foodscienceandtechnology(ppt60)-电子商务(编辑修改稿)

foodscienceandtechnology(ppt60)-电子商务(编辑修改稿)内容摘要：

f moisture (evaporate)  Develop flavors  Inactivate natural toxic substances (soybean meal) B. Need to control application of heat (often necessary to heat and rapidly cool the product)  Rapid heating and cooling often require maximum contact of the food with the heating/cooling source (., heat exchangers in the pasteurization of milk).  Steamjacketed stainless steel kettle or tank often used for heating liquid foods (mixing propeller usually included to prevent scorching and even distribution of temperature).  Canning using a retort (pressure cooker)  Roasting circulating hot air C. Cooling  Again, a heat exchanger can be used, but with cold water pumped through the unit.  Commercial blast freezers reach 26C  Liquid nitrogen: 196C Evaporation to concentrate foods 2 to 3fold A. To remove water, to recover desirable food volatiles, and to remove undesirable volatiles. B. Can be solar (raisins), heated kettle (water from a sugar syrup). C. Very mon in the industry: Vacuum evaporation reduced pressure allows liquids to boil at lower temperatures (the lower temperature causes less damage to food quality). Drying to take foods to near total dryness (often 2 to 3% water) Examples  Dried milk processed by spray drying (atomized liquid mixed with heated air)。 liquid foods are easiest to dry.  Mashed potatoes and tomato puree processed by drum drying (drum heated from within, applied layer of food flashes off its moisture on contact with heated drum, and thin film of food scraped off drum with long knives).  Peas and diced onions dried by moving through a long tunnel oven (subject of overheating and shrinkage), but a preferred method is,  vacuum freezedrying (used for coffee), food frozen, dehydrated under vacuum from the frozen state. Forming foods made into specific shapes (., fish sticks) Application of pressure within an appropriate form. Range of pressures used, varies considerably dependent upon the product. For example: Extrusion {Breakfast cereals Extrusion cooking} Formulated dough or mash is extruded under high pressure with heat. Packaging (food containers) To protect food from microbial contamination, physical dirt, insect invasion, light, moisture pickup or loss, flavor pickup or loss, and physical abuse (damage). Containers include metal cans, glass and plastic bottles, paper and paperboard, plastic and metallic films, and binations of these. Packaging is automated. New processes To increase the range of options within each unit operation, to improve quality or increase efficiency. Examples include: supercritical fluid extraction, ohmic heating, and high hydrostatic pressure processing. QUALITY FACTORS IN FOODS Appearance factors Textural factors Flavor factors Additional quality factors Appearance factors A. Size and shape  Size: Easily measured (., fruits and vegetables can be sized according to the openings they can pass through。 the basis for automated separating and grading machines).  Shape: Some of the most difficult food engineering problems are the designing of equipment to pack oddshaped food pieces. B. Color and gloss  Food color: Helps determine quality, ripeness and spoilage.  Color and transparency/cloudiness: Can be measured with a spectrophotometer (measures light transmission through a liquid).  Solids and liquids: Reflected color can be measured by parison with defined colored chips.  Hunter colorimeter: Color measurement by division into three ponents value, hue and chroma.  Value lightness or darkness of the color.  Hue predominate wavelength reflected (which determines what the perceived color is).  Chroma intensity strength of the color.  Instruments available to measure shine or gloss. C. Consistency viscosity。 many types of viseters to measure consistency.  Bostwick Consistometer time it takes for food to flow down an inclined trough. Textural factors A. Food qualities we feel. B. Food texture can be measured by resistance to force.  Squeezing (pression).  Shear (force applied so that one part of the food slides past the other).  Cutting.  Tensile strength (pulling apart). C. Texture changes do not remain constant in a food.  Change in water conten。