Method for synergistically extracting Chinese yam starch and protein, extract and application

Abstract

The invention provides a method for synergistically extracting Chinese yam starch and protein as well as an extract and application thereof. The method comprises the following steps: firstly, extracting Chinese yam starch by using an alkali extraction method, and extracting Chinese yam protein from an extracting solution from which the starch is extracted by using an acid precipitation method according to the characteristic of water solubility of the Chinese yam protein. According to the operation method, the two main components in the Chinese yam can be utilized to the maximum extent, extraction of Chinese yam starch through an alkali extraction method and extraction of Chinese yam protein through an alkali extraction and acid precipitation method are linked, the operation method is simple and easy to implement, efficient allocation of resources is facilitated, and energy waste is reduced.

Description

Technical Field

[0001] The invention belongs to the technical field of starch processing, and particularly relates to a method for synergistically extracting yam starch and protein, an extract and an application thereof. Background Art

[0002] Chinese yam is a crop that can be used as both medicine and food. Traditional Chinese medicine believes that Chinese yam "treats injuries, replenishes deficiency, removes cold and heat evil spirits, strengthens qi and strength, and grows muscles. Long-term use can improve hearing and vision, and prolong life without hunger." Modern research shows that Chinese yam can induce the production of interferon and enhance human immune function. The choline and lecithin contained in Chinese yam help improve people's memory and improve intelligence and brain health. Usually, Chinese yam (dry weight) contains 75%~84% starch, 6%~8% crude protein, and 1.2%~1.8% crude fiber. Starch, as the main component of Chinese yam, has better anti-digestion, anti-constipation and blood lipid-lowering effects than corn, wheat and sweet potato starch. Chinese yam is rich in various proteins, mainly storage protein Dioscorin, which accounts for 80%~85% of the total soluble protein. Yam storage protein is rich in aspartic acid and glutamic acid, and its total content of histidine, phenylalanine, methionine and tyrosine (14.92%) is slightly greater than that of sweet potato protein (12.34%). These four amino acids can play a positive role in the scavenging activity of free radicals due to their special structure. At present, the concept of health and wellness has long been deeply rooted in people's hearts, and consumers' demand for nutritious and health-care foods is constantly increasing. Yam starch and protein have high nutritional value and have extremely broad application prospects.

[0003] At present, the extraction methods of starch include water immersion, mechanical separation, alkali extraction, enzyme extraction, etc., among which the alkali extraction method has a high extraction efficiency and is the most widely used. However, a large amount of waste liquid will be generated in the process of extracting yam starch using the alkali extraction method, which contains a large amount of high-value by-products, especially soluble proteins. Starch is extracted by alkali extraction, and the starch automatically settles, and then the acid precipitation part in the alkali extraction acid precipitation method is used for connection. The waste liquid after starch extraction is acid-precipitated to obtain yam protein. In the past, extracting starch or protein alone often causes another waste of resources. The synergistic extraction method can maximize the use of these two main components in yam, and also help to expand the application range of yam starch and yam protein to meet market demand. Therefore, it is necessary to develop a method for the synergistic extraction of iron stick yam starch and protein. Summary of the invention

[0004] The purpose of the present invention is to provide a method for the synergistic extraction of yam starch and protein, an extract and an application thereof. The present invention optimizes the synergistic extraction process through experiments, which is simple and easy to implement, and at the same time improves the usable value of yam starch waste liquid, thereby achieving the purpose of efficiently utilizing the nutritional components of yam.

[0005] In order to achieve the above-mentioned purpose, the present invention adopts the following technical solutions:

[0006] The present invention provides a method for synergistically extracting yam starch and protein, the extraction method comprising the following steps: (1) preparing yam pulp; (2) adding alkaline extracting solution to the yam pulp for extraction; (3) screening and separating the alkaline extract to obtain an extract and a precipitate, and separating the extract and the precipitate and retaining them respectively; (4) drying the precipitate to obtain yam starch; (5) The acidity of the extract is adjusted with an acidifier to produce a precipitate in the extract to obtain yam protein.

[0007] Furthermore, in step (2), the liquid-to-solid ratio of the alkaline extract to the yam slurry is 3-7:1.

[0008] Furthermore, in step (2), the leaching time of the alkaline leaching solution is 1 to 5 hours.

[0009] Furthermore, the pH value of the alkaline extract is 8-12.

[0010] Furthermore, in step (3), the leaching temperature of the alkaline leaching solution is 25-45°C.

[0011] Furthermore, the acidity is adjusted to a pH value of 3 to 4.

[0012] Furthermore, the optimal extraction method is that the extraction temperature of the alkaline extract is 35° C., the extraction time is 2 to 3 hours, the pH value of the alkaline extract is 11, and the liquid-to-solid ratio of the alkaline extract to the yam slurry is 5.

[0013] Furthermore, in the method for synergistic extraction of yam starch and protein, the protein extraction rate is 50% to 55%, and the yam starch extraction rate is 60% to 70%.

[0014] The invention also provides yam starch and yam protein obtained by the extraction method.

[0015] Furthermore, the resistant starch content of the yam starch is 30% to 40%, and the essential amino acid content of the yam protein is 35% to 40%.

[0016] Furthermore, the yam starch has strong thermal stability.

[0017] Furthermore, the total amount of essential amino acids contained in the yam protein is 216.25 mg / g pro.

[0018] The invention also provides application of the yam starch and protein in preparing food.

[0019] Compared with the prior art, the advantages and positive effects of the present invention are:

[0020] 1. The present invention provides a method for synergistically extracting yam starch and protein, which connects the extraction of starch by alkali extraction and the extraction of protein by alkali extraction and acid precipitation. The method is simple and easy to implement, and has guiding significance for the research and development of related technologies.

[0021] 2. The present invention performs acid precipitation on the extract after extracting yam starch to obtain yam protein. The synergistic extraction method can maximize the use of the two main components in yam, which is beneficial to the efficient allocation of resources and reduces energy waste.

[0022] 3. The present invention optimizes the extraction process parameters through experimental verification and obtains the best synergistic extraction process, specifically, the alkali solution extraction temperature is 35°C, the pH value of the alkali solution extraction solution is 11, the extraction time is 2-3h, and the liquid-to-solid ratio of the alkaline extraction solution to the iron stick yam slurry is 5.

[0023] 4. The present invention provides a method for the coordinated extraction of yam starch and protein. The yam starch and yam protein obtained according to the optimal process have a yam starch extraction rate of up to 70% and a yam protein extraction rate of up to 55%.

[0024] 5. The essential amino acid content of the yam protein provided by the present invention is 35% to 40%, and the resistant starch content of the yam starch is 30% to 40%. Compared with other conventional starches, the content is higher and the thermal stability is stronger. Yam starch is expected to become an emerging natural starch resource for the research and development of healthy foods. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 The effect of extraction temperature on the extraction rate of yam starch; Figure 2 The effect of extraction pH on the extraction rate of yam starch; Figure 3 The effect of the extraction liquid-solid ratio on the extraction rate of yam starch; Figure 4 The effect of extraction time on the extraction rate of yam starch; Figure 5 The effect of extraction temperature on the extraction rate of yam protein; Figure 6 The effect of extraction pH on the extraction rate of yam protein; Figure 7 The effect of the extraction liquid-solid ratio on the protein extraction rate of yam; Figure 8 The effect of extraction time on the extraction rate of yam protein. DETAILED DESCRIPTION

[0026] The technical solution of the present invention is further described in detail below in conjunction with the accompanying drawings and specific embodiments.

[0027] The liquid-to-solid ratio described in the present invention is the ratio of volume (mL) to mass (g).

[0028] Determination of experimental conditions: 1. Effect of different extraction conditions on the starch extraction rate of iron yam A 0.2 mol / L sodium hydroxide solution was prepared to study the effect of different extraction conditions on the extraction rate of iron yam starch.

[0029] Extraction rate = X 1 / X 0 ; X 1 is the starch content obtained by extraction, X 0 is the starch content in the fresh iron stick yam sample. The starch content in the fresh iron stick yam sample measured in this experiment is X 0 It is 17.19%, and its measurement method adopts the acid hydrolysis method of GB5009.9-2023.

[0030] 2. Effect of different extraction conditions on protein extraction rate of iron yam A 0.2 mol / L sodium hydroxide solution was prepared to study the effect of different extraction conditions on the protein extraction rate of Dioscorea opposita.

[0031] Extraction rate = Y 1 / Y 0 ; Y 1 is the protein content obtained by extraction, Y 0 is the protein content in the fresh iron stick yam sample. The protein content Y in the fresh iron stick yam sample measured in this experiment 0 It is 2.20%, and its measurement method adopts GB5009.5-2016 Kjeldahl nitrogen determination method.

[0032] Example 1

[0033] This embodiment provides a method for synergistic extraction of yam starch and protein, comprising the following steps: (1) Accurately weigh 5 portions of 20.00g of iron stick yam paste; (2) Pour 60 mL of an extract adjusted to a pH of 11 using a 0.2 mol / L sodium hydroxide solution, wherein the liquid-to-solid ratio of the alkaline extract to the iron stick yam slurry is 3, and extract for 3 h at 25°C, 30°C, 35°C, 40°C, and 45°C, respectively; (3) After the extraction is completed, sieve through 80 mesh and 200 mesh sieves, transfer to a centrifuge tube, and centrifuge for 10 minutes (7000r / min). After centrifugation, the extract and precipitate are obtained, and the extract and precipitate are separated and retained respectively; (4) Resuspend the precipitate in distilled water four times and in anhydrous ethanol twice; finally, place the precipitate in an oven and dry it at 40°C until constant weight.

[0034] Figure 1 The effect of temperature on the extraction rate of iron stick yam starch was shown in Table 1. The best extraction rate was 52.70% at 35°C (Table 1). Between 25°C and 35°C, the extraction rate of iron stick yam starch increased with the increase of temperature, but it decreased after exceeding 35°C. This may be because too high a temperature will cause the starch to begin to gelatinize, and the slurry viscosity will increase, which is not conducive to the release of starch.

[0035] Example 2

[0036] This embodiment provides a method for synergistic extraction of yam starch and protein, comprising the following steps: (1) Accurately weigh 5 portions of 20.00g of iron stick yam paste; (2) Using 0.2 mol / L sodium hydroxide solution to adjust the pH value of alkaline extract to 8, 9, 10, 11, and 12, pour 60 mL of the alkaline extract into the iron stick yam slurry, respectively, the liquid-to-solid ratio of the alkaline extract to the iron stick yam slurry is 3, and extract at 35°C for 3 h; (3) After the extraction is completed, the extract is sieved through an 80-mesh sieve and a 200-mesh sieve, transferred to a centrifuge tube, and centrifuged for 10 minutes (7000 r / min). After centrifugation, an extract and a precipitate are obtained, and the extract and the precipitate are separated and retained respectively; (4) Resuspend the precipitate in distilled water four times and in anhydrous ethanol twice; finally, place the precipitate in an oven and dry it at 40°C until constant weight.

[0037] Figure 2 The effect of pH value on the extraction rate of iron yam starch was shown in Table 1. The best extraction rate was 59.93% when the pH value was 11 (Table 1). Combined with the data analysis, it can be seen that when the pH value is low, the protein solubility is low and some starch particles are bound. When the pH value is higher than 11, the concentration of sodium hydroxide is too high, which increases the viscosity of the extraction system and is not conducive to the diffusion of starch molecules.

[0038] Example 3

[0039] This embodiment provides a method for synergistic extraction of yam starch and protein, comprising the following steps: (1) Accurately weigh 5 portions of 20.00g of iron stick yam paste; (2) Using 0.2 mol / L sodium hydroxide solution to adjust the pH of the alkaline extract to 11, pour the iron stick yam slurry into 60 mL, 80 mL, 100 mL, 120 mL, and 140 mL of the alkaline extract, respectively, with the liquid-to-solid ratio of the alkaline extract to the iron stick yam slurry being 3, 4, 5, 6, and 7, and extract at 35°C for 3 h; (3) After the extraction is completed, sieve through 80 mesh and 200 mesh sieves, transfer to a centrifuge tube, and centrifuge for 10 minutes (7000r / min). After centrifugation, the extract and precipitate are obtained, and the extract and precipitate are separated and retained respectively; (4) Resuspend the precipitate in distilled water four times and in anhydrous ethanol twice; finally, place the precipitate in an oven and dry it at 40°C until constant weight.

[0040] Figure 3 The effect of different liquid-solid ratios on the starch extraction rate of iron stick yam is shown in Table 1. The best extraction rate is 66.37% when the liquid-solid ratio is 5 (Table 1). This is because excessive solvent will cause the solution to become thinner, making it impossible for the protein contained in the iron stick yam starch particles to dissolve, resulting in a decrease in the starch extraction rate.

[0041] Example 4 This embodiment provides a method for synergistic extraction of yam starch and protein, comprising the following steps: (1) Accurately weigh 5 portions of 20.00g of iron stick yam paste; (2) Pour 100 mL of alkaline extract adjusted to pH 11 by 0.2 mol / L NaOH solution, wherein the liquid-to-solid ratio of the alkaline extract to the iron stick yam slurry is 5, and extract at 35° C. for 1 h, 2 h, 3 h, 4 h, and 5 h respectively; (3) After the extraction is completed, the extract is sieved through an 80-mesh sieve and a 200-mesh sieve, transferred to a centrifuge tube, and centrifuged for 10 minutes (7000 r / min). After centrifugation, an extract and a precipitate are obtained, and the extract and the precipitate are separated and retained respectively; (4) The precipitate was resuspended in distilled water 4 times and in anhydrous ethanol 2 times. Finally, the precipitate was placed in an oven and dried at 40°C to constant weight.

[0042] Figure 4 The effect of time on the extraction rate of iron yam starch was shown in Table 1. The optimal extraction rate was 66.55% at 3 hours (Table 1). Combined with data analysis, when the extraction time was higher than 3 hours, the iron yam starch particles were soaked in alkali solution for too long, causing the starch structure to become loose, which was not conducive to the precipitation of starch.

[0043] Table 1 Starch extraction rate

[0044] Example 5

[0045] This embodiment provides a method for synergistic extraction of yam starch and protein, comprising the following steps:

[0046] The pH value of the extract retained in Example 1 was adjusted to 3.5 with 0.1 mol / L hydrochloric acid solution, and the extract was stirred at 600 rpm during the adjustment. After the adjustment, the extract was stirred at 800 rpm for 10 minutes. Centrifuged for 10 minutes (8500 r / min), the supernatant was removed, and freeze-dried to obtain iron stick yam protein.

[0047] Figure 5 The effect of temperature on the protein extraction rate of iron yam is shown in Table 2. The best extraction rate is 44.25% at 35°C (Table 2). Combined with data analysis, it can be seen that this is because the extraction temperature is closely related to the solubility of protein. When the temperature is too low, the solubility of protein in alkali solution is significantly reduced, and its molecular movement becomes slow, making it difficult to fully disperse in the solvent; when the temperature is too high, the protein is prone to denaturation, the spatial structure changes, and it is more likely to undergo hydrolysis, thereby changing the original extractable state of the protein.

[0048] Example 6

[0049] This embodiment provides a method for synergistic extraction of yam starch and protein, comprising the following steps: The pH value of the extract retained in Example 2 was adjusted to 3.5 with 0.1 mol / L hydrochloric acid solution, and the extract was stirred at 600 rpm during the adjustment. After the adjustment, the extract was stirred at 800 rpm for 10 minutes. Centrifuged for 10 minutes (8500 r / min), the supernatant was removed, and freeze-dried to obtain iron stick yam protein.

[0050] Figure 6 The effect of pH value on the protein extraction rate of iron yam was shown in Table 2. The best extraction rate was 46.30% when the pH value was 11 (Table 2). When the pH value was too low, the protein solubility was low; when the pH value was too high, the natural conformation of the protein would change and further denature, causing the originally soluble protein to coagulate and precipitate.

[0051] Example 7

[0052] This embodiment provides a method for synergistic extraction of yam starch and protein, comprising the following steps: The pH value of the extract retained in Example 3 was adjusted to 3.5 with 0.1 mol / L hydrochloric acid solution, and the extract was stirred at 600 rpm during the adjustment. After the adjustment, the extract was stirred at 800 rpm for 10 minutes. Centrifuged for 10 minutes (8500 r / min), the supernatant was removed, and freeze-dried to obtain iron stick yam protein.

[0053] Figure 7 The effect of liquid-solid ratio on the protein extraction rate of iron yam was shown in Table 2. The best extraction rate was 52.99% when the liquid-solid ratio was 5 (Table 2). Combined with data analysis, since sufficient solvent is required to dissolve protein from solid matter, when the liquid-solid ratio is too low, the solvent cannot fully contact all the proteins in the raw material. In addition, when the liquid-solid ratio is low, the concentration of soluble protein in the solution will increase rapidly, forming a high concentration gradient, which is not conducive to further dissolution of protein. When the liquid-solid ratio is too high, the protein is easily over-diluted and difficult to collect in subsequent operations.

[0054] Example 8

[0055] This embodiment provides a method for synergistic extraction of yam starch and protein, comprising the following steps: The pH value of the extract retained in Example 4 was adjusted to 3.5 with 0.1 mol / L hydrochloric acid solution, and the extract was stirred at 600 rpm during the adjustment. After the adjustment, the extract was stirred at 800 rpm for 10 minutes. Centrifuged for 10 minutes (8500 r / min), the supernatant was removed, and freeze-dried to obtain iron stick yam protein.

[0056] Figure 8 The effect of extraction time on the protein extraction rate of iron yam was shown in Table 2. The best extraction rate was 53.68% at 2h (Table 2). When the extraction time was too short, the protein was not fully dissolved and dispersed, resulting in the protein in the raw material remaining in the material. When the extraction time was too long, the possibility of protein denaturation increased, and the stable spatial conformation was destroyed, resulting in a decrease in protein extraction rate.

[0057] Table 2 Protein extraction rate

[0058]

[0059] Example 9: Determination of swelling power and solubility of yam starch In this embodiment, the yam starch is the yam starch extracted by the alkaline extracting solution in Example 4 for 3 hours; sweet potato starch, corn starch, potato starch and cassava starch are all commercially available products.

[0060] (1) Accurately weigh 0.100 g (±0.002) of yam starch, sweet potato starch, corn starch, potato starch and cassava starch sample (W0) and 10 mL of pure water into a 50 mL centrifuge tube, making sure that the sample does not adhere to the tube wall, to obtain a starch mixture suspension.

[0061] (2) Place in a constant temperature shaking water bath at 55℃, 65℃, 75℃, 85℃, and 95℃ for 30 min respectively.

[0062] (3) Subsequently, the mixture was centrifuged at 4000 r / min for 20 min, and the supernatant was slowly transferred to an aluminum box. The box was dried in an oven at 105°C until constant weight was reached and weighed (W1). The precipitate obtained by centrifugation was weighed (W2).

[0063] , Where: W0: dry weight of starch sample (g); W1: weight of supernatant dried to constant weight (g); W2: weight of precipitate after centrifugation (g); S: solubility of sample (%); SP: swelling power of sample (g / g).

[0064] Table 3 Solubility of starch

[0065]

[0066] Table 4 Swelling power of starch

[0067]

[0068] Tables 3 and 4 show the solubility and swelling power of iron stick yam starch, respectively. Swelling power generally refers to the amount of water that can be absorbed per gram of starch at a specified temperature, while solubility corresponds to the percentage of leached amylose and amylopectin. It can be seen that the solubility and swelling power of the five starches increase with the increase of temperature. The solubility and swelling power of yam starch increase significantly at 75°C. It can be inferred that its gelatinization temperature is about 65~75°C. The gelatinization temperature of potato and cassava starch is relatively low, about 55°C~65°C. Under 95°C, the solubility and swelling power of yam starch, sweet potato starch, and corn starch are significantly lower than those of potato starch and cassava starch, indicating that yam starch has poor solubility at high temperatures. It can be seen from Table 4 that the swelling power of potato starch and cassava starch increases significantly after 65°C, indicating that their swelling temperature range is large. In contrast, the swelling power of yam starch is between cassava starch and sweet potato starch at 75~95°C, and its swelling capacity is average.

[0069] Example 10: Determination of thermal properties of yam starch

[0070] In this embodiment, the yam starch is the yam starch extracted by the alkaline extracting solution for 3 hours in Example 4. Sweet potato starch, corn starch, potato starch and cassava starch are all commercially available products.

[0071] (1) Accurately weigh 3 mg of yam starch, sweet potato starch, corn starch, potato starch and cassava starch samples respectively into aluminum crucibles, add distilled water at a starch sample to distilled water mass ratio of 1:3 (starch dry basis), seal the crucible, equilibrate in a 4℃ refrigerator for 12 h, and measure the starch sample solution after equilibration at room temperature for 1 h.

[0072] (2) Using an empty aluminum pot as a control, set nitrogen as the flowing gas, and the heating rate to 10°C / min, scan the starch sample solution in the range of 25°C~110°C.

[0073] (3) The thermal data analysis software STARe Default DB V16.00 was used to determine the onset temperature (To), peak temperature (Tp), final temperature (Tc) and enthalpy change (ΔH) of the starch sample solution.

[0074] Table 5 Thermal properties of starch

[0075]

[0076] Table 5 shows the thermal properties of iron stick yam starch. The starting temperature (To) refers to the temperature at which starch begins to gelatinize. At this time, starch granules begin to absorb water, internal hydrogen bonds begin to break, and certain physical properties in the system begin to change. The peak temperature (Tp) is the temperature corresponding to when the thermal effect of starch reaches its peak during thermal analysis. At this temperature, the various changes in the starch gelatinization process are most drastic. The final temperature (Tc) indicates the temperature at the end of the starch gelatinization process. When this temperature is reached, the gelatinization process of starch granules is basically completed, the starch molecules have fully absorbed water, expanded, and dispersed, and the changes in the physical properties of the starch system gradually tend to stabilize. ΔH represents enthalpy change, which refers to the heat absorbed or released by starch during the gelatinization and other thermal processes.

[0077] The To of yam starch has no significant difference from sweet potato starch and corn starch, but is significantly higher than potato starch and cassava starch, while the Tp and Tc values ​​are significantly higher than the other four starches. This indicates that the gelatinization temperature of yam starch is higher, and on the other hand, it also indicates that yam starch has stronger thermal stability than other starches. In contrast, the ΔH of yam starch is significantly lower than that of the four starches, which means that the changes in its energy thermal conversion process are relatively small.

[0078] Example 11: In vitro digestibility determination of yam starch

[0079] (1) The yam starch in this example is the yam starch extracted by the alkaline extracting solution for 3 hours in Example 4. Sweet potato starch, corn starch, potato starch and cassava starch are all commercially available products.

[0080] (2) Prepare an amylase solution by suspending 1.0 g of porcine pancreatic α-amylase (9.4 U / mg) in 10 mL of water and stirring at 37°C for 12 min. Centrifuge the mixture (3255 r / min, 10 min) to remove the precipitate. Add 20 mg of saccharifying enzyme (100 U / mg).

[0081] (3) Disperse yam starch, sweet potato starch, corn starch, potato starch, and cassava starch (100 mg) in 2 mL of distilled water, keep in a 100°C water bath for 30 min, cool to 25°C, add 7 mL of 0.1 M sodium acetate buffer (pH 5.0, 400 mM calcium chloride), add 1 mL of the freshly prepared enzyme solution, and incubate in a constant temperature shaker at 37°C (260 rpm).

[0082] (4) Take 0.1 mL of the supernatant at intervals of 0 min, 20 min, and 120 min and place it in a 1.5 mL centrifuge tube. Add 0.9 mL of 95% ethanol and mix. Centrifuge (10,000 r / min, 2 min) and retain the supernatant.

[0083] (5) The amount of starch digestibility was determined using the Megazyme Glucose Kit. Starch was divided into rapidly digestible starch (RDS), slowly digestible starch (SDS), and resistant starch (RS) based on the hydrolysis rate.

[0084] , Wherein: G20 and G120 are the hydrolyzed glucose contents after adding enzyme for 20 min and 120 min, respectively; FG is the hydrolyzed glucose content without adding enzyme; TS is the total starch content (GB5009.9-2023 acid hydrolysis method).

[0085] Table 6 In vitro digestibility of iron yam starch

[0086]

[0087] Table 6 shows the in vitro digestion characteristics of starch. RDS (rapidly digestible starch) refers to starch that can be quickly digested and absorbed within 20 minutes under in vitro simulated digestion conditions. SDS (slowly digestible starch) refers to starch that is digested within 20 to 120 minutes. It is slowly but completely digested in the small intestine, which helps to maintain the stability of glucose concentration in human blood. RS (resistant starch) refers to starch that cannot be digested and absorbed by amylase in the small intestine of the human body and directly enters the colon to be fermented by microbial flora. Resistant starch has a similar effect to dietary fiber, which helps to regulate the balance of intestinal flora, promote intestinal health, increase satiety, and to a certain extent help control weight, reduce blood lipids, etc., which has positive significance for preventing some chronic diseases. As can be seen from Table 6, the resistant starch content of yam starch is 30.57%, which is significantly higher than the other four starches, and the rapidly digestible starch of yam starch is significantly lower than the other four starches, and the slowly digestible starch content is not significantly different from corn starch, which is significantly lower than the other three starches. It can be inferred that the digestibility of yam starch is better than that of the other four starches.

[0088] Example 12: Amino Acid Analysis of Yam Protein

[0089] The yam protein in this example is the yam protein extracted by using the alkaline extracting solution in Example 8 for 2 hours.

[0090] (1) Weigh an appropriate amount of yam protein sample into a 25 mL hydrolysis tube, add 10 mL HCl (1+1), place in an electric heated air drying oven, and hydrolyze at 110 °C for 22 h. After cooling, transfer to a 20 mL colorimetric tube and adjust the volume to obtain a protein hydrolyzed solution.

[0091] (2) Accurately take 100 μL of protein hydrolyzate solution into a 5 mL centrifuge tube, place it in a vacuum drying oven, dry it at 60 °C for 2 h (to completely dry out the solvent), fill the centrifuge tube with nitrogen, accurately add 50 μL of derivatization reagent (ethanol: phenyl isothiocyanate: water: triethylamine = 7:1:1:1, prepare it before use, and fill it with nitrogen during preparation), derivatize it at room temperature for 30 min, add 0.45 mL of mobile phase A, mix well, and pass it through a 0.45 μm organic membrane for testing.

[0092] (3) Test conditions, chromatographic column is C 18 SHISEIDO (4.6mm*250mm*5μm), injection volume is 10μL, column temperature is 40℃, wavelength is 254nm.

[0093] (4) Mobile phase: A: 0.1 mol / L anhydrous sodium acetate + acetonitrile = 97 + 3, mix well and adjust the pH to 6.5 (31.815 g sodium acetate + 3880 mL water + 120 mL acetonitrile); B: acetonitrile + water = 80 + 20.

[0094] (5) The mobile phase gradient is shown in the table below.

[0095] Table 7 Mobile phase gradient

[0096]

[0097] (6) The hydrolyzed amino acid content is calculated according to the formula:

[0098]

[0099] Where W is the target substance content in the sample, in mg / kg; C is the concentration of the target substance in the sample solution, in mg / L; C 0 is the concentration of the target substance in the blank control, in mg / L; V is the fixed volume, in mL; N is the dilution factor; m is the sample volume, in g.

[0100] (7) The amino acid score (AAS) and chemical score (CS) were calculated according to the corresponding formulas based on the essential amino acid pattern for adults recommended by the World Health Organization (WHO) in 2007 and the amino acid pattern of reference egg protein.

[0101]

[0102]

[0103] Wherein: Asample,i (i=1,2,…,9) is the mass fraction of a certain essential amino acid in the sample protein to be tested (mg / g protein); Apattern,i (i=1,2,…,9) and Areference,i (i=1,2,…,9) are the mass fractions of the corresponding essential amino acids in the 2007 WHO scoring pattern and the reference protein (egg) respectively (mg / g protein).

[0104] Table 8 Amino acid composition of iron stick yam protein

[0105]

[0106] In the table, EAA is the essential amino acid content, and TAA is the total amino acid content.

[0107] Table 8 shows the amino acid composition of yam protein. The proportion of essential amino acids in food is one of the key indicators to measure its protein quality. By comparing the essential amino acid proportion data of different foods, it is possible to intuitively confirm which food has more advantages in providing high-quality protein. For example, the essential amino acid proportion of milk and eggs is generally around 38%~40%. Combined with Table 8, it can be seen that the essential amino acid proportion of yam protein is 35.89%, which is considerable and is expected to become an emerging protein resource for food research and development and production. Among them, leucine has the highest content, accounting for 23.45% of essential amino acids. Among non-essential amino acids, glutamic acid has the highest content, reaching 26.18%, and aspartic acid and arginine are also high. These three amino acids account for 61.54% of the non-essential amino acids in yam protein. Among them, the content of acidic amino acids (glutamic acid, aspartic acid) is 161.30 mg / g, the content of basic amino acids (arginine, lysine, histidine) is 99.26 mg / g, and the rest are neutral amino acids. It can be predicted that the isoelectric point of yam protein is acidic.

[0108] Table 9 Amino acid scores of iron stick yam protein

[0109]

[0110] Table 9 shows the amino acid score of yam protein. The amino acid score can directly reflect the degree of fit between the essential amino acid composition of food protein and the needs of the human body, so as to judge the nutritional value of the protein to the human body. As shown in Table 9, the total amount of essential amino acids contained in yam protein is 216.25 mg / g pro, which is somewhat different from the WHO standard of 294.4 mg / g pro. In the amino acid score, tryptophan has the highest score of 148.57.

[0111] Table 10 Chemical scoring of iron stick yam protein

[0112]

[0113] Table 10 shows the chemical score of yam protein. It can be seen from the table that the essential amino acids of yam protein are all lower than the values ​​of the egg model. In summary, the proportion of essential amino acids in yam protein is high, but the score in the amino acid model is average. It can be tried to be used with other proteins to improve its utilization value.

[0114] In summary, the present invention obtains a method with a high comprehensive extraction rate of yam starch and protein by continuously optimizing the extraction process. It can be seen from Table 1 that the optimal extraction process of yam starch is an alkaline extraction temperature of 35°C, an extraction time of 3h, a pH of the alkaline extract of 11, and a liquid-solid ratio of the alkaline extract to the yam slurry of 5; it can be seen from Table 2 that the optimal extraction process of synergistically extracted yam protein is an alkaline extraction temperature of 35°C, an extraction time of 2h, a pH of the alkaline extract of 11, and a liquid-solid ratio of the alkaline extract to the yam slurry of 5; the extraction rate of yam starch obtained is as high as 70%, and the extraction rate of yam protein is as high as 55%.

[0115] The yam starch extracted by the present invention helps to regulate the balance of intestinal flora, promote intestinal health, increase satiety, and can also help control weight and reduce blood lipids to a certain extent. Combined with Table 6, it can be seen that the resistant starch content of yam starch is 30.57%, which is higher than the other conventional starches, so yam starch is expected to become an emerging natural starch resource for the research and development of healthy foods; experiments show that the solubility and swelling power of the yam starch described in the present invention increase with the increase of temperature, the gelatinization temperature is relatively high, and the thermal stability is relatively good; the essential amino acid content of the yam protein extracted by the present invention is nearly 40%, which shows that it has rich nutritional value, but its amino acid score and chemical score are general, and it needs to be used with other proteins to improve its utilization value. The synergistic extraction of yam starch and protein makes the most of the two main components in yam, and at the same time verifies some characteristics of yam starch and yam protein through a large number of experiments, provides theoretical support for later related research, and also helps to expand the application range of yam starch and yam protein to meet market demand.

[0116] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the aforementioned embodiments, it is still possible for a person skilled in the art to modify the technical solutions described in the aforementioned embodiments, or to replace some of the technical features therein with equivalents, and these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions claimed to be protected by the present invention.

Claims

1. A method for synergistic extraction of yam starch and protein, characterized in that: The extraction method comprises the following steps: (1) preparing yam pulp; (2) adding alkaline extracting solution to the yam pulp for extraction; (3) screening and separating the alkaline extract to obtain an extract and a precipitate, and separating the extract and the precipitate and retaining them respectively; (4) drying the precipitate to obtain yam starch; (5) The acidity of the extract is adjusted with an acidifier to produce a precipitate in the extract to obtain yam protein.

2. The method for synergistically extracting yam starch and protein according to claim 1, characterized in that: In the step (2), the liquid-to-solid ratio of the alkaline extract to the yam slurry is 3-7:

1.

3. The method for synergistic extraction of yam starch and protein according to claim 1, characterized in that: In the step (2), the leaching time of the alkaline leaching solution is 1 to 5 hours.

4. The method for synergistically extracting yam starch and protein according to claim 1, characterized in that: In the step (2), the pH value of the alkaline extract is 8-12.

5. The method for synergistic extraction of yam starch and protein according to claim 1, characterized in that: In the step (3), the leaching temperature of the alkaline leaching solution is 25-45°C.

6. The method for synergistic extraction of yam starch and protein according to claim 1, characterized in that: The pH value of the acidity adjustment is 3-4.

7. The method for synergistically extracting yam starch and protein according to claim 1, characterized in that: The best extraction method is that the leaching temperature of the alkaline leaching solution is 35° C., the leaching time is 2 hours, the pH value of the alkaline leaching solution is 11, and the liquid-to-solid ratio of the alkaline leaching solution to the yam pulp is 5.

8. Yam starch and yam protein obtained by the method described in any one of claims 1 to 7.

9. The yam starch and yam protein according to claim 8, characterized in that: The resistant starch content of the yam starch is 30% to 40%, and the essential amino acid content of the yam protein is 35% to 40%.

10. Use of the yam starch and yam protein according to claim 8 in preparing food.

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