Effects of magnetic field-assisted freezing on the quality of frozen noodles

Abstract: Frozen food has been much more popular in China in recent years. It is also a high requirement for the eating quality with the popularity of frozen food. The size of the internal ice crystal has been the most important factor in the quality. Common freezing includes flat plate freezing, spiral tunnel freezing, and liquid nitrogen spraying. Different freezing can often be chosen, according to the characteristics of the product. The process can convert the free water into ice in food, thus reducing the water activity in the food matrix. The immobilization of free water can inhibit the growth of microorganisms, and then slow down the enzymatic and chemical degradation reactions for less food spoilage. The speed and size of the ice crystals can be critical to the quality of the frozen food. It is preferred that the small-sized ice crystals are normally distributed within the cells in some foods with a cellular structure (such as fruits, vegetables, and meat). As such, the high quality of foods can also be maintained for the least damage to the cellular structure. But, the large ice crystals can result in an icy and sandy taste, which is unacceptable to the consumers. Therefore, it is a common demand from the industry and consumers to reduce the size of ice crystals for the better quality of products. A magnetic field has been an emerging physical way to fully characterize by the strong penetration in the food raw materials. There are some variations in the motion and water distribution state of water molecules in food, thereby accelerating the freezing rate. Therefore, the frozen product quality can be much closer to the fresh state. This study aims to explore the effect of magnetic field-assisted freezing on the quality of frozen cooked noodles. Different magnetic field intensities were selected to assist the frozen noodles: 3, 6, 9, 12, 15, and 18 Gs. The control group (CK) was set as the blank group without the addition of a magnetic field. The results showed that the freezing rate of frozen cooked noodles was significantly (P<0.05) accelerated by 4 min, while the whiteness, hardness, chewiness, shear force, and the content of bound water in the water distribution state significantly (P<0.05) increased by 2.37%, 7.40%, 12.41%, 19.20%, and 10.95%, respectively, whereas, the cooking loss, the content of freezer water, and the aging degree of starch molecules significantly (P<0.05) decreased by 17.88%, 9.44%, and 0.22%, respectively, compared with the CK under the magnetic field intensity of 12 Gs. There were much more uniform and fine ice crystals in the micro-structure in this case. The freezing rate of the noodles was accelerated under the action of the magnetic field. The growth of ice crystals was then inhibited for less mechanical damage to the inside of the frozen cooked noodles. There were also some changes in the movement state of the water molecules in the frozen cooked noodles. The disorder has developed into order, which reduced the energy consumed by the movement of water molecules. The water distribution state also changed to make the internal structure of the frozen cooked noodles more stable with the increase in the bound water. The best freezing performance was also achieved in the magnetic field strength of 12 Gs. The magnetic field can be expected to improve the quality of frozen cooked noodles.