A method for brewing Chinese rice wine using proanthocyanidins to reduce the content of ethyl carbamate

Abstract

The present invention discloses a method for brewing yellow rice wine by using proanthocyanidins to reduce the content of ethyl carbamate, belonging to the fields of food safety and fermentation brewing. The present invention solves the problems that the methods for reducing ethyl carbamate in the current yellow rice wine brewing process have certain risks and unpredictability, are prone to cause acidification of yellow rice wine, require a large amount of time, energy and high costs. The method for brewing yellow rice wine by using proanthocyanidins to reduce the content of ethyl carbamate inhibits the production of ethyl carbamate by adding proanthocyanidins during the fermentation and aging processes of yellow rice wine. The method of the present invention can effectively overcome the drawbacks existing in the current ways of degrading ethyl carbamate during the fermentation and aging processes of yellow rice wine, is safe, efficient, saves time and energy, and reduces production costs. The method of the present invention is applicable to the brewing of yellow rice wine.

Description

Technical Field

[0001] The present invention relates to the fields of food safety and fermentation brewing, and particularly relates to a method for brewing Chinese rice wine by using proanthocyanidins to reduce the content of ethyl carbamate. Background Art

[0002] Ethyl carbamate (EC) is a chemical substance widely present in fermented foods and alcoholic beverages, and is mainly metabolized during food fermentation and storage. Nettleship and Henshaw first discovered in 1943 that ethyl carbamate could cause malignant tumors in the lungs of mice. Subsequently, a large number of studies have proven that EC can cause tumors in multiple species. Therefore, in 2007, the World Health Organization (WHO) classified ethyl carbamate as a "Group 2A" carcinogen.

[0003] The most common formation method of ethyl carbamate is the direct esterification of carbamoyl compounds (mainly including urea and citrulline) with ethanol under acidic heating conditions. Urea is generated by yeast degrading arginine during the brewing process of wine. According to the regulation of nitrogen metabolism in cells, part of the urea in the cells is released into the wine; citrulline is generated from arginine under the action of arginine deiminase, and citrulline can be secreted extracellularly into the wine. The urea and citrulline entering the wine can be esterified with ethanol to form ethyl carbamate.

[0004] Currently, there are three main approaches to controlling ethyl carbamate (EC) content in winemaking. First, genetically engineered bacteria are used to reduce ethyl carbamate in the fermentation broth. These methods fall into two categories: one involves constructing mutant strains that modify genes related to urea metabolism and cell membrane transport, and the other involves influencing the expression of genes related to urea metabolism through metabolic regulation. According to the Regulations on the Safety Management of Agricultural Genetically Modified Organisms, products produced using genetically modified agricultural organisms must undergo review, registration, or evaluation in accordance with relevant laws. Therefore, the use of genetically engineered bacteria for food fermentation still carries certain risks and unpredictability. Second, strains that are low-yielding or degrade EC and its precursors are screened to control EC at the source. Patent publication number CN104845811A discloses a method for brewing rice wine using Oenococcus oeni to degrade ethyl carbamate. The method includes soaking rice, steaming rice, watering, placing the rice in a vat and setting it in a pot, adding koji and water, fermentation, and post-processing. Oenococcus oeni CICC6066 is inoculated into the fermentation broth 5-20 days after fermentation. This invention degrades EC produced during the winemaking process by adding Oenococcus oeni bacteria, which produce enzymes capable of degrading it. However, improper addition of Oenococcus oeni can easily cause the wine to become rancid. Strain screening requires considerable time and effort, and the bacteria also suffer from genetic instability. A third approach involves exogenous addition of certain substances. Adding urease catalyzes the hydrolysis of urea into ammonia and carbon dioxide, reducing extracellular urea secretion and ultimately reducing ethyl carbamate. While enzymatic degradation of ethyl carbamate is safe and effective, this method is relatively costly. Summary of the invention

[0005] The invention discloses a rice wine brewing method using proanthocyanidins to reduce the content of ethyl carbamate, which solves the problems that the current method for reducing ethyl carbamate in the rice wine brewing process has certain risks and unpredictability, easily causes rice wine to become rancid, requires a lot of time and energy, and is high in cost.

[0006] The specific technical solutions are as follows:

[0007] A method for brewing yellow rice wine by utilizing proanthocyanidins to reduce ethyl carbamate content, the method comprising the following steps:

[0008] Step 1: Soak the raw materials at room temperature according to the material-water mass ratio;

[0009] Step 2: Steam the raw materials and then sprinkle water on them to control the temperature of the raw materials;

[0010] Step 3: Place the raw materials in a vat and ferment them for 30 to 40 hours.

[0011] Step 4: After 48 hours of nesting in the tank, add proanthocyanidins to the raw materials;

[0012] Step 5: After fermentation ends, heat the wine for 30 minutes, filter it after cooling to room temperature, and then place it in a stainless steel tank for aging;

[0013] Step 6: Add proanthocyanidins during the aging stage.

[0014] Furthermore, in the said Step 1, the mass ratio of the material to water is 1:1.2, and the soaking time is 44h - 48h.

[0015] Furthermore, in the said Step 2, control the temperature of the raw materials at 28°C - 32°C.

[0016] Furthermore, in the said Step 3, the koji is wheat koji, which is stirred evenly with rice soaking water and then added. The addition amount of the koji is 2% of the mass of the raw materials.

[0017] Furthermore, in the said Step 4, the addition amount of proanthocyanidins is 0.1g / L - 1g / L.

[0018] Furthermore, in the said Step 5, the temperature for heating the wine is 80°C - 85°C.

[0019] Furthermore, in the said Step 6, the addition amount of proanthocyanidins is 0.1g / L - 1g / L.

[0020] The present invention provides a method for inhibiting the production of ethyl carbamate during the fermentation and aging of yellow rice wine by adding proanthocyanidins. This method does not require the introduction of genetically engineered strains and does not require subsequent treatment, and can effectively overcome the drawbacks existing in the current methods for degrading ethyl carbamate. The main principle of the method of the present invention involves the influence of proanthocyanidins on yeast metabolism and the alcoholysis reaction in the fermentation system.

[0021] The method provided by the present invention is safe, efficient, time - and energy - saving, and reduces production costs. Description of the Drawings

[0022] Figure 1 is the EC concentration after the fermentation of yellow rice wine;

[0023] Figure 2 is the EC concentration in the sample after the aging of yellow rice wine;

[0024] Figure 3 is the flavor wheel of yellow rice wine;

[0025] Figure 4 is the flavor wheel of yellow rice wine after fermentation;

[0026] Figure 5 is the taste wheel of yellow rice wine after fermentation. Detailed Embodiments

[0027] Experimental Strains and Raw Materials

[0028]

[0029] Example 1

[0030] Soak the glutinous rice at room temperature for 44 hours, and control the material-water mass ratio to 1:1.2. After steaming the glutinous rice, sprinkle water on it to keep the temperature of the glutinous rice at about 28°C. Put the glutinous rice into a pot and add malt koji that has been stirred evenly with rice soaking water after 30 hours. The amount of malt koji added is 2% of the mass of the glutinous rice. 48 hours after putting the glutinous rice into the pot, add 0.1g / L and 1g / L proanthocyanidins (PAS) to the fermentation liquid respectively. After the fermentation is completed, the concentration of EC is detected. This embodiment sets up 3 parallel experiments, of which Group 1 is a blank control group, Group 2 is added with 0.1g / L proanthocyanidins, and Group 3 is added with 1g / L proanthocyanidins.

[0031] After fermentation, the wine was decocted at 80°C for 30 minutes to eliminate any unpleasant flavors and improve its quality. After cooling to room temperature, the wine was filtered and then aged in stainless steel tanks. At the beginning of the aging period, 0.1g / L and 1.0g / L PAS were added to the second and third groups, respectively. Samples were collected after 50 days to measure changes in EC concentration. The finished product was then tested for EC, color, and flavor.

[0032] Example 2

[0033] Soak the rice at room temperature for 44 hours, and control the material-water mass ratio to 1:1.2. After steaming the rice, sprinkle water on it to keep the rice temperature at about 28°C. Put the rice into a pot and add malt koji that has been stirred evenly with rice soaking water after 30 hours. The amount of malt koji added is 2% of the rice mass. 48 hours after putting the rice into the pot, add 0.1g / L and 1g / L proanthocyanidins (PAS) to the fermentation liquid respectively. After the fermentation is completed, the concentration of EC is detected. This embodiment sets up 3 parallel experiments, of which Group 1 is a blank control group, Group 2 is added with 0.1g / L proanthocyanidins, and Group 3 is added with 1g / L proanthocyanidins.

[0034] After fermentation, the wine was decocted at 80°C for 30 minutes to eliminate any unpleasant flavors and improve its quality. After cooling to room temperature, the wine was filtered and then aged in stainless steel tanks. At the beginning of the aging period, 0.1g / L and 1.0g / L PAS were added to the second and third groups, respectively. Samples were collected after 50 days to measure changes in EC concentration. The finished product was then tested for EC, color, and flavor.

[0035] Example 3

[0036] Soak the corn at room temperature for 48 h, and control the mass ratio of material to water at 1:1.2. Steam the corn and then sprinkle it with water to keep the temperature of the corn at about 32 °C. Put the corn into the vat and build the pot. After 40 h, add wheat koji evenly stirred with the soaking water. The addition amount of wheat koji is 2% of the mass of the corn. 48 h after building the nest in the vat, add 0.1 g / L and 1 g / L proanthocyanidins (PAS) to the fermentation broth respectively. After the fermentation is completed, detect the concentration of EC. This example sets 3 parallel experiments, where the first group is the blank control group, the second group is added with 0.1 g / L proanthocyanidins, and the third group is added with 1 g / L proanthocyanidins.

[0037] After the fermentation is completed, heat the raw wine at 85 °C for 30 min to remove the off-flavors of the raw wine and improve the wine quality. After cooling to room temperature, filter it, and then place it in a stainless steel tank for aging. At the beginning of the aging stage, add treatments of 0.1 g / L and 1.0 g / L PAS to the second group and the third group respectively, and sample and detect the change of EC concentration every 50 days. Conduct EC detection, color comparison and flavor summary on the finished product.

[0038] Example 4

[0039] Soak the barley at room temperature for 48 h, and control the mass ratio of material to water at 1:1.2. Steam the barley and then sprinkle it with water to keep the temperature of the barley at about 32 °C. Put the barley into the vat and build the pot. After 40 h, add wheat koji evenly stirred with the soaking water. The addition amount of wheat koji is 2% of the mass of the rice. 48 h after building the nest in the vat, add 0.1 g / L and 1 g / L proanthocyanidins (PAS) to the fermentation broth respectively. After the fermentation is completed, detect the concentration of EC. This example sets 3 parallel experiments, where the first group is the blank control group, the second group is added with 0.1 g / L proanthocyanidins, and the third group is added with 1 g / L proanthocyanidins.

[0040] After the fermentation is completed, heat the raw wine at 85 °C for 30 min to remove the off-flavors of the raw wine and improve the wine quality. After cooling to room temperature, filter it, and then place it in a stainless steel tank for aging. At the beginning of the aging stage, add treatments of 0.1 g / L and 1.0 g / L PAS to the second group and the third group respectively, and sample and detect the change of EC concentration every 50 days. Conduct EC detection, color comparison and flavor summary on the finished product.

[0041] Example 5

[0042] Result determination

[0043] 1. Detection of EC concentration.

[0044] EC in the samples was analyzed using a gas chromatography (GC) system (Guengerich and Kim, 1991; Wang et al., 2021), which was equipped with a mass selective detector using an electron impact (70 eV) ionization source. The mass spectrometry was carried out in the selected ion monitoring mode, and propyl carbamate was added as an internal standard. The temperature programming was set to hold at 80 °C for 2 min, then rise to 230 °C at a rate of 10 °C / min and hold at this temperature for 2 min. A CPWax capillary column with a specification of 60 m in length, 0.25 mm in inner diameter, and 0.25 μm in film thickness was used for the separation of EC. The inlet temperature was 250 °C and the ion source temperature was 230 °C. 1.0 μL of the sample was injected into the gas chromatography system without splitting.

[0045] 2. Determination of chromaticity.

[0046] A WSC-SM colorimeter was used to measure the color difference of the supernatant obtained during the brewing process. The specific measurement method referred to the operation procedure of the colorimeter, and the red value (a) and yellow value (b) displayed on the colorimeter were recorded.

[0047] 3. Sensory evaluation of the samples.

[0048] The experimenter poured the wine samples into plastic cups with three-digit random codes and presented them to the evaluators in sequence quickly. The evaluators smelled and tasted the samples to be tested independently without external interference and obtained their own evaluation results. After each tasting of the wine sample, the evaluators needed to rinse their mouths with pure water and rest for 10 min to avoid olfactory fatigue. The experiment was repeated 3 times. The experimenter provided the sensory descriptive words of wine, yellow rice wine, and white liquor to the evaluators for reference, calculated the mean value of the appropriateness of all evaluators, selected the words with a mean value greater than 4 for variance analysis, scored after obtaining the main attribute descriptive words, and drew a sensory radar chart.

[0049] Result analysis

[0050] 1. Changes in EC during the fermentation stage.

[0051] By adding PAS during the fermentation process, it was found that as the addition amount of PAS increased, the inhibition degree of EC generation increased. Among them, the EC concentration in No. 1 yellow rice wine decreased by 20.81%, and the most decreased was No. 4 yellow rice wine, with the EC concentration decreasing by 8.06% compared with the control group, as Figure 1 shown.

[0052] 2. Changes in EC during the aging stage.

[0053] The formation of EC during the aging stage is an important source of EC in the final product of yellow rice wine. As the aging process proceeds, the content of ethyl carbamate in different experimental groups continuously increases. In the control group, the NO.2 group had the largest increase in EC concentration, with an increase of 123.94%. After 300 days of aging, in the experimental group treated with 1 g / L proanthocyanidins in the NO.1 group, the amount of EC generated over time was the lowest. However, compared with the control, the NO.2 yellow rice wine had the largest reduction in EC, with a reduction of 30.35%, as Figure 2 shown.

[0054] 3. Color change.

[0055] By analyzing the color difference data of yellow rice wine (NO.1 - NO.4) (Table 1) after fermentation, it can be seen from the data that the PAS treatment mainly affects the red value. In yellow rice wine, due to the antioxidant effect of PAS, long-term aging will cause the pigment macromolecules in the wine liquid to oxidize and turn yellow. The addition of PAS reduces the increase in the yellow value of the wine liquid by reducing pigment oxidation.

[0056] 4. Flavor change.

[0057] The flavor wheel is a scientific and effective descriptive language classification system, usually in the form of a 2 - 3 - layer wheel to visually express the sensory characteristics and commonalities of product flavors, and classify and refine flavors layer by layer from the inside out. After discussion by the tasting panel and summarizing the obtained descriptive languages, a yellow rice wine flavor wheel is constructed from a flavor descriptor thesaurus that consumers can understand and experience( Figure 3 ). The yellow rice wine flavor wheel is divided into 3 layers and mainly includes 4 aspects: aroma, taste, flavor, and aftertaste. The aroma part includes 32 aroma descriptors; the taste part includes 8 taste descriptors, divided into purity, softness, fullness, and harmony; the flavor part includes 5 descriptors, divided into basic flavor and astringency. This flavor wheel provides a more comprehensive set of descriptive languages for the flavor expression of yellow rice wine and an important basis for the standardization of the sensory quality of yellow rice wine.

[0058] Based on the flavor wheel, the attributes of each aspect are further adjusted. Together with experienced evaluators and enterprise marketing personnel, a 20 - member expert tasting panel was formed. After tasting the wine samples, the specific scores of each index are shown in the figure. From the scoring of yellow rice wine( Figure 4 ), it can be seen that the PAS mainly affects the traditional aroma of yellow rice wine, but the average score change does not exceed 1 point, and it has little impact on other aromas.

[0059] 5. Taste change.

[0060] PAS has the ability to bind with proteins in saliva to produce precipitation, making the inner wall of the oral cavity lose its smoothness and causing the contraction of the tongue epithelial tissue, thus producing a dry feeling. The possible reasons include the reversible binding theory, the selectivity theory, and the coprecipitation theory. Through the data of yellow rice wine ( Figure 5 ), it can be seen that the addition of PAS affects the astringency in the taste. The astringency of the wine is positively correlated with the addition amount of PAS. When the addition amount is 0.1 g / L, the influence on the astringency of yellow rice wine is small, but when the addition amount is 1.0 g / L, the astringency of yellow rice wine increases significantly, and there will be a certain degree of bitterness, but neither reduces the overall quality of yellow rice wine.

[0061] Table 1 Color difference data of yellow rice wine after fermentation

[0062]

Claims

1. A method for brewing Chinese rice wine using proanthocyanidins to reduce the content of ethyl carbamate, characterized in that, The method includes the following steps: Step 1: Soak the raw materials at room temperature according to the mass ratio of raw materials to water; Step 2: Steam the raw materials and then sprinkle water, controlling the temperature of the raw materials; Step 3: Put the raw materials into the vat and make a nest. After 30 - 40 hours, add koji for fermentation; Step 4: After 48 hours of making a nest in the vat, add proanthocyanidins to the raw materials; Step 5: After the fermentation is completed, fry the wine for 30 min, filter it after cooling to room temperature, and then age it in a stainless steel tank; Step 6: Add proanthocyanidins during the aging stage; The addition amount of proanthocyanidins in Step 4 is 0.1 g / L - 1 g / L; The addition amount of proanthocyanidins in Step 6 is 0.1 g / L - 1 g / L.

2. The method according to claim 1, wherein In Step 1, the mass ratio of raw materials to water is 1:1.2, and the soaking time is 44 h - 48 h.

3. The method according to claim 1, wherein In Step 2, control the temperature of the raw materials at 28°C - 32°C.

4. The method according to claim 1, wherein In Step 3, the koji is wheat koji, which is stirred evenly with rice soaking water and then added. The addition amount of the koji is 2% of the mass of the raw materials.

5. The method according to claim 1, characterized in that In Step 5, the temperature for frying the wine is 80°C - 85°C.

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