Home > News > Content

What Parts Should Be Kept Or Removed During Wheat Flour Milling

Nov 14, 2020

Wheat flour milling is the process of repeatedly grinding wheat from raw grains to flour by squeezing and crushing by a flour mill. From the perspective of the crushing process, the wheat skin, aleurone layer, endosperm and other parts will be subjected to varying degrees of force. In terms of the quality of wheat flour milling or the grade of flour, the ingredients retained or removed during the wheat milling process are different. Analyze the structure of wheat grains from the perspectives of nutrition and human absorption, the edible quality of pasta foods, and the storage of finished flour to determine which parts of wheat flour should be removed or retained.

   1. The epidermis, mesocarp, endocarp, seed coat, and nape of the cortex: These cortical tissues mainly contain cellulose, hemicellulose, and a small amount of phytate, which cannot be digested and absorbed by the human body. The skin layer also has a negative impact on the eating quality of pasta foods and should be removed during the wheat flour milling process.

   2. Aleurone layer: The aleurone layer contains protein, B vitamins, minerals and a small amount of cellulose. From a nutritional point of view, aleurone is a very nutritious part of wheat grains, especially B vitamins are necessary for the human body, and lack of it will cause beriberi. However, from the perspective of the eating quality of pasta foods, the protein in the aleurone layer does not participate in the composition of gluten protein, and at the same time adversely affects the taste and appearance of pasta foods such as bread, noodles, biscuits, and dumplings. Therefore, in principle, the flour should be removed during the grinding process. When grinding low-precision flour, part of the aleurone layer can be milled into the flour to increase the nutrition of the flour and increase the flour extraction rate.

   3. Embryo: Wheat germ is extremely nutritious. Compared with endosperm flour, it provides 3 times higher biological value protein, 7 times fat, 15 times sugar and 6 times mineral content. Wheat germ is also known as a plant resource rich in vitamin E and rich in thiamine, riboflavin and niacin. The fat contained in wheat germ is mainly unsaturated fatty acids essential to the human body, of which 1/3 is linoleic acid. In addition, it also contains a small amount of plant sterols and phospholipids. From a nutritional point of view, wheat germ should be retained. However, the content of lipase and protease in wheat germ is high, and the activity is strong. After one week, the acid value of fresh wheat germ will rise so that it cannot be eaten. If the embryo is ground into flour, the shelf life of the flour will be greatly shortened. At the same time, the embryo is mixed into the flour, which will have a certain negative impact on the eating quality of the pasta food, so the embryo should be taken out in the flour milling process.

   4. Endosperm: The endosperm mainly contains gluten protein, starch and a small amount of minerals and oil. From the perspective of nutrition, the above substances should be retained. From the perspective of edible quality, gluten protein and starch are the key substances that make up a dough with a special gluten network structure. It is with such a special structure of dough that wheat flour can produce a wide variety, beautiful shape, and delicious, and meet the different peoples of the world. Various pasta foods of habit. Therefore, the endosperm part is extracted from wheat flour.

   The analysis of wheat tissue structure, nutrient composition, edible quality and storage performance shows that the endosperm, wheat husk (including aleurone layer) and embryo should be separated in wheat flour milling. To completely separate the wheat husk and endosperm, theoretically a better physical method is to peel and make flour, peel off the cortex, extract the embryo, retain the endosperm, and grind the pure endosperm powder that is not contaminated by the cortex to a large extent. However, due to the special structure of wheat grains, it is impossible to completely peel and make flour. First of all, there is no obvious separation layer between the two tissue structures of the cortex and the endosperm. On the contrary, the two tissues are tightly integrated and obviously cannot be peeled off like the hulling method. If the gradual friction peeling method is used, since the structure of the wheat cortex is tight and tough, while the endosperm structure is relatively loose, the compression resistance of the two is obviously different. Therefore, the force used in the gradual friction peeling method should not be too large, otherwise it will crush the wheat grains. . At the same time, because the wheat grain has a ventral groove that contains 1/4 to 1/3 of the entire epidermal tissue, and the irregularity of its shape, it is impossible to peel off the cortex including the ventral groove without breaking the endosperm. of.