Food Analysis(食品分析)20

1、determination of carbohydrates,contents,introduction definition classification structure of carbohydrates distribution of carbohydrates in food function of carbohydrates in food processing determination of carbohydrates,introduction,definition chemically, carbohydrates are organic molecules in which

2、 carbon, hydrogen and oxygen bond together in the ratio: cx(h2o)y where x and y are whole numbers that differ depending on the specific carbohydrate to which we are referring 多羟基醛或者酮及其衍生物和缩合物 carbohydrates are the main energy source for the human body. carbohydrates are the most abundant class of or

3、ganic compounds found in living organisms,classification（从组成上分） simple sugars monosaccharides:不能再被水解的多羟基醛或者酮，是碳水化合物的基本单位。如葡萄糖、果糖、半乳糖等。 complex carbohydrates oligosaccharides ：210个单糖分子缩合而成，水解后生成单糖。 如蔗糖、麦芽糖、乳糖等。 polysaccharides：由许多单糖分子缩合而成，如淀粉、纤维素、果胶等,monosaccharides,two of the most common monosacchar

4、ides are glucose and fructose. both glucose and fructose have the same chemical formula (c6h12o6) however they have different structures as seen below,glucose,fructose,disaccharides,have two sugar units bonded together. for example, common table sugar is sucrose a disaccharide that consists of a glu

5、cose unit bonded to a fructose unit,lactose,lactose: is found exclusively in the milk of mammals and consists of galactose and glucose in a b-(1,4) glycosidic bond,maltose,maltose: the major degradation product of starch, is composed of 2 glucose monomers in an a-(1,4) glycosidic bond,complex carboh

6、ydrates,definition polymers of the simple sugars. long chains of simple sugar units bonded together ，often referred to as polysaccharides). several polysaccharides starch cellulose pectin,amylose,cellulose,characteristic of monosaccharides,another characteristic of monosaccharides is that they can a

7、ct as mild reducing agents. this is because the aldehydo group that is present can be oxidized to form a carboxylic acid group, or in the presence of a base, a carboxylate ion group,fructose can also act as a reducing sugar, even though it has a ketone group instead of an aldehyde group. under basic

8、 conditions, the fructose molecules can, essentially, have the location of the carbonyl bond switched to convert them into a glucose molecule. this occurs in a number of steps involving removing hydrogens from the #1-c and its oxygen and moving them to the #2-c and its oxygen,any monosaccharide mole

9、cule thats in a ring form will, within a fraction of a second, be in the open form and, thus, be able to react with the oxidizing agent and reduce it,equilibrium of ring form and open form,not reducing sugars,reducing sugars,characteristics of starch insoluble in hot water blue complex compound by r

10、eaction with iodine. insoluble in 30% of ethanol solution or above. hydrolyzed by acid and enzyme, the ultimate product is glucose. specific rotatory power is between +201.5 and +205,characteristics of cellulose insoluble in water no reducibility(无还原性) uneasy to be hydrolyzed.concentrated h2so4 is n

11、eeded in the hydrolysis of cellulose for a long time at high temperature.(水解比淀粉困难得多，需用浓硫酸在一定时间下长时间加热水解) can not be digested by body, but can be used by some animal, such as cows.(人体不能产生分解纤维素的酶，一些草食动物可以消化纤维素。,distribution of carbohydrates in food,carbohydrates comprise more than 75% of the dry matter

12、 of plants, corn ,vegetable, fruits and so on. monosacchrides and oligosaccharides is usually found in vegetables and fruits polysaccharides can mainly be found in corn, seed, root and so on,function of carbohydrates in food processing,texture of food mouth-feel of food sweet taste flavor for food,d

13、etermination of carbohydrates,determination of reducing sugar determination of sucrose determination of total sugar quantitative determination of different carbohydrates determination of starch determination of cellulose determination of pectin,determination of reducing sugar,preparation of samples,

14、water,40-50， soluble sugar,above 40-50 ,soluble sugar, starch,dextrin, etc,70-75% ethanolprotein,dextrin,starch cant be soluble,sample containing oilextract fats, then separate sugar,adding clarifier to remove the interruption(no effect on sugar,determination of reducing sugar,reducing sugars,aldehy

15、de,carboxylate,red precipitate,sugars that contain aldehyde groups that are oxidised to carboxylic acids are classified as reducing sugars. common test reagents are : benedicts reagent (cuso4 / citrate) fehlings reagent (cuso4 / tartrate) they are classified as reducing sugars since they reduce the

16、cu2+ to cu+ which forms as a red precipitate, copper (i) oxide. in order for oxidation to occur, the cyclic form must first ring-open to give the reactive aldehyde. so any sugar that contains a hemi-acetal will be a reducing sugar. but glycosides which are acetals(乙缩醛） are not reducing sugars,b-d-gl

17、ucose,methyl b-d-glucopyranoside,sucrose,hemi-acetal = reducing sugar,acetals = non-reducing sugar,碱性铜盐法 原理,氧化还原反应滴定法次甲基蓝为指示剂,注意： 1）已知的还原糖溶液标定碱性酒石酸铜溶液 2）在酒石酸铜溶液中加入少量亚铁氰化钾，络合氧化亚铜 3）沸腾条件下进行滴定 4）快速完成测定,3，5二硝基水杨酸比色法测定还原糖 原理： 3，5-二硝基水杨酸溶液与还原糖(各种单糖和麦芽糖)溶液共热后被还原成棕红色的氨基化合物，在一定范围内，还原糖的量和棕红色物质的颜色深浅的程度成一定比例关系。

18、在540nm波长下测定棕红色物质的消光值，查标准曲线，便可求出样品中还原糖的含量,酶比色法 葡萄糖氧化酶(god)在有氧条件下， 催化-d-葡萄糖(葡萄糖水溶液)氧化， 生成d-葡萄糖酸-内酯和过氧化氢。 受过氧化物酶(pod)催化，过氧化氢 与4-氨基安替比林和苯酚生成红色醌亚胺。在505nm波长处测醌亚胺的吸光度， 酶电极法 葡萄糖氧化酶(god)在有氧条件下催化d葡萄糖(葡萄糖水溶液状态)氧化，生成d葡萄糖酸内酯和过氧化氢。过氧化氢与过氧化氢型电极接触产生电流。该电流值与d葡萄糖的浓度呈线性比例，在酶电极葡萄糖分析仪上直接显示葡萄糖含量,determination of sucrose,

19、principle sucrose-monosaccharidesdetermine,acid treatment,enzyme treatment,determination of total sugar,definition including reducing sugar and sucrose that can be hydrolyzed to reducing sugar at the conditions. principles as above methods 蒽酮比色法,contents,determination of starch determination of cell

20、ulose determination of pectin,determination of starch by acid or enzyme hydrolysis,principle,samples,remove impurity,sample with starch,starch hydrolysis,reducing sugar,碱性铜盐法,酶比色法,蒽酮比色法,ethyl ether,ethanol,remove lipids,remove soluble sugar,acid,amylase,attention samplesremove lipids by ethyl ether

21、samples remove soluble sugar by 80% of ethanol(dextrin is reserved), if the ethanol concentration is 10%, dextrin is removed with soluble sugar together. kept starch hydrolyzed completely by controlling the experiments strictly. it can be indicated by iodine,polarimetry,principle,starch extraction b

22、y cacl2-hac solution,protein precipitated by sncl2,determination of,calculation,weighing method,principle,sample + koh in ethanol,filtering,starch 、cellulose,adding koh in water,filtering,cellulose,supernate,hac-ethanol,filtering, collecting precipitate,drying at 100,burning at 550,calculate the los

23、s,determination of amylose,principle,starch + iodine,complex with color,mixing the different concentration of amylose and amylopectin at definite content of total starch,620nm, determine od,calibration curve,淀粉是葡萄糖的聚合物，由单体葡萄糖通过糖苷键的形式连接而成，线性连接的分子是直链淀粉，分支连接的则为支链淀粉，单纯的直链和支链是不存在的，淀粉分子实际上是由两种形式的混合物构成的. 淀粉与水构成的混悬液在受热的情况下会发生一定的变化。 在较低的温度条件下，淀粉通过氢键作用结合水分子而分散，此时的变化属于物理变化，淀粉的结构不发生变化。 当温度上升到一定程度后，淀粉分子会大量吸收水分而发生急剧膨胀，分子结构发生伸展，此时即使停止加热，分子也不能恢复原来的