Dietary fiber is the edible part of plants that cannot be digested and absorbed by the human small intestine, and has health implications for the human body. The total amount of carbohydrates and polymers such as lignin with a polymerization degree of ≥ 3 in plant-based foods includes cellulose, hemicellulose, pectin, inulin, etc. According to solubility, dietary fiber is divided into soluble dietary fiber (IDF) and insoluble dietary fiber (SDF). Among them, insoluble dietary fiber is the most abundant in food, mainly including cellulose, hemicellulose, lignin, keratin, etc. Grains such as bran, potatoes, beans, vegetables, fruits, etc. are good sources of insoluble dietary fiber; Soluble dietary fiber is rich in oats, barley, fruits, and some legumes. The dietary fiber content in food is related to plant maturity and food processing level.
The unique role of dietary fiber in maintaining human health and preventing diseases has been increasingly confirmed by research, and it has become one of the indispensable and important substances in human diet. Since the 1980s, some Western countries have gradually used dietary fiber as a functional food ingredient in the food industry. Nowadays, there are more and more foods and health foods marked as rich in dietary fiber on the market. Therefore, the determination of dietary fiber is of great significance for food production, food development, and the evaluation of food nutritional value.
The main methods for measuring dietary fiber include non enzymatic gravimetric method, enzymatic gravimetric method, and enzymatic chemical method. The following is an introduction to the enzymatic gravimetric method for determining total, soluble, and insoluble dietary fiber in food (according to GB/T5009.88-2008).
Take a dry sample and digest it with amylase, protease, and glucosidase to remove protein and starch. After enzymatic digestion, the sample solution is precipitated and filtered with ethanol, and the residue is washed with ethanol and acetone. After drying, weigh the material to obtain the total dietary fiber (TDF) residue; Take another sample and filter it directly after enzymatic hydrolysis by the three enzymes mentioned above. Wash the residue with hot water, dry it, and weigh it to obtain insoluble dietary fiber residue; The filtrate was precipitated, filtered, and dried with 4 times the volume of 95% ethanol, and then weighed to obtain soluble dietary fiber residue. After drying and weighing the residue obtained above, determine the protein and ash content separately. The total, insoluble, and soluble dietary fiber content in the sample can be calculated by subtracting protein, ash, and blank from the residues of total dietary fiber (TDF), insoluble dietary fiber (IDF), and soluble dietary fiber (SDF).
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