Study On Effects Of Drying Technics And Maillard Reaction Products On Preservation And Quality Of Semi-dry Noodles

Semi-dry noodle, as a new kind of instant noodle, is getting into popular increasingly owing to its merits of sweet flavor,convenience,good taste and so on. However, semi-dry noodle deteriorates easily at room temperature because of its high moisture content,so preservation is always the main concern of semi-dry noodle industry. The preservation means used by semi-dry industry at present have many drawbacks, such as large addition amount and bad impacts on noodle quality. In this paper, effects of different drying methods and chitosan-xylose Maillard Reaction Products (MRPs) on preservation of semi-dry noodle were studied, aiming at providing semi-dry noodle with long shelf-life and good quality by optimizing the drying process and adding MRPs.Disposed by different drying methods, the drying characteristics and germ-decreasing regulations of semi-dry noodle were studied. For hot-air drying, its drying efficiency was low and constant rate period was short. Microorganism counts decreased sharply during early stage of drying process but it was nearly unchangeable during later stage. Compared with hot-air drying, the drying efficiency of ultraviolet-microwave drying was high, and it microorganism counts still decreased fast during later stage of drying process. It showed that to hot air drying, with increase of drying temperature, microorganism counts decreased, but the textural and cooking quality of semi-dry noodle debased as well. 125℃was the suitable drying temperature. At this temperature, the microorganism counts decreased significantly, but the quality of semi-dry noodle didn't debase a lot. For noodle dried by ultraviolet-microwave, its microorganism counts were distinctly lower than that dried by hot air, but there was little difference between different microwave powers. When microwave power was 2000 W, the textural and cooking quality of the noodle debased a lot. When microwave power was 1000 W, the textural quality was close to that dried at 115~125℃by hot air. So 1000 W was the suitable drying power.The spoilage microorganisms in semi-dry noodle were isolated and identified by means of morphological test and biochemistry test. Results showed that growth of bacteria and mold was the main cause of the spoilage of semi-dry noodle. Bacilli was the dominant spoilage bacteria during the early stage of storage. With time passing, Staphylococci grew fast and became the preponderant bacteria. Mold grew slowly during storage.With minimum inhibition concentration(MIC) against the spoilage strains as index,chitosan with high molecular weight(4.0×105) was chosen to have maillard reaction with xylose. With extension of reaction time,antibacterial activity of Maillard Reaction Products (MRPs) increased. MRPs of 6 h possessed the highest antibacterial activity. Addition of MRPs could improve the textural and cooking quality of semi-dry noodle. Addition of 0.35% MRPs (6 h) to semi-dry noodle resulted in an extension of shelf life for 7 more days than noodle without any preservative (at room temperature). The discoloration caused by the addition of MRPs was limited, and MRPs could inhibit browning of the noodle effectively. MRPs were endowed with good copper-chelating activity and inhibitory effect on PPO activity. It was probable that MRPs could inhibit PPO by chelating the Cu2+in the active site, leading to the postponement of phenol oxidation.