet (UV) detector (220 nm / 280 nm), with a Diamonsil C18 column (4.6 mm × 250 mm, 5 μm) as the chromatographic column, mobile phases A and B being acetonitrile and water respectively, and the detection wavelength being 250 nm.

[0086] Analysis of test results

[0087] Analysis of organic acids in Xuanwei hams of different grades

[0088] Organic acids are important non-volatile flavor substances and have an important impact on the flavor attributes of ham. As shown in Table 1, six organic acids were detected, including tartaric acid, malic acid, lactic acid, glacial acetic acid, citric acid, and succinic acid. Whether in the biceps femoris (BF) or semimembranosus (SM), as the quality of ham decreased from premium grade (A) to spoiled product (D), the contents of various organic acids such as tartaric acid, malic acid, lactic acid, glacial acetic acid, citric acid, and succinic acid, as well as the total content, all decreased significantly. There were significant differences in the organic acid contents among different grades within the same muscle type (P < 0.05), indicating that the organic acid content is a key factor affecting quality. For muscles of the same grade in different parts, the contents of most organic acids in BF were higher than those in SM, and there were significant differences in the organic acid contents between different muscle types (P < 0.05), indicating that muscle type also has an important impact on the organic acid content. Among the various organic acids, the changes in tartaric acid and malic acid were obvious among different qualities and muscle types, and the content gap was relatively stable; the content of glacial acetic acid was high and showed an obvious decreasing trend; the content of citric acid was low and fluctuated greatly; the content of succinic acid was high, and within the same grade, the content difference between BF and SM was relatively large.

[0089] Table 1 Organic acid contents in different muscle parts of Xuanwei ham with different grades

[0090]

[0091] Note: Different capital letters (A - D) indicate significant differences between muscles of the same part with different grades (P < 0.05), and different lowercase letters (a - b) indicate significant differences between muscles of different parts with the same grade (P < 0.05).

[0092] Analysis of amino acids in Xuanwei ham with different grades

[0093] As shown in Table 2, a total of 17 kinds of amino acids were detected. According to the taste characteristics of amino acids, they can be divided into bitter, umami, sweet, and tasteless amino acids, including 8 bitter amino acids (histidine, arginine, tyrosine, valine, methionine, phenylalanine, isoleucine, leucine); 2 umami amino acids (aspartic acid, glutamic acid); 6 sweet amino acids (serine, glycine, threonine, alanine, proline, lysine), and 1 tasteless amino acid (cysteine). In terms of bitter amino acids, leucine is the bitter amino acid with the highest content. Its content shows a significant decreasing trend (P<0.05) with the decrease of grades in the four grades A, B, C, and D. The leucine content in the three grades A, B, and C all reached more than 300mg / 100g. There was a significant difference between the D quality and the hams of the three qualities A, B, and C. The leucine content of the D quality ham was significantly lower than that of the other three qualities. Histidine is the amino acid with the lowest content (P<0.05), and there was no significant difference between different grades of hams (P>0.05). For other bitter amino acids, the content generally shows a decreasing trend with the decrease of quality (P<0.05). The content of bitter amino acids in hams with better quality is relatively higher, indicating that free amino acids are unlikely to be the key factors causing unpleasant flavors (bitter, sour, astringent) in hams. In terms of umami amino acids, two umami amino acids were detected, namely glutamic acid and aspartic acid. The content of glutamic acid is higher than that of aspartic acid, and its content is close to 1 / 8 of the total amino acids, which is the main umami amino acid in Xuanwei ham. With the decrease of ham grades, the content of glutamic acid, whether it is BF or SM, shows a downward trend (P<0.05). The content of hams in the three qualities A, B, and C is higher than 450mg / 100g, while the content of the D quality ham is much lower than that of the other three qualities of hams, indicating that umami is an important taste index for evaluating the quality of hams. For aspartic acid, with the decrease of ham quality, the content of aspartic acid also decreases significantly. In terms of numerical values, the content of A and B reached more than 200mg / 100g, and the content of C and D was relatively close, between 100-130mg / 100g. For the same grade and different parts of muscle, the content of BF was significantly higher than that of SM. Glutamic acid and aspartic acid account for about 1 / 6 of the total amino acids, and the content is relatively high. As a umami amino acid, the content of glutamic acid directly affects the umami degree of ham. During the curing and fermentation process, the change of glutamic acid content can significantly affect the taste of ham. In terms of sweet amino acids, the content of total sweet amino acids is close to 2 / 5 of the total amino acid content. With the decrease of ham quality, the content of sweet amino acids shows a gradually decreasing trend, with the highest content in A quality and the lowest content in D quality.The two dominant sweet-tasting amino acids with the highest contents are alanine and lysine, and their contents in Grade A quality reach over 500 mg / 100 g. Among them, the content of alanine even reaches over 700 mg / 100 g, which is the amino acid with the highest content in Xuanwei ham.

[0094] For muscles of the same grade but different parts, except for alanine, proline, and lysine, there are no significant differences in other sweet-tasting amino acids between BF and SM. For the tasteless cysteine, there is no significant change trend among the four grades A, B, C, and D. At the same time, the content of cysteine is relatively low among the four grades A, B, C, and D (less than 4 mg / 100 g), and there is also no significant difference between BF and SM. This indicates that cysteine may not be the main amino acid in Xuanwei ham and has little impact on the taste.

[0095] In terms of total free amino acids, the total amino acid content of Grade A quality Xuanwei ham is significantly higher than that of other hams (P < 0.05), and the average total content of BF and SM is 4874.49 mg / 100 g. The total amino acid content of BF is higher than that of SM, which may be related to the water and salt contents. The activity of aminopeptidase is considered the main factor for the release of free amino acids in meat.

[0096] The amino acid taste threshold ratio (TAV) is a proportional relationship that measures the concentration of a specific amino acid in a sample and its corresponding taste threshold. Generally speaking, if TAV is greater than 1, it means that this component has an obvious impact on the taste of food; conversely, if TAV is less than 1, it indicates that it does not bring an obvious effect of enhancing the taste. Among the A, B, and C qualities, only the TAVs of serine, proline, and threonine are less than 1. In the ham of Grade D quality, the TAVs of serine, glycine, threonine, and proline are less than 1, indicating that there is a greater loss of sweet-tasting amino acids in spoiled hams.

[0097] Table 2 Amino acids in different muscle parts of Xuanwei ham with different grades

[0098]

[0099]

[0100]

[0101] Note: Different capital letters (A - D) indicate significant differences (P < 0.05) between muscles of the same part with different grades, and different lowercase letters (a - b) indicate significant differences (P < 0.05) between muscles of different parts with the same grade.

[0102] It can also be verified from Table 2 that the results of amino acid test grading are consistent with the existing ham grading, confirming that the method of the present invention is reliable and accurate.

[0103] Nucleotide Analysis of Xuanwei Ham at Different Grades

[0104] Three kinds of flavor nucleotides, namely AMP, GMP, and IMP, were detected in the muscles of Xuanwei ham at different grades and different parts. The results are shown in Table 3. The content of AMP gradually decreased with the decrease of ham grade. The contents of AMP in BF and SM decreased from 9.65 mg / 100 g and 8.71 mg / 100 g in the premium grade to 5.84 mg / 100 g and 5.24 mg / 100 g in grade D respectively (P<0.05). For the same grade, among different parts, the AMP content in BF was significantly higher than that in SM (P<0.05). The contents of GMP in BF and SM decreased from 10.83 and 9.73 mg / 100 g in grade A to 5.21 mg / 100 g and 4.89 mg / 100 g in grade D respectively. For the same grade, among different parts, BF was significantly higher than SM. The contents of IMP in BF and SM decreased from 5.42 mg / 100 g and 4.71 mg / 100 g in grade A to 1.95 mg / 100 g and 1.57 mg / 100 g in grade D (P<0.05). For the same grade, there were significant differences among different parts, and the IMP content in BF was significantly higher than that in SM. The contents of AMP, GMP, and IMP nucleotides decreased with the decrease of the quality of Xuanwei ham. It may be that as the quality of the ham decreases, the microorganisms in the ham fermentation process will consume or decompose the nucleotides in the ham, the endogenous enzymes will accelerate the degradation of nucleotides, and the oxidation reaction may damage the structure of nucleotides and reduce their content.

[0105] Table 3 Nucleotide Contents in Different Muscular Parts of Xuanwei Ham at Different Grades

[0106]

[0107]

[0108] Note: Different capital letters (A - D) indicate significant differences among the muscles of the same part at different grades (P<0.05), and different lowercase letters (a - b) indicate significant differences among the muscles of different parts at the same grade (P<0.05).

[0109] Electronic Tongue Analysis of Xuanwei Ham at Different Grades

[0110] As attached Figure 1As shown. For the same part and different qualities, the response value of umami decreases with the decline of ham quality, and the umami response value of ham of D quality is much lower than that of ham of A quality, indicating that the spoilage of ham has a great impact on the umami of Xuanwei ham and seriously affects the quality of Xuanwei ham. For the same quality and different muscle parts, there is no significant difference in umami between BF and SM. In terms of sour taste, for the same part and different qualities, for the hams of four grades A, B, C, and D, the sour taste increases with the decline of quality. For the same quality and different muscle parts, there is no significant difference in sour taste between BF and SM. In terms of astringency, for the hams of four grades A, B, C, and D of the same part and different qualities, the astringency increases with the decline of quality, indicating that with the decline of quality, the astringency also increases, which has a significant impact on the enhanced body taste of ham. For the same quality and different muscle parts, there is no significant difference in astringency between BF and SM. In terms of bitter taste, for the same part and different qualities, with the decline of the quality of Xuanwei ham, the response value of bitter taste increases, indicating that bitter taste is also an important taste affecting the quality of Xuanwei ham. For the same quality and different muscle parts, there is no significant difference in bitter taste between BF and SM. In terms of salty taste, for the same part and different qualities, with the decline of the quality of Xuanwei ham, the response value of salty taste also decreases, indicating that our salt content is decreasing, and this result is consistent with the measurement of our salt content. For the same quality and different muscle parts, there is no significant difference between BF and SM, which is inconsistent with the measurement of salt content. This may be because the high content of umami compounds and salt produce a synergistic salt-enhancing effect. It should be noted that the response values of umami and salty taste are significantly higher than those of sour taste, bitter taste, and astringency, indicating that umami and salty taste are the most important taste attributes in ham, which is consistent with the reports. The richness is the aftertaste value of umami, reflecting the residual situation of umami. In this study, for the same part and different qualities, the richness decreases with the decline of ham grade, indicating that the umami of better-quality ham is more intense and the aftertaste of umami is more significant. For the same quality and different muscle parts, there is no significant difference in richness between BF and SM. The higher richness of high-quality ham may be due to the accumulation of flavor components such as amino acids, organic acids, and nucleotides, which increases the richness intensity of high-quality ham.

[0111] As attached Figure 2As shown, in order to further show whether there are differences between the taste values of each group, PCA analysis was used. The contribution rate of PC1 was 83.2%, the contribution rate of PC2 was 14.5%, and the cumulative contribution rate of 97.7% could represent the overall taste characteristics of the samples. Sample A was mainly concentrated in the second quadrant, samples B and C were mainly in the third quadrant, and sample D was in the first quadrant and far from the other three quality hams. This indicates that there are significant differences between the hams of quality A and those of B, C, and D, and there are significant differences between D and A, B, and C with relatively large differences, while the differences between B and C are not significant. This shows that the electronic tongue can effectively distinguish Xuanwei hams of different grades. PC1 was positively correlated with bitterness, sourness, and astringency, and negatively correlated with saltiness and umami; PC2 was positively correlated with sourness, bitterness, astringency, umami, and richness, and negatively correlated with saltiness. Bitterness, sourness, and astringency were relatively close to D, indicating that bitterness, sourness, and astringency are important tastes of spoiled hams. The hams of quality A were mainly close to umami and richness, and they were all in the second quadrant, indicating that umami is an important taste affecting the quality grade of Xuanwei hams.

[0112] The preferred embodiments of the present invention disclosed above are only used to help illustrate the present invention. The preferred embodiments do not describe all the details in detail, nor do they limit the invention to the specific embodiments described. Obviously, many modifications and variations can be made according to the content of this specification. These embodiments are selected and specifically described in this specification to better explain the principles and practical applications of the present invention, so that those skilled in the art can well understand and utilize the present invention. The present invention is only limited by the claims and their full scope and equivalents.

[0113] Correlation analysis

[0114] To further understand the influence of non-volatile compounds on the quality changes of Xuanwei hams of different grades, all the above indicators were combined and analyzed by the principal component analysis method (PCA). As shown in the appendix Figure 3As shown in the figure, principal component analysis can well distinguish four samples A, B, C, and D, indicating good differences among them. PC1 explains 84.2% of the variance, and PC2 explains 7.3% of the variance. From the perspective of PC1, the BF and SM of hams of grades A and B are mainly concentrated on the right side of PC1, while the BF and SM of C and D are mainly concentrated on the left side of PC1, and D is far from the hams of the other three grades. This shows that there is good discrimination between hams of grades A, B, and C of Xuanwei ham and spoiled hams; in addition, free amino acids, organic acids, and nucleotides are also mainly concentrated on the right side of PC1, indicating that the content of taste substances has an important impact on the quality of Xuanwei ham. From the perspective of PC2, different muscle parts of hams of the same grade can be well distinguished, and there is a certain distance between BF and SM, indicating certain differences between them. The spoiled ham of grade D is far from the non-volatile taste substances, indicating that the spoiled ham has less non-volatile taste substances.

[0115] In summary, this patent provides a method for grading ham quality based on the analysis of non-volatile flavor substances. This method evaluates the ham quality through the content of non-volatile compounds (such as amino acids), can accurately grade and warn of the risk of spoilage, has the potential for industrial application, can promote the standardization process of the industry, and clarifies the relationship between each index and the ham quality. The above-described embodiments are only descriptions of the preferred embodiments of the present invention, and do not limit the scope of the present invention. Without departing from the design spirit of the present invention, various deformations and improvements made by those of ordinary skill in the art to the technical solutions of the present invention shall fall within the protection scope determined by the claims of the present invention.

Claims

1. A method for grading the quality of ham based on the analysis of non-volatile flavor substances, characterized in that The method is specifically carried out according to the following steps: First, take the naturally fermented and mature Xuanwei ham, cut off the oxidized layer, and quickly separate the biceps femoris and semimembranosus muscles; Second, measure the amino acids of the biceps femoris and semimembranosus muscles separated in the first step respectively. Set the biceps femoris to be represented by BF and the semimembranosus to be represented by SM. Grade the quality of the ham according to the total amino acid content or the content of umami amino acids, which are divided into Grade A, Grade B, Grade C, and Grade D from high to low.

2. The method for grading the quality of ham based on the analysis of non-volatile flavor substances according to claim 1, characterized in that For the Grade A quality described in the second step: the total amino acid content of the BF part ≥ 4650 mg / 100 g, and the total amino acid content of the SM part ≥ 4437 mg / 100 g; For the Grade B quality: the total amino acid content of the BF part ≥ 3997 mg / 100 g and < 4650 mg / 100 g, and the total amino acid content of the SM part ≥ 3856 mg / 100 g and < 4437 mg / 100 g; For the Grade C quality: the total amino acid content of the BF part ≥ 3023 mg / 100 g and < 3997 mg / 100 g, and the total amino acid content of the SM part ≥ 2726 mg / 100 g and < 3856 mg / 100 g; For the Grade D quality: the total amino acid content of the BF part < 3023 mg / 100 g, and the total amino acid content of the SM part < 2726 mg / 100 g.

3. A method for grading the quality of ham based on the analysis of non-volatile flavor substances according to claim 1, characterized in that For the Grade A quality described in the second step: the umami amino acid content of the BF part ≥ 798 mg / 100 g, and the umami amino acid content of the SM part ≥ 749 mg / 100 g; For the Grade B quality: the umami amino acid content of the BF part ≥ 677 mg / 100 g and < 798 mg / 100 g, and the umami amino acid content of the SM part ≥ 625 mg / 100 g and < 749 mg / 100 g; For the Grade C quality: the umami amino acid content of the BF part ≥ 480 mg / 100 g and < 677 mg / 100 g, and the umami amino acid content of the SM part ≥ 438 mg / 100 g and < 625 mg / 100 g; For the Grade D quality: the umami amino acid content of the BF part < 480 mg / 100 g, and the umami amino acid content of the SM part < 438 mg / 100 g.

4. A method for grading the quality of ham based on the analysis of non-volatile flavor substances according to claim 2 or 3, characterized in that If the measured values of the BF part and the SM part fall into different grades, the lower grade shall prevail.

5. A method for grading the quality of ham based on the analysis of non-volatile flavor substances according to claim 1, characterized in that Total amino acids include bitter amino acids, umami amino acids, sweet amino acids, and tasteless amino acids.

6. A method for grading the quality of ham based on the analysis of non-volatile flavor substances according to claim 1, characterized in that Umami amino acids include aspartic acid and glutamic acid.

7. A method for grading the quality of ham based on the analysis of non-volatile flavor substances according to claim 5, characterized in that Bitter amino acids include histidine, arginine, tyrosine, valine, methionine, phenylalanine, isoleucine, and leucine.

8. A method for grading the quality of ham based on the analysis of non-volatile flavor substances according to claim 5, characterized in that Sweet amino acids include serine, glycine, threonine, alanine, proline, and lysine; the tasteless amino acid is cysteine.

9. A method for grading the quality of ham based on the analysis of non-volatile flavor substances according to claim 1, characterized in that The said Xuanwei ham is carried out according to the following steps: S1. Remove the blood stains and dirt from the fresh pork leg, and then cut and shape it to obtain the leg embryo; S2. Carry out four times of salting and curing on the leg embryo processed in S1. After each salting, stack and press the salted leg embryo, and control the total salt amount to be 9 - 14% of the mass of the leg embryo, and the total curing time is two months; S3. Rinse the leg embryos after marinating in S2 to remove the surface salt, then air-dry and sun-dry them until there is no moisture on the surface, and then hang them in the fermentation chamber for natural fermentation to obtain naturally fermented and mature Xuanwei ham.

10. The method for grading the quality of ham based on the analysis of non-volatile flavor substances according to claim 9, characterized in that The natural fermentation described in S3 is 360 - 380 days.

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