食品工程学品质变化速.pptx

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1、1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。第1页/共21页 食品加工中的品质变化速度Velocity of Quality Change during Food ProcessingVelocity of Quality Change during Food Processing第2页/共21页 食品原料：食品原料：多组分，不

2、均质，多样性生物材料；品质变化：品质变化：物理的，化学的，生化的及其综合变化；食品反应工学食品反应工学-品质变化速度论 第3页/共21页食品加工操作（处理）：物理性物理性-机械的，扩散的，热的操作。机械的，扩散的，热的操作。如洗净，浸渍，发泡，混和，如洗净，浸渍，发泡，混和，过滤，抽提，结晶，冷冻，浓缩，干燥等。过滤，抽提，结晶，冷冻，浓缩，干燥等。化学性化学性-反应的操作。如化学反应，酶反应，微生物发酵，杀菌，烹反应的操作。如化学反应，酶反应，微生物发酵，杀菌，烹饪等。饪等。第4页/共21页 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

3、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）第5页/共21页 Quality includes safety quality and sensorial qualityQuality includes safety quality and sensorial qualityFood safety:that is the freedom from harmful chemical or microbial Food safety:t

4、hat is the freedom from harmful chemical or microbial contaminations at the production,processing,distribution and contaminations at the production,processing,distribution and consumption.consumption.Major sensorial quality attributes of foods are texture,color,flavor,Major sensorial quality attribu

5、tes of foods are texture,color,flavor,appearance and nutritive value,some undesirable changes may appearance and nutritive value,some undesirable changes may occur either prior to or during distribution andoccur either prior to or during distribution and consumption.consumption.第6页/共21页 Deteriorativ

6、e reaction in foodsDeteriorative reaction in foodsA.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 1012 1020 over uncatalyzed reaction.(2)Highly specific,enable the food process

7、ors 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 invo

8、lving 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 第7页/共21页 B.Chemical changeschemical rea

9、ctions 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 o

10、f specific natural pigment-glycolytic changes第8页/共21页 Sensory QualitySensory Qualitya.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 con

11、centrated 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

12、 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 To.Nutritional QualityNutritional Qualityfour major fact

13、ors which impact on nutrient degradation and can be controlled to varyingextents by packaging are Light,O2 concentration,To and Aw第9页/共21页 C.Physical changesphysical properties include geometrical(size,shape,volume,density and surface area as related to homogeneous food units,as well as geometrical

14、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

15、 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第10页/共21页 D.Biological changea.Microbiologicala.Microbiological-major groups of microorganisms found in foods are bacteria and

16、fungi(yeasts and molds)-foods are frequently classified on the basis of their stability as non-perishable,semi-perishable,perishable Factors affecting microbial growth1.intrinsic parameters:Moisture,pH2.extrinsic parameters:Temperature(e.g.30 40oC referred to mesophiles),RH%,gases in environment.b.M

17、acrobiologicalb.Macrobiological1.Insect Pests1.Insect Pests-flies and cockroaches,moth,beetles2.Rodents2.Rodents-proper sanitation(all packaging material apart from metal and glass can be attacked by rats and mice)第11页/共21页案例第12页/共21页MethodsSurimiSurimiSurimi pasteSurimi pasteHeat-induced gelHeat-in

18、duced gel1.1.Defrosting(half-thawedDefrosting(half-thawed).).2.Grinding with NaCl,additives,chilled distill water,etc.2.Grinding with NaCl,additives,chilled distill water,etc.3.Stuffing into a 35 mm diameter folded PVDC tube 3.Stuffing into a 35 mm diameter folded PVDC tube casing,ca.100g each sampl

19、e.casing,ca.100g each sample.Incubated at a certain temperature for a definite time,Incubated at a certain temperature for a definite time,including:including:*One-step heating(60C kamaboko gel)*Two-step heating(cooking at 85C/30min after one-step setting)Measure indices:breaking force(g),breaking s

20、train(mm),whiteness,folding breaking force(g),breaking strain(mm),whiteness,folding test,composition analysis,and SDS-PAGE,etc.test,composition analysis,and SDS-PAGE,etc.第13页/共21页Gelation curve of walleye pollack surimi by heating temperature and heating timeHeating temperature第14页/共21页Three-dimensi

21、onal configuration of breaking force of walleye pollack surimi gels Steep mountain and V valley type Steep mountain and V valley type surimisurimi Easy set and easy collapse surimi Easy set and easy collapse surimi 第15页/共21页V-valley type surimi Silver carp Big-head carp Chinese snake-head Blunt snou

22、t bream Plateau type surimi Tilapia Grass carp Mud carp Common carp第16页/共21页Calculation of gelation rate:Calculation of gelation rate:Where TWhere T1/21/2 is the time(sec.)required for reaching the half-maximal is the time(sec.)required for reaching the half-maximal breaking force.breaking force.K=1

23、/(TK=1/(T1/21/2),s),s-1-1K KD D=(lnG=(lnG0 0-lnG-lnGt t)1/t,s1/t,s-1-1Where the GWhere the G0 0 and Gand Gt t were the breaking force before and after heating for t were the breaking force before and after heating for t second.second.Calculation of gel disintegration rate:Calculation of gel disinteg

24、ration rate:T1/2(1500sec)160g(0.5Fmax)ABC第17页/共21页Arrhenius Arrhenius equation:equation:K=KK=K0 0exp(-Ea/RT)exp(-Ea/RT)85 70 60 50 40 30 (C)*Heat-induced gelation of surimi occurs due to different mechanism at the upper and lower temperature sides of a boundary of around 50C.第18页/共21页Disintegrationrateconstantsofdifferentsurimigels第19页/共21页WANG XI-CHANG SHOU,WANG XI-CHANG SHOU,ChinaChina第20页/共21页感谢您的观看！第21页/共21页