Method for prolonging storage time of whole wheat flour

Abstract

The invention relates to the technical field of grain processing, in particular to a method for prolonging the storage time of whole wheat flour, which comprises the following steps: S1, preparing whole wheat flour; and S2, controlling the water content of the whole wheat flour to 7-14%. The water content of the whole wheat flour is controlled to be 7%-14%, the activity of various enzymes in the whole wheat flour is indirectly regulated and controlled, the fatty acid value of the whole wheat flour in the storage period rises slowly, and the stability is good.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of grain processing, in particular to a method for prolonging the storage time of whole wheat flour. BACKGROUND

[0002] Whole wheat flour is an important whole grain, which retains the bran and germ components of wheat kernels and has more dietary fiber, minerals, vitamins and polyphenolic antioxidants compared with refined wheat flour. As a healthy food raw material, whole wheat flour has been favored by more and more consumers in recent years. However, the fat content in wheat bran and wheat germ is high, and the rapid hydrolysis of fat accompanied by high activity of lipase leads to fat oxidation and rancidity, reduces the nutritional quality, functional properties and sensory acceptability of whole wheat flour, affects its storage stability, causes the short shelf life of whole wheat flour, and limits its wide application in food.

[0003] Moisture is one of the important factors affecting the storage stability of grain and its products. During the storage of whole wheat flour, moisture not only affects the growth and reproduction of microorganisms, but also may cause changes in enzyme activity, affect the oxidation reaction rate and the decomposition of fatty acids, and thus affect the flavor, taste and nutritional ingredients of whole wheat flour. High moisture content can provide a suitable environment for the growth of mold and other microorganisms, leading to deterioration of whole wheat flour and the production of harmful substances. Therefore, moisture content is one of the key factors affecting the storage stability of whole wheat flour.

[0004] At present, domestic and foreign scholars have conducted extensive research on the storage conditions of wheat flour and the change rule of wheat flour quality during storage. Experiments usually choose different storage methods (such as nitrogen filling, use of deoxidizing agent and vacuum packaging, etc.) or set relatively extreme temperature conditions (5, 10, 30, 35 ℃, etc.) for storage. These research results show that temperature is the main factor affecting the quality of wheat flour, and low temperature conditions can effectively delay the quality deterioration; different storage methods have little difference in the influence on the quality of wheat flour. Some scholars have also studied the influence of packaging materials on the shelf life of whole wheat flour, and the results show that compared with paper bag packaging, the nutritional substances of wheat flour packaged in aluminum and PET multilayer composite bags do not change significantly during storage under different temperature and relative humidity conditions. Some scholars have also studied the change rule of the quality of wheat flour with different moisture contents under different temperature and relative humidity storage conditions, and the results show that the moisture content, fatty acid value and sensory score value of wheat flour are related to the storage conditions, which provides a theoretical basis for the prediction of edible quality change and the evaluation of edible period of wheat flour. However, there are few reports on the influence of moisture content on the quality change of whole wheat flour during storage. SUMMARY

[0005] The application aims to provide a method for prolonging the storage time of wholemeal flour by improving the moisture content in the preparation process of wholemeal flour, and improving the quality and storage stability of wholemeal flour.

[0006] To achieve the above-mentioned purpose, the application provides a method for prolonging the storage time of wholemeal flour, comprising the following steps: S1, preparing wholemeal flour; S2, controlling the water content of the wholemeal flour to 7%-14%.

[0007] In the application, the preparation method of wholemeal flour in S1 comprises a direct pulverization method or a backfilling method.

[0008] In the application, the direct pulverization method comprises pulverizing and sieving the wheat kernels by a hammer cyclone mill to obtain the wholemeal flour.

[0009] In the application, in the backfilling method, the backfilling material comprises at least one of wheat germ, bran, and regrind.

[0010] In the application, the bran comprises common bran or bran subjected to puffing treatment, and the bran subjected to puffing treatment is preferred.

[0011] In the application, the backfilling method comprises the following methods: Method I: after the wheat is tempered, the wheat is ground, separated, and sieved by a buhr mill to obtain wheat flour, regrind, and bran, then the wheat flour, the regrind, and the pulverized bran are mixed to obtain the wholemeal flour; Method II: the wheat flour, the regrind, the pulverized bran, and the pulverized wheat germ are mixed in a certain proportion to obtain the wholemeal flour; Method III: the wheat flour, the regrind, and the pulverized bran are mixed in a certain proportion to obtain the wholemeal flour; Method IV: the wheat flour, the regrind, the pulverized wheat germ, and the bran subjected to puffing treatment and pulverization are mixed in a certain proportion to obtain the wholemeal flour; Method V: the wheat flour, the regrind, and the bran subjected to puffing treatment and pulverization are mixed in a certain proportion to obtain the wholemeal flour.

[0012] In the application, in Method I, the mass ratio of the wheat flour, the regrind, and the pulverized bran is 70:15:15; In Method II, the mass ratio of the pulverized bran, the regrind, the pulverized wheat germ, and the wheat flour is 17.8:10:2.2:70; In Method III, the mass ratio of the pulverized bran, the regrind, and the wheat flour is 20:10:70; In Method IV, the mass ratio of the pulverized wheat germ, the regrind, the wheat flour, and the bran subjected to puffing treatment and pulverization is 2.2:10:70:17.8; In mode V, the mass ratio of the secondary flour, the wheat flour, and the puffed and crushed bran is 10:70:20.

[0013] In the present application, in modes II-V, the crushed bran, the secondary flour, the crushed wheat germ, and the puffed and crushed bran are obtained by processing in a flour mill.

[0014] In the present application, the mode for controlling the water content of the whole wheat flour in S2 includes one of sun drying, air drying, oven drying, freeze drying, and air blowing.

[0015] In the present application, the water content of the whole wheat flour is controlled to 8%-10% in S2.

[0016] The present application has the following beneficial effects: The present application provides a method for prolonging the storage time of whole wheat flour, comprising the following steps: S1, preparing whole wheat flour; S2, controlling the water content of the whole wheat flour to 7%-14%.

[0017] The present application found in experiments that the water content has a significant influence on the changes in the fatty acid value, the malondialdehyde content, and the enzyme activity of the whole wheat flour during storage; during storage, the rising trend of the fatty acid value and the malondialdehyde content of the low-water-content whole wheat flour is slower than that of the high-water-content whole wheat flour sample; the initial enzyme activity of the low-water-content whole wheat flour sample is lower; during storage, the activities of the lipase and the fatty oxidation enzyme in the whole wheat flour show a downward trend, while the activity of the peroxidase shows a fluctuating trend; the storage stability of the low-water-content whole wheat flour is better. Therefore, by controlling the water content of the whole wheat flour to 7%-14%, the activity of various enzymes in the whole wheat flour is indirectly regulated, so that the rising of the fatty acid value of the whole wheat flour during storage is slow, and the stability is better.

[0018] The method for prolonging the storage time of whole wheat flour provided by the present application is simple, low in cost, and easy to operate, realizes the stable storage of the whole wheat flour under different storage modes, and prolongs the shelf life of the whole wheat flour.

[0019] The technical solutions of the present application will be further described in detail below with reference to the drawings and examples. BRIEF DESCRIPTION OF DRAWINGS

[0020] Figure 1 is a fatty acid value determination result graph; Among them, Figure 1 A in is the curve of the change of the fatty acid value of the whole wheat flour prepared in Examples 1-6 with the storage time under different water contents; Figure 1 B in is the curve of the change of the fatty acid value of the whole wheat flour prepared in Examples 7-12 with the storage time under different water contents; Figure 1 C in is the curve of the change of the fatty acid value of the whole wheat flour prepared in Examples 13-19 with the storage time under different water contents; Figure 1D in FIG. 1 is a graph showing the change in the fatty acid value of the whole meal flour prepared in Examples 20 to 26 with the storage time at different moisture contents; Figure 1 E in FIG. 1 is a graph showing the change in the fatty acid value of the whole meal flour prepared in Examples 27 to 32 with the storage time at different moisture contents; Figure 1 F in FIG. 1 is a graph showing the change in the fatty acid value of the whole meal flour prepared in Examples 33 to 38 with the storage time at different moisture contents; Figure 2 FIG. 2 is a graph showing the results of the malondialdehyde content measurement; wherein, Figure 2 A in FIG. 2 is a graph showing the change in the malondialdehyde content of the whole meal flour prepared in Examples 1 to 6 with the storage time at different moisture contents; Figure 2 B in FIG. 2 is a graph showing the change in the malondialdehyde content of the whole meal flour prepared in Examples 7 to 12 with the storage time at different moisture contents; Figure 2 C in FIG. 2 is a graph showing the change in the malondialdehyde content of the whole meal flour prepared in Examples 13 to 19 with the storage time at different moisture contents; Figure 2 D in FIG. 2 is a graph showing the change in the malondialdehyde content of the whole meal flour prepared in Examples 20 to 26 with the storage time at different moisture contents; Figure 2 E in FIG. 2 is a graph showing the change in the malondialdehyde content of the whole meal flour prepared in Examples 27 to 32 with the storage time at different moisture contents; Figure 2 F in FIG. 2 is a graph showing the change in the malondialdehyde content of the whole meal flour prepared in Examples 33 to 38 with the storage time at different moisture contents; Figure 3 FIG. 3 is a graph showing the results of the lipase activity measurement; wherein, Figure 3 A in FIG. 3 is a graph showing the change in the lipase activity of the whole meal flour prepared in Examples 1 to 6 with the storage time at different moisture contents; Figure 3 B in FIG. 3 is a graph showing the change in the lipase activity of the whole meal flour prepared in Examples 7 to 12 with the storage time at different moisture contents; Figure 3 C in FIG. 3 is a graph showing the change in the lipase activity of the whole meal flour prepared in Examples 13 to 19 with the storage time at different moisture contents; Figure 3 D in FIG. 3 is a graph showing the change in the lipase activity of the whole meal flour prepared in Examples 20 to 26 with the storage time at different moisture contents; Figure 3 E in FIG. 3 is a graph showing the change in the lipase activity of the whole meal flour prepared in Examples 27 to 32 with the storage time at different moisture contents; Figure 3 F in FIG. 3 is a graph showing the change in the lipase activity of the whole meal flour prepared in Examples 33 to 38 with the storage time at different moisture contents; Figure 4 FIG. 4 is a graph showing the results of the lipoxygenase activity measurement; wherein, Figure 4A in the figure is the curve of the change of the activity of the lipoxygenase with the storage time of the whole wheat flour prepared in Examples 1-6 at different moisture contents; Figure 4 B in the figure is the curve of the change of the activity of the lipoxygenase with the storage time of the whole wheat flour prepared in Examples 7-12 at different moisture contents; Figure 4 C in the figure is the curve of the change of the activity of the lipoxygenase with the storage time of the whole wheat flour prepared in Examples 13-19 at different moisture contents; Figure 4 D in the figure is the curve of the change of the activity of the lipoxygenase with the storage time of the whole wheat flour prepared in Examples 20-26 at different moisture contents; Figure 4 E in the figure is the curve of the change of the activity of the lipoxygenase with the storage time of the whole wheat flour prepared in Examples 27-32 at different moisture contents; Figure 4 F in the figure is the curve of the change of the activity of the lipoxygenase with the storage time of the whole wheat flour prepared in Examples 33-38 at different moisture contents; Figure 5 The results of the determination of the flavor substances of the whole wheat flour prepared in Examples 13-19 are shown in the table below. In the table, the horizontal coordinate 12-0 represents the whole wheat flour with a moisture content of 12.47% stored for 0 weeks, 12-4 represents the whole wheat flour with a moisture content of 12.47% stored for 4 weeks, and 12-6 represents the whole wheat flour with a moisture content of 12.47% stored for 6 weeks; 9-0 represents the whole wheat flour with a moisture content of 9.3% stored for 0 weeks, 9-4 represents the whole wheat flour with a moisture content of 9.3% stored for 4 weeks, and 9-6 represents the whole wheat flour with a moisture content of 9.3% stored for 6 weeks; 7-0 represents the whole wheat flour with a moisture content of 7.38% stored for 0 weeks, 7-4 represents the whole wheat flour with a moisture content of 7.38% stored for 4 weeks, and 7-6 represents the whole wheat flour with a moisture content of 7.38% stored for 6 weeks. Figure 6 The heat map of the correlation analysis of the moisture content and the storage time of the whole wheat flour prepared in Examples 13-19 with the volatile components is shown in the table below. DETAILED DESCRIPTION

[0021] The present application is further described below in conjunction with the accompanying drawings and examples. Unless otherwise defined, the technical terms or scientific terms used in the present application shall have the usual meanings understood by those with ordinary skills in the art to which the present application pertains. The features mentioned in the present application or the features mentioned in the specific examples can be combined arbitrarily, and the specific examples are only used to illustrate the present application and not to limit the scope of the present application.

[0022] Example 1 S1, the wheat grains were crushed by a hammer-type cyclone mill and passed through a punch screen with a pore size of 0.8 mm to obtain whole wheat flour; S2, the obtained whole wheat flour was placed in a blast drying oven and dried at a temperature of 40 until the moisture content of the whole wheat flour was 12.59%.

[0023] Example 2 The wholemeal flour was prepared in the same way as in Example 1, except that the moisture content of the wholemeal flour was controlled to 10.97% in S2.

[0024] Example 3 The wholemeal flour was prepared in the same way as in Example 1, except that the moisture content of the wholemeal flour was controlled to 10.15% in S2.

[0025] Example 4 The wholemeal flour was prepared in the same way as in Example 1, except that the moisture content of the wholemeal flour was controlled to 9.12% in S2.

[0026] Example 5 The wholemeal flour was prepared in the same way as in Example 1, except that the moisture content of the wholemeal flour was controlled to 8.36% in S2.

[0027] Example 6 The wholemeal flour was prepared in the same way as in Example 1, except that the moisture content of the wholemeal flour was controlled to 7.35% in S2.

[0028] Example 7 S1, after the wheat flour was moistened, the wheat grains were ground, separated and sieved by a Brϋker test mill to obtain wheat flour, secondary flour and bran, and then the bran was crushed, and the wheat flour, secondary flour and crushed bran were mixed in a mass ratio of 70:15:15 to obtain wholemeal flour; S2, the obtained wholemeal flour was placed in a blast drying oven, and dried at a temperature of 40 to control the moisture content of the wholemeal flour to 12.80%.

[0029] Example 8 The wholemeal flour was prepared in the same way as in Example 7, except that the moisture content of the wholemeal flour was controlled to 11.34% in S2.

[0030] Example 9 The wholemeal flour was prepared in the same way as in Example 7, except that the moisture content of the wholemeal flour was controlled to 10.64% in S2.

[0031] Example 10 The wholemeal flour was prepared in the same way as in Example 7, except that the moisture content of the wholemeal flour was controlled to 9.40% in S2.

[0032] Example 11 The wholemeal flour was prepared in the same way as in Example 7, except that the moisture content of the wholemeal flour was controlled to 8.37% in S2.

[0033] Example 12 The same as the preparation of whole wheat flour in Example 7, except that the water content of the whole wheat flour is controlled to 7.35% in S2.

[0034] Example 13 S1, the crushed bran, the second flour, the crushed wheat germ, the wheat flour are mixed in a mass ratio of 17.8:10:2.2:70, and the whole wheat flour is obtained; S2, the obtained whole wheat flour is placed in a blast drying oven, and dried at a temperature of 40 to control the water content of the whole wheat flour to 13.76%.

[0035] Example 14 The same as the preparation of whole wheat flour in Example 13, except that the water content of the whole wheat flour is controlled to 12.47% in S2.

[0036] Example 15 The same as the preparation of whole wheat flour in Example 13, except that the water content of the whole wheat flour is controlled to 11.21% in S2.

[0037] Example 16 The same as the preparation of whole wheat flour in Example 13, except that the water content of the whole wheat flour is controlled to 10.14% in S2.

[0038] Example 17 The same as the preparation of whole wheat flour in Example 13, except that the water content of the whole wheat flour is controlled to 9.30% in S2.

[0039] Example 18 The same as the preparation of whole wheat flour in Example 13, except that the water content of the whole wheat flour is controlled to 8.41% in S2.

[0040] Example 19 The same as the preparation of whole wheat flour in Example 13, except that the water content of the whole wheat flour is controlled to 7.38% in S2.

[0041] Example 20 S1, the crushed bran, the second flour, the wheat flour are mixed in a mass ratio of 20:10:70, and the whole wheat flour is obtained; S2, the obtained whole wheat flour is placed in a blast drying oven, and dried at a temperature of 40 to control the water content of the whole wheat flour to 13.64%.

[0042] Example 21 The same as the preparation of whole wheat flour in Example 20, except that the water content of the whole wheat flour is controlled to 12.30% in S2.

[0043] Example 22 The wholemeal flour was prepared in the same way as in Example 20, except that the moisture content of the wholemeal flour was controlled to 11.32% in S2.

[0044] Example 23 The wholemeal flour was prepared in the same way as in Example 20, except that the moisture content of the wholemeal flour was controlled to 10.26% in S2.

[0045] Example 24 The wholemeal flour was prepared in the same way as in Example 20, except that the moisture content of the wholemeal flour was controlled to 9.35% in S2.

[0046] Example 25 The wholemeal flour was prepared in the same way as in Example 20, except that the moisture content of the wholemeal flour was controlled to 8.51% in S2.

[0047] Example 26 The wholemeal flour was prepared in the same way as in Example 20, except that the moisture content of the wholemeal flour was controlled to 7.42% in S2.

[0048] Example 27 S1, the crushed germ, the secondary powder, the wheat flour, and the puffed and crushed bran were mixed in a mass ratio of 2.2:10:70:17.8 to obtain the wholemeal flour; S2, the obtained wholemeal flour was placed in a blast drying oven and dried at a temperature of 40 to control the moisture content of the wholemeal flour to 12.32%.

[0049] Example 28 The wholemeal flour was prepared in the same way as in Example 27, except that the moisture content of the wholemeal flour was controlled to 11.50% in S2.

[0050] Example 29 The wholemeal flour was prepared in the same way as in Example 27, except that the moisture content of the wholemeal flour was controlled to 10.02% in S2.

[0051] Example 30 The wholemeal flour was prepared in the same way as in Example 27, except that the moisture content of the wholemeal flour was controlled to 9.28% in S2.

[0052] Example 31 The wholemeal flour was prepared in the same way as in Example 27, except that the moisture content of the wholemeal flour was controlled to 8.02% in S2.

[0053] Example 32 The wholemeal flour was prepared in the same way as in Example 27, except that the moisture content of the wholemeal flour was controlled to 7.62% in S2.

[0054] Example 33 S1. Mix wheat bran, wheat flour, and puffed and pulverized bran in a mass ratio of 10:70:20 to obtain whole wheat flour; S2. Place the obtained whole wheat flour in a forced-air drying oven at 40°C. At a certain temperature, dry until the moisture content of the whole wheat flour reaches 12.22%.

[0055] Example 34 The whole wheat flour was prepared in the same way as in Example 33, except that the moisture content of the whole wheat flour was controlled to 11.21% in S2.

[0056] Example 35 The whole wheat flour was prepared in the same way as in Example 33, except that the moisture content of the whole wheat flour was controlled to 10.18% in S2.

[0057] Example 36 The whole wheat flour was prepared in the same way as in Example 33, except that the moisture content of the whole wheat flour was controlled to 9.15% in S2.

[0058] Example 37 The whole wheat flour was prepared in the same way as in Example 33, except that the moisture content of the whole wheat flour was controlled to 8.13% in S2.

[0059] Example 38 The whole wheat flour was prepared in the same way as in Example 33, except that the moisture content of the whole wheat flour was controlled to 7.68% in S2.

[0060] Performance testing: Whole wheat flour samples with different moisture contents prepared in Examples 1-38 were placed in polyethylene self-sealing bags, sealed, and subjected to accelerated storage experiments in a constant temperature and humidity chamber at a temperature of 40°C. The relative humidity was 70%. Samples were taken once a week during the period to determine the fatty acid value, malondialdehyde content, enzyme activity, and flavor compounds.

[0061] Determination of fatty acid value: Refer to GB T 5510-2011 "Grain and Oil Inspection - Determination of Fatty Acid Values ​​in Grains and Oilseeds" specifies the determination of fatty acid values. Results are as follows: Figure 1 As shown.

[0062] from Figure 1 It can be seen that moisture content has a significant impact on the fatty acid value of whole wheat flour. The fatty acid value of all whole wheat flour samples increased with the extension of storage time, and the degree of increase in fatty acid value was related to the sample preparation method. Figure 1As can be seen from A in the figure, after 6 weeks of accelerated storage, the fatty acid value of the whole wheat flour with an initial moisture content of 12.59% in Example 1 was 111.28 mg. 100g, still meets LS standards The T 3244-2015 grain industry standard for whole wheat flour specifies the fatty acid value requirement for whole wheat flour (≤116mg). (100g). The whole wheat flour samples obtained in Examples 3-6 showed no significant difference in fatty acid values ​​during accelerated storage, indicating good storage stability. From Figure 1 As shown in B, after 6 weeks of accelerated storage, the fatty acid values ​​of samples with an initial moisture content below 10% (Examples 10-12) all met the standard requirements. However, the fatty acid values ​​of whole wheat flour samples with initial moisture contents of 12.8% (Example 7), 11.34% (Example 8), and 10.64% (Example 9) reached 147.79, 130.25, and 121.03 mg, respectively, after 6 weeks of accelerated storage. All samples, weighing 100g, exceeded the industry standard requirements for whole wheat flour. Furthermore, the fatty acid values ​​of whole wheat flour samples with initial moisture contents of 9.3% (Example 17), 8.41% (Example 18), and 7.38% (Example 19), and initial moisture contents of 10.26% (Example 23), 9.35% (Example 24), 8.51% (Example 25), and 7.42% (Example 26) did not exceed 116mg after 6 weeks of accelerated storage. 100g. (From) Figure 1 As can be seen from A, E, and F, after 6 weeks of accelerated storage, the fatty acid values ​​of all whole wheat flour samples prepared by direct cyclone milling (moisture content 7.35%-12.59%, Examples 1-6) and whole wheat flour samples prepared by adding puffed bran (Examples 27-38) all met the requirements of the whole wheat flour industry standard.

[0063] Based solely on fatty acid value analysis, in order to achieve a 6-month shelf life, the moisture content of whole wheat flour prepared by direct cyclone milling (Examples 1-6) and whole wheat flour prepared by adding puffed bran (Examples 27-38) should be controlled below 12.5%; the moisture content of whole wheat flour prepared by adding ordinary bran (Examples 7-26) should be controlled below 10.0%.

[0064] Determination of malondialdehyde content: The malondialdehyde (MDA) content was determined by spectrophotometry according to GB 5009.181-2016, "National Food Safety Standard - Determination of Malondialdehyde in Food". The results are as follows: Figure 2 As shown.

[0065] from Figure 2It can be seen that with the extension of storage time, the malondialdehyde (MDA) content in whole wheat flour samples with different moisture contents all showed an increasing trend, and the increase in MDA content was closely related to the initial moisture content and the preparation method. For whole wheat flour prepared using the same method, the trend of MDA content increase slowed down as the moisture content of the sample decreased. Figure 2 The malondialdehyde increase in whole wheat flour with a moisture content of 12.59% (Example 1) was 1.98 times that of whole wheat flour with a moisture content of 7.35% (Example 6).

[0066] After 6 or 7 weeks of accelerated storage, the malondialdehyde content of whole wheat flour prepared by direct cyclone milling (Examples 1-6) and whole wheat flour prepared by adding puffed bran (Examples 27-38) was mostly around 3.0 mg. The content of malondialdehyde in whole wheat flour prepared by adding ordinary bran (Examples 7-26) is mostly below 3.0 mg. More than Kg.

[0067] It is evident that reducing the initial moisture content of whole wheat flour or puffing the bran can significantly reduce the production of malondialdehyde during whole wheat flour storage, alleviate lipid oxidative rancidity, and mitigate the deterioration of food quality during storage.

[0068] Measurement of lipase activity (LA): Lipase activity was determined using the p-nitrophenol method, and 1 mmol of the solution was prepared. L of p-nitrophenol (P-NP) standard solution, then using 1 mol The standard solution was diluted with L of sodium carbonate solution to create 10 different concentration gradients.

[0069] Take 1 mL of each gradient solution and add 1 mL of 0.5 mol of water sequentially. L of trichloroacetic acid and 3 mL of 0.5 mol L of sodium hydroxide solution was thoroughly mixed, and its absorbance was measured at a wavelength of 410 nm to plot a standard curve for p-nitrophenol (P-NP). The assay was performed using p-nitrobenzene palmitic acid (P-NPP) as a slightly modified substrate. Results are as follows... Figure 3 As shown.

[0070] from Figure 3 It was found that the lipase activity of whole wheat flour samples decreased with prolonged storage time. For whole wheat flour prepared by the same method, the lipase activity of samples with high moisture content was significantly higher than that of samples with low moisture content, indicating that the risk of lipid hydrolysis is higher in high-moisture whole wheat flour samples than in low-moisture samples, and their storage stability is worse. Extrusion treatment of bran can significantly reduce the lipase activity of whole wheat flour. Figure 3E in Table 1 shows wholemeal flour with 12.32% moisture content (Example 27) which has an initial LA of 42.09 U mL, significantly lower than Figure 3 C in Table 1 shows wholemeal flour with 12.47% moisture content (Example 14, initial LA of 79.28 U mL). Figure 3 E in Table 1 shows wholemeal with 12.32% moisture content (Example 27) which has an initial LA of 42.09 U mL, while Figure 3 F in Table 1 shows wholemeal flour with 12.22% moisture content (Example 33) which has an initial LA of 27.67 U mL, the difference between them is mainly due to the addition or non-addition of wheat germ. The high-moisture wholemeal flour sample has a greater decrease in lipase activity during storage, which may be due to the increased mobility of protein molecules with increasing moisture, which in turn increases the extensibility of the protein, promotes the hydrolysis of peptide bonds, leading to disulfide bond exchange and deamination of glutamine and aspartic acid, thus reducing the thermal stability of the enzyme and making it more susceptible to inactivation during heat treatment.

[0071] Determination of lipoxidase (LOX) activity: Determination of lipoxidase (LOX) activity, specifically including: 2g of wholemeal flour samples obtained from Examples 1-38 were weighed and mixed with 10mL of phosphate buffer solution (pH 7.5, 0.1mol L), incubated at 4 for 30min, then the activity of lipoxidase in the wholemeal flour sample was determined by ultraviolet spectrophotometry. The results are shown in Figure 4 .

[0072] As can be seen from Figure 4 , the initial lipoxidase activity of wholemeal flour prepared from unexpanded bran is very high (Examples 7-26), but after one week of storage, LOX decreases significantly and then stabilizes. Wholemeal flour with 12.47% moisture content (Example 14) has an initial LOX activity of 4166.75 U g, which is 8.5 times that of wholemeal flour with 12.32% moisture content (Example 27). Wholemeal flour with 12.30% moisture content (Example 21) has an initial LOX activity of 4042.26 U g, which is 9.3 times that of wholemeal flour with 12.22% moisture content (Example 33). Expanding treatment can well inactivate the lipoxidase activity in bran, thereby improving the storage stability of wholemeal flour.

[0073] Determination of flavor substances: The volatile flavor components of the wholemeal flour samples with moisture contents of 12.47% (Example 14), 9.3% (Example 17) and 7.38% (Example 19) were identified and analyzed during storage, and the results are shown in Table 1. Figure 5 As can be seen from Table 1, Figure 5 the volatile flavor compounds identified in the wholemeal flour with different initial moisture contents mainly include aldehydes, alcohols, esters, acids, ketones, heterocyclic compounds and hydrocarbons, among which aldehydes, alcohols and heterocyclic compounds are predominant, and the hydrocarbons have a relatively high odor threshold value but are not the main flavor compounds because they have no flavor activity and make little contribution to the flavor of the wholemeal flour.

[0074] Among them, the flavor compounds of the wholemeal flour sample with a moisture content of 12.47% (Example 14) at different storage times are shown in Table 1.

[0075] Table 1 Flavor compounds of the wholemeal flour sample of Example 14 at different storage times

[0076] Note: “-” represents not detected, 0 W represents storage for 0 weeks, 4 W represents storage for 4 weeks, and 6 W represents storage for 6 weeks.

[0077] As can be seen from Table 1, the relative content of n-hexanol increased from 9.01% to 25.79% and the relative content of hexanal increased from 1.01% to 2.43% when stored for 4 weeks, and the relative contents further increased when stored for 6 weeks, and volatile substances such as hexanoic acid and octenal began to appear, indicating that the wholemeal flour sample with a moisture content of 12.47% (Example 14) had a rancid taste after 4 weeks of storage, and the rancid taste was more obvious after 6 weeks of storage.

[0078] The correlation between the moisture content and storage time of the wholemeal flour sample and the volatile components was analyzed, and the results are shown in Table 2. Figure 6 As can be seen from Table 2, Figure 6 with the extension of the storage time, the oxidation and hydrolysis of fatty acids in the wholemeal flour produced small molecular aldehydes, alcohols and ketones, which caused the wholemeal flour to have a rancid taste, among which octenal had a smell similar to that of spoiled food and was a common rancid taste component after oil spoilage; hexanol and octanol had a mild and slightly sweet wine aroma and a strong oil smell and citrus aroma; hexanal was produced by the autoxidation of linoleic acid and mainly had an oil, grass and apple aroma; 1-octen-3-ol had a distinct mushroom flavor and herbal aroma and some fishy smell; hexanoic acid had a strong fatty smell but a relatively soft acid taste, similar to the smell of Daqu liquor, and had a certain stimulating effect.

[0079] It should be pointed out finally that the above examples are only used to illustrate the technical solutions of the present application but not to limit it, and although the present application has been described in detail with reference to the preferred embodiments, it should be understood by those skilled in the art that the technical solutions of the present application can still be modified or replaced equivalently, and these modifications or equivalent replacements should not make the modified technical solutions deviate from the spirit and scope of the technical solutions of the present application.

Claims

1. A method of extending the shelf life of wholegrain flour, characterised in that, The method comprises the following steps: S1, preparing whole wheat flour; S2, controlling the moisture content of the whole wheat flour to 7%-14%.

2. The method of extending the shelf life of wholegrain flour according to claim 1, wherein, The method for preparing the whole wheat flour in S1 comprises a direct pulverization method or a backfilling method.

3. A method of extending the shelf life of wholegrain flour according to claim 2, characterised in that, In the backfilling method, the backfilling material comprises at least one of wheat germ, bran and secondary powder.

4. The method of extending the shelf life of wholegrain flour according to claim 1, wherein, The method for controlling the moisture content of the whole wheat flour in S2 comprises one of sun drying, air drying, oven drying, freeze drying and air blowing.

5. The method of extending the shelf life of wholegrain flour according to claim 1, wherein, The method for controlling the moisture content of the whole wheat flour in S2 comprises controlling the moisture content to 8%-10%.

Images