食品分析（Food analysis）

1、食品分析（Food analysis）1, the iodine value (iodine value) of the definition and significance of determinationDefinition: iodine chloride or bromide iodine absorbed by 100g oil, converted into iodine grams.Significance: the unsaturation of fatty acids in fats and oils.2. Sample pretreatment of food analy

2、sis (dry ashing, wet digestion)Its used to destroy organic compoundsDry ashing method:Under aerobic condition, the organic matter was decomposed into CO2 and H2O by high temperature combustion, and the residual white or light grey inorganic matter was ash.Advantage：This method basically does not add

3、 or add little reagent, so the blank value is low.Because of the small ash content, more samples can be processed, and the measured components can be enriched.The organic matter is decomposed thoroughly, and the operation is simple.Shortcoming:It takes a long time.2. Because of the high temperature,

4、 it is easy to cause the loss of volatile elements.(3) the crucible has the effect of retention on the tested components, which reduces the determination results and recovery rate.Wet digestion method:The use of strong oxidizing agents (sulfuric acid, nitric acid, perchloric acid, hydrogen peroxide,

5、 Potassium Permanganate, etc.) heating digestion is complete, the decomposition of organic matter in the sample, the measured elements in ionic state exists in solution.Advantage：The decomposition rate of organic matter is fast and the time is short.Due to the low heating temperature, can reduce the

6、 emission of volatile metal loss.Shortcoming:Produce harmful gas.It is easy to produce a large amount of foam overflow in the early stage.The reagent dosage is large and the blank value is high.3. The definition of sulfuric acid sulfonationSulfuric acid sulfonation method (sulfonation method)Samples

7、 were treated with concentrated sulfuric acid, the introduction of polar functional groups SO3 typical fat, pigment, wax and other interfering substances become more polar, soluble in water and acid compounds separated from those soluble in organic solvent component test. It is mainly used for the d

8、etermination of organochlorine pesticide residues.4, food analysis and inspection of the sample collection requirements, the principle of correct sampling, food analysis of sample shrinkageThe principle of correct sampling(1) the collected samples should be uniform and representative, which can refl

9、ect the composition, quality and sanitary condition of all the food examined.(2) sampling method should be consistent with the purpose of analysis.(3) the sampling process and try to maintain the original physical and chemical indicators, to prevent fugitive components (such as water, odor, volatile

10、 acid, etc.).(4) prevent impurity or contamination.(5) the sampling method should be as simple as possible and the size of the treatment equipment should be appropriate.Sampling requirements(1) objective sampling (random sampling)For each part of a batch of food, there is an equal opportunity to be

11、sampled. Sampling from all parts of the product in a balanced and selective manner.But not at random.Random - to ensure that all parts of the material are equal to the possibility of being pumped.(2) selective sampling (representative sampling)Samples can be taken at will, sampled at different produ

12、ction dates, and can be sampled at a certain time interval on the production lineSampling quantity(1) the quantity of sampling should be able to reflect the hygienic quality of food and meet the requirement of sample quantity in the inspection and analysis project. Generally, the amount of samples i

13、n bulk is not less than 0.5kg.(2) the sample of adulteration is different from the general component analysis. The items in the analysis and inspection are not clear in advance, belong to capture analysis, and the amount of sampling should be relatively more.(3) the amount of sampling is different a

14、ccording to the nature of the object. The sample shall be in three copies for inspection, reexamination, reference or arbitration.Sample shrinkage: four point method5, food analysis professional terminology: water, weighing, accurate name, accurate name, detection limit, blank testThe water is disti

15、lled water and deionized waterCommonly used glass instruments with scales are marked at 20 degrees centigrade.Precision weighing must be called according to the number listed, accurate to 0.0001g. (0.1mg)Precise appointment - must be accurate to 0.0001g, close to the value listed, not more than 10%

16、of the value listed.Detection limit the minimum value that can be detectedBlank test - Test without sample, according to actual test procedure6, the definition of relative density, calculation of milk thickenerRelative density D - the mass of a substance at a certain temperature and the mass ratio o

17、f water at the same volume and at a certain temperature.Milk density meter: the relative density of milk is determined, the calibration is 20 /4 /15 and 15 C C.Relative density d= (milk consistency meter reading /1000) +1.0007. The classification of viscosity and the change of viscosity with tempera

18、ture.Viscosity classification: absolute viscosity, kinematic viscosity, conditional viscosity, and relative viscosity. The temperature is up, the viscosity decreases(1) absolute viscosity, also called dynamic viscosity.It is the magnitude of the tangential force required at the flow rate of 1cm / s

19、at the level of L cm2, and the unit is Pa. S.(2) kinematic viscosity, also known as dynamic viscosity.It is the ratio of the absolute viscosity of the liquid to its density at the same temperature, and the unit is m2 / s.(3) the conditional viscosity is the ratio of the time to which a certain amoun

20、t of liquid flows out (s) in the specified viscometer, or the time at which the time is the same as the required temperature.(4) relative viscosity is the ratio of absolute viscosity of a liquid to absolute viscosity of another liquid at a given temperature. The liquid used for comparison is usually

21、 water or an appropriate liquid.8. The existence form of water in foodFree water: stagnant water, capillary water, free flowing waterWith water: combined water, adjacent waters, multilayer water9. Definition of water content and water activity in foodThe water content has a direct impact on the sens

22、ory properties, composition ratio and storage stability of food.Water activity: the ratio of fugacity of water to fugacity of pure water, which can be approximately expressed as the ratio of vapor partial pressure and pure water vapor pressure.Significance of determination of water activity:(1) the

23、growth and reproduction of microorganism in food, the water is free of water, so the growth of microbes in food in the water does not depend on the total water content (%), but depends on the water activity (Aw, also known as water activity).(2) because a part of water is bound to proteins, carbohyd

24、rates, and some soluble substances, such as amino acids, sugars, salts, etc., this binding water is useless to microorganisms. Therefore, water activity is usually used to indicate the water that can be used by microorganisms in food.(3) method for determination of general food moisture quantitative

25、ly water moisture, can not say whether the water is used by microorganisms, the lack of scientific guidance for food production and preservation; and water activity reflects the food and water affinity size, said the available value contained in foods water as a biological chemical reaction and micr

26、obial growth.10. The constant weight of water and ashMoisture 2mgAsh 0.5mg11. The definition of coarse ash and the significance of carbonizationCrude ash: residue after high temperature ignition of food. Some components in food are volatilized and burned, and some are burned into the product by carb

27、onization. Therefore, the remaining substances are not completely accurate raw materials, only belong to rough ash.Carbonization significance: to prevent the rapid evaporation of moisture in the sample, because of the high temperature, so that the sample flying, prevent foaming and expansion of the

28、material foaming at high temperature and overflow, reduce the possibility of carbon particles wrapped.12. Determination of crude ash, acid insoluble, water insoluble ash (see the reverse of the print version)Determination of arsenic in 13, silver salt method, the role of various reagents(1) concentr

29、ated H2SO4: providing H+(2) concentrated H2SO4 + KI + SnCL2: make As3+ - As5+(3) no arsenic zinc particles + concentrated H2SO4: produce atomic state H(4) concentrated H2SO4 + KI + SnCL2 + no arsenic zinc particles: produce AsH3 gas, use quantitative As content(5) effect of lead acetate on Cotton: r

30、emoval of H2S(6) solution DDC-Ag in the test tube: produces colloidal Ag (red brown), and spectrophotometry is used as the standard curve.Specific see book P17114, protein determination: catalyst, mixed indicator color, operation stepsCatalyst: CuSO4Color of mixed indicator: wine red (acid) - gray r

31、ed (neutral) - blue-green (alkaline)The procedures are as follows: 1. Digestion of samples distillation absorption titrationSpecific see book P12515. The principle of determination of fat content in milk by Luo Zi Gothic method (alkaline ether extraction)The use of colloidal properties and fat globu

32、le membrane ammonia ethanol solution to destroy milk non lipid components dissolved in ammonia ethanol solution, and fat free, with ether petroleum ether extract fat, distilled after removing the solvent residue, namely milk fat.16, fat extraction commonly used organic solvents (3 kinds, advantages

33、and disadvantages)(1) anhydrous ether: strong fat dissolving ability, low boiling point, flammable, saturated 2% water, can only extract free fat;(2) petroleum ether: boiling point higher than ether, less flammable, fat soluble weaker than ether, can only extract free fat;(3) chloroform and methanol

34、 mixed liquid: the extraction efficiency of lipoprotein and phospholipid is higher, especially suitable for the extraction of fat from aquatic products, poultry and egg products.17. Soxhlet extraction method for determination of crude fat principle, advantages and disadvantages, calculationPrinciple

35、: the pre treated, dispersed and dried samples were extracted by ether or petroleum ether and other solvents to make the fat in the solvent into the solvent, and the residue obtained after solvent recovery was crude fat.Merits and demerits:(1) suitable for high lipid content, less bound lipid conten

36、t or hydrolysis treatment (bound state has been transformed into free state), the sample should be dry, ground, not easy to moisture absorption caking.(2) and Fei Shichang (8 16hrs) the amount of solvent, the need for specialized equipment, Soxhlet extractor.Fat (%) = (m2-m1) / m * 100M2 - accept th

37、e quality of bottles and fats, G; ML - accept the quality of bottles, g;M - the quality of the sample (such as the mass gauge after moisture determination), G.18, oil acid value and peroxide value of the definition, operation and calculationThe acid value (Acid Value) - the quality of free fatty aci

38、d in the oil and 1 g KOH required (mg). Oil acid value indicates the concentration of free fatty acids in oils.Take an appropriate amount of oil extraction of oil sample flask with neutral ether ethanol mixed solvent with phenolphthalein with 0.1mol/L KOH titration to pink.X: acid (KOH), mg/g V: KOH

39、 volume, mLC: KOH concentration, mol/L M: sample quality, G56.11: KOH mg equivalent to 1mL 1.000mol/L KOH.Peroxide value - an indicator of the degree of oxidation of oils and fatty acids, which is expressed by peroxide value. The active oxygen content in the 1 kilogram sample is expressed in terms o

40、f the number of peroxides.19. The definition of invert sugarSucrose = hydrolyzed fructose + glucose20. Determination of total sugar, reducing sugar and sucrose(total sugar reducing sugar) x coefficient 0.9 = sucrose21. Pretreatment, operation steps and operation points of determination of reducing s

41、ugar and sucrosePretreatment: 1. Extraction: the commonly used extractants were water and ethanol solution2, clarification: the clarifier does not use Cu, so as not to affect the subsequent quantification, and the clarifier is neutral or alkaline.Procedures: sample treatment, calibration, reagent (a

42、lkaline copper tartrate) reagent, pre titration of sample solution, precision titration, and result calculationOperation points:More fat, except fat: add petroleum ether separation.(2) starch, dextrin and protein should be removed except starch, dextrin and protein: adding 70-75% ethanol precipitati

43、on.Alcohol, CO2, alcohol, CO2: heating, evaporation.4. More acids, except acid: alkali neutralization.The soluble sugar was extracted by adding water or ethanol as extractant in the pretreatment process.22. Determination of starch in food(1): the enzymatic hydrolysis of starch hydrolysis for disaccharide, in hydrochloric acid hydrolysis into simple sugars, reducing sugar was determined by.(2) acid hydrolysis: hydrolysis of starch into reducing sugar.(3) polarimetry using starch opticity.23. Solubility of vitaminsVitamin classification: f