CN1285376A - Process for preparation of water-proof and heat-resistant plastic soybean protein film - Google Patents

Abstract

The invention discloses a method for preparing a soybean protein film. It is produced by grading commercially available soybean dregs protein extracts, mixing them with glycerin and then hot pressing them. This thermoplastic film is non-toxic, edible, transparent, resistant to boiling water, cold and vacuum extraction, and its strength and elongation are up to 5.5MPa and 140%. Moreover, the production process is simple, the cost is low, and there is no pollution in the production process. It can be used as food packaging and biodegradable materials, and has application prospects in the fields of medicine, daily use, chemical industry and environmental protection.

Description

Preparation method of water-resistant thermoplastic soybean protein film

The invention relates to a preparation method of a water-resistant thermoplastic soybean protein film, which is a functional material prepared from soybean protein in soybean dregs and belongs to the field of macromolecules.

Due to the increasing consumption of non-renewable resources and the severe environmental pollution caused by the non-degradability of synthetic materials, renewable and environmentally friendly materials are attracting more and more attention. Emerging "industrial protein plastics" fall into this category, which are non-toxic and harmless to the environment and are expected to replace some petrochemicals. Soybean protein isolate is isolated from the by-products of soybean dregs after oil refining, accounting for about 50% (w/w) of soybean dregs, and is a natural polymer composed of various amino acids (Whitaker, J.R.Food proteins.1977, p498 .). Soybean dregs are generally used as animal feed, while soybean protein isolate can be used in food and adhesive industries (J.Japanese Soc.Food Sci.and Tech.1995, 42(9), 672; J.Amer.Oil Chem.Soc. 2000, 77, 101.). The soybean protein film prepared by cast method has high cost, high energy consumption, high brittleness, poor cold resistance, and is not thermoplastic, so its practicability is limited (J.Amer.Oil Chem.Soc.1994, 71(11), 1281) . Making thermoplastic protein films or soybean protein sheets by hot pressing has not been reported in China, and it has only been reported in recent years abroad (Ind.Eng.Chem.Res.1994, 33 (7), 1821; J.Polym.Eng. 1999, 19(6), 383). In these reports, the water resistance, especially the hot water resistance, of the thermoplastic soybean protein film is not high enough.

The purpose of the invention is to provide a new method for preparing a water-resistant thermoplastic soybean protein film material. The method makes full use of soybean protein, which is a cheap renewable resource, and is prepared in a simple and rapid method. The thermoplastic material is non-toxic, edible, resistant to boiling water, low cost, cold-resistant, resistant to vacuum extraction, and transparent. This kind of membrane material is degradable, has no pollution in the process of raw material extraction and production, has low energy consumption, and is beneficial to environmental protection. It is especially important for solving the forming problems encountered in the preparation process of natural polymer materials.

To achieve the above object, the technical scheme adopted in the present invention is as follows:

A method for preparing a water-resistant thermoplastic soybean protein film: add 0.4-0.7 times of glycerin to soybean protein powder, mix together for 30 minutes, heat press at 100-180°C, 5-20 Mpa, and cool to 60-20 minutes after 20 minutes. At 80°C, a golden-yellow transparent water-resistant thermoplastic soybean protein film is obtained.

According to the technical solution of the present invention, the soybean protein powder is prepared as follows: dissolve the commercially available soybean protein in alkaline water, centrifuge to remove impurities, adjust the pH to 5.70-6.5 with acid, and centrifuge after the protein powder is pre-precipitated. , take out the precipitate, add water, adjust the pH to 4.5, make the protein fully precipitate, centrifuge, wash and vacuum dry.

The commercially available soybean protein used in the present invention is purchased from Hubei Yunmeng County Longyun Protein Food Co., Ltd., and its standard is 卾Q/YZW×01-96. Glycerin is commercially available without any treatment.

The water-resistant thermoplastic soybean protein film of the invention can be used as packaging materials in the fields of chemical industry, food and environment, and can also be used as medical materials, such as the immobilization of drug enzymes, drug delivery and release.

Compared with the prior art, the beneficial effects obtained by adopting the technical solution of the present invention are as follows:

1. The hot pressing process is adopted, the process is simple, the cost is low, and the energy consumption is low. The resulting film of the present invention is thermoplastic,

It can be hot-pressed repeatedly, because the plasticizer used is glycerin with high boiling point and no low-boiling point compounds exist.

2. For the first time, a water-resistant natural polymer film was obtained. Tests have shown that it is resistant to both cold and boiling water.

Moreover, the water resistance of the soybean protein classified by the method can be greatly improved.

3. The film obtained by the present invention has high cold resistance, and tests show that its glass transition temperature Tg is around -70°C

right. However, the Tg of general starch and cellulose films is only around room temperature, and their cold resistance is poor.

4. The film obtained by the present invention is resistant to vacuum extraction and has high environmental stability. Tests show that: at 2mmHg

After extraction under vacuum for 7 hours, the film still maintains good elasticity.

The technical scheme of the present invention is further described below in conjunction with specific embodiment:

The preparation of embodiment 1 soybean protein powder:

Disperse 400g of commercially available soybean protein isolate in 6 liters of deionized water, add dropwise 2M NaOH until the pH=13, stir for 30 minutes, and then centrifuge at 8000 rpm for 10 minutes. Take the supernatant and adjust the pH to 5.70 with 2M HCL. At this time, a white flocculent viscous protein precipitate is produced, and it is centrifuged at 8000 rpm for 10 minutes. Take the precipitate and add 2 liters of water to adjust the pH to 4.5 to re-precipitate. After centrifugation at 8000 rpm for 10 minutes, the precipitate was taken, washed three times with water and acetone, and dried in vacuum to obtain a brown-white product. The product is crushed at high speed, passed through a 140-mesh sieve, dried and stored.

Example 2

Take 3g of soybean protein powder in the above-mentioned Example 1, add 1.5g of glycerin, grind it with a mortar for 30 minutes, mix it well and spread it between two copper-nickel alloy glazing plates, the size of the glazing plate is 18.5cm×10.5cm× 1mm. Then hot pressing is carried out, the temperature is controlled at 150° C., and the pressure is 15 MPa. Hot press for 20 seconds, blow with wind for 20 minutes and cool to 80°C, take a mold to get a yellow transparent film. The performance of the membrane is shown in Table 1.

Example 3

Get 3g of the soybean protein powder in the above-mentioned Example 1, add 2g of glycerin, grind it with a mortar for 30 minutes, mix well and spread it between two above-mentioned glazing boards. After hot pressing, the temperature is controlled at 180°C, the pressure is 10Mpa, and hot pressing is performed for 20 seconds. Cool to 80°C by blowing with wind for 20 minutes, and take it out to obtain a yellow transparent film.

Table 1. The effect of fractionation on the properties of soybean protein films

source   Dry mechanical properties Tensile strength Elongation (MPa) (%) Water resistance ^a Tensile strength Elongation (MPa) (%) Boiling water resistance ^b Tensile strength Elongation (MPa) (%) Example 2 Fractionated protein control Commercially available protein 5.5 1403.0 60 2.4 1300.65 90 1.9 160 too soft too soft

Continuation of Table 1:

source Tensile strength after vacuuming for 7 hours Elongation (MPa) (%) Transmittance(%) Glass transition temperature (Tg) Example 2 Fractionated protein control Commercially available protein 14 427 100 7876 -75-70

^a Soak in water at 25°C for 15°C.

^b Soak in boiling water for 15 minutes.

Claims (2)

1. A method for preparing a water-resistant thermoplastic soybean protein film, which is formed by mixing protein powder extracted from soybean dregs with glycerin and hot pressing at 100-180°C and 10-15Mpa, characterized in that: soybean protein powder and glycerin The weight ratio is 1:0.4-1:0.7. 2. The method according to claim 1, characterized in that the soybean protein powder is prepared as follows: commercially available soybean protein is dissolved in alkaline water, centrifuged to remove impurities, and the pH is adjusted to 5.70-6.5 with acid, and the After the pre-precipitation of the protein, centrifuge, take the precipitate and add water, adjust the pH=4.5 to make the protein fully precipitate, centrifuge, wash and dry in vacuum.