【正文】 freezing milk will break its emulsion and casein will curdle。 however, often animal feeding tests must be used, especially for quality of protein sources (biological value). B. Sanitary quality ? Analysis for bacteria, yeasts, molds and insect fragments. ? Xrays to detect physical contaminants (., glass chips, stones, metal fragments). C. Keeping quality (storage stability) ? Measured under storage and handling conditions to match conditions encountered in normal distribution. ? Normal storage tests may take a year。 ultrasonics also used to screen internal tissue of whole fruits and vegetables. Disintegrating A. Breakdown of large food particles into smaller particles. ? Examples: Cutting, grinding, pulping, homogenizing. ? Some cutting now done with highpressure water jets and laser beams. B. Disintegration often involves heat buildup due to friction and some products require cooling (., meats to avoid protein denaturation and coffee to avoid burned flavors). ? Grinding of frozen meat is done to avoid this. ? Or addition of dry ice that dissipates as carbon dioxide. C. Homogenization Pumping A. One of the most mon operations in the food industry ? (both liquids and solids suspended in liquids) B. Many kinds of pumps pump selected depends upon nature of food to be moved. Rotary gear pumps have close tolerances among moving parts, chunktype foods would be reduced to purees, and sometimes this is the intent, so the pump serves two purposes. ? A singlescrew pump (with large clearances) best for moving food with large pieces without disintegration (., corn kernels, grapes, small shrimp). C. It is essential that all food pumps can be easily disassembled for thorough cleaning (stainless steel is the most mon material used to make pumps for the food industry). Mixing A. Again, very mon operation in the food industry。 Crick discover the doublehelix structure of DNA, laying the foundation for understanding geics and developing rebinant DNA technology 1960s: First mercial plant for freezedrying food opens (1960 for coffee). Computer control in processing plants first introduced. FDA approves irradiation to disinfest wheat and wheat flour (1963), to inhibit sprouting in potatoes (1964), and to extend the shelflife of potatoes (1965). Aseptic canning adopted by food manufacturers. 1970s: Hazard Analysis Critical Control Point (HACCP) system jointly developed by NASA, Pillsbury Co., and the . Army Natick Laboratories. Rebinant DNA technology developed (1973). 1980s: Modifiedatmosphere packaging(MAP) introduced to increase shelflife and protect them from spoilage, oxidation, dehydration, weight loss, and freezer burn. FDA approves irradiation to control Trichinella spiralis in pork (1985), to disinfest and/or delay ripening in some fresh fruits and vegetables (1986), and to control microanisms in spices and herbs (1986). 1990s: ? HACCP bees widely adopted by food manufacturers largely due to regulations by FDA and USDA. ? FDA approves use of irradiation to control harmful bacteria in fresh and frozen poultry (1990) and red meats (1997). ? Pasteurization process for shell eggs by ohmic heating (using electricity). ? Flash pasteurization process of fresh juices mercially applied leading to notfromconcentrate citrus juices. ? Orange juice fortified with calcium. ? Highpressure processed guacamole es to . market (1998). ? Steam pasteurization and vacuuming of beef carcasses introduced to reduce microbial hazards. ? Rebinant enzyme, chymosin, replaces ren in most cheese manufacture. ? First food from a transgenic plant (a tomato with delayed ripening) es to market (1994). ? Active packaging systems introduced that interact with package contents or the package?s internal atmosphere are developed to enhance product freshness UNIT OPERATIONS Materials handling Harvesting and transportation while maintaining product quality to and in the processing plant. ? Low temperature storage to maintain perishable produce appearance and vitamin content. ? Volume restrictions due to “field heat” produced by fruits amp。 vegetables. ? Care of handling livestock and fragile products such as eggs. ? Safety issues from static electricity buildup igniting sugar dust or fine flo