Effects And Mechanisms Of Processing Technology On The Quality Of Frozen Cooked Noodle

Noodle, a traditional staple food in many Asian countries, has been very appreciated by consumers. The request for healthy, nutritious, good quality and ready-to-eat foods has pushed the noodle industry to develop a new noodle product, frozen cooked noodle. However, besides the basic process of fresh noodle, during the production of frozen cooked noodle, precooking and freezing have been employed. Generally, the final quality of the product largely depends on the physicochemical transformations of wheat constituents as influenced by the processing conditions and the processing conditions themselves. Therefore, it is essential to investigate the effects and mechanisms of precooking and freezing on the quality of frozen cooked noodle, which is a prerequisite for improved quality of frozen cooked noodle.Firstly, the effect of steaming on the quality of frozen cooked noodle(control, white salted and yellow alkaline noodle) was investigated. The results indicated that for control and white salted noodle, the precooking loss decreased significantly(P<0.05); the reheating loss was not less than or equal to that of non-steam-treated noodle until the steaming time was 3 min, and then it slightly decreased; however, yellow alkaline noodle exhibited an increase in the precooking loss except those of steaming 6 and 8 min, and an increase in reheating loss except that of steaming 8 min. In addition, with the increase of steaming time from 1 to 3 min, water absorption obviously decreased, and the hardness and tensile force increased significantly(P<0.05); then with the increase of steaming time, they slightly increased.Secondly, the changes of microstructure, water absorption, the extractability of gluten proteins in SDS buffer(SDSEP) and starch gelatinization of steamed noodle were determined. Steamed noodle except yellow alkaline noodle had compact microstructure compared with fresh noodle. With the increase of steaming time, water absorption of all steamed noodle increased slowly. For control and white salted noodle, with the increase of steaming time from 1 to 3 min, SDSEP decreased dramatically, and then they decreased slowly; reduction in SDSEP of yellow alkaline noodle was found to be 62.2%, when noodle were steamed for 1 min, while no differences were observed from 2 to 8 min. Gelatinization enthalpy in control noodle disappeared after 3 min of steaming, while the enthalpy disappeared after 2 min for white salted and yellow alkaline noodle. The present study indicated that protein polymerization and starch gelatinization when subject to limiting water conditions during steaming accounted for improved noodle quality.Thirdly, the impact of cooling on the quality of frozen cooked noodle was evaluated, as well as water distribution, microstructure and physicochemical behavior of protein and starch. The results showed that with the increase of cooling temperature, the cooling rate of cooked noodle decreased, and as a result, reheating loss and water absorption increased; the hardness and tensile force decreased. The quality of frozen cooked noodle was the best when they were cooled by 5 ℃ water. In addition, with the increase of cooling temperature, the gradient in moisture content of reheated noodle decreasd, and the central of noodle showed a higher degree of starch swelling; after the frozen cooked noodles were freeze dried, the porosity of cross-sections showed the increase in moisture content in the central of noodle. However, the cooling temperature had no effect on extractability of protein and during cooling and freezing, amylopectin retrogradation enthalpy was not detectable.Finaly, the impact of freezing on the quality of frozen cooked noodle was evaluated, as well as water distribution, microstructure, formation and distribution of ice, and physicochemical behavior of protein and starch. The results showed that with the decrease of freezing temperature, the freezing rate increased, and as a result, the freezing time and zone of maximum ice crystal formation decreased; reheating loss and water absorption decreased; the hardness and tensile force increased, and the differences between frozen cooked noodle freezed by-40,-60 and-80 ℃ were rather small. MRI images showed that with the freezing condition at-18 ℃, the gradient in moisture content of reheated noodle decreased. SEM images showed that with the freezing condition at-18 ℃, the protein network was seriously damaged, and starch granules had lost their shapes, but when the freezing condition was at-40,-60 or-80 ℃, the microstructure in the centre part of reheated noodle was still continuous and dense. In addition, fast freezing produced a large number of very small ice crystals. However, the freezing had no effect on extractability of protein and during freezing, amylopectin retrogradation enthalpy was not detectable.