,单击此处编辑母版标题样式,单击此处编辑母版文本样式,第二级,第三级,第四级,第五级,*,单击此处编辑母版标题样式,单击此处编辑母版文本样式,第二级,第三级,第四级,第五级,*,现代食品工程学,Advanced Food Engineering/,Engineering Properties of Foods,2,科学回答：是什么？为什么？,技术回答：做什么？怎么做？,科学是发现，技术是发明。,科学是创造知识的研究,技术是综合利用知识于需要的研究,工程：依靠、使用复杂的系统、工具、设备或装备来完成的工作。,食品加工中的品质变化速度,Velocity of Quality Change during Food Processing,食品原料：,多组分，不均质，多样性生物材料；,品质变化：,物理的，化学的，生化的及其综合变化；,食品反应工学,-,品质变化速度论,食品加工操作（处理）：,物理性,-,机械的，扩散的，热的操作。如洗净，浸渍，发泡，混和，过滤，抽提，结晶，冷冻，浓缩，干燥等。,化学性,-,反应的操作。如化学反应，酶反应，微生物发酵，杀菌，烹饪等。,内容,:,品质变化速度式设定,;,感官性状的变化（,味道、气味、色泽、质地,）；,营养成分的变化（,碳水化合物、蛋白质、脂质、维生素等,）；,氧化（,酶促和非酶促；油脂氧化、维生素氧化、血红蛋白氧化等,）；,着色（,酶促着色、非酶促着色,）；,漂洗；,糊化（,糊化与老化,）；,蛋白质变性（,加热、冻结、其他,）；,其他品质变化（,盐渍、糖渍、醋渍、薰蒸等,）,Quality includes safety quality and sensorial quality,Food safety:that is the freedom from harmful chemical or microbial contaminations at the production,processing,distribution and consumption.,Major sensorial quality attributes of foods are texture,color,flavor,appearance and nutritive value,some undesirable changes may occur either prior to or during distribution and,consumption.,Deteriorative reaction in foods,A.enzymatic changes,-enzymes are complex,globular proteins that have 3 important characteristics:,(1)Act as catalysts,accelerate the rate of chemical reactions by factors of 10,12,10,20,over uncatalyzed reaction.,(2)Highly specific,enable the food processors to selectively modify particular food components.,(3)Have a regulatory role,control the biochemical processes.,Types of enzymes:,Exogenous addition of enzyme(from microorganism)in the milk during manufacturing certain cheeses,intentional fermentation(desirable),spoilage(undesirable).,Endogenous involving autolysis of fish postharvest(off-flavor),the senescence and spoilage of fruits and vegetables postharvest,glycolysis in postmortem,prerigor muscle and suberization(wound healing)of plant tissues postharvest,oxidation of lipids by lipase and lipoxygenase,B.Chemical changes,chemical reactions lead to deterioration of food quality or impairment of safety,-non-enzymatic browning(Maillard reaction=reducing sugar+amino acid),-lipid hydrolysis/oxidation,-protein denaturation,-protein cross-linking,-protein hydrolysis,-oligo-and polysaccharide hydrolysis,-polysaccharide synthesis,-degradation of specific natural pigment,-glycolytic changes,Sensory Quality,a.Lipid oxidation,-development of off-flavor.,-react with protein and result in extensive cross-linking.,b.Non-enzymatic browning,、,-one of the major deteriorative chemical reactions occurs during storage of dried and concentrated foods.,-leads to formation of insoluble brown polymers(mw 1000).,c.Color change,-change in structure or content of chlorophyll,hem pigment,anthocyanins,carotenoids.,d.Flavor changes,-flavor has evolved to a usage that implies and overall integrated perception of the contributing senses of smell and taste at the time of food consumption.,the permeability of packaging materials is of importance in retaining desirable volatile components within package,or in permitting undesirable components to permeate through package from the ambient T,o,.,Nutritional Quality,four major factors which impact on nutrient degradation and can be controlled to varying,extents by packaging are Light,O,2,concentration,T,o,and Aw,C.Physical changes,physical properties include geometrical(size,shape,volume,density and surface area as related to homogeneous food units,as well as geometrical textural characteristics such as referring to particle size and shape;referring to particle shape and orientation),thermal,optical,mechanical,rheological,electrical,and hydrodynamic properties,-for foods containing solid carbohydrates,the largest effect in physical properties results from sorption of water,especially for the recrystallization of amorphous carbohydrate,e.g.in boiled sweets leading to stickiness and graining,in milk powders leading to caking and lumpiness,D.Biological change,a.Microbiological,-major groups of microorganisms found in foods are bacteria and fungi(yeasts and molds),-foods are frequently classified on the basis of their stability as non-perishable,semi-perishable,perishable,Factors affecting microbial growth,1.intrinsic parameters:Moisture,pH,2.extrinsic parameters:Temperature(e.g.30,40,o,C referred to mesophiles),RH%,gases in environment.,b.Macrobiological,1.Insect Pests,flies and cockroaches,moth,beetles,2.Rodents,-proper sanitation(all packaging material apart from metal and glass can be attacked by rats and mice),案例,Methods,Surimi,Surimi paste,Heat-induced gel,1.,Defrosting(half-thawed,).,2.Grinding with NaCl,additives,chilled distill water,etc.,3.Stuffing into a 35 mm diameter folded PVDC tube,casing,ca.100g each sample.,Incubated at a certain temperature for a definite time,including:,*One-step heating(,60,C,kamaboko gel,),*Two-step heating(,cooking at 85,C,/30min after one-step setting,),Measure indices:,breaking force(g),breaking strain(mm),whiteness,folding test,composition analysis,and SDS-PAGE,etc.,Gelation curve of walleye