食品工程学品质变化速实用教案

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 ( g n g j ) 、 设 备 或 装 备 来 完 成 的 工 作 。第1页/共21页第一页，共21页。第2页/共21页第二页，共21页。第3页/共21页第三页，共21页。第4页/共21页第四页，共21页。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

2、、醋渍、薰蒸等）第5页/共21页第五页，共21页。 第6页/共21页第六页，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 1012 1020 over uncatalyzed reaction.(2) Highly specific, enable the food process

3、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).Endogen

4、ous 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 第7页/共21页第七页，共21页。B. Chem

5、ical 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 cross-linking- protein hydrolysis- oligo- and polysaccharide hydrolysis-

6、 polysaccharide synthesis- degradation of specific natural pigment- glycolytic changes第8页/共21页第八页，共21页。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

7、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

8、 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 To.four major factors

9、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页第九页，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

10、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 res

11、ults 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页第十页，共21页。D. Biological change- major groups of microorganisms found in foods are bacteria and

12、 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 en

13、vironment.-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页第十一页，共21页。案例第12页/共21页第十二页，共21页。* One-step heating (60C kamaboko gel)* Two-step heating (cooking at 85C/30min after one-step setting)Measure

14、indices: 第13页/共21页第十三页，共21页。Heating temperature第14页/共21页第十四页，共21页。Three-dimensional configuration of breaking force of walleye pollack surimi gels 第15页/共21页第十五页，共21页。 Silver carp Big-head carp Chinese snake-head Blunt snout bream Tilapia Grass carp Mud carp Common carp第16页/共21页第十六页，共21页。 T1/2(1500sec)160g (0.5Fmax)ABC第17页/共21页第十七页，共21页。85 70 60 50 40 30 (C)* He