Method for judging fermentation end point of red date flavor fermentation liquor and application of method

Abstract

The invention relates to a method for judging the fermentation end point of red date flavor fermentation liquor and application of the method, and the fermentation end point of the red date flavor fermentation liquor is judged by adopting a method of combining sensory evaluation with detection of a gas chromatograph-mass spectrometer. The sensory score of the fermented bouquet (not obvious) is lower than 6, and after analysis by a gas chromatograph-mass spectrometer, when the ratio of the total content of the characteristic honey sweet flower aroma substances, namely beta-damascenone and phenethyl alcohol, to the content of the characteristic bouquet aroma substance component, namely amyl alcohol, is 0.4-0.5, the fermentation end point is determined. Compared with the prior art, the method has the advantages that the fermentation end point of the red date fermentation liquid can be simply and quickly judged, and technical support can be provided for quality detection in the mixed fermentation process of the red date juice and regulation and control of the flavor quality of the red date fermentation beverage.

Description

Technical Field

[0001] The invention relates to the technical field of mixed bacteria fermentation technology, and in particular to a method for judging the fermentation end point of red date flavor fermentation liquid and application thereof. Background Art

[0002] Jujube is a traditional economic forest fruit in my country, with many varieties and abundant annual output. Jujube is an important pillar industry for Xinjiang's regional economic development. However, with the improvement of people's living standards, consumers pay more attention to the nutritional health and flavor characteristics of food. There are more and more fermented and processed products based on red dates: red date wine, red date vinegar, fermented red date beverages, etc.

[0003] Fermentation is the metabolic activity of microorganisms under anaerobic or aerobic conditions. It has the advantages of improving the nutritional value of food, controlling food production costs, and increasing food flavor and taste. Microbial fermentation can not only release volatile aroma compounds, but also biosynthesize volatile substances by adding biological enzymes. Lactic acid bacteria and yeast are classic strains in traditional fermented foods. Yeast plays an outstanding role in fermented beverages because it can continuously accumulate a certain concentration of ethanol and carbon dioxide and produce rich aroma compounds. Lactic acid bacteria are particularly important in the fermentation process. In addition to producing the required organic acids, amino acids and peptides that inhibit the growth of undesirable organisms, they can also inhibit the growth of harmful bacteria under highly acidic conditions.

[0004] In recent years, there have been more and more inventions on the research of microbial inoculation and fermentation of red date juice. The difference in inoculated substrates makes the speed of microorganisms participating in metabolism different. The co-fermentation of red date juice by lactic acid bacteria and non-brewer's yeast can enrich the aroma of red date juice and neutralize the original sweetness of red date juice. However, the mixed bacteria fermentation agent inoculated in the red date fermentation liquid is complex and diverse, and it is difficult to determine its fermentation end point. Flavor is one of the important indicators reflecting the quality of fermented products. Good flavor can promote people's consumption and love of fermented products. At present, most of the flavor analysis and determination of fermented products are carried out by sensory evaluation or flavor instrument analysis methods.

[0005] Chinese invention patent CN 118415286 A discloses a method for preparing a fermented red date liquid. The aroma components of the fermented red date liquid prepared during the production process are detected by combining a GS-MS (gas chromatography-mass spectrometry) instrument detection method with sensory evaluation, the content of β-damascone is determined by GC-MS (8860-5977B) and the aroma activity value is calculated, and sensory evaluation is performed by quantitative description analysis. However, this method does not dynamically analyze the content changes of some key aroma components during the fermentation process of the red date juice, and only selects the content of β-damascone to be detected when the fermentation is 18 hours, and it is impossible to accurately judge the fermentation end point. Summary of the invention

[0006] The purpose of the present invention is to provide a method for determining the fermentation endpoint of red date flavored fermented liquid and its application, so as to determine the fermentation endpoint more simply, quickly and accurately.

[0007] The purpose of the present invention can be achieved by the following technical solutions:

[0008] On the one hand, the present invention provides a method for judging the fermentation endpoint of red date flavored fermented liquid, which uses a sensory evaluation combined with gas chromatography-mass spectrometry detection method to judge the fermentation endpoint of red date flavored fermented liquid: when the sensory score of the honey-sweet floral aroma is higher than 6, the sensory score of the (less obvious) fermentation wine aroma is lower than 6, and after gas chromatography-mass spectrometry analysis, when the total content of characteristic honey-sweet floral aroma substances, namely β-damasketone and phenylethanol, is ratioed to the content of characteristic wine aroma substance component, namely pentanol, by 0.4-0.5, the fermentation endpoint is reached.

[0009] Preferably, the detection conditions of the gas chromatography in the gas chromatography-mass spectrometry instrument include:

[0010] Chromatographic column: Agilent HP-INNOWAX polar capillary column, specification: 60m×0.25mm×0.25um;

[0011] Inlet temperature: 230~270℃;

[0012] Split mode: split ratio (5-10): 1;

[0013] Carrier gas: helium, carrier gas flow rate: 10-15 mL / min;

[0014] Heating conditions: programmed heating, the initial column temperature is 35-45℃ and maintained for 1-4min, then increased to 75-95℃ at 2.5-3.5℃ / min and maintained for 0.5-2min, then increased to 160-190℃ at 3.5-6℃ / min and maintained for 0.5-2min, and increased to 230-250℃ at 4-6℃ / min and maintained for 8-12min.

[0015] Preferably, the helium is high-purity helium with a purity of 99.999%.

[0016] Preferably, the detection conditions of the mass spectrometer in the gas chromatography-mass spectrometry instrument include:

[0017] Ionization method: electron bombardment ion source EI;

[0018] Ionization energy: 70 eV;

[0019] Solvent delay time: 5.00~7.50min;

[0020] Ion source temperature: 130~170℃;

[0021] Quadrupole temperature: 230~260℃;

[0022] Transmission line temperature: 220~240℃;

[0023] Scan mode: full scan mode;

[0024] Scanning ion range (m / z): 50~500amu.

[0025] Preferably, the reference standard compounds corresponding to the honey-sweet floral aroma are 50wt.% phenylethanol and 50wt.% β-damascone, and the reference standard compounds corresponding to the fermented wine aroma are 50wt.% amyl alcohol and 70wt.% ethanol.

[0026] In a second aspect, the present invention provides an application of the method for determining the fermentation endpoint of red date flavored fermented liquid in preparing red date flavored fermented liquid.

[0027] In a third aspect, the present invention provides a method for preparing a red date flavored fermented liquid, comprising the following steps:

[0028] S1: add water to the red dates to squeeze out the juice and pulp, and adjust the pH and sugar content;

[0029] S2: inoculating Lactobacillus plantarum and Pichia pastoris into red date juice for fermentation;

[0030] S3: Sample the red dates flavored fermentation liquid at different fermentation time periods. When the sensory evaluation score of the honey-sweet floral aroma is higher than 6, the sensory score of the fermentation wine aroma is lower than 6, and after gas chromatography-mass spectrometry analysis, the total content of the characteristic honey-sweet floral aroma substances, i.e. β-damascenone and phenylethanol, and the content of the characteristic wine aroma substance component, i.e. pentanol, is 0.4-0.5, stop the fermentation.

[0031] Preferably, in step S1, the mass ratio of the red dates to water for pulping is 1:(5-7) (g / g), the pH value of the red date juice before inoculation is 4.50-4.85, and the sugar content is 11-15%.

[0032] Preferably, in step S2, the inoculation amount of the Lactobacillus plantarum and Pichia pastoris accounts for 2-5% of the total volume of the red date juice; the Lactobacillus plantarum is a mixed bacteria of two strains of Lactobacillus plantarum, and the volume ratio of Lactobacillus plantarum to Pichia pastoris is (2-2.5):1 (v / v).

[0033] More preferably, the two strains of Lactobacillus plantarum have a preservation number of CGMCC NO: 1.1856 and CGMCC NO: 1.12934, respectively, and the preservation number of Pichia pastoris is CGMCC NO: 2.4869.

[0034] Further preferably, the volume ratio of Lactobacillus plantarum 1.1856, Lactobacillus plantarum 1.12934, and Pichia pastoris 2.4869 is (0.9-1.2):(0.9-1.2):(0.8-1.1) (v / v).

[0035] Preferably, in step S2, the fermentation is dynamic fermentation or static fermentation, and the fermentation temperature is 33-36°C.

[0036] Preferably, the fermentation liquid is sterilized before the sensory evaluation, the sterilization method is pasteurization, the sterilization temperature is 80-85° C., and the sterilization time is 10-20 min.

[0037] Further preferably, the dynamic fermentation refers to dynamic fermentation at a certain rotation speed, and the fermentation rotation speed is 100-150 rpm / min.

[0038] In a fourth aspect, the present invention further provides a red date flavored fermented liquid obtained by the above-mentioned preparation method.

[0039] The present invention provides a method for judging the end point of a red date flavored fermentation liquid. By inoculating Lactobacillus plantarum and Pichia pastoris at the same time, the red date substrate can be fully utilized to improve the taste and flavor of the red date juice, and the sweet and sour feeling of the red date juice is significantly increased, while a honey-sweet rose fragrance is newly produced, so that the flower fragrance is used as an evaluation standard when judging the fermentation end point. In addition, the inoculated yeast is non-brewer's yeast, so the absence of a relatively obvious wine fragrance is also one of the evaluation standards of the red date flavored fermentation liquid.

[0040] The wine aroma and floral aroma produced during the mixed fermentation process are equally important. The higher the content of wine aroma compounds, the closer the overall aroma of the fermentation liquid is to the wine aroma, thereby masking the unique floral aroma produced by the mixed fermentation of red date juice. Therefore, the present invention adopts dynamic sampling and performs GC-MS and sensory evaluation analysis on the red date fermentation liquid, focusing on the changes in the content and sensory scores of characteristic wine aroma compounds (pentanol) and honey-sweet floral aroma compounds (β-damasketone, phenylethanol) during the fermentation process, and finding the content ratio range for the overall aroma to be close to a coordinated balance, thereby determining the fermentation endpoint of the mixed fermentation of red date juice.

[0041] Compared with the prior art, the present invention has the following beneficial effects:

[0042] (1) The present invention combines sensory evaluation and GC-MS analysis to make a simpler, faster and more accurate judgment on the fermentation endpoint of red date flavored fermentation liquid, thus making up for the shortcomings of the existing methods.

[0043] (2) On the one hand, the present invention adopts sensory evaluation. When sampling sensory organs during the fermentation process, a standard sample with a certain dilution concentration is used as a reference sample for reference, making it easier to determine the fermentation endpoint.

[0044] (3) On the other hand, the present invention detects the volatile components with characteristic wine aroma and floral aroma through GC-MS and calculates the content, thereby determining the change pattern of the content, which has a certain reference value and significance for judging the end point of fermentation.

[0045] (4) The present invention adopts GC-MS and is simple to operate, so that the detection method is rapid and comprehensive, and the fermentation status of the red date flavor fermented liquid during the fermentation stage can be monitored at any time, thereby achieving quality control of the red date flavor fermented liquid during the fermentation stage.

[0046] (5) A method for determining the fermentation endpoint of a mixed-bacteria fermentation agent under both static and dynamic fermentation conditions was proposed, which can provide technical support for the quality inspection of the mixed-bacteria fermentation process of red date juice and the regulation of the flavor quality of red date fermented beverages. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] Figure 1 The process flow chart of the red date flavor fermentation liquid of the present invention is as follows;

[0048] Figure 2 Lactic acid bacteria and yeast used in the fermentation of the present invention (left: Lactobacillus plantarum 1.1856; middle: Lactobacillus plantarum 1.12934; right: Pichia pastoris 2.4869);

[0049] Figure 3 This is the peak spectrum of volatile substances detected by GC-MS in Example 1 of the present invention;

[0050] Figure 4 This is the peak spectrum of volatile substances detected by GC-MS in Example 2 of the present invention;

[0051] Figure 5 The graph of the change of the content of the volatile component amyl alcohol at 12h, 15h, 18h, 21h and 24h of the dynamic fermentation of Example 1 of the present invention is shown;

[0052] Figure 6 The content change curve of the volatile component β-damascenone at 12h, 15h, 18h, 21h and 24h of dynamic fermentation in Example 1 of the present invention is shown;

[0053] Figure 7The graph of the change of the content of phenylethanol, a volatile component, at 12h, 15h, 18h, 21h and 24h of the dynamic fermentation of Example 1 of the present invention is shown;

[0054] Figure 8 The sensory radar charts of the dynamic fermentation at 12h, 15h, 18h, 21h and 24h of Example 1 of the present invention are shown;

[0055] Fig. 9 This is a curve diagram of the change in the content of the volatile component amyl alcohol at 24h, 48h, 72h, 84h and 96h of static fermentation in Example 2 of the present invention;

[0056] Fig.10 The graph of the change in the content of the volatile component β-damascenone at 24h, 48h, 72h, 84h and 96h of static fermentation in Example 2 of the present invention is as follows;

[0057] Fig.11 The graph of the change of the content of phenylethanol, a volatile component, at 24h, 48h, 72h, 84h and 96h of static fermentation in Example 2 of the present invention;

[0058] Fig.12 These are sensory radar charts of static fermentation at 24h, 48h, 72h, 84h and 96h in Example 2 of the present invention. DETAILED DESCRIPTION

[0059] The present invention is described in detail below in conjunction with the accompanying drawings and specific embodiments. This embodiment is implemented based on the technical solution of the present invention, and provides a detailed implementation method and specific operation process, but the protection scope of the present invention is not limited to the following embodiments.

[0060] Unless otherwise specified, the reagents, methods, instruments and equipment used in the present invention are conventional reagents, methods, instruments and equipment in the art. Unless otherwise specified, the reagents and materials used in the following examples are commercially available.

[0061] Preparation of red date flavor fermentation liquid Figure 1 As shown, it generally includes adding water to red dates to squeeze out the juice and pulp it, adjusting the pH value and sugar content before inoculation, preparing the strain seed liquid, and fermenting it after inoculation.

[0062] A method for determining the end point of a red date flavored fermentation liquid comprises the following steps:

[0063] Step 1: adding water to the pitted red dates in a certain proportion to squeeze out the juice and pulp, wherein the mass ratio of the red dates to the water is 1:(5-7), to obtain red date juice;

[0064] Step 2: adding 8-12% white sugar to the red date juice to adjust the sugar content of the red date juice to 11-15%, and adding 5-10% 0.5 mol / L edible citric acid to the red date juice to adjust the pH value of the red date juice to 4.50-4.85 before inoculation;

[0065] Step 3: pasteurize the red date juice and cool it to room temperature, the sterilization temperature is 85-95°C, and the sterilization time is 15-25 minutes;

[0066] Step 4: culturing two lactobacilli and one yeast in corresponding liquid culture media respectively, centrifuging to obtain bacterial mud after activation, discarding the upper culture medium, washing with sterile water, and finally shaking to obtain seed liquid, and inoculating the lactobacilli and yeast seed liquids into red date juice at the same time, wherein the inoculation volume ratio of plant lactobacillus 1.1856, plant lactobacillus 1.12934, and pichia pastoris 2.4869 is (0.9-1.2):(0.9-1.2):(0.8-1.1), the inoculation amount accounts for 2%-5% of the total volume of the red date juice, and the fermentation temperature is 33-36°C;

[0067] Step 5: During the fermentation process, sensory and GC-MS tests are performed at different time periods of the fermentation to determine the end point of the fermentation, that is: when the sensory evaluation senses a honey-sweet floral aroma (sensory score higher than 6) and a less obvious fermented wine aroma (sensory score lower than 6), and after GC-MS instrument analysis, when the total content of the characteristic honey-sweet floral aroma substances, i.e., β-damasketone and phenylethanol, is compared with the content of the characteristic wine aroma substance component, i.e., pentanol, is 0.4-0.5, then the above conditions are met and it can be determined as the fermentation end point.

[0068] Among them, the pretreatment method for GC-MS instrument detection is headspace solid phase microextraction (HS-SPME);

[0069] The detection conditions of the gas chromatography include:

[0070] Chromatographic column: Agilent HP-INNOWAX polar capillary column, specification: 60m×0.25mm×0.25um;

[0071] Inlet temperature: 230~270℃;

[0072] Split mode: split ratio (5-10): 1;

[0073] Carrier gas: helium, carrier gas flow rate: 10-15 mL / min;

[0074] Heating conditions: programmed heating, the initial column temperature is 35-45℃ and maintained for 1-4min, then increased to 75-95℃ at 2.5-3.5℃ / min and maintained for 0.5-2min, then increased to 160-190℃ at 3.5-6℃ / min and maintained for 0.5-2min, and increased to 230-250℃ at 4-6℃ / min and maintained for 8-12min.

[0075] Preferably, the mass spectrometry detection conditions include:

[0076] Ionization method: electron bombardment ion source EI;

[0077] Ionization energy: 70 eV;

[0078] Solvent delay time: 5.00~7.50min;

[0079] Ion source temperature: 130~170℃;

[0080] Quadrupole temperature: 230~260℃;

[0081] Transmission line temperature: 220~240℃;

[0082] Scan mode: full scan mode;

[0083] Scanning ion range (m / z): 50~500amu.

[0084] Example 1

[0085] (1) Preparation of red date juice: The mass ratio of pitted red dates to hot water is 1:6. After soaking in hot water for 30 minutes, the juice is squeezed and pulped to obtain red date juice. After cooling to room temperature, the pH value is adjusted to 4.70 with 0.5 mol / L edible citric acid, and the sugar content is adjusted to 12-15% with white sugar. The red date juice is packaged and pasteurized at 90°C for 20 minutes.

[0086] (2) Lactobacillus plantarum 1.1856 and Lactobacillus plantarum 1.12934 were streaked and activated in MRS solid medium (37°C static culture for 48 hours); the strains were activated for the second time in MRS liquid medium, and the required activation conditions were 37°C, 180rpm / min shaking culture for 20 hours to fully activate the strains; similarly, Pichia pastoris 2.4869 was streaked and activated in YPD solid medium (30°C static culture for 48 hours); the strains were activated for the second time in YPD liquid medium, and the required activation conditions were 30°C, 180rpm / min shaking culture for 18 hours to fully activate the strains. The inoculation amount of the mixed starter was 3% of the total volume of the red date juice, the volume ratio of lactic acid bacteria to yeast was 2:1, and the culture was kept constant at 34°C in an incubator at a speed of 120rpm / min.

[0087] (3) Determination of the end point of fermentation: Sampling was carried out at 12h, 15h, 18h, 21h, and 24h of fermentation and evaluated by a 10-person sensory evaluation panel. At the same time, GC-MS was used to detect and calculate the content of the characteristic aroma compounds of wine and floral aroma.

[0088] (I) Sensory evaluation

[0089] Sampling was performed at 12h, 15h, 18h, 21h, and 24h of fermentation, and a sensory evaluation panel consisting of 10 people evaluated the sample. The trained sensory assessors were required to score each descriptor, and the reference sample of the sweet date fragrance was finally collected to obtain the sensory result table of Example 1, and the results were shown in Table 2. The scoring criteria are shown in Table 1, wherein the reference sample of the sweet date fragrance was the dried red date used for juicing; the reference sample of the honey sweet flower fragrance was 50wt.% phenylethanol and 50wt.% β-damasketone; the reference sample of the wine aroma was 50wt.% amyl alcohol and 70wt.% ethanol; the reference sample of the fermented sour aroma was 10wt.% acetic acid, and the reference sample of the peculiar smell was the solid culture medium of yeast.

[0090] Table 1 Sensory evaluation of red date flavor fermented liquid

[0091]

[0092]

[0093] Table 2 Sensory scoring table of dynamic fermentation of red date juice fermentation liquid at different fermentation time periods in Example 1

[0094]

[0095] (ii) GC-MS analysis

[0096] Sampling was performed at 12h, 15h, 18h, 21h, and 24h of fermentation, and the total content of characteristic wine aroma components (pentanol) and the content of characteristic honey-sweet floral aroma substances (β-damasketone, phenylethyl alcohol) were measured. The test results are shown in Table 3. The analysis conditions of GC-MS are as follows:

[0097] The detection conditions of gas chromatography include: chromatographic column: Agilent HP-INNOWAX polar capillary column, specification is 60m×0.25mm×0.25um; injection port temperature: 250°C; split ratio 5:1; carrier gas is high-purity helium (99.999%), carrier gas flow rate: 12mL / min; programmed temperature, column initial temperature is 40°C maintained for 2min, increased to 85°C at 3°C / min and maintained for 1min, then increased to 180°C at 5°C / min and maintained for 1min, and increased to 230°C at 5°C / min and maintained for 10min.

[0098] The detection conditions of mass spectrometry include: electron bombardment ion source mode; ionization energy 70eV; solvent delay time: 5.00min; ion source temperature: 150℃; quadrupole temperature: 250℃; transmission line temperature: 230℃; scanning mode: full scan Scan mode; scanning ion range (m / z): 50~500amu.

[0099] Table 3 GC-MS test results of dynamic fermentation of red date juice fermentation liquid at different fermentation time periods in Example 1

[0100]

[0101] Through GC-MS detection and quantitative calculation of content, the results are as follows Figures 5 to 7 As shown in Table 3, no β-damascone was detected in the red date flavor fermentation liquid at the 12th and 15th hours of fermentation, and then the content continued to rise and stabilized within 18h-24h, while the content of amyl alcohol and phenylethanol continued to increase with the extension of fermentation time. Figure 8 From the sensory radar chart, we can see that the sensory score of the 18th hour of fermentation is generally good, and the preference is second only to the 12th hour at the beginning of fermentation. Through the detection of volatile aroma components by GC-MS, we can see that the production of β-damasketone may give the red date fermentation liquid a floral aroma, thereby softening the aroma of sour aroma substances produced by long-term fermentation of lactic acid bacteria. During the 18-24h of fermentation, although the content of phenylethanol, a floral aroma substance, is still rising, the content of amyl alcohol increases rapidly, the wine aroma characteristics are significantly enhanced, and the odor increases with the increase of fermentation time, resulting in a rapid decrease in the preference of sensory evaluators for 24h, and the preference score of the 21st hour of fermentation is second only to the 18th hour of fermentation. This may be because some evaluators prefer the characteristics of beer aroma.

[0102] It can be seen that the sensory score at the 18th hour of fermentation was generally good, with the highest degree of liking, that is, when the wine aroma score in the descriptor was lower than 6, the floral aroma score was higher than 6, and the total content of the characteristic honey-sweet floral aroma substances β-damasketone and phenylethanol in the GC-MS measurement results was ratioed to the content of the characteristic wine aroma substance component pentanol was 0.493, the fermentation endpoint of the dynamic fermentation of red date juice to prepare red date flavored fermented liquid was judged to be completed, and the flavor was good.

[0103] Example 2

[0104] (1) The red date juice and activated seed liquid described in Example 1 were taken, the inoculation amount of the mixed starter was 3% of the total volume of the red date juice, the volume ratio of lactic acid bacteria to yeast was 2:1, and static constant temperature culture was carried out in an incubator at 34°C.

[0105] (2) Determination of fermentation endpoint: Sampling was performed at 24h, 48h, 72h, 84h, and 96h of fermentation, and a sensory evaluation panel consisting of 10 people evaluated the samples, and finally the average scores were collected to obtain the sensory result table of Example 2, as shown in Table 4. At the same time, GC-MS was tested, and the results were shown in Table 5. The analysis and detection conditions were as shown in Example 1, and the contents of the characteristic aroma compounds of wine aroma and floral aroma were calculated.

[0106] Table 4 Sensory scoring table of static fermentation of red date juice fermentation liquid at different fermentation time periods in Example 2

[0107]

[0108] Table 5 GC-MS test results of static fermentation of red date juice fermentation liquid at different fermentation time periods in Example 2

[0109]

[0110] from Figures 9-11 As can be seen from Table 5, the contents of amyl alcohol, β-damascone, and phenylethanol increased slowly at 24h and 48h in static fermentation, among which the amyl alcohol content increased almost linearly after 48h, while β-damascone increased rapidly within 48-72h and then tended to be flat, and phenylethanol increased rapidly within 48-72h and then decreased, with a trend similar to that of dynamic shaking fermentation. In the sensory evaluation, the results are as follows Fig.12 As shown in the figure, the first three days of fermentation had a higher liking score, and the sweet jujube aroma decreased with the extension of fermentation time, while the sour and wine aromas of fermentation increased with the extension of fermentation time. The score of the honey sweet floral aroma increased first and then decreased, which may be because the wine aroma compounds increased rapidly after 72 hours. The wine aroma was too heavy, thus covering up the floral aroma. At the same time, after 72 hours of static fermentation, the odor also increased significantly, so no characteristic aroma of the red jujube flavor could be felt.

[0111] It can be seen that the sensory score at the 72nd hour of fermentation is generally good and the degree of liking is high. When the wine aroma score in the descriptor is lower than 6 and the floral aroma score is higher than 6, and the total content of the characteristic honey-sweet floral aroma substances β-damasketone and phenylethanol in the GC-MS measurement results is ratioed to the content of the characteristic wine aroma substance component pentanol is 0.453, the fermentation endpoint of static fermentation of red date juice to prepare red date flavored fermented liquid is judged to be completed.

[0112] The above description of the embodiments is to facilitate the understanding and use of the invention by those skilled in the art. It is obvious that those skilled in the art can easily make various modifications to these embodiments and apply the general principles described herein to other embodiments without creative work. Therefore, the present invention is not limited to the above embodiments, and improvements and modifications made by those skilled in the art based on the disclosure of the present invention without departing from the scope of the present invention should be within the scope of protection of the present invention.

Claims

1. A method for determining the fermentation endpoint of red date flavored fermented liquid, characterized in that: The end point of fermentation of red dates flavored fermented liquid was determined by combining sensory evaluation with gas chromatography-mass spectrometry: when the sensory score of the sweet floral aroma was higher than 6 and the sensory score of the fermented wine aroma was lower than 6, and after analysis by gas chromatography-mass spectrometry, the ratio of the total content of the characteristic sweet floral aroma substances, i.e. β-damasketone and phenylethanol, to the content of the characteristic wine aroma substance component, i.e. pentanol, was 0.4-0.5, it was the end point of fermentation.

2. The method for determining the fermentation endpoint of red date flavored fermented liquid according to claim 1, characterized in that: The detection conditions of the gas chromatography in the gas chromatography-mass spectrometry instrument include: Chromatographic column: Agilent HP-INNOWAX polar capillary column, specification: 60m×0.25mm×0.25um; Inlet temperature: 230~270℃; Split mode: split ratio (5-10): 1; Carrier gas: helium, carrier gas flow rate: 10-15 mL / min; Heating conditions: programmed heating, the initial column temperature is 35-45℃ and maintained for 1-4min, then increased to 75-95℃ at 2.5-3.5℃ / min and maintained for 0.5-2min, then increased to 160-190℃ at 3.5-6℃ / min and maintained for 0.5-2min, and increased to 230-250℃ at 4-6℃ / min and maintained for 8-12min.

3. The method for determining the fermentation endpoint of red date flavored fermented liquid according to claim 1, characterized in that: The detection conditions of the mass spectrometer in the gas chromatography-mass spectrometry instrument include: Ionization method: electron bombardment ion source EI; Ionization energy: 70 eV; Solvent delay time: 5.00~7.50min; Ion source temperature: 130~170℃; Quadrupole temperature: 230~260℃; Transmission line temperature: 220~240℃; Scan mode: full scan mode; Scanning ion range (m / z): 50~500amu.

4. The method for determining the fermentation endpoint of red date flavored fermented liquid according to claim 1, characterized in that: The reference standard compounds corresponding to the honey-sweet floral aroma are 50wt.% phenylethanol and 50wt.% β-damascone, and the reference standard compounds corresponding to the fermented wine aroma are 50wt.% amyl alcohol and 70wt.% ethanol.

5. Use of the method for determining the fermentation endpoint of red date flavored fermented liquid as claimed in any one of claims 1 to 4 in preparing red date flavored fermented liquid.

6. A method for preparing a red date flavored fermented liquid, characterized in that: The following steps are involved: S1: add water to the red dates to squeeze out the juice and pulp, and adjust the pH and sugar content; S2: inoculating Lactobacillus plantarum and Pichia pastoris into red date juice for fermentation; S3: Sample the red dates flavored fermentation liquid at different fermentation time periods. When the sensory evaluation score of the honey-sweet floral aroma is higher than 6, the sensory score of the fermented wine aroma is lower than 6, and after gas chromatography-mass spectrometry analysis, the ratio of the total content of the characteristic honey-sweet floral aroma substances, i.e. β-damasketone and phenylethanol, to the content of the characteristic wine aroma substance component, i.e. pentanol, is 0.4-0.5, stop the fermentation.

7. The method for preparing a red date flavored fermented liquid according to claim 6, characterized in that: In step S1, the mass ratio of the red dates to water is 1:(5-7), the pH value of the red date juice before inoculation is 4.50-4.85, and the sugar content is 11-15%.

8. The method for preparing a red date flavored fermented liquid according to claim 6, characterized in that: In step S2, the inoculation amount of the Lactobacillus plantarum and Pichia pastoris accounts for 2-5% of the total volume of the red date juice; the Lactobacillus plantarum is a mixed bacteria of two strains of Lactobacillus plantarum, and the volume ratio of Lactobacillus plantarum to Pichia pastoris is (2-2.5):

1.

9. The method for preparing a red date flavored fermented liquid according to claim 6, characterized in that: In step S2, the fermentation is dynamic fermentation or static fermentation; the fermentation temperature is 33-36°C; the fermentation liquid is sterilized before the sensory evaluation, the sterilization method is pasteurization, the sterilization temperature is 80-85°C, and the sterilization time is 10-20min.

10. A red date flavored fermented liquid, characterized in that: The method is obtained by the preparation method according to any one of claims 6 to 9.

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