The methods for sealing of food packaging are such as heat sealing and seaming. For canned foods, sealing is ordinarily operated by a seaming approach. It can be achieved by a double steamer that is mainly consisting of a chuck, a lifter, and first and second operation seaming rolls. The cans, either of two-piece or of three-piece, sealed by this manner are referred to as sanitary cans. According to the degree of swelling, swelled cans can be categorized as the followings: hard swell, soft swell, springer, and flipper. In general, swelled cans are progressive in the order of flipper followed by springer, soft swell, and hard swell. The swelling of cans is ascribed either to incomplete exhausting in canning process, or to the formation of gases, such as H2 or CO2, through microbial action and chemical reaction during storage. The conditions for sterilization vary with nature and pH value of canned foods. Those that have a pH of 4.6 or below are defined as acid foods, and those that have a pH value above 4.6 are defined as non-acid foods. The temperature of boiling water is enough for acid canned food to complete sterilization. However, the temperature applied in the sterilization process for non-acid canned food should be over than 100℃. In this case, the retort, a heating equipment that can be operated at high temperature and high pressure, is commonly employed to meet the sterilization conditions. While all microorganisms and their spores are completely killed by the method of absolute sterilization, only pathogenic and toxin-forming microbes are sterilized by the method of commerical sterilization. Pasteurization is belong to the latter and only suitable for the sterilization of acid foods and those with high concentration of sugar or salt. In high temperature short time (HTST) process, the heating time is in the range of a few seconds to several minutes with appropriately high temperature applied. However, sterilization is completed within a few seconds at heating temperature ranging from 135 to 150℃ in ultra high temperature (UHT). As for low temperature long time (LTLT) process, a combination of relatively low heat temperature and prelonged time is employed. Drying is a method that dehydrates foods to form solid final products. Concentration means, however, foods partially dehydrated to become products that retain the liquid condition. Nevertheless, mucilages, the compounds secreted into the endosperm of plant seeds, may act to prevent them from excessive dehydration. The drying methods commonly utilized in the food processing can be classified into two groups. One, such as sun drying, is in a natural manner while the other is in an artificial manner, including hot-air drying, fluidized-bed drying, pneumatic drying, foam-mat drying, rotary drying, drum drying, spray drying, puff drying, microwave drying, and vacuum freeze-drying. Water is removed from foods through its diffusion and evaporation for all drying methods mentioned above, except for vacuum freeze-drying.
