introduction
1. What is food analysis?
Food analysis and inspection is a discipline that studies and evaluates food quality, changes and hygienic conditions. It uses the basic theories and techniques of sensory, physical, chemical and instrumental analysis to analyze the composition, sensory characteristics, physical and chemical properties of food. Analyze and detect the properties and hygienic conditions, and study the applied science of detection principles, detection technologies and detection methods.
2. What are the tasks of food analysis and inspection?
(1) According to the designated technical standards, modern science and technology and testing methods are used to analyze and inspect the raw materials, auxiliary materials, semi-finished products, packaging materials and finished products of food production, so as to evaluate the quality, nutrition, safety and hygiene of the food. , ensuring food quality meets the requirements of food standards
(2) Monitor food production process parameters and processes, determine process parameters and process requirements, and grasp production conditions to ensure food quality, thereby guiding and controlling the production process.
(3) Provide basic data for food production enterprises to calculate costs and formulate production plans.
(4) Develop new food resources, improve food quality and find sources of food contamination, so that consumers can obtain delicious, nutritious, economical and hygienic food, and provide a basis for the research and application of new food production processes and technologies.
(5) Inspection agencies conduct inspections of products of manufacturing companies or commodities on the market in accordance with the requirements of the government's quality supervision administrative departments, providing a basis for the government management departments to conduct macro-monitoring of food quality.
(6) When a product quality dispute occurs, the third-party inspection agency conducts arbitration inspection of the disputed product upon entrustment by the relevant agency that resolves the dispute, providing technical basis for the relevant agency to resolve product quality disputes.
(7) In the import and export trade, according to international standards, national standards and contract regulations, the imported and exported food is tested to ensure the quality of the imported and exported food and maintain the country's export reputation.
(8) When a food poisoning incident occurs, the inspection agency conducts arbitration inspections of residual food to provide technical basis for timely investigation and resolution.
3. What does food analysis and inspection include?
Sensory testing of food
Physical and chemical testing of food: general composition analysis of food, detection of food additives, detection of toxic and harmful substances in food
Detection of Functional Foods Detection of Genetically Modified Foods Analysis of Food Packaging Materials and Containers
Rapid identification of chemical food poisoning Detection of spoiled food Detection of adulterated food
Chapter 2 General Procedures for Food Analysis and Inspection
1. General procedures for food analysis and inspection: sample collection and preparation → sample preprocessing → data processing of analysis and inspection results
2. What are the principles of sampling?
(1) When sampling, attention must be paid to the production date, batch number, representativeness and uniformity of the sample; the sampling quantity should reflect the hygienic quality of the food and the sample size requirements of the inspection items, and should be made in triplicate for inspection, re-inspection and backup. Each serving should not be less than 0.5kg
(2) The container holding the sample must not contain the substance to be tested and interfering substances; all sampling tools must be clean, dry, and odor-free; all harmful substances or interfering substances should be prevented from being brought into the sample before inspection
(3) Fill in the sampling record carefully. Indicate the sampling unit, address, date, sample batch number, sampling conditions, packaging conditions, sampling quantity, on-site sanitary conditions, transportation, storage conditions, appearance, inspection items and sampler, etc.
(4) After sampling, it should be quickly sent to the laboratory for inspection within 4 hours. Try to avoid changes in the sample before sight and keep it in its original physical and chemical state. There should be no contamination or deterioration, escape of ingredients, increase or decrease in moisture, or influence of enzymes before inspection.
3. What are the steps for sampling?
Batch of food to be inspected (sampling) → original sample (mixed, processed and divided) → average sample → duplicate sample
Check samples and keep samples
4. What are the samples and processing methods?
Organic matter destruction method (dry ashing, wet ashing), distillation method normal pressure distillation, vacuum distillation, steam distillation), solvent extraction method (solution chromatography, soaking method), salting out method chemical separation method ( Sulfation and saponification method, precipitation separation method, masking method), chromatographic separation method (adsorption chromatography separation, distribution chromatography separation, ion exchange chromatography separation) concentration method (normal pressure concentration method, vacuum concentration method)
5. Data processing methods
Example: 0.0121+25.04+1.05782=? The number of digits in the result is calculated based on the smallest number of digits after the decimal point.
0.0121*5.64*1.06=? The result is calculated with the least significant digits
Chapter 3 Food Sensory Testing
1. What does food sensory evaluation include?
Taste evaluation Smell evaluation Visual evaluation Hearing evaluation Tactile evaluation Mouthfeel evaluation
2. What are the evaluation indicators for food analysis methods? Three degrees: precision, accuracy, sensitivity
Chapter 4 Analysis of General Ingredients in Food
1. Determination methods of moisture in food: direct drying method, reduced pressure drying method, infrared drying method, Karl Fischer method, distillation method, conductivity method, near-infrared spectrophotometry, gas chromatography, microwave oven method
(1) Direct drying method
Calculation: X=m1-m2/m1-m3
In the formula: X—moisture content in the sample, g/100g
m1—the mass of the weighing bottle (or evaporating dish plus sea sand, glass rod) and sample, g
m2—the mass of the weighing bottle (or evaporating dish plus sea sand, glass rod) and sample after drying, g
m3—The mass of the weighing bottle (or evaporating dish plus sea sand or glass rod), g
Calculation results retain three significant figures. The absolute difference between two independent measurement results obtained under repeatability conditions shall not exceed 5% of the arithmetic mean.
2. Determination of total ash content
Calculation: X=m1-m2/m3-m2
In the formula: X—ash content in the sample, g/100g
m1—crucible and ash content, g
m2—mass of crucible, g
m3—mass of crucible and sample, g
Calculation results retain three significant figures. The absolute difference between two independent measurement results obtained under repeatability conditions shall not exceed 5% of the arithmetic mean.
3. Methods to accelerate ashing: change the operating method
Add ashing aids: nitric acid, ethanol, ammonium carbonate, hydrogen peroxide. These substances disappear completely after burning and do not increase the quality of residual ash.
Add inert insoluble substances such as magnesium oxide and calcium carbonate
4. Classification of acidity: total acidity (referring to the total amount of all acidic substances in food), effective acidity (referring to the activity of hydrogen ions in the ionic state in food), volatile acidity (referring to volatile organic acids in food)
5. Determination of total acidity
Principle: RCOOH+NaOH→RCOONa+water
Using phenolphthalein as the indicator, titrate until the solution turns light red and does not fade for 30 seconds as the titration end point. According to the consumed standard solution
The amount of liquid, calculate the total acidity content in the sample
6. Determination of volatile acidity—direct method
7. Determination of effective acidity (pH value) - potentiometric method (indicating electrode: glass electrode; reference electrode: calomel electrode)
8. Classification of fats: vegetable oils (unsaturated fatty acids and essential fatty acids) and animal oils (saturated fatty acids)
9. Method for measuring fat:
Soxhlet extraction method (crude fat: after the sample is extracted with a solvent such as anhydrous ether or petroleum ether, only the fat in the sample enters the solvent, and the residual substance obtained by evaporating the solvent is called crude fat), acid hydrolysis method, Alkaline hydrolysis method, saponification method, Luozi-Gothrie method, Babcock's method, chloroform-methanol extraction method
Chloroform-methanol extraction method: This method is suitable for samples with a high ratio of bound lipids, especially fish, shellfish, eggs, meat, poultry and their products that contain a lot of phospholipids. The remaining lipids were extracted with petroleum ether.
10. What are reducing sugars? Glucose, fructose, lactose, maltose
10. What do non-reducing sugars include? Disaccharides, trisaccharides, polysaccharides
11. Determination of reducing sugars: direct titration method (Fehling's method), potassium permanganate titration method
Direct titration (Fehling's method)
Calculation: A
X= *100
M*V/250*1000
In the formula:
A—Alkaline copper tartrate solution (half and half solutions A and B) is equivalent to the mass of reducing sugar, mg
V—average volume of sample solution consumed during measurement, ml
m—mass (or volume) of the sample, g (ml)
250—Total volume of sample solution, ml calculation result expressed to one decimal place
Calculation: X1=(V-V0)*c*71.54
In the formula: X1—The mass of reducing sugar in the sample is equivalent to the mass of cuprous oxide, mg
V—The volume of potassium permanganate standard solution consumed by the sample solution for determination, ml
V0—the volume of potassium permanganate standard solution consumed by the blank test, ml
c—Concentration of potassium permanganate standard solution, mol/L
71.54-1ml potassium permanganate standard solution [c(1/5KMno4)=0.1000mol/L] is equivalent to the mass of cuprous oxide, mg
According to the mass of cuprous oxide calculated from the above formula, look up the table and then calculate the content of reducing sugar in the sample.
X2=m1/(m2*(V1/250)*1000)*100
In the formula: X2 - reducing sugar content in the sample, g/100g
m1—Look up the table to get the mass of reducing sugar, mg
m2—sample mass, g
V1—volume of sample liquid for measurement, m1
250—Total volume after sample processing, ml
Calculation results retain three significant figures
12. Determination principle of total sugar: The sample is treated to remove impurities such as protein, dilute hydrochloric acid is added to hydrolyze sucrose into reducing sugar under heating conditions, and then the total amount of reducing sugar in the sample after hydrolysis is measured by direct titration.
Direct titration calculation: X=p/[m*(50/V1)*(V2/100)*1000]*100
In the formula:
p—10ml alkaline copper tartrate is equivalent to the mass of invert sugar, mg
V1—total volume of sample treatment solution, ml
V2—volume of sample hydrolyzate consumed during measurement, ml
m—sample mass, g
13. The extraction agent used in the determination of starch is calcium oxide.
14. Determination and calculation of insoluble dietary fiber:
X=(m2-m1)/m*100
In the formula: X—insoluble dietary fiber content in the sample, g/100g or g/100ml
m1—aluminum futures price glass wool quality, g
m2—Filter plus glass wool and mass of fiber in the sample, g
m—mass of the sample, g
15. Determination methods of protein and amino acid content
Protein: Kjeldahl method, acetylacetone and formaldehyde spectrophotometer method, biuret spectrophotometer method, dye binding spectrophotometer method, salicylic acid colorimetric method, phenol reagent method, fluorescence method
Amino acids: acid-base titration (double indicator titration, potentiometric titration), ninhydrin colorimetry
16. Why does the Kjeldahl method measure crude protein? The Kjeldahl nitrogen determination method can be used to determine the protein content of all animal and plant foods, but the sample often contains non-protein nitrogen-containing compounds such as nucleic acids, alkaloids, nitrogen-containing lipids, porphyrins, and nitrogen-containing pigments. , so the measurement result becomes the crude protein content
17. What is the role of adding copper sulfate and potassium sulfate in the Kjeldahl nitrogen determination method? What are absorbents?
Copper sulfate serves as a catalyst to increase the reaction rate; potassium sulfate can increase the reaction temperature. The absorbent is boric acid
18. What is the principle of determining protein content by biuret method?
In alkaline solution, diuretic can form a purple-red complex with copper ions. This reaction is called diuretic reaction. Peptide bonds in protein molecules can also undergo a double urethane reaction with copper ions. The purple-red depth of the solution is proportional to the protein content within a certain range, and the second is related to the amino acid composition and molecular mass of the protein.
19. Vitamins are divided into two categories: one is fat-soluble vitamins, including vitamin A, vitamin D, and vitamin E; the other is water-soluble vitamins, including B vitamins and vitamin C.
20 Vitamin determination methods: colorimetry, UV spectrophotometry, high performance liquid chromatography, gas chromatography, fluorescence method
21. Determination method of vitamin A: high performance liquid chromatography, colorimetric method
22. Antimony trichloride colorimetry
Principle: Vitamin A interacts with antimony trichloride in chloroform to generate a blue substance, the color depth of which is proportional to the content of vitamin A. Although the blue substance is unstable, it can be compared at a wavelength of 620nm within a certain period of time. color determination
Instruments: Spectrophotometer, reflux condensation device
Reagents: Anhydrous sodium sulfate, acetic anhydride, diethyl ether, anhydrous ethanol, chloroform 250g/L antimony trichloride-chloroform solution 50% hydrogen
Potassium oxide solution VA or retinyl acetate standard solution
23. Determination of β-carotene: high performance liquid chromatography. Developing agent in chromatography: petroleum ether
24. Determination of total ascorbic acid (vitamin C) - 2,4-dinitrophenylhydrazine colorimetric method
Principle: Total ascorbic acid includes reduced, dehydrogenated and disaccharide gululonic acid. Use acid-treated activated carbon to oxidize reduced ascorbic acid to dehydroascorbic acid, and then continue to oxidize it to diketogululonic acid, which then reacts with 2,4-dinitrophenylhydrazine to form red azidine. According to The content of chlorine in the sulfuric acid solution is directly proportional to the ascorbic acid content, and colorimetric quantification is performed.
Calculation: X=Cv/m*F*(100/1000)
In the formula: X—the total ascorbic acid content in the sample, mg/100g
c—Concentration of total ascorbic acid in the sample oxidation solution obtained from the standard curve or calculated from the regression equation, micrograms/ml
V—the volume of the sample brought to volume with 10g/L oxalic acid solution, ml
F—Dilution factor during oxidation treatment of type sample
m—mass of the sample, g
Chapter 6 Testing of Common Food Additives
1. Determination of nitrite - naphthylethylenediamine hydrochloride method (P207)
Principle: After protein precipitation and fat removal from the sample, nitrite and p-aminobenzene sulfonic acid are diazotized under weakly acidic conditions to produce a diazonium salt. This diazonium salt is then coupled with the coupling reagent (naphthylethylenediamine hydrochloride). A purple-red dye is formed, and its maximum absorption wavelength is 550nm. Measure its absorbance and compare it quantitatively with the standard.
Calculation: The sodium nitrite content in the sample is calculated according to the following formula
X=1000m2/[m1*(V2/V1)*1000]
Where: X—nitrite content in the sample, mg/kg
m2—Nitrite content in poplar for determination, micrograms
m1—mass of the sample, g
V2—volume of sample solution for determination, ml
V1—Total volume of sample processing solution, ml
2. Determination of nitrate
Principle: After the protein is precipitated and the fat is removed from the sample, the sample extract is passed through a cadmium column to remove the nitrate in it.
Reduced to nitrite ions. Under weakly acidic conditions, after diazotization of nitrite and p-aminobenzene sulfonic acid,
It is coupled with naphthylethylenediamine hydrochloride to form a red dye, and the total amount of nitrite is measured. According to the measured nitrite before and after reduction,
The change in the amount of salt can be used to determine the nitrate content
Chapter 7 Detection of Toxic and Harmful Elements in Food
1. Toxic and harmful elements frequently measured in food: lead, cadmium, mercury, arsenic, fluorine, aluminum, tin
2. Determination methods for lead: graphite furnace atomic absorption spectrometry, flame atomic absorption spectrometry, dithizone spectrophotometry
3. Determination methods of cadmium: graphite furnace atomic absorption spectrometry, flame atomic absorption spectrometry, 6-bromobenzothiazole azonaphthol spectrophotometry,
4. Mercury determination methods: cold atomic absorption spectrometry, dithizone spectrophotometry
5. Determination methods of arsenic: silver salt method, arsenic spot method
6. Determination methods of pesticides: colorimetric method, spectrophotometric method, electrochemical analysis method
7. The relative density of emulsion decreases with the increase of temperature; the weight of sugar decreases with the increase of temperature (1 degree of weight = 1/1000 g/ml; 1.000+31.2/1000=1.0312g/ml)
Design experiment 1. Amino acid nitrogen content in vegetables
2. Content of total acidic substances in vegetables