A low-bitter and high-umami yeast extract and its preparation method and application

Abstract

The present application discloses a low-bitter and high-umami yeast extract and its preparation method and application. The preparation method of the yeast extract comprises the following steps: mixing yeast with water, heating and adjusting the pH value, adding protease for enzymolysis, collecting the supernatant to obtain a yeast hydrolyzate; adding 0.2-0.4% propanethiol of the solid mass of the yeast hydrolyzate, and reacting for 12-16 hours to obtain a reaction solution containing the yeast extract. The method of the present invention utilizes a specific sulfur compound, propanethiol, to react with the yeast extract to produce a low-bitter and high-umami yeast extract. The method does not require additional production equipment, has low production cost, is pollution-free, is simple to operate, is highly feasible, and is easy to promote.

Description

Technical Field

[0001] The present invention relates to the technical field of yeast extract processing, and in particular to a low-bitterness and high-umami yeast extract and a preparation method and application thereof. Background Art

[0002] Edible yeast is widely used in food processing due to its high protein content (more than 40% on a dry basis) and rich in various nutrients and delicious precursors. Yeast extract is mainly made from edible yeast. It is a kind of food ingredient with delicious taste and rich taste obtained through modern bio-enzyme hydrolysis technology. It has the advantages of being green, natural, and high in nutritional value, and is widely used in the food industry.

[0003] Since yeast protein is rich in umami amino acids (including glutamic acid and aspartic acid up to 30%), in the actual production of yeast extracts prepared by biological enzymatic hydrolysis, a low degree of hydrolysis will not only make the production cost too high, but also lead to poor product stability and flavor quality. Therefore, manufacturers often increase the degree of hydrolysis of yeast protein to improve the utilization rate of yeast protein, reduce production costs, release more umami amino acids and small molecule peptides, and obtain products with better flavor quality. However, since yeast protein contains a large amount of bitter amino acids, as the degree of hydrolysis increases, more bitter small molecule peptides and free amino acids will be released from yeast protein, making the bitterness of yeast extract particularly prominent. In long-term research and actual production, people have found that when the degree of hydrolysis of yeast protein exceeds 20%, the yeast protein hydrolysate often exhibits obvious bitterness, which affects its flavor quality and limits the market acceptance of the product. Therefore, it is necessary to take certain measures to reduce its bitterness while ensuring high hydrolysis degree and high flavor quality, so as to prepare low-bitter and high-umami yeast extracts and give the products stronger market competitiveness. Summary of the invention

[0004] The object of the present invention is to provide a low-bitter and high-umami yeast extract and a preparation method and application thereof. The present invention utilizes the reaction between specific sulfur-containing compounds and yeast extract components to improve the flavor quality of the yeast extract.

[0005] The purpose of the present invention is achieved through the following technical solutions:

[0006] A method for preparing a low-bitter and high-umami yeast extract comprises the following steps:

[0007] (1) Mix yeast and water, adjust the solid concentration, raise the temperature to 50-60°C, adjust the pH value of the system to 8.0-8.5, then add protease, keep the temperature for 18-22 hours, inactivate the enzyme, centrifuge, and collect the supernatant to obtain yeast hydrolyzate;

[0008] (2) Adjust the pH value of the yeast hydrolysate to 5.5-6.5, add 0.2-0.4% propanethiol based on the solid mass of the yeast hydrolysate, stir evenly, and react at 40-50° C. for 12-16 h to obtain a reaction solution containing yeast extract.

[0009] The yeast described in step (1) is yeast milk, active dry yeast or inactivated dry yeast powder.

[0010] The solid concentration of the adjusted solids in step (1) is preferably 10 to 18%.

[0011] In steps (1) and (2), the pH is adjusted using 0.3-0.6 mol / L NaOH solution and 0.3-0.6 mol / L HCl solution.

[0012] The protease described in step (1) is alkaline protease and flavor protease, with alkaline protease 37071 and Flavourzyme 500 MG from Novozymes being the best, respectively. The amount of addition is 0.7-1.3% of the dry matter mass of yeast, wherein the addition ratio of alkaline protease to flavor protease is (2-3):1.

[0013] The enzyme inactivation conditions described in step (1) are to keep the mixture at 90-95°C for 15-30 minutes.

[0014] The centrifugation in step (1) can be performed using a tubular centrifuge or a butterfly centrifuge. The centrifugation parameters can be adjusted according to the centrifugation effect of the centrifuge, with the centrifugation clear liquid being free of obvious precipitate visible to the naked eye after centrifugation at 4000×g in a laboratory centrifuge for 10 min.

[0015] The reaction solution is concentrated (preferably concentrated to a solid content of 50-70%) and then sterilized to obtain a paste yeast extract.

[0016] The reaction solution is concentrated (preferably to a solid content of 30-45%), sterilized, and spray-dried to obtain a powdered yeast extract.

[0017] The concentration is carried out under reduced pressure at 50-55°C and -0.09mPa-0.095mPa.

[0018] The sterilization is preferably carried out at 90-95°C for 30 min.

[0019] The spray drying air inlet temperature is 185-190°C, and the air outlet temperature is 80-85°C.

[0020] The yeast extract prepared by the method has good flavor quality, prominent umami taste and weak bitterness, and can be used in the food industry.

[0021] Compared with the prior art, the present invention has the following advantages and effects:

[0022] (1) The method of the present invention utilizes a specific sulfur compound, propanethiol, to react with yeast extract to produce a low bitterness and high umami taste yeast extract. The method does not require additional production equipment, has low production cost, is pollution-free, is simple to operate, has strong feasibility, and is easy to promote.

[0023] (2) The method of the present invention is not limited to the type and state of the yeast raw material and has wide adaptability, which makes the method of the present invention have broad application prospects in the food processing industry.

[0024] (3) The product prepared by the present invention better meets the market requirements for the product, and the market competitiveness of the product is further improved, thereby improving the overall economic benefits of the yeast extract. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 This is the accumulation diagram of the peptide molecular weight distribution of yeast extract. DETAILED DESCRIPTION

[0026] The present invention is further described in detail below in conjunction with embodiments and drawings, but the embodiments of the present invention are not limited thereto.

[0027] The test indicators and experimental methods involved in the embodiments of the present invention are as follows:

[0028] (1) Sensory evaluation method: 12 trained tasters (6 males and 6 females, aged between 20 and 35 years old) were selected to conduct sensory evaluation on yeast extract products. The sample was diluted to a solid concentration of 5 mg / ml, and 30 ml of the sample solution was placed in a 50 ml plastic cup. The sensory personnel were asked to take 2 ml of the sample solution and put it in their mouths, taste it for 3 to 5 seconds, spit out the sample solution, rinse their mouths with warm water, and then taste the next sample. After repeating the evaluation two to three times, a sensory description and score were made. The sensory scoring used the 7-point linear coordinate method to score the sensory samples from 0 (very weak) to 7 (very strong). In order to unify the sensory scoring standards, the sensory five-flavor score of yeast extract product 3 was 3 points;

[0029] (2) Amino acid determination method:

[0030] The L8900 fully automatic amino acid analyzer was used to determine the content and proportion of each free amino acid in the sample, and the pretreatment referred to GB5009.124-2016 and GB / T30897-2020.

[0031] (3) Bitterness is generally considered an unpleasant flavor that changes the overall taste of food and affects consumers' taste experience. The bitterness brought by hydrophobic substances, especially hydrophobic amino acids, is often considered to be inseparable from the bitter characteristics of the food. The hydrophobic value is an important parameter for judging the hydrophobic amino acids in food and their bitterness intensity. The hydrophobic value is usually used to describe the hydrophobic properties of amino acid side chains. Hydrophobic amino acids are often located inside the three-dimensional structure of proteins, in contact with the hydrophobic core of the protein but not in contact with water. When proteins are hydrolyzed into small peptides or amino acids, these hydrophobic amino acids may be released and bind to bitter receptors on taste buds to produce bitterness. The higher the hydrophobic value, the stronger the hydrophobicity of the amino acid, and generally the higher its bitterness intensity. Therefore, by measuring or calculating the hydrophobic value of amino acids in food, its bitterness intensity can be predicted, thus providing a basis for sensory evaluation of food and product development.

[0032] Calculation method of hydrophobic value Q:

[0033] ;

[0034] ;

[0035] Where, AAi: content of each amino acid in 100 g of product (g);

[0036] Mi: molar mass of various amino acids (g / mol);

[0037] ∑AAi / Mi: total moles of amino acids in 100 g of product (mol);

[0038] △fti: amino acid side chain hydrophobicity value (kJ / mol);

[0039] Q: The average hydrophobic value of the product.

[0040] (4) Determination of peptide molecular weight distribution:

[0041] The peptide molecular weight of yeast extract products was determined by gel chromatography. The analytical column was a TSK gel chromatography column (G2000 SWXL, 7.8 mm×300 mm), the elution mode was isocratic elution, and the mobile phase was phosphate buffer containing 0.1% trifluoroacetic acid. Chromatographic conditions: flow rate 1 mL / min, injection volume 20 μL, UV detector absorption wavelength 214 nm. Standards: bovine serum albumin (68000 Da), ovalbumin (44500 Da), horse heart cytochrome C (12384 Da), aprotinin (6511 Da), vitamin B12 (1355 Da), glutathione (301 Da) and phenylalanine (165 Da). According to the peak time of the standard and the logarithmic value of its molecular weight, the linear fitting equation was obtained: y=-0.7677x+12.854 (R 2 =0.9997).

[0042] Example 1

[0043] A method for preparing a low-bitter and high-umami yeast extract comprises the following steps:

[0044] (1) 650 g of fresh yeast milk (water content of about 84.0%) was mixed with 43 g of water, and the initial pH of the system was adjusted to 8.5 at 50°C using 0.5 mol / L NaOH solution and 0.5 mol / L HCl solution. Then, 0.6 g of alkaline protease (Novozymes, enzyme activity of 800,000 to 1,000,000 U) and 0.2 g of flavor protease Flavourzyme 500MG (Novozymes) were added. The mixture was hydrolyzed at constant temperature for 18 h, then heated to 95°C and kept for 15 min to inactivate the enzyme. The mixture was then cooled to 70°C and separated by a tubular centrifuge to collect the supernatant to obtain a yeast hydrolysate A with a solid mass of 82.2 g.

[0045] (2) The pH of yeast enzymatic hydrolysate A was adjusted to 5.5 using 0.5 mol / L NaOH solution and 0.5 mol / L HCl solution, 0.2 g of propylthiol was added, and the mixture was stirred evenly at room temperature (about 25°C). The mixture was reacted at 40°C for 12 h to obtain yeast reaction solution A.

[0046] (3) After the yeast reaction solution A is concentrated to a solid content of 40% at 50°C and -0.090 mPa, it is spray-dried at an inlet air temperature of 185-190°C and an outlet air temperature of 80-85°C to obtain a powdered yeast extract product A.

[0047] The sensory evaluation results of yeast extract product A are shown in Table 1.

[0048] The amino acid distribution results of yeast extract product A are shown in Tables 2 and 3.

[0049] The peptide molecular weight distribution of yeast extract product A is shown in Figure 1 .

[0050] The hydrophobicity values ​​of yeast extract product A are shown in Table 4.

[0051] Example 2

[0052] A method for preparing a low-bitter and high-umami yeast extract comprises the following steps:

[0053] (1) Take 100 g of active dry yeast powder (water content of about 6.8%) and mix it evenly with 521 g of water, adjust its mass concentration to 15%, then heat it to 60°C, and then use 0.5 mol / L NaOH solution and 0.5 mol / L HCl solution to adjust the initial pH of the system to 8.0, then add 0.6 g alkaline protease (Novozymes, enzyme activity of 800,000-1,000,000 U) and 0.3 g flavor protease Flavourzyme 500MG (Novozymes), keep it warm for 20 h, then heat it to 95°C for 15 min to inactivate the enzyme, then cool the material to 70°C, separate and collect the supernatant using a tubular centrifuge, and obtain yeast enzymatic solution B with a solid mass of 76.7 g;

[0054] (2) The pH of yeast enzymatic hydrolysate B was adjusted to 6.0 using 0.5 mol / L NaOH solution and 0.5 mol / L HCl solution, 0.25 g of propylthiol was added, and the mixture was stirred evenly at room temperature (about 25°C). The mixture was reacted at 50°C for 14 h to obtain yeast reaction solution B.

[0055] (3) The yeast reaction solution B was concentrated to a solid content of 55% at 50°C and -0.095 mPa, and the sample was sterilized by keeping it at 95°C for 30 min to obtain a paste yeast extract product B.

[0056] The sensory evaluation results of yeast extract product B are shown in Table 1.

[0057] The amino acid distribution results of yeast extract product B are shown in Tables 2 and 3.

[0058] The peptide molecular weight distribution of yeast extract product B is shown in Figure 1 .

[0059] The hydrophobicity values ​​of yeast extract product B are shown in Table 4.

[0060] Example 3

[0061] A method for preparing a low-bitter and high-umami yeast extract comprises the following steps:

[0062] (1) 100 g of inactivated dry yeast powder (water content 5.30%) was mixed with 531 g of water and the solid concentration was adjusted to 15%. The mixture was heated to 55°C and the initial pH of the mixture was adjusted to 8.5 using 0.5 mol / L NaOH solution and 0.5 mol / L HCl solution. 0.8 g of alkaline protease (Novozymes, enzyme activity 800,000-1,000,000 U) and 0.4 g of flavor protease Flavourzyme 500MG (Novozymes) were added. The mixture was hydrolyzed for 22 h and then heated to 95°C for 15 min to inactivate the enzyme. The mixture was then cooled to 70°C and the supernatant was separated and collected using a tubular centrifuge to obtain a yeast hydrolysate C with a solid mass of 75.8 g.

[0063] (2) The pH of yeast enzymatic hydrolysate C was adjusted to 6.5 using 0.5 mol / L NaOH solution and 0.5 mol / L HCl solution, 0.3 g of propyl mercaptan was added, and the mixture was stirred evenly at room temperature (about 25°C). After reacting at 45°C for 16 h, yeast reaction solution C was obtained at room temperature;

[0064] (3) The yeast reaction solution C was concentrated to a solid content of 60% at 55°C and -0.095 mPa, and the sample was then sterilized at 95°C for 30 min to obtain a paste yeast extract product C.

[0065] The sensory evaluation results of yeast extract product C are shown in Table 1.

[0066] The amino acid distribution results of yeast extract product C are shown in Tables 2 and 3.

[0067] The peptide molecular weight distribution of yeast extract product C is shown in Figure 1 .

[0068] The hydrophobicity values ​​of yeast extract product C are shown in Table 4.

[0069] Comparative Example 1

[0070] A method for preparing a low-bitter and high-umami yeast extract (compared with the example, no propyl mercaptan is added), comprising the following steps:

[0071] (1) 100 g of inactivated dry yeast powder (water content 5.30%) was mixed with 531 g of water and the solid concentration was adjusted to 15%. The mixture was heated to 55°C and the initial pH of the system was adjusted to 8.5 using 0.5 mol / L NaOH solution and 0.5 mol / L HCl solution. 0.8 g of alkaline protease (Novozymes, enzyme activity of 800,000 to 1,000,000 U) and 0.4 g of flavor protease Flavourzyme 500MG (Novozymes) were added. The mixture was hydrolyzed for 22 h and then heated to 95°C for 15 min to inactivate the enzyme. The mixture was then cooled to 70°C and the supernatant was separated and collected using a tubular centrifuge to obtain a yeast hydrolyzate 1 with a solid mass of 75.8 g.

[0072] (2) The pH of yeast enzymatic hydrolysate 1 was adjusted to 6.5 using 0.5 mol / L NaOH solution and 0.5 mol / L HCl solution, and the yeast reaction solution 1 was obtained after reacting at 45°C for 16 h;

[0073] (3) The yeast reaction solution 1 was concentrated to a solid content of 60% at 55°C and -0.095 mPa, and the sample was then sterilized by keeping it at 95°C for 30 min to obtain a paste yeast extract product 1.

[0074] The sensory evaluation results of yeast extract product 1 are shown in Table 1.

[0075] The amino acid distribution results of yeast extract product 1 are shown in Tables 2 and 3.

[0076] The peptide molecular weight distribution of yeast extract product 1 is shown in Figure 1 .

[0077] The hydrophobicity values ​​of yeast extract product 1 are shown in Table 4.

[0078] Comparative Example 2

[0079] A method for preparing a low-bitter and high-umami yeast extract (adding an excess of propylthiol compared with the example), comprising the following steps:

[0080] (1) 100 g of inactivated dry yeast powder (water content 5.30%) was mixed with 531 g of water and the solid concentration was adjusted to 15%. The mixture was heated to 55°C and the initial pH of the system was adjusted to 8.5 using 0.5 mol / L NaOH solution and 0.5 mol / L HCl solution. 0.8 g of alkaline protease (Novozymes, enzyme activity of 800,000 to 1,000,000 U) and 0.4 g of flavor protease Flavourzyme 500MG (Novozymes) were added. The mixture was hydrolyzed for 22 h and then heated to 95°C for 15 min to inactivate the enzyme. The mixture was then cooled to 70°C and the supernatant was separated and collected using a tubular centrifuge to obtain a yeast hydrolysate 2 with a solid mass of 75.8 g.

[0081] (2) The pH of yeast enzymatic hydrolysate 2 was adjusted to 6.5 using 0.5 mol / L NaOH solution and 0.5 mol / L HCl solution, 0.8 g of propylthiol was added, and the mixture was stirred evenly at room temperature (about 25°C). The mixture was reacted at 45°C for 16 h to obtain yeast reaction solution 2;

[0082] (3) The yeast reaction solution 2 was concentrated to a solid content of 60% at 55°C and -0.095 mPa, and the sample was then sterilized at 95°C for 30 min to obtain a paste yeast extract product 2.

[0083] The sensory evaluation results of yeast extract product 2 are shown in Table 1.

[0084] The amino acid distribution results of yeast extract product 2 are shown in Tables 2 and 3.

[0085] The peptide molecular weight distribution of yeast extract product 2 is shown in Figure 1 .

[0086] The hydrophobicity values ​​of yeast extract product 2 are shown in Table 4.

[0087] Comparative Example 3

[0088] A method for preparing a low-bitter and high-umami yeast extract (compared with the example, no propanethiol is added and no heat treatment is performed), comprising the following steps:

[0089] (1) Take 100 g of inactivated dry yeast powder (water content 5.30%) and mix it evenly with 531 g of water, adjust its solid concentration to 15%, heat it to 55°C, and then use 0.5 mol / L NaOH solution and 0.5 mol / L HCl solution to adjust the initial pH of the system to 8.5, then add 0.8 g alkaline protease (Novozymes, enzyme activity is 800,000-1,000,000 U) and 0.4 g flavor protease Flavourzyme 500MG (Novozymes), keep it warm for 22 h, then heat it to 95°C and keep it warm for 15 min to inactivate the enzyme, then cool the material to 70°C, separate and collect the supernatant using a tubular centrifuge to obtain yeast enzymatic solution 3 with a solid mass of 75.8 g;

[0090] (2) The yeast hydrolysate 3 was concentrated to a solid content of 60% at 55°C and -0.095 mPa, and the sample was then sterilized at 95°C for 30 min to obtain a paste yeast extract 3.

[0091] The sensory evaluation results of yeast extract product 3 are shown in Table 1.

[0092] The amino acid distribution results of yeast extract product 3 are shown in Tables 2 and 3.

[0093] The peptide molecular weight distribution of yeast extract product 3 is shown in Figure 1 .

[0094] The hydrophobicity values ​​of yeast extract product 3 are shown in Table 4.

[0095] Comparative Example 4

[0096] A method for preparing a low-bitter and high-umami yeast extract (compared with the embodiment, the yeast hydrolysate is mixed with propanethiol, and no thermal reaction and subsequent reaction are performed), comprising the following steps:

[0097] (1) 100 g of inactivated dry yeast powder (water content 5.30%) was mixed with 531 g of water and the solid concentration was adjusted to 15%. The mixture was heated to 55°C and the initial pH of the system was adjusted to 8.5 using 0.5 mol / L NaOH solution and 0.5 mol / L HCl solution. 0.8 g of alkaline protease (Novozymes, enzyme activity of 800,000 to 1,000,000 U) and 0.4 g of flavor protease (Novozymes, Flavourzyme, enzyme activity of 500 MG) were added. The mixture was hydrolyzed for 22 h and then heated to 95°C for 15 min to inactivate the enzyme. The mixture was then cooled to 70°C and the supernatant was separated and collected using a tubular centrifuge to obtain yeast hydrolyzate 4 with a solid mass of 75.8 g.

[0098] (2) The pH of yeast hydrolyzate 2 was adjusted to 6.5 using 0.5 mol / L NaOH solution and 0.5 mol / L HCl solution, 0.3 g of propyl mercaptan was added, and the mixture was stirred evenly at room temperature (about 25°C) to obtain yeast extract product 4.

[0099] The sensory evaluation results of yeast extract product 4 are shown in Table 1.

[0100] The amino acid distribution results of yeast extract product 4 are shown in Tables 2 and 3.

[0101] The peptide molecular weight distribution of yeast extract product 4 is shown in Figure 1 .

[0102] The hydrophobicity value of yeast extract product 4 is shown in Table 4.

[0103] Comparative Example 5

[0104] A method for preparing a low-bitter and high-umami yeast extract (compared with the example, only enzymatic hydrolysis and centrifugal separation were performed, and no propanethiol was added and no subsequent reaction was performed), comprising the following steps:

[0105] 100 g of inactivated dry yeast powder (water content 5.30%) was mixed with 531 g of water and the solid concentration was adjusted to 15%. Then the temperature was raised to 55°C, and the initial pH of the system was adjusted to 8.5 using 0.5 mol / L NaOH solution and 0.5 mol / L HCl solution. Then 0.8 g of alkaline protease (Novozymes, enzyme activity of 800,000 to 1,000,000 U) and 0.4 g of flavor protease (Novozymes Flavourzyme, enzyme activity of 500 MG) were added. After keeping the temperature for 22 h, the temperature was raised to 95°C for 15 min to inactivate the enzyme. Then the material was cooled to 70°C, and the supernatant was separated and collected using a tubular centrifuge to obtain a yeast hydrolysate 5 with a solid mass of 75.8 g.

[0106] The sensory evaluation results of yeast extract product 5 are shown in Table 1.

[0107] The amino acid distribution results of yeast extract product 5 are shown in Tables 2 and 3.

[0108] The peptide molecular weight distribution of yeast extract product 5 is shown in Figure 1 .

[0109] The hydrophobicity value of yeast extract product 5 is shown in Table 4.

[0110] Table 1 Sensory five taste evaluation table of embodiments and comparative examples

[0111]

[0112] Table 2 Free amino acid composition of yeast extract (unit: %)

[0113]

[0114] Table 3 Total amino acid composition of yeast extract (unit: %)

[0115]

[0116] Table 4 Hydrophobicity values ​​of yeast extracts (unit: kJ / mol)

[0117]

[0118] Tables 1 to 4 are sensory evaluations of yeast extracts obtained in Examples and Comparative Examples, as well as free amino acids, percentages of total amino acids, and hydrophobicity values. Figure 1 This is the accumulation diagram of the molecular weight distribution of yeast extract peptides.

[0119] According to the sensory evaluation results in Table 1, the yeast extract products (Examples 1 to 3) prepared by the method of the present invention all obtained high umami scores (5.40 to 5.85) and low bitterness scores (0.68 to 0.98). The umami and sweetness scores of the yeast extract products obtained in the comparative examples (yeast extract products 1 to 5) were significantly lower than those of the yeast extracts obtained in the examples, and showed stronger bitterness and sourness, which shows that the yeast extract with better flavor quality can be prepared according to the method of the present invention.

[0120] Among them, the difference between Comparative Example 1 and the Example is that propanethiol was not added to the yeast hydrolysate, and only a thermal reaction was performed. The overall flavor of the obtained yeast extract product 1 was worse than that of the yeast extract products A to C of the Example, indicating that the addition of propanethiol and the yeast hydrolysate for thermal reaction can significantly improve the flavor quality of the yeast extract;

[0121] The difference between Comparative Example 2 and the Example is that the amount of propanethiol added exceeds the scope of the present invention. Although the umami (5.19) and salty taste scores of yeast extract 2 are higher (3.57), and the bitterness score is lower (1.80), excessive propanethiol will make yeast extract product 2 have a significant sulfur odor, which seriously affects the flavor quality of the yeast extract.

[0122] The difference between Comparative Example 3 and the Example is that propanethiol was not added to the yeast hydrolysate and no thermal reaction was performed. The difference between Comparative Example 4 and the Example is that propanethiol was added and mixed with the yeast hydrolysate, but no thermal reaction occurred. Comparative Example 5 is a yeast hydrolysate. The flavor quality of the yeast extracts prepared in Comparative Examples 3, 4, and 5 is poor, and the umami, saltiness, and sweetness scores of the yeast extracts in Comparative Examples 3 and 4 are slightly higher, and the bitterness and sourness scores are slightly lower. This is because the hydrolysate can use its own amino and carbonyl compounds to perform a mild Maillard reaction during concentration and sterilization. Although propanethiol was added to the yeast hydrolysate in Comparative Example 4, the propanethiol did not undergo a thermal reaction, but instead caused the product to produce sourness and bitterness.

[0123] Table 2 shows the free amino acid composition of yeast extracts. During food processing, proteins are hydrolyzed by proteases to generate small peptides and free amino acids, which directly affect the sensory properties of food, including the taste, aroma and overall flavor of food. According to the results in Table 2, the free umami amino acids in the products (yeast extracts A-C) prepared by the method of the present invention account for as high as 34.93% to 35.82%, while the bitter amino acids account for only 24.35% to 25.09%, and the hydrophobic amino acids account for a relatively low proportion (33.88% to 34.01%), so that the overall flavor of the yeast extracts A-C of the examples is better, showing a higher umami taste and a lower bitterness intensity.

[0124] Compared with the example, the free umami amino acids in the yeast extract of comparative example 1 account for a lower proportion, and the bitter amino acids account for a higher proportion, which indicates that the addition of propanethiol to react with the yeast hydrolysate will consume part of the free bitter amino acids in the hydrolysate; the difference between comparative example 2 and the example is that the addition amount of propanethiol exceeds the range specified in the present invention, and the umami amino acids in the yeast extract product 2 account for a lower proportion than those in the example product, while the bitter amino acids account for a higher proportion than those in the example product, indicating that only by adding an appropriate amount of propanethiol can a better flavor quality improvement effect be achieved.

[0125] The difference between Comparative Example 3 and the embodiment is that propanethiol was not added to heat react with the yeast hydrolysate, in Comparative Example 4, the yeast hydrolysate was mixed with propanethiol, but no subsequent heat reaction occurred, and in Comparative Example 5, the yeast hydrolysate was not subjected to any subsequent reaction. The free amino acid distribution of the three showed that the umami and sweet amino acids were low, and the bitter amino acids were high. Among them, studies have shown that leucine and isoleucine have obvious bitterness. The proportion of isoleucine and leucine in the products prepared in Comparative Examples 3, 4, and 5 is higher than that of yeast extracts A to C prepared according to the method of the present invention, thereby showing a higher bitterness intensity. The difference in the results of Comparative Examples 3 and 5 is due to the fact that heat reactions such as concentration and sterilization are conducive to the reaction of bitter substances such as hydrophobic amino acids, which in turn affects the content of free amino acids.

[0126] Table 3 shows the total amino acid composition of yeast extract. Monomeric amino acids have certain flavor properties, such as glutamic acid and aspartic acid have umami taste, and hydrophobic amino acids such as proline, valine, leucine, isoleucine and phenylalanine are often associated with bitter taste. Yeast extract products A-C prepared by the process of the present invention have a high proportion of umami amino acids and sweet amino acids, and a low proportion of bitter amino acids, so that yeast extracts A-C have a strong umami taste and a weak bitter taste.

[0127] The yeast extracts obtained in Comparative Examples 1 to 5 have a high proportion of bitter amino acids, which is also an important reason for their strong bitterness. In Comparative Examples 1, 3, and 5, no propanethiol was added to react with the yeast hydrolysate, so that the hydrophobic amino acids in the obtained yeast extract products accounted for a relatively high proportion, and thus tasted a stronger bitter taste. In Comparative Example 3, the yeast hydrolysate was directly concentrated and sterilized, indicating that appropriate thermal reaction is conducive to the further reaction and consumption of hydrophobic substances. Although propanethiol was added to Comparative Example 4, the yeast hydrolysate in Comparative Examples 4 and 5 did not undergo any subsequent reactions, so compared with the examples, the proportion of umami amino acids was low and the proportion of sweet amino acids was low. Among them, the proportion of alanine in yeast extract product 5 is 78.68% of that in yeast extract product A of Example 1 using the method of the present invention, resulting in insufficient umami taste and more prominent bitterness. Studies have shown that a reduction in the proportion of alanine will not only reduce the sweetness of the product, but also affect the umami perception. The difference between Comparative Example 2 and the example lies in the amount of propanethiol added. Since excessive propanethiol is added in Comparative Example 2, a high content of sulfur-containing compounds will produce irritating, spicy, sulfur-smelling and other tastes, thereby affecting the taste characteristics of the yeast extract.

[0128] Table 4 shows that the yeast extracts (Examples 1-3) prepared according to the method of the present invention have lower hydrophobicity values ​​(4.60-4.70) and better flavor quality; while the hydrophobicity values ​​of the comparative products are higher, the bitterness is stronger, and the flavor quality is poor. Compared with the examples, no propanethiol was added to comparative examples 1, 3, and 5, and the hydrophobicity values ​​of the obtained yeast extracts were significantly higher than those of the yeast extracts in the examples, indicating that the addition of propanethiol to react with the yeast hydrolysate will reduce the hydrophobicity value of the yeast extract and further reduce its bitterness intensity. Although propanethiol was added to the yeast hydrolysate in comparative example 4, no thermal reaction occurred, so its hydrophobicity value was also higher than that of the yeast extract in the examples. There are also differences in the hydrophobicity values ​​of comparative examples 1, 3, 4, and 5, indicating that the thermal reaction and the subsequent concentration and sterilization process have an impact on the hydrophobicity value of the yeast extract, thereby affecting the final comprehensive quality of the product. In comparative example 2, excessive propyl mercaptan was added to react with yeast hydrolyzate, which reduced the hydrophobic value of yeast extract and thus reduced its bitterness intensity. However, the reaction of propyl mercaptan was not complete, and its sulfur and irritating taste would also bring sourness, bitterness and other undesirable tastes to the product. In comparative example 4, propyl mercaptan was added to mix with yeast extract, but no subsequent thermal reaction occurred, which would also bring sourness and bitterness due to the incomplete reaction of propyl mercaptan.

[0129] Figure 1 The figure is a stacking diagram of the peptide molecular weight distribution of the yeast extract obtained in the embodiment and the comparative example. The molecular weight distribution of the peptides A to C of the yeast extract products in the embodiment generally shows that the proportion of large molecular weight peptides is low (12.08% to 14.04%) and the proportion of small molecular weight peptides is high (13.56% to 14.46%), mainly because the addition of propanethiol and the yeast enzymatic hydrolysate to produce a thermal reaction will cause the large molecular weight peptides to break and generate small peptides with lower molecular weight. Among them, the proportion of 500 to 1000 Da peptide segments in the yeast extract of the embodiment is relatively low (4.85% to 5.07%), and the proportion of peptide segments less than 500 Da is relatively high (13.56% to 14.46%). Studies have shown that the molecular weight of bitter peptides is mostly distributed in the range of 500 to 1000 Da, while low molecular weight peptides less than 500 Da have good flavor qualities such as umami and sweetness. It can be seen that the yeast extract prepared by the method of the present invention contains a higher content of umami peptides and has better flavor quality.

[0130] The difference between the results of the peptide molecular weight distribution of yeast extracts in Comparative Examples 1, 3, 4, and 5 and the Example shows that the absence of propyl mercaptan to react with the yeast hydrolysate will result in a higher proportion of peptides greater than 5000 Da in the yeast extract. The differences between Comparative Examples 1, 3, 4, and 5 show that a certain degree of thermal reaction is conducive to the cleavage of large molecular peptides into small molecular peptides with higher umami taste; some short peptides will also undergo Maillard reaction during the concentration and sterilization process, thereby affecting the peptide molecular weight distribution of the final yeast extract; in addition, in Comparative Example 2, the yeast hydrolysate and propyl mercaptan undergo sufficient thermal reaction (the propyl mercaptan content is too high), resulting in an increase in the proportion of low molecular weight peptides in the peptide molecular weight distribution of the yeast extract, but the incompletely reacted propyl mercaptan will cause the yeast extract to have an unpleasant sulfur odor.

[0131] The above embodiments are preferred implementation modes of the present invention, but the implementation modes of the present invention are not limited to the above embodiments. Any other changes, modifications, substitutions, combinations, and simplifications that do not deviate from the spirit and principles of the present invention should be equivalent replacement methods and are included in the protection scope of the present invention.

Claims

1. A method for preparing a low-bitter and high-umami yeast extract, characterized in that The following steps are involved: (1) Mix yeast and water, adjust the solid concentration, raise the temperature to 50-60°C, adjust the pH of the system to 8.0-8.5, then add protease, keep the temperature for 18-22 hours, inactivate the enzyme, centrifuge, and collect the supernatant to obtain yeast hydrolyzate; (2) adjusting the pH value of the yeast hydrolysate to 5.5 to 6.5, adding 0.2 to 0.4% of the solid mass of the yeast hydrolysate to propanethiol, stirring evenly, and reacting at 40 to 50° C. for 12 to 16 hours to obtain a reaction solution containing yeast extract; The protease described in step (1) is alkaline protease and flavor protease; The alkaline protease and flavor protease are added in a ratio of (2-3):1; The amount of the protease added in step (1) is 0.7-1.3% of the dry matter mass of the yeast; The reaction solution is concentrated, sterilized and spray-dried to obtain a powdered yeast extract.

2. The preparation method according to claim 1, characterized in that: The yeast described in step (1) is yeast milk, active dry yeast or inactivated dry yeast powder.

3. The preparation method according to claim 1, characterized in that: The solid concentration is adjusted in step (1), and the adjusted solid concentration is 10-18%.

4. A yeast extract, characterized in that The method is prepared by the method described in any one of claims 1 to 3.

5. Use of the yeast extract according to claim 4 in food.

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