石河子大学：《畜产品加工工艺学》课程教学资源（试卷习题）畜产-双语-思考题（答案）.pdf_大学文库

may vary from one region to another, the basic ingredients and manufacturing are essentially consistent(p.75): 9. LA: Lactobacillus acidophilus(p.77) 10. LAB: lactic acid bacteria (p.73) 三、简述题 1. What is the Stoke's Law ???(p.39)? Centrifugation is based on Stoke's Law. The particle sedimentation velocity increases with: • increasing diameter • increasing difference in density between the two phases • decreasing viscosity of the continuous phase If raw milk were allowed to stand, the fat globules would begin to rise to the surface in a phenomena called creaming. Raw milk in a rotating container also has centrifugal forces acting on it. This allows rapid separation of milk fat from the skim milk portion and removal of solid impurities from the milk. 2.How to Separate the cream from milk?(p.39) Centrifuges can be used to separate the cream from the skim milk. The centrifuge consists of up to 120 discs stacked together at a 45 to 60 degree angle and separated by a 0.4 to 2.0 mm gap or separation channel. Milk is introduced at the outer edge of the disc stack. The stack of discs has vertically aligned distribution holes into which the milk is introduced. Under the influence of centrifugal force the fat globules (cream), which are less dense than the skim milk, move inwards through the separation channels toward the axis of rotation. The skim milk will move outwards and leaves through a separate outlet. 3. What is the Pasteurization of milk?(p.40) The process of pasteurization was named after Louis Pasteur who discovered that spoilage organisms could be inactivated in wine by applying heat at temperatures below its boiling point. The process was later applied to milk and remains the most important operation in the processing of milk. Definition: The heating of every particle of milk or milk product to a specific temperature for a specified period of time without allowing recontamination of that milk or milk product during the heat treatment process. 4. How to standardize the milk?(p.40) The streams of skim and cream after separation must be recombined to a specified fat content. This can be done by adjusting the throttling valve of the cream outlet; if the valve is completely closed, all milk will be discharged through the skim milk outlet. As the valve is progressively opened, larger amounts of cream with diminishing fat

contents are discharged from the cream outlet. With direct standardization the cream and skim are automatically remixed at the separator to provide the desired fat content. Some basic standardization problems including mass balance and Pearson square approach can be viewed here. 5. What is the Pasteurization of milk?(p.40) The process of pasteurization was named after Louis Pasteur who discovered that spoilage organisms could be inactivated in wine by applying heat at temperatures below its boiling point. The process was later applied to milk and remains the most important operation in the processing of milk. Definition: The heating of every particle of milk or milk product to a specific temperature for a specified period of time without allowing recontamination of that milk or milk product during the heat treatment process. 6. What is the Batch method of Pasteurization of milk?(p.42) The batch method uses a vat pasteurizer which consists of a jacketed vat surrounded by either circulating water, steam or heating coils of water or steam. In the vat the milk is heated and held throughout the holding period while being agitated. The milk may be cooled in the vat or removed hot after the holding time is completed for every particle. As a modification, the milk may be partially heated in tubular or plate heater before entering the vat. This method has very little use for milk but some use for milk by-products (e.g. creams, chocolate) and special batches. The vat is used extensivly in the ice cream industry for mix quality reasons other than microbial reasons. 7. What is the Continuous method of Pasteurization of milk?(p.42) Continuous process method has several advantages over the vat method, the most important being time and energy saving. For most continuous processing, a high temperature short time (HTST) pasteurizer is used. The heat treatment is accomplished using a plate heat exchanger. This piece of equipment consists of a stack of corrugated stainless steel plates clamped together in a frame. There are 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. 8. What is Beverage Milks?(p.66) The production of beverage milks combines the unit operations of clarification, separation (for the production of lower fat milks), pasteurization, and homogenization. The process is simple, as indicated in the flow chart. While the fat content of most raw milk is 4% or higher, the fat content in most beverage milks has been reduced to 3.4%. Lower fat alternatives, such as 2% fat, 1% fat, or skim milk (<0.1% fat) or also

available in most markets.These products are either produced by partially skimming the whole milk,or by completely skimming it and then adding an appropriate amount of cream back to achieve the desired final fat content. Vitamins may be added to both full fat and reduced fat milks.Vitamins A and D(the fat soluble ones)are often supplemented in the form of a water soluble emulsion to offset that quantity lost in the fat separation process. 9.What is Recombined Milk?(p.67) Beverage milks can also be prepared by recombining skim milk powder and butter with water.This is often done in countries where there is not enough milk production to meet the demand for beverage milk consumption.The concept is simple.Skim milk powder is dispersed in water and allowed to hydrate.Butter is then emulsified into his mixt丸re by either blending melted butter into the liquid mixture while hot,or by dispersing solid butter into the liquid through a high shear blender device.In some cases,a non-dairy fat source may also be used.The recombined milk product is then pasteurized, homo enized and pa ged as in regular mi produ e fina mpo mately and eithe 2% ole milk,approx T30 he n and g must be lumping of the powder.Its disper sal in water is the key to su 10.How to treatment of Milk for Cheesemaking?(p.72) oducts st first be clarified, ay then be subiected to a sub-pasteu ent of 63-65 C for 15 to 16 sec.This thermization trea atment results in a reduction of high initial bacteria counts before stor age it must he followed by oner pasteurization While HTST pasteurization (72C for 16 sec)is often used,an alternative heat treatment of 60 C for 16 sec may also be used.This less severe heat treatment is thought to result in a better final flavour cheese by preserving some of the natural flora.If used,the cheese must be stored for 60 days prior to sale,which is similar to the regulations for raw milk cheese. 11.Why is milkfat important to ice cream ?(p.85) Milkfat is important to ice cream for the following reasons ·: increases the e rich hness of flavou to to its r aids in melting rtie also e to its role in fat destabilization aids in lubricating the free ezer barrel during manufacturing (Non-fat mixes are extremely hard on the freezing equipment) The limitations of excessive use of butterfat in a mix include:

available in most markets. These products are either produced by partially skimming the whole milk, or by completely skimming it and then adding an appropriate amount of cream back to achieve the desired final fat content. Vitamins may be added to both full fat and reduced fat milks. Vitamins A and D (the fat soluble ones) are often supplemented in the form of a water soluble emulsion to offset that quantity lost in the fat separation process. 9. What is Recombined Milk?(p.67) Beverage milks can also be prepared by recombining skim milk powder and butter with water. This is often done in countries where there is not enough milk production to meet the demand for beverage milk consumption. The concept is simple. Skim milk powder is dispersed in water and allowed to hydrate. Butter is then emulsified into this mixture by either blending melted butter into the liquid mixture while hot, or by dispersing solid butter into the liquid through a high shear blender device. In some cases, a non-dairy fat source may also be used. The recombined milk product is then pasteurized, homogenized and packaged as in regular milk production. The final composition is similar to that of whole milk, approximately 9% milk solids-not-fat, and either 2% or 3.4% fat. The water source must be of excellent quality. The milk powder used for recombining must be of high quality and good flavour. Care must be taken to ensure adequate blending of the ingredients to prevent aggregation or lumping of the powder. Its dispersal in water is the key to success. 10. How to treatment of Milk for Cheesemaking?(p.72) Like most dairy products, cheesemilk must first be clarified, separated and standardized. The milk may then be subjected to a sub-pasteurization treatment of 63-65° C for 15 to 16 sec. This thermization treatment results in a reduction of high initial bacteria counts before storage. It must be followed by proper pasteurization. While HTST pasteurization (72° C for 16 sec) is often used, an alternative heat treatment of 60° C for 16 sec may also be used. This less severe heat treatment is thought to result in a better final flavour cheese by preserving some of the natural flora. If used, the cheese must be stored for 60 days prior to sale, which is similar to the regulations for raw milk cheese. 11. Why is milkfat important to ice cream ?(p.85) Milkfat is important to ice cream for the following reasons: • increases the richness of flavour in ice cream • produces a characteristic smooth texture by lubricating the palate • helps to give body to the ice cream, due to its role in fat destabilization • aids in good melting properties, also due to its role in fat destabilization • aids in lubricating the freezer barrel during manufacturing (Non-fat mixes are extremely hard on the freezing equipment) The limitations of excessive use of butterfat in a mix include:

pasteurized using a continuous plate heat exchanger for 30 min at 85C or 10 min at 95 C.These heat treatments,which are much more severe than fluid milk pasteurization,are necessary to acheive the following: produce a relatively sterile and condusive environment for the starter culture denature and coagulate whey proteins to enhance the viscosity and texture The mix is then ho oge mized using high pre ssures of 2000-2500 psi.Beside thoroughly r cers and ation als preven creaming and ng the ngoff during incub tion a consistency an d to ar optimu th t e yogurt sta added A ratio of 11 ST to lb inoculation is added to the iacketed fermentation tank a erature of 43c is maintained for 4-6 h under au escent (no agitation)conditions This temperature is a compromise between the optimums for the two micoorganisms (ST39 C:LB 45 C).The titratable acidity is carefully monitored until the TA is 0.85 to 0.90%.At this time the jacket is replaced with cool water and agitation begins, both of which stop the fermentation.The coagulated product is cooled to 5-22C. depending on the product.Fruit and flavour may be incorporated at this time,then packaged.The product is now cooled and stored at refrigeration temperatures(5 C) to slow down the physical.chemical and microbiological degradation. 3.How can raw milk be homogenized ?(p.52) Milk is an oil-in-water emuulsion,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 reduce ency for creaming of fat globules.Three factors contribute to this enhance stability of homogenized milk:a decre ase in the mean diameter of the globules (a facto aw), s (caus I rise to be for the g0 they dont ing the to the heat the cryo-gl comp hich ends to cluster fat globules causing them to rise 4.What's the Membrane Processing and how can it be used in dairy industry? Membrane processing is a technique that permits concentration and separation without the use of heat.Particles are separated on the basis of their molecular size and of pressure and specially designed semi-permeal e mem ranes. ere are some I e w developments in terms of commercial reality and is gaining readily in its applications

pasteurized using a continuous plate heat exchanger for 30 min at 85° C or 10 min at 95° C. These heat treatments, which are much more severe than fluid milk pasteurization, are necessary to acheive the following: • produce a relatively sterile and condusive environment for the starter culture • denature and coagulate whey proteins to enhance the viscosity and texture The mix is then homogenized using high pressures of 2000-2500 psi. Besides thoroughly mixing the stabilizers and other ingredients, homogenization also prevents creaming and wheying off during incubation and storage. Stability, consistency and body are enhanced by homogenization. Once the homogenized mix has cooled to an optimum growth temperature, the yogurt starter culture is added. A ratio of 1:1, ST to LB, inoculation is added to the jacketed fermentation tank. A temperature of 43° C is maintained for 4-6 h under quiescent (no agitation) conditions. This temperature is a compromise between the optimums for the two micoorganisms (ST 39° C; LB 45° C). The titratable acidity is carefully monitored until the TA is 0.85 to 0.90%. At this time the jacket is replaced with cool water and agitation begins, both of which stop the fermentation. The coagulated product is cooled to 5-22° C, depending on the product. Fruit and flavour may be incorporated at this time, then packaged. The product is now cooled and stored at refrigeration temperatures (5° C) to slow down the physical, chemical and microbiological degradation. 3. 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. 4. What’s the Membrane Processing and how can it be used in dairy industry? Membrane processing is a technique that permits concentration and separation without the use of heat. Particles are separated on the basis of their molecular size and shape with the use of pressure and specially designed semi-permeable membranes. There are some fairly new developments in terms of commercial reality and is gaining readily in its applications:

• proteins can be separated in whey for the production of whey protein concentrate (WPC) • milk can be concentrated prior to cheesemaking at the farm level • apple juice and wine can be clarified • waste treatment and product recovery is possible in edible oil, fat, potato, and fish processing • fermentation broths can be clarified and separated • whole egg and egg white ultrafiltration as a preconcentration prior to spray drying The following topics will be covered in this section: • Principle of Operation • Types of Membrane Processing o Reverse Osmosis o Ultrafiltration o Microfiltration • Hardware Design • Electrodialysis • Ion Exchange 5. What is evaporation of milk?(p.58) Evaporation refers to the process of heating liquid to the boiling point to remove water as vapour. Because milk is heat sensitive, heat damage can be minimized by evaporation under vacuum to reduce the boiling point. The basic components of this process consist of: • heat-exchanger • vacuum • vapour separator • condenser The heat exchanger is enclosed in a large chamber and transfers heat from the heating medium, usually low pressure steam, to the product usually via indirect contact surfaces. The vacuum keeps the product temperature low and the difference in temperatures high. The vapour separator removes entrained solids from the vapours, channelling solids back to the heat exchanger and the vapours out to the condenser. It is sometimes a part of the actual heat exchanger, especially in older vacuum pans, but more likely a separate unit in newer installations. The condenser condenses the vapours from inside the heat exchanger and may act as the vacuum source. 6. Please describe the Starter Culture of yogurt???? The starter culture for most yogurt production in North America is a symbiotic blend of Streptococcus salivarius subsp. thermophilus (ST) and Lactobacillus delbrueckii subsp. bulgaricus (LB). Although they can grow independantly, the rate of acid production is much higher when used together than either of the two organisms grown individually. ST grows faster and produces both acid and carbon dioxide. The formate and carbon dioxide produced stimulates LB growth. On the other hand, the proteolytic

activity of LB produces stimulatory peptides and amino acids for use by ST.These microorganisms are ultimately responsible for the formation of typical yogurt flavour and texture.The yogurt mixture coagulates during fermentation due to the drop in pH. The streptococci are responsible for the initial pH drop of the yogurt mix to approximately 5.0.The lactobacilli are responsible for a further decrease to pH 4.0. The following fermentation products contibute to flavour: ·lactic acid cetic diacety 7.How to produce Whipped Cream Structure(p.79) The structure of whipped cream is very similar to the fat and air structure that exists ir ce cream.Cream is an emulsion with a fat content of 35-4 When you whip a bow of heavy cream the air es tha cau e the fat glo dsorb to and spread around air bubb As the fat partially coalesces,it causes one fat-stabilized air bubble to be linked to the next and starts to be and takes on a smooth textur sults from the forr mation of this oalesced fat structure stabilizing the air bubbles.The water,lactose and proteins are trapped in the spaces around the fat-stabilized air bubbles.The crystalline fat content is essential (hence whipping of cream is very temperature dependent)so that the fat globules partially coalesce into a 3-dimensional structure rather than fully coalesce into larger and larger globules that are not capable of structure-building.This is caused by the crysta within the globules that cause th em to stic ns and clusters n au entity of the glob ripti pped cream is whipped too far wil begin churn and butter particles will form Below are cann aph mage of whi If clow,you understand whipped cream tructure. The structure of whir ed cream as determined by scannin electron microscopy A Overview showing the relative size and prevaler e of air bubbles (a)and fat globule (f);bar=30 um.B.Internal structure of the air bubble.showing the laver of partially coalesced fat which has stabilized the bubble;bar=5 um.C.Details of the partially coalesced fat layer,showing the interaction of the individual fat globules.Bar=3 um. 五、英翻汉

activity of LB produces stimulatory peptides and amino acids for use by ST. These microorganisms are ultimately responsible for the formation of typical yogurt flavour and texture. The yogurt mixture coagulates during fermentation due to the drop in pH. The streptococci are responsible for the initial pH drop of the yogurt mix to approximately 5.0. The lactobacilli are responsible for a further decrease to pH 4.0. The following fermentation products contibute to flavour: • lactic acid • acetaldehyde • acetic acid • diacetyl 7. How to produce Whipped Cream Structure(p.79) The structure of whipped cream is very similar to the fat and air structure that exists in ice cream. Cream is an emulsion with a fat content of 35-40%. When you whip a bowl of heavy cream, the agitation and the air bubbles that are added cause the fat globules to begin to partially coalesce in chains and clusters and adsorb to and spread around the air bubbles. As the fat partially coalesces, it causes one fat-stabilized air bubble to be linked to the next, and so on. The whipped cream soon starts to become stiff and dry appearing and takes on a smooth texture. This results from the formation of this partially coalesced fat structure stabilizing the air bubbles. The water, lactose and proteins are trapped in the spaces around the fat-stabilized air bubbles. The crystalline fat content is essential (hence whipping of cream is very temperature dependent) so that the fat globules partially coalesce into a 3-dimensional structure rather than fully coalesce into larger and larger globules that are not capable of structure-building. This is caused by the crystals within the globules that cause them to stick together into chains and clusters, but still retain the individual identity of the globules. Please see a further description of this process for details. If whipped cream is whipped too far, the fat will begin to churn and butter particles will form. Below are scanning electron micrographs image of whipped cream. If you compare the schematics above with the "real thing" below, you should be able to fully understand whipped cream structure. The structure of whipped cream as determined by scanning electron microscopy. A. Overview showing the relative size and prevalence of air bubbles (a) and fat globules (f); bar = 30 um. B. Internal structure of the air bubble, showing the layer of partially coalesced fat which has stabilized the bubble; bar = 5 um. C. Details of the partially coalesced fat layer, showing the interaction of the individual fat globules. Bar = 3 um. 五、英翻汉

1.Cream(p.66) During thes of hoe the fat-deplete an pro age m and the 00 the Thi ith f nte in the 35 450/ used for further ocessing in the dairy industry for the duction of ic creamo butter or can he old to other food processing industri These industrial normally have higher fat contents than creams for retail sale.normally in the range of 45-50%fat.A product known as"plastic"cream can be produced from certain types of milk separators.This product has a fat content approaching 80%fat,but it remains as an oil-in-water emulsion(the fat is still in the form of globules and the skim milk is the continuous phase of the emulsion),unlike butter which also has a fat content of 80%but which has been churned so t at the fat occupies the continuous phase and the skim milk is dispersed throughout in the form of tiny droplets(a water-in-oil emulsion) )1 prod For retail the fat is nor eam for gher fa ave of th ust be asteu sure freedom fror atho normally hom zed as the high fat content will lead to ey sive fat globule regation and clustering.which leads to excessive viscosity and a loss of whipping ability.This phenomena has been used,however,to produce a spoonable cream product to be used as a dessert topping.Lower fat creams(10%or 18%)can be homogenized,usually at lower pressure than whole milk. 2.Milk Powder Milk used in the production of milk powders is first clarified,standardized and ther eiven a heat tr nt This heat treatment is usually more evere than that requi ired for pasteurization.Besides destroying all the pathogenic and most of the sp ilage 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 Homogeniza a y be applied to e free fat content Spray drying is th ethod r producing n K pow After drying. de n t be store d ng per (up ure. out 6 m ratures

1. Cream(p.66) During the separation of whole milk, two streams are produced: the fat-depleted stream, which produces the beverage milks as described above or skim milk for evaporation and possibly for subsequent drying, and the fat-rich stream, the cream. This usually comes off the separator with fat contents in the 35-45% range. Cream is used for further processing in the dairy industry for the production of ice cream or butter, or can be sold to other food processing industries. These industrial products normally have higher fat contents than creams for retail sale, normally in the range of 45-50% fat. A product known as "plastic" cream can be produced from certain types of milk separators. This product has a fat content approaching 80% fat, but it remains as an oil-in-water emulsion (the fat is still in the form of globules and the skim milk is the continuous phase of the emulsion), unlike butter which also has a fat content of 80% but which has been churned so that the fat occupies the continuous phase and the skim milk is dispersed throughout in the form of tiny droplets (a water-in-oil emulsion). For retail cream products, the fat is normally standardized to 35% (heavy cream for whipping), 18% or 10% (cream for coffee or cereal). Higher fat creams have also been produced for retail sale, a product known as double cream has a fat content of 55% and is quite thick. Creams for packaging and sale in the retail market must be pasteurized to ensure freedom from pathogenic bacteria. Whipping cream is not normally homogenized, as the high fat content will lead to extensive fat globule aggregation and clustering, which leads to excessive viscosity and a loss of whipping ability. This phenomena has been used, however, to produce a spoonable cream product to be used as a dessert topping. Lower fat creams (10% or 18%) can be homogenized, usually at lower pressure than whole milk. 2. 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 3. homogenization not required 4. maximum shelf life extended to approximately 3 years Low-heat SMP is given a pasteurization heat treatment and is used in the production of cheese, baby foods etc. High-heat SMP requires a more intense heat treatment in addition to pasteurization. This product is used in the bakery industry, chocolate industry, and other foods where a high degree of protein denaturation is required. Instant milk powder is produced by partially rehydrating the dried milk powder particles causing them to become sticky and agglomerate. The water is then removed by drying resulting in an increased amount of air incorporated between the powder particles. 3. Cheese : Traditionally, cheese was made as a way of preserving the nutrients of milk. In a simple definition, cheese is the fresh or ripened product obtained after coagulation and whey separation of milk, cream or partly skimmed milk, buttermilk or a mixture of these products. It is essentially the product of selective concentration of milk. Thousands of varieties of cheeses have evolved that are characteristic of various regions of the world. Some common cheesemaking steps will be outlined here. Also included is a document entitled Making Cheese at Home, which includes some helpful references, several simple cheese making procedures and information about sourcing cheese making supplies. • Treatment of Milk • Additives • Inoculation and Milk Ripening • Coagulation o enzyme o acid o heat-acid • Curd Treatment • Cheese Ripening Treatment of Milk for Cheesemaking Like most dairy products, cheesemilk must first be clarified, separated and standardized. The milk may then be subjected to a sub-pasteurization treatment of 63-65° C for 15 to 16 sec. This thermization treatment results in a reduction of high initial bacteria counts before storage. It must be followed by proper pasteurization. While HTST pasteurization (72° C for 16 sec) is often used, an alternative heat treatment of 60° C for 16 sec may also be used. This less severe heat treatment is