Quality standard of raw milk from farm
This standard is applicable to the inspection and rating of purchased fresh milk.
1 definition
1. 1 purchased fresh milk: purchased fresh milk refers to the constant milk squeezed from the breasts of healthy cows that are normally raised, free from infectious diseases and mastitis.
2. Quality requirements for purchasing fresh milk
2. 1 physical and chemical indicators
Physical and chemical indicators are only qualified indicators, without grading, as shown in table 1.
Item 1 in the table refers to standard fat,% ≥ 3. 10 protein,% ≥ 2.95 density (20℃/4℃) ≥ 1.0280 acidity (expressed by lactic acid),% ≤ 0. 162 impurity degree.
Normal milk should be milky white or yellowish, should not contain foreign bodies visible to the naked eye, and should not have red, green or other different colors. No bitter, salty, astringent and other abnormal smells such as feed, silage and mold.
2.3 bacterial indicators
There are two indicators of bacteria in milk, each of which can be used. Calculate and evaluate the total number of bacteria in the plate according to the classification index of the total number of bacteria per milliliter in Table 2. According to the fading time grading index in Table 8, methylene blue reduction fading method is used for grading. Only one of them can be used, and they cannot be duplicated.
Classification in Table 2, classification index of the total number of bacteria on the first-class plate, 10000/ml Ⅰ≤ 50 Ⅱ≤100 Ⅲ≤ 200 Ⅳ≤ 400, classification index of the first-class methylene blue fading time Ⅰ≥ 4hii≥ 2.5hiii.
3. 1 milk sampling method
3. 1. 1 Scope of application: This law describes the method of sampling raw milk and sterilized milk from large or small containers.
3. 1.2 stipulates that sampling must be conducted by a recognized agent with certain technology. The agent must be free from infectious diseases. The sample shall be accompanied by a report signed by the person in charge of sampling. The report shall record in detail the sampling place, milk type, owner, date and time, names and positions of the sampler and participants, and if necessary, it shall also include the packaging form, atmospheric temperature, humidity, sterilization method of sampling instruments, whether preservatives are added to the sample and relevant special circumstances.
3. 1.3 Each sample must be labeled and sealed, and the weight of the sample should be indicated if necessary. Samples must be sent to the laboratory for inspection within 24 hours after collection. Samples for testing bacteria should be collected at 4℃
3. 1.4 All sampling instruments and sample containers used for chemical analysis must be clean and dry. Sampling instruments used for bacterial inspection must be cleaned and sterilized, and the sterilization method should be different according to containers made of different materials.
3. 1.4. 1 Store in hot air at 170℃ for 2 hours (better under aseptic conditions).
3. Keep1.4.2 in steam (pressure cooker) at 120℃ for 15 ~ 20min (preferably aseptic storage).
3. 1.4.3 Soak in 100℃ boiling water 1 min (use the appliance immediately).
3. 1.4.4 Soak in 70% alcohol, and burn the alcohol with flame before use.
The sampling container should be made of glass, stainless steel and some plastic products, and be tightly covered with suitable rubber plugs, plastic plugs or screw plugs. When using a rubber stopper, the container must be covered with a non-adsorbed odorless substance (such as a certain plastic) or a suitable plastic bag must be used.
3. 1.5 Small containers shall be sampled with the contents of sealed containers as samples. Fresh milk samples used for chemical analysis can be added with appropriate amount of preservatives that have no influence on the analysis, and indicated in the label and report. Preservatives are not allowed to be used in samples used for bacterial and sensory inspection, but they must be kept in a refrigerated container at 0 ~ 5℃, and the temperature shall not exceed 10℃ during transportation, and direct sunlight must be avoided.
3. 1.6 Before sampling in large containers, it should be continuously stirred up and down for more than 25 times until it is fully mixed, and then directly sampled with a long-handled spoon.
3. 1.7 Before inspection, all raw milk and sterilized milk samples should be heated to 40℃ after being taken out of the cold storage, shaken violently up and down to completely melt and mix the internal fat, and then cooled to 20℃.
3.2 Determination of fat content in milk
Methods and treatment
According to Rose-Guttery's milk fat determination method, a certain amount of milk is dissolved in ammonia-containing ethanol solution, and the fat is extracted with ether and petroleum ether, and then the solvent is evaporated, and the residual substances are weighed to determine the weight of milk fat.
Reagents and solutions
3.2.2. 1 ammonia (GB 63 1-77).
3.2.2.2 95% ethanol (GB 679-80).
3.2.2.3 ether (Hg 3- 1002-76) and petroleum ether (Hg 3-1003-76)1:1mixed solution.
Instruments and equipment
3.2.3. 1 chemical equilibrium: sensitivity 0. 1mg.
3.2.3.2 extraction tube: there are frosted glass plugs, cork plugs or plugs that have no corrosive pollution to the solvent used. When using a cork, first use ether and then use petroleum ether to treat the cork, and then place it at 60℃ or 60℃
3.2.3.3 flask: 250ml or150ml.
3.2.3.4 oven: it can be adjusted to102 2℃ for use.
3.2.3.5 electric heating plate: equipped with safety device.
operational approach
3.2.4. 1 sample preparation: treat the sample according to 3. 1.7, but don't shake it so hard that the milk bubbles and the butter and fat stir.
3.2.4.2 blank test: When determining the fat content of the sample, use the same extraction tube and the same amount of reagent, and use 10ml distilled water as a blank test. When the blank test value exceeds 0.5mg, check the reagent used and replace the impure reagent.
3.2.4.3 put the flask in a drying oven and heated it for 0.5 ~ 65438+/-0h (then put the pumice used to remove the solvent), and weighed it when the flask was cooled to the temperature of the balance room.
3.2.4.4 immediately put the fully mixed sample 10 ~ 1 1g into the extraction tube and directly weigh it on the balance or weigh its weight difference. Then add 25% ammonia solution 1.5 ml or corresponding amount of ammonia solution with known higher concentration, and mix thoroughly. Add 10ml ethanol into the non-plug container, slowly and fully mix the liquid, add 25ml ether, tightly plug the container, vigorously shake 1 ~ 2 min, and cool. If necessary, cool it in tap water. Carefully remove the plug, add 25ml petroleum ether and shake for 0.5 ~15min. Let the container stand for about 30 minutes until the upper layer becomes transparent and clearly separated from the water layer. Remove the plug, wash the plug and the inner wall of the container mouth with several milliliters of mixed solvent,
All the washing liquid is poured into the container. Carefully transfer as much supernatant as possible to the flask with a pipette or siphon.
Note: When the siphon is not used for pipetting, a small amount of water must be added to raise the interface between the two layers to facilitate dumping.
Clean the inner and outer walls of the container mouth or the lower part of the front end of the siphon with a few milliliters of mixed solvent. The washing liquid for cleaning the outer wall of the container flows into the flask, while the washing liquid for cleaning the inner wall of the nozzle and siphon flows into the extraction bottle.
3.2.4.5 repeated the above operations with15ml ether and15ml petroleum ether for the second extraction. Repeat the above operation for the third extraction, only omitting the last washing process.
3.2.4.6 should pay attention to evaporating or distilling solvents (including ethanol) as much as possible. When the capacity of the flask is small, it is necessary to remove a part of the extracted solvent by the above method. If the smell of the solvent has disappeared, put the flask side into a drying oven and heat it for 65438±0h hours, then cool it to room temperature, weigh it, and bake it repeatedly until the weight is constant. If the extract is insoluble or controversial, repeatedly add petroleum ether and slowly heat and shake it to completely extract the fat in the flask. At this point, the insoluble matter should be precipitated before dumping, and the outer wall of the bottle mouth should be washed three times. As mentioned above, the flask was placed horizontally in the drying furnace, heated for 65438+/-0h, and then cooled to the temperature of the balance room. After weighing, the weight of fat is expressed as the difference between the weight of 3.2.4.6 and the final weight.
3.2.5 Calculation
Calculate the fat content of the sample according to the formula (1). f(%)= a/w× 100…… 1
Where: f refers to the fat content of the sample,%;
A-fat weight, g;
W—— sample weight, g
For100g milk, the difference between the two parallel determination results is less than 0.03g..
3.3 Determination of protein Content in Milk
3.3. 1 method principle
The content of nitrogen in milk was determined by semi-micro Kjeldahl method, and the content of protein in milk was calculated (%).
Reagents and solutions
3.3.2. 1 hydrochloric acid (GB 622-77): 0.05n standard solution.
3.3.2.2 sodium hydroxide (GB 629-81): saturated solution.
3.3.2.3 boric acid (GB 628-78): 2% solution.
3.3.2.4 mixed catalyst: anhydrous potassium sulfate or sodium sulfate, copper sulfate and selenium in the weight ratio of100:10: 2.
3.3.2.5 mixed indicator: 0.2% methyl red and 0. 1% methylene blue are mixed in equal volume.
Instruments and equipment
3.3.3. 1 electric furnace: 1 ~ 2 sets of adjustable electric furnaces with supporting frames.
3.3.3.2 Kjeldahl flask: 250 ml.
3.3.3.3 semi-micro Kjeldahl nitrogen determinator.
3.3.3.4 volumetric flask: 100 ml.
operate
3.3.4. 1 in a clean kjeldahl flask, add about 2g of catalyst, and then suck it with a 10ml pipette.
3.3.4.2 put the Kjeldahl flask with reagent into the adjustable electric furnace in the fume hood, first heated it with low fire, and then increased the firepower until white smoke came out, until the solution in the flask became transparent blue, and then continued to heat it for about 20 ~ 30 min.
3.3.4.3 moved the cooled solution into a 100ml volumetric flask, washed the Kjeldahl flask repeatedly with distilled water for 5 ~ 6 times, and poured all the washing liquid into the volumetric flask. Finally, when the liquid temperature is 20℃, the volume is 100ml.
3.3.4.4 distillation: suck 10ml sample from volumetric flask, put it into the reaction chamber of semi-micro Kjeldahl nitrogen determinator, add about 4ml saturated sodium hydroxide, loosen the steam pipe clamp, the sample reacts with saturated sodium hydroxide under the action of introduced hot steam, add NH3, cool it by cooling tube, and flow into the receiving cup containing 2% boric acid solution to become NH4HB4O7. Make the original purplish-red boric acid solution (with a proper amount of mixed indicator) turn into light apple green until the solution in the boric acid receiving cup increases to about 30ml, then remove the receiving cup, and at the same time rinse the residual droplets at the end of the cooling tube (immersed in the receiving cup) into the receiving cup with a small amount of distilled water.
3.3.4.5 titration: titrate the liquid in the receiving cup with 0.05N hydrochloric acid standard solution until it appears reddish purple, and read it.
Calculate the number of milliliters of hydrochloric acid consumed.
Results and calculations
CP(%)=(n×v×0.0 14×6.38/(w×( 10/ 100))× 100× 100……………………(2)
Where: CP-protein content,%;
N-equivalent concentration of hydrochloric acid;
V—— the volume of hydrochloric acid standard solution consumed by titration, ml;
0.0 14- 1.0 ml equivalent hydrochloric acid solution is equivalent to 0.0 14 g nitrogen;
6.38—— Convert the nitrogen content in milk into the converted value of protein quality;
W-weight of milk sample, g
3.4 Determination of milk density
3.4. 1 instruments and equipment
Thermometer: 0 ~100℃;
Milk Densitometer (milk consistency meter): 20℃/4℃;
Measuring cylinder: 250ml, the diameter should be such that the distance between the periphery of the milk consistency meter and the inner wall of the measuring cylinder is not less than 0.5cm when it sinks into the milk consistency.
operate
Heat the milk sample to 40℃, shake it upside down, mix it evenly, cool it to about 20℃ (10 ~ 25℃), and carefully inject it into a glass measuring cylinder with a height greater than the length of the densimeter and a volume of about 250ml until it reaches 3/4 of the volume of the measuring cylinder. When injecting milk, milk should be prevented from foaming. When putting milk into the measuring cylinder, you should hold the upper part of the measuring cylinder, carefully sink it into the milk in the measuring cylinder and let it float freely to avoid contact with the wall of the measuring cylinder. After the isotropy instrument is allowed to stand for 2 ~ 3min, aim the eyes at the height of the latex surface in the cylinder. Because the contact between the milk surface and the milk thickener forms a crescent shape, the height of the milk thickener at the apex of the crescent surface is the density value.
Representation of results
The milk consistency meter used should be expressed as the value at 20℃. Therefore, if the milk sample has another temperature, the temperature difference must be corrected. When the temperature is 1℃ higher than 20℃, it is necessary to add 0.2 to the calculated milk consistency or 0.0002 to the density value; However, when the temperature is lower than 1℃ of 20℃, it is necessary to subtract 0.2 from the obtained milk consistency meter or 0.0002 from the density value. If it is an old densimeter, the standard is made at 15℃/ 15℃, and must be measured and read at the same temperature as 15℃. This density value is 0.002 higher than that obtained by measuring milk with a densimeter with a scale of 20℃/4℃ at 20℃, and 2 higher than the reading of the latter.
3.5 Determination of milk acidity
3.5. 1 reagents and solutions
3.5. 1. 1.95% ethanol (GB 679-80): 0.5% neutral phenolphthalein solution.
3.5. 1.2 sodium hydroxide (GB 629—8 1) (carbonate-free): 1/9N solution.
3.5. 1.3 glacial acetic acid (GB 676-78).
3.5. 1.4 rosaniline acetate concentrated solution: weigh 0. 12g rosaniline acetate, gradually add 50ml of 95% ethanol (including 0.5ml of glacial acetic acid), and then add 95% ethanol to dilute to100ml.
3.5. 1.5 dilute solution of rosaniline acetate: absorb 1ml of the above solution and dilute it with 1: 1 distilled water to 95% ethanol solution and dilute it to 500ml. The above two solutions should be kept in small brown bottles in a cool place and plugged with rubber stoppers.
3.5. 1.6 phenolphthalein (HGB3039-59): Preparation of 0.5% neutral solution: dissolve 1g phenolphthalein in 165438+200ml 95% ethanol, add 80ml distilled water, and then use about 0./kloc drop by drop.
Instruments and equipment
3.5.2. 1 acid burette and alkaline burette: each 10ml.
3.5.2.2 volumetric flask: 100ml, 500ml.
operate
Take two 10ml milk through a straw, and put them into two 50ml triangular bottles respectively, and add 1ml diluted rosaniline acetate solution into one bottle as a color control; Add 1ml phenolphthalein solution into another bottle, then quickly add 1/9N sodium hydroxide solution 1ml from the dropper, and then continue to add it drop by drop, without stopping shaking until the color is the same as the light magenta in the control bottle. The total titration time should be about 20s. Titration is best carried out in sunlight. If it is done at night, it must be illuminated by fluorescent lamps. If the color of rosaniline is not used as a control, the titration end point can be determined after the milk sample appears light magenta and can be kept for 5 seconds.
Representation of results
Grams of lactic acid per 100ml of milk = ml of 1/9N sodium hydroxide solution consumed when titrating 10ml of milk ÷ 10 (the gram molecular weight of lactic acid is set to 90).
Grams of lactic acid per 100ml milk sample can also be used as = milk sample acidity T×0.009(0.009 is the conversion coefficient of lactic acid, that is, 1ml0. 1N sodium hydroxide is equivalent to 0.009g lactic acid).
Note: "T" titration of milk: Take 10ml of milk to be tested, add 20ml of distilled water, add1.5ml of 0.5% neutral phenolphthalein solution, and titrate with 0. 1N sodium hydroxide standard solution until the solution is light magenta, which does not disappear within 30s, and consumes 0./kloc-. The difference between the results of two parallel tests shall not be greater than 0.5 t.
You can also use alcohol test to quickly judge the freshness of the purchased raw milk. The alcohol test method is to mix 1 ~ 2ml neutral alcohol with milk in a test tube, and shake the milk sample without floc to meet the following acidity standards. Milk with floc is positive in alcohol test, which indicates that its acidity is high. The test temperature is 20℃.
The acidity of floc will not appear in the thick and thick wine.
Less than 68 20 tons
Below 70 19 t
Below 72 18 t
3.6 Determination of impurity degree of milk
3.6. 1 method principle
A quantitative milk sample is filtered by a cotton filter plate with a certain size, and the concentration of impurities in the milk sample can be measured by comparing the color of impurity precipitation with the standard color plates with different impurity precipitation amounts.
Instruments and equipment
3.6.2. 1 cotton filter plate: 32mm in diameter.
3.6.2.2 air pump: 368W.
3.6.2.3 standard shade guide: 28.6 mm in diameter.
operate
Take 500ml milk sample, heat it to 60℃ and filter it on cotton filter plate. In order to speed up the filtration, vacuum pump can be used for suction filtration, and the milk attached to the filter plate can be washed clean with water. After the filter plate is dried in the oven, the quality of impurities on the filter plate can be obtained by comparing it with the standard colorimetric plate.
Representation of results
According to the milligrams of impurities in every 500ml of milk represented by the selected standard shade guide closest to the color of cotton filter plate, the milligrams of impurities in every 500ml of milk sample can be read out. If you multiply this number by 2, you can get the concentration (ppm) of impurities in the milk sample or the number of milligrams of impurities per kilogram.
3.7 Determination of Mercury in Milk
The determination of mercury in milk is carried out according to GB 5009. 1 ~ GB 5009.70-85 "Physical and chemical part of food hygiene inspection method".
3.8 Determination of BHC and DDT residues in milk
HCH and DDT residues in milk were determined according to GB 5009. 1 ~ 5009.70-85.
3.9 Determination of Total Bacteria in Milk
The total number of bacteria in milk was determined according to GB 4789. 1 ~ 4789.28-84 "Microbiology part of food hygiene inspection methods".
3. 10 Reduction Fading Test of Milk Methylene Blue
3. 10. 1 definition
The hygienic quality of milk in this method includes the concentration and metabolic intensity of bacteria and the time required for somatic cell metabolism to consume a certain amount.
3. 10.2 method principle
The greater the concentration of microorganisms and somatic cells, the more vigorous the metabolism, the more oxygen consumption per unit time, and the shorter the reduction fading time of methylene blue. On the contrary, the fading time of methylene blue is correspondingly longer. A certain amount of methylene blue was added to a certain volume of milk, covered with a small amount of sterilized liquid paraffin, isolated from external oxygen, and stood in a water bath at 38℃ to observe the fading time of methylene blue.
3. 10.3 reagent
Preparation of Meilan solution: Weigh 4.9ml of analytically pure methylene blue, add part of distilled water to a constant volume bottle of 100ml to make it completely dissolve, then fix the volume to 100ml, plug the bottle cap and put it in the refrigerator for later use. The service life is 14 days.
Liquid paraffin (analytically pure) must be boiled for 30 minutes before use.
3. 10.4 instruments and equipment
Analytical balance: sensitivity 0.1mg;
Constant temperature tank (internal height not less than 21cm);
Test tube:18×1.8cm;
Metal test tube rack;
Pipes: 1 and 20ml.
Glassware must be disinfected before use, and absorbent cotton is placed at the upper end of the straw to prevent saliva from entering the sample during operation.
3. 10.5 operation method
Suck 20ml of each milk sample to be tested with a sterile straw, put them into numbered test tubes arranged in sequence on the test tube rack, then add 1 ml methylene blue standard solution to each test tube, cover the nozzle with a small piece of clean sulfuric acid paper, then press it with your thumb, shake it upside down and mix it evenly, and then put it on the test tube rack in sequence. Add a small amount of disinfectant liquid paraffin to the upper part of each test tube for sealing, and then put the test tube together with the pipe rack at 38℃.
3. 10.6 result representation
Hours and minutes are used as time units to indicate the fading time of methylene blue reduction in each sample.
Additional notes:
This standard was put forward by the Ministry of Agriculture, Animal Husbandry and Fisheries of People's Republic of China (PRC) and the Ministry of Health.
This standard was drafted by Animal Husbandry Institute of China Academy of Agricultural Sciences.
Main drafter of this standard: Wang Peng.
Since the implementation of this standard, Appendix A (supplement) of GB 5408-85 "Sterilized Milk" and "General Technical Requirements for Fresh Milk" is invalid.