Production Methods and Multifunctional Applications of Soybean Dietary Fiber
1. Physiological Functions of Multifunctional Soybean Dietary Fiber
Soybean dietary fiber mainly refers to the general term for those macromolecular carbohydrates that cannot be digested by human digestive enzymes, mainly including cellulose, pectin, xylan and mannose, etc. Although dietary fiber cannot provide the human body with any nutrients, it has important physiological functions for the human body. Dietary fiber has significant effects in lowering blood pressure and plasma cholesterol, and regulating gastrointestinal function, blood sugar and insulin levels. Multifunctional Soybean Fiber (MSF) is mainly composed of dietary fiber and protein, with contents of 67.98% (dry basis) and 19.75% respectively, making it a good protein-fiber additive. Studies have shown that adding a small amount of MSF has a good strengthening effect on medium-gluten or low-gluten flour; within a certain addition range, it can not only increase the dietary fiber and protein content of products, but is also very beneficial for improving the quality of products such as bread, noodles and biscuits. MSF may be the best-functioning of all dietary fibers, far beyond what other synthetic fibers (such as litesse, polydextrose) can match. Multifunctional soybean dietary fiber is a high-quality dietary fiber obtained from fresh okara as raw material through special heat treatment, and it has good effects in regulating blood sugar, lowering blood lipids and promoting defecation.
2. Production Process Flow of Multifunctional Soybean Dietary Fiber
Wet okara → acid adjustment (adjust pH to 3-5 with 1 mol/L hydrogen chloride) → hot water soaking (80°C-100°C, 2 h) → neutralization (adjust pH to neutral with 1 mol/L sodium hydroxide) → dehydration and drying (oven drying at 65°C-70°C or air-flow drying to a moisture content of 8%) → pulverization → sieving (80 mesh) → okara powder → extrusion (feed moisture 16.8%, 150°C, screw speed 150 r/min) → cooling → pulverization → functional activation and ultra-fine pulverization → MSF.
3. Key Operating Points for Preparing Multifunctional Soybean Dietary Fiber
(1) Moist heat treatment deodorization procedure This procedure includes acid adjustment, heat treatment and neutralization of okara. ① Acid adjustment. Soak the okara in water, and adjust the pH to 3-5 with 1 mol/L hydrochloric acid solution. This is because heating under acidic conditions helps remove the off-flavor of okara, and the addition of acid can also leach out some pigment substances, improving the color of the product. ② Heat treatment. Heat the soaked okara to 80°C-100°C and carry out moist heat treatment for about 2 h, so as to inactivate lipoxygenase, reduce the beany flavor, and deactivate anti-nutritional factors. ③ Neutralization. Adjust the pH of the mixed liquid to neutral with 1 mol/L NaOH solution.
(2) Extrusion cooking Extrusion cooking is an important procedure for producing high-quality multifunctional soybean fiber powder. Extrusion cooking treatment has the following effects: ① It can increase the content of soluble dietary fiber. When okara powder is extrusion cooked, under various strong forces, part of the hemicellulose (such as arabinoxylan) and insoluble pectin substances undergo melting or breakage of some connecting bonds, transforming into water-soluble polymers, increasing the soluble fiber content to 10%-16%, which not only meets the requirement for balanced dietary fiber, but more importantly, water-insoluble dietary fiber promotes intestinal peristalsis, while water-soluble dietary fiber plays a greater role in the physiological metabolism of the human body. Therefore, an increase in the soluble dietary fiber content is beneficial for enhancing the functional properties of the product. ② It can improve the physicochemical properties of soybean fiber. Extrusion cooking treatment changes the degree of polymerization, relative molecular mass, monosaccharide composition and their relative contents in the total fiber of various polymer components in soybean fiber. The increase in soluble dietary fiber content can improve some physicochemical properties of soybean fiber powder (such as water-holding capacity, ion exchange capacity and gel properties, etc.). Since the water-soluble polymer components are all gelling polysaccharides, they can form a three-dimensional network structure with a certain viscoelasticity, playing a role similar to the gluten network structure, thereby improving the rheological properties of gluten and becoming a flour quality improver, enhancing its value in food use. ③ It can reduce the negative effect of phytic acid on the absorption of trace mineral elements. Extrusion can reduce the chelating effect of phytic acid with metal ions, improve the effect of okara powder on the body's absorption of trace elements, and enhance the exchange capacity between dietary fiber and cations, improving the functionality of the product. ④ It can improve product quality. During the extrusion cooking process, through the effect of heat, anti-nutritional factors in okara can be further eliminated, lipase can be killed, and the protein in okara can be moderately denatured, thereby improving the flavor and storage performance of the product and facilitating the body's digestion and absorption.
(3) Ultra-fine pulverization and functional activation Functional activation treatment is a key step in preparing highly active multifunctional dietary fiber, including ultra-fine pulverization, which can achieve optimization and recombination of the internal components of the fiber; the encapsulation of certain groups of the fiber can prevent these groups from combining with mineral elements and affecting the body's mineral metabolism balance. Only dietary fiber that has undergone activation treatment is a truly physiologically active substance and can be used in functional foods. Dietary fiber that has not undergone activation treatment can only be regarded as a low-energy filler. ① Ultra-fine pulverization. The smaller the particle size of the final product, the larger the specific surface area, and the water-holding capacity and swelling capacity of the dietary fiber also increase correspondingly. At the same time, it can also reduce the rough mouthfeel. Therefore, when the extrusion-cooked okara powder is dried to a moisture content of 6%-8%, ultra-fine pulverization should be carried out to expand the specific surface area of the fiber. ② Functional activation. Since the surface of dietary fiber carries reactive hydroxyl groups, it will combine with certain mineral elements, thereby possibly affecting mineral metabolism in the body. If appropriate wall materials are used for encapsulation treatment, this problem can be solved, that is, functional activation is completed. An aqueous solution prepared from hydrophilic colloids (such as carrageenan) and glycerol can be used as the wall material, and fiber microcapsule products can be made by spray drying, giving a smooth and pleasant feeling when consumed and improving edibility. In addition, multifunctional soybean fiber can also be fortified with mineral elements.
4. Application of Soybean Dietary Fiber in Foods
Soybean dietary fiber is very widely used in foods. As a food additive, it can be used in meat products, bread, biscuits, pastries, noodles and seasoning sauces, and can also be used in frozen foods and fillings, various beverages and ice cream, as well as health products. Adding soybean fiber not only helps improve the texture of products and enhances the characteristic flavor of products, but also gives products good nutritional functional properties. The following introduces a production process for high-dietary-fiber biscuits for the elderly.
(1) Ingredients Biscuit special flour 46.6%, multifunctional soybean fiber 11.7%, shortening 7.3%, high-fructose syrup 3.5%, sucrose 7.3%, brown sugar 2%, honey 3.2%, sodium bicarbonate 0.9%, ammonium bicarbonate 0.8%, salt 0.9%, water 11.6%.
(2) Method First pour the shortening and honey into a horizontal mixer and beat evenly, then add sucrose, brown sugar, high-fructose syrup, salt and water, and add the pre-dissolved ammonium bicarbonate aqueous solution and sodium bicarbonate aqueous solution, then add the flour and soybean fiber and stir for 10 min until the dough is mature. The kneaded dough temperature is 49-52°C. After shaping in molds, place in a band oven and bake for 6 min.
Through experiments, if the addition amount of multifunctional soybean fiber is below 12%, replacing biscuit special flour has no effect on biscuit quality; increasing the addition amount requires combining with other food additives.
With the improvement of people's living standards and the enhancement of health awareness, the demand for health functional foods is becoming stronger and stronger. Because multifunctional soybean dietary fiber is inexpensive and of good quality, and has multiple physiological functions and quality-improving effects, it has received widespread attention and welcome from researchers and consumers. The market potential for developing soybean dietary fiber foods is huge, with great prospects.