食品工程学品质变化速PPT课件

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页第2页/共21页多组分，不均质，多样性生物材料；物理的，化学的，生化的及其综合变化； -品质变化速度论 第3页/共21页第4页/共21页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、

2、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）第5页/共21页 第6页/共21页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

3、 1012 1020 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 cert

4、ain 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 pos

5、tharvest, oxidation of lipids by lipase and lipoxygenase 第7页/共21页B. Chemical changeschemical 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

6、cross-linking- protein hydrolysis- oligo- and polysaccharide hydrolysis- polysaccharide synthesis- degradation of specific natural pigment- glycolytic changes第8页/共21页a. Lipid oxidation- development of off-flavor.- react with protein and result in extensive cross-linking.b. Non-enzymatic browning、- o

7、ne 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 evolv

8、ed 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 p

9、ermeate through package from the ambient To.four major factors 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

10、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 carboh

11、ydrates, 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第10页/共21页D. Biological change- major groups of m

12、icroorganisms 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 4

13、0oC referred to mesophiles), RH%, gases in environment.-flies and cockroaches, moth, beetles- 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* One-step heating (60C kamaboko gel)* Two-step heating (cooking at 85C/30min after

14、one-step setting)Measure indices: 第13页/共21页01002003004005000min10min30min1hour2hour3hour5hour10hourHeating timeBreaking force (g)304050607085Heating temperature第14页/共21页Three-dimensional configuration of breaking force of walleye pollack surimi gels 第15页/共21页 Silver carp Big-head carp Chinese snake-

15、head Blunt snout bream Tilapia Grass carp Mud carp Common carp第16页/共21页 320g (Fmax)0501001502002503003500100200300400500600Incubation time (min)Breaking force (g)T1/2(1500sec)160g (0.5Fmax)ABC第17页/共21页Arrhenius 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)Walleye pollackSilver carp Big-head carp Grass carp 85 70 60 50 40 30 (C)* Heat-induced gelation of surimi occurs due to different mechanism at the upper and lower tempera