食品工程学品质变化速度ppt课件

1、科学回答：是什么？为什么？技术回答：做什么？怎样做？科学是发现，技术是发明。科学是发明知识的研讨技术是综合利用知识于需求的研讨工程：依托、运用复杂的系统、工具、设备或配备来完成的任务。漂洗；漂洗；糊化糊化与老化；糊化糊化与老化；蛋白量变性加热、冻结、其他；蛋白量变性加热、冻结、其他；其他质量变化盐渍、糖渍、醋渍、其他质量变化盐渍、糖渍、醋渍、薰蒸等薰蒸等intentional fermentation (desirable), spoilage (undesirable).Endogenous involving autolysis of fish postharvest (off-flavo

2、r), 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 changeschemical reactions lead to deterioration of food quality or

3、 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- gly

4、colytic changesNutritional Qualityfour major factors which impact on nutrient degradation and can be controlled to varyingextents by packaging are Light, O2 concentration, To and AwC. Physical changesphysical properties include geometrical (size, shape, volume, density and surface area as related to

5、 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 large

6、st 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 lumpinessD. Biological changea. Microbiological- major groups of microorgan

7、isms 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 growth1. intrinsic parameters: Moisture, pH2. extrinsic parameters: Temperature (e.g. 30 40oC refer

8、red to mesophiles), RH%, gases in environment.b. Macrobiological1. Insect Pestsflies and cockroaches, moth, beetles2. Rodents- proper sanitation (all packaging material apart from metal and glass can be attacked by rats and mice)案例案例Measure indices: breaking force (g), breaking strain (mm), whitenes

9、s, folding test, composition analysis, and SDS-PAGE, etc.01002003004005000min10min30min1hour2hour3hour5hour10hourHeating timeBreaking force (g)304050607085Heating temperatureThree-dimensional configuration of breaking force of walleye pollack surimi gels SilvercarpBig-headcarpChinesesnake-headBlunts

10、noutbream Tilapia Grass carp Mud carp Common carp320g (Fmax)0501001502002503003500100200300400500600Incubation time (min)Breaking force (g)T1/2(1500sec)160g (0.5Fmax)ABCArrhenius plots for gelation rates of freshwater fish and walleye pollack protein10.00100.001000.003.33.23.13.02.92.81/T103 (K-1)Gelation rate K105 (s-1)WalleyepollackSilvercarpBig-headcarpGrasscarp857060504030(C)* Heat-induced gelation of surimi occurs due to different mechanism at the upper and lower temperature sides of a boundary of around