Method for extracting peanut oil and protein by using Tween 20 and glutathione composite solution

Abstract

The invention discloses a method for preparing peanut oil and protein powder by utilizing a Tween 20 and glutathione composite solution, and belongs to the technical field of deep processing of agricultural products and comprehensive utilization of byproducts of the agricultural products. The method mainly solves the problems of serious emulsification and low protein yield of the existing oil preparation process by the peanut aqueous solution method. Tween 20 can cause emulsion demulsification by replacing interfacial protein, but cannot improve the protein yield. The reduced glutathione depolymerizes peanut protein by reducing disulfide bonds among peanut protein aggregates, so that the protein yield is increased, and the functional properties of the protein are improved. The method comprises the following steps: grinding peanut kernels, extracting by using a Tween 20 and glutathione composite solution with a certain concentration, and carrying out three-phase centrifugation to directly obtain free oil. After protein in a water phase obtained after centrifugation is precipitated by adjusting an isoelectric point, the peanut protein powder can be obtained by spray drying. When the method is used for processing peanuts, the production of emulsion can be inhibited, and the obtained grease is good in quality; the peanut protein yield is high (more than 85%), the functional characteristics are good, and the method can be widely applied to food processing.

Description

Technical Field

[0001] The invention belongs to the technical field of peanut oil and protein extraction, and particularly relates to a method for preparing oil and protein by a peanut aqueous solution method. Background Art

[0002] Peanuts are rich in fat and protein and are an important source of edible oil, protein and food raw materials in the world. my country is one of the world's important peanut producers, and about half of my country's peanuts are used for oil production. At present, the main means of industrial production of peanut oil are pressing (mainly hot pressing) and organic solvent extraction. The oil obtained by pressing is of good quality but low yield; the oil yield by extraction is high, but the crude oil needs multiple steps of refining before it can be eaten, and the problems of air pollution and production safety caused by organic solvents cannot be ignored. In addition, neither of these two oil-making processes can fully and effectively utilize peanut protein, and peanut meal is mainly used as feed. In order to avoid the use of organic solvents and efficiently extract peanut protein at the same time, the aqueous (enzyme) method for simultaneous extraction of peanut oil and protein has been studied and reported by many scholars, but it is still limited to laboratory or pilot levels.

[0003] In 1956, Sugarman used an aqueous solution method to extract oil and protein from peanuts simultaneously (US Patent, 2762820); in 1975, Lanzani et al. used protease and cellulase to achieve a peanut oil extraction rate of 75-78% (RivItal Sostanze Grasse, L11: 226-229); in 1999, Zhang Xin et al. imitated the production process of sesame oil and used a water substitution method to produce fragrant peanut oil (Food Science, 20 (4): 32-34); in 2002, Sharma et al. used a composite protease to treat peanuts, and the oil yield was 86-92% (J Am Oil Chem Soc, 79 (3): 215-218). Patent CN1419837A reported a method for extracting peanut oil and peanut protein using a composite enzyme (cellulase, pectinase and neutral protease), with an oil yield of 94-96% and a protein yield of 73-75%. In order to extract peanut oil and peanut hydrolyzed protein at the same time, Hua Di et al. used Alcalase to hydrolyze peanuts in 2006. Through a one-step enzymatic reaction, 79.32% of free oil and 71.38% of hydrolyzed protein could be extracted. (Food and Machinery, 22(6):16-19). In 2009, Zhang Shaobing et al. roasted peanuts at different temperatures and then extracted oil by aqueous enzymatic method. The results showed that after roasting peanuts at 190℃ for 20 minutes, the extracted oil had a strong aroma, and the yields of free oil and hydrolyzed protein were about 76% and 79%, respectively (Natural Science Edition of Henan University of Technology, 30(5):9-12). In 2016, Zhang et al. used Tween 20 to assist in the extraction of peanut oil by aqueous method and found that Tween 20 could effectively demulsify the peanuts, and the yield of free oil was 76.1%. Patent CN1555714A uses Alcalase alkaline protease to extract peanut oil, and recovers hydrolyzed protein powder in the form of small peptides. The total free oil yield is 91.6%, and the peanut hydrolyzed protein yield is 84%. Patent CN101401658A conducted a pilot test on the laboratory-level aqueous enzymatic method to extract oil and hydrolyzed protein from peanuts, introduced a three-phase separator to simultaneously separate oil, oil-water mixture and insoluble residue, and tried to use a disc separator to separate oil and water. Among them, the total free oil yield is 73.77%, and the hydrolyzed protein yield is 55.10%. Patent CN103113977A grinds the peanuts and then acid-leaches them, removes the supernatant rich in soluble sugars, and then alkali-extracts and enzymolyzes the precipitate. After three-phase centrifugation, peanut oil and high-purity peanut peptides (protein content>75%) are obtained at the same time.

[0004] As mentioned above, the use of proteases or surfactants can effectively break the emulsion and significantly increase the free oil yield in the aqueous solution process. However, due to the fact that peanut protein is easy to aggregate and precipitate during the extraction process, there are still more residual proteins and oils in the solid phase obtained by the aqueous solution method, resulting in the product yield (especially protein) is still not ideal. Therefore, taking effective measures to narrow the product yield gap between the aqueous solution method and the traditional oil processing method has become the key to promoting the technical upgrading and industrial development of the aqueous solution method. Summary of the invention

[0005] In order to solve the deficiencies of the prior art, the present invention aims to provide a method for depolymerizing peanut protein based on reduced glutathione (hereinafter referred to as glutathione) to improve the yield of aqueous preparation products. The technical scheme of the present invention is: peanut kernels or blanched peanut kernels are ground by dry method, extracted with a certain concentration of Tween 20 and glutathione composite solution under a high pH environment, free oil, water phase and residue are obtained after three-phase centrifugation, the water phase is adjusted to the isoelectric point of peanut protein, and peanut protein powder is obtained after spray drying.

[0006] 1. Process conditions

[0007] (1) Cleaning and screening: remove impurities and moldy kernels from peanut kernels.

[0008] (2) Dry grinding: After the peeled peanut kernels are coarsely crushed using a crusher, the peanuts are further ground into a slurry using a sand disc mill, and the average particle size is controlled to be less than 30 μm.

[0009] (3) Extraction of Tween 20 and glutathione complex solution: Disperse peanut paste in 4-6 times the weight of Tween 20

[0010] In the composite solution of glutathione (1-2wt%) + glutathione (0.05-0.1wt%), the pH of the system is adjusted to 10-11 with NaOH, the temperature is 50-60°C, and the extraction time is 30-50min.

[0011] (4) Three-phase centrifugation: After the extraction is completed, a three-phase horizontal screw centrifuge is used to separate the free oil, water phase and solid phase, with a separation factor of 4000-5000×g.

[0012] (5) Isoelectric precipitation of peanut protein: The pH of the aqueous phase was adjusted to 4.0-4.5 with HCl, and the mixture was slowly stirred for 30 min and then centrifuged to obtain a protein precipitate.

[0013] (6) Spray drying: dilute the precipitate with an appropriate amount of water, adjust the pH to 7.0, and then spray dry the precipitate at an inlet air temperature of 120-130°C and an outlet air temperature of 70-75°C to obtain peanut protein powder.

[0014] 2. Analytical methods

[0015] Crude protein determination: Kjeldahl method (N×5.46);

[0016] Crude fat determination: Soxhlet extraction method;

[0017] Material particle size distribution: measured by laser particle size analyzer;

[0018] Free oil yield: free oil weight / oil content in raw materials × 100%;

[0019] Peanut protein yield: nitrogen content in peanut protein powder / nitrogen content in raw materials × 100%;

[0020] Purity of peanut protein powder: protein content in peanut protein powder / weight of peanut protein powder × 100%;

[0021] Determination of emulsification and emulsion stability: spectrophotometric method.

[0022] The beneficial effects of the present invention are as follows: the equipment and process route are simple, the production investment is small, and the product yield is high; no organic solvent is used, the operation is safe, and the environmental pollution is low; the obtained peanut oil is of high quality and does not require refining; the obtained peanut protein powder has high purity (protein content>80%) and good functional properties, and can be widely used as an ingredient in food processing. The present invention is applied to peanut processing, which can increase the supply rate of edible oil and vegetable protein and significantly improve the added value of peanut products.

[0023] Background technology CN1419837A, CN1555714A, CN101401658A and CN103113977A all use different types of proteases to obtain free oil when extracting peanut oil, and obtain peanut peptides with small molecular weight instead of peanut protein. Compared with peanut peptides, peanut protein has better emulsification and gelation, so it is suitable for adding to various foods such as meat products and flour products. In order to obtain unhydrolyzed peanut protein, the present invention abandons the use of protease demulsification, but uses the stronger interfacial activity of small molecule surfactant Tween 20 to compete with protein for the interface, so that the emulsion is unstable. At the same time, under the high pH extraction environment, the mutual repulsion of protein molecules is strengthened, and it is easier to desorb from the emulsion interface. Combining these two factors obtains an ideal demulsification effect. In addition, in order to overcome the disadvantage that the yield of the product using only small molecule surfactants is not high enough, the present invention introduces reduced glutathione in the oil water agent processing technology for the first time, and utilizes the characteristics that glutathione can reduce the disulfide bonds of peanut protein to deaggregate peanut protein, thereby improving its yield. It was also found that the functional properties of the extracted peanut protein (especially emulsification) were significantly improved, and the antioxidant activity of glutathione made the peanut protein powder easier to store. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 To compare the emulsifying properties of plant proteins from different sources. DETAILED DESCRIPTION

[0025] Example 1

[0026] After the peanut kernels are screened and impurities are removed, the peanut kernels are coarsely crushed using a crusher, and then the peanuts are further ground into a slurry using a sand disc mill. The peanut slurry is dispersed in a 1wt% Tween 20+0.05wt% glutathione composite solution of 4 times the weight, and the system pH is adjusted to 10.5, the temperature is 50°C, and the extraction time is 30min. After the extraction is completed, a three-phase horizontal screw centrifuge is used to separate the system to obtain free oil, aqueous phase and solid phase. The pH of the aqueous phase is adjusted to 4.5, and after slowly stirring for 30 minutes, a two-phase horizontal screw centrifuge is used to separate the supernatant and precipitate. After the precipitate is diluted with a small amount of water, the pH is adjusted to 7.0, and then spray-dried (inlet air temperature 120°C, outlet air temperature 75°C) to obtain peanut protein powder with improved functional properties (see figure).

[0027] The free oil yield is 81.6%, the peanut protein yield is 86.5%, and the purity of peanut protein powder is 82.4%.

[0028] Example 2

[0029] After the peanut kernels are screened and impurities are removed, the peanut kernels are coarsely crushed using a crusher, and then the peanuts are further ground into a slurry using a sand disc mill. The peanut slurry is dispersed in a 1.2wt% Tween 20+0.08wt% glutathione composite solution of 5 times the weight, and the system pH is adjusted to 11.0, the temperature is 50°C, and the extraction time is 40min. After the extraction is completed, a three-phase horizontal screw centrifuge is used to separate the system to obtain free oil, aqueous phase and solid phase. The pH of the aqueous phase is adjusted to 4.5, and after slowly stirring for 30 minutes, a two-phase horizontal screw centrifuge is used to separate the supernatant and precipitate. After the precipitate is diluted with a small amount of water, the pH is adjusted to 7.0, and then spray dried (inlet air temperature 130°C, outlet air temperature 70°C) to obtain peanut protein powder.

[0030] The free oil yield is 82.5%, the peanut protein yield is 89.2%, and the purity of peanut protein powder is 81.4%.

Claims

1. A method for extracting peanut oil and protein using a composite solution of Tween 20 and glutathione, characterized in that The peanut kernels are ground into a slurry by a dry method, and then dispersed in a composite solution of Tween 20 (1-2wt%) + glutathione (0.05-0.1wt%) of 4-6 times the weight, and the pH of the system is adjusted to 10.0-11.0 by using NaOH, the temperature is 50-60°C, and the extraction time is 30-50min; after the extraction, a three-phase horizontal screw centrifuge is used to separate to obtain free oil, water phase and solid phase; the pH of the water phase is adjusted to 4.0-4.5 by using HCl, and the mixture is slowly stirred for 30 minutes and then centrifuged to obtain a supernatant and a protein precipitate; the protein precipitate is diluted with an appropriate amount of water and adjusted to pH 7.0, and then spray-dried, with an inlet air temperature of 120-130°C and an outlet air temperature of 70-75°C, to obtain peanut protein powder.

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