several flow patterns that can be used.Gaskets are used to define the boundaries of the channels and to prevent leakage.The heating medium can be vacuum steam or hot water. 四、论述题 1.How can raw milk be homogenized?(p.52) Milk is an oil-in milk Ho ical tr of the fat globules in brought about by passing milk under high pr ere thro orifice which results in a decrease in the average diameter and an increase e in number and surface area,of the fat globules.The net result,from a practical view,is a much reduced tendency for creaming of fat globules.Three factors contribute to this enhanced stability of homogenized milk:a decrease in the mean diameter of the fat globules(a factor in Stokes Law),a decrease in the size distribution of the fat globules(causing the speed of rise to be similar for the majority of globules such that they don't tend to cluster during creaming),and an increase in density of the globules(bringing them closer to the continuous phase)oweing to the adsorption of a protein membrane.In addition,he ks down the cryo-globulin complex,which tends to ster glob using them to rise 五、英翻汉(20分 1.Milk Powder Milk used in the product of milk powders is first a heat on Besides destro ng all the atho ost of the s ead3g microorganisms,it also inactivates the enz me lip e which could cause lipolysis during storage. The milk is then evaporated prior to drying for the following reasons: less occluded air and longer shelf life for the powder viscosity increase leads to larger powder particles less energy required to remove part of water by evaporation:more economical Homogeniation maybe applied to crease the free fat content.Spray drying is the most use for producing n ilk powders After drying,the pov aged ion from mo r long periods (up to about 6 6 months)of time a t temperature Skim milk(SMP)processing is similar to that described above except for the following point 2 smilkfat(0.05-0.10%) prior to evaporat can be more or less severeseveral flow patterns that can be used. Gaskets are used to define the boundaries of the channels and to prevent leakage. The heating medium can be vacuum steam or hot water. 四、论述题 1. How can raw milk be homogenized ?(p.52) Milk is an oil-in-water emulsion, with the fat globules dispersed in a continuous skimmilk phase. If raw milk were left to stand, however, the fat would rise and form a cream layer. Homogenization is a mechanical treatment of the fat globules in milk brought about by passing milk under high pressure through a tiny orifice, which results in a decrease in the average diameter and an increase in number and surface area, of the fat globules. The net result, from a practical view, is a much reduced tendency for creaming of fat globules. Three factors contribute to this enhanced stability of homogenized milk: a decrease in the mean diameter of the fat globules (a factor in Stokes Law), a decrease in the size distribution of the fat globules (causing the speed of rise to be similar for the majority of globules such that they don't tend to cluster during creaming), and an increase in density of the globules (bringing them closer to the continuous phase) oweing to the adsorption of a protein membrane. In addition, heat pasteurization breaks down the cryo-globulin complex, which tends to cluster fat globules causing them to rise. 五、英翻汉(20 分) 1. Milk Powder Milk used in the production of milk powders is first clarified, standardized and then given a heat treatment. This heat treatment is usually more severe than that required for pasteurization. Besides destroying all the pathogenic and most of the spoilage microorganisms, it also inactivates the enzyme lipase which could cause lipolysis during storage. The milk is then evaporated prior to drying for the following reasons: • less occluded air and longer shelf life for the powder • viscosity increase leads to larger powder particles • less energy required to remove part of water by evaporation; more economical Homogenization may be applied to decrease the free fat content. Spray drying is the most used method for producing milk powders. After drying, the powder must be packaged in containers able to provide protection from moisture, air, light, etc. Whole milk powder can then be stored for long periods (up to about 6 months) of time at ambient temperatures. Skim milk powder (SMP) processing is similar to that described above except for the following points: 1. contains less milkfat (0.05-0.10%) 2. heat treatment prior to evaporation can be more or less severe