Determination of raw milk quality

Transcription

1 MILK ~ 1 ~ Determination of raw milk quality Milk evaluation during reception and sampling rules According to PN-A Sample of milk could pick up only authorized person 2. Tools and vessels have to be clean, dry and odorless 3. Vessels should made of glass or plastic with food contact certification DEFINITIONS 1. batch of raw milk the amount of milk supplied by single provider at one time 2. packaging unit of raw milk package of milk delivered to dairy plant : tank, pitcher 3. raw milk sample a quantity of milk picked up from packaging unit of raw milk form one provider 4. general sample combined milk samples picked up proportionally form each package delivered by one provider 5. periodic sample sample given to estimation fat and protein content combined from raw milk sample or general samples collected daily by 14, 15 or 16 days 6. laboratory sample sample picked up form raw milk sample, periodic sample or general sample Milk sampling to physicochemical tests 1. Picking up order to test: - microbiology - counting somatic cells - determination inhibiting compounds - physicochemical 2. Prior to sampling milk has to be mixed 3. Milk samples should be picked up form each packaging unit proofing its place of origin 4. samples for fat and protein content could be treated with preservatives such as: sodium trihydrogen Bronopol, Microtabs, Mlekostat CC 5. Picking up periodic sample: ATTENTION combine succeeding samples from the same provider pouring milk into the same bottle, mixing content and adding preservative according to producer instructions 6. Preserved samples should not be store over 16 days at 0-8 C. Samples without preservative could be store up to 24 hours

2 MILK ~ 2 ~ MILK EVALUATION ACCORDING TO RECEPTION PARAMETERS 1. Package evaluation 2. Evaluation of milk smell and appearance Evaluate milk feature ATTENTION without prior mixing. Define smell immediately after package opening as close to milk surface as possible. Define appearance, observing if there are fat pellets on surface and visible mechanical contaminants 3. Milk temperature measure Measure temperature in each vessel using suitable thermometer or temperature sensor. Glass or mercury thermometers are strictly forbidden. 4. Acidity - freshness of milk evaluation In case of titratable method or ph evaluation pick up 100 ml from each package General requirements Milk should derived from animals: - healthy - free of brucellosis and tuberculosis - free of visible mastitis symptoms Milk can not be supplemented with anything or be taken out something Definition of milk Milk is the normal mammary secretion of milking animals obtained from one or more milkings without either addition to it or extraction from it, intended for consumption as liquid milk or for further processing It is forbidden to deliver or receive milk: - adulterated

3 MILK ~ 3 ~ - from diseased cattle (goats, sheep, buffalos) or during its treatment - after treatment but before the end of used medicines withdrawal time - not later than 3 weeks before calving and not earlier than 6 days after calving - in case of reception ban established by official veterinarian Milk received parameters Appearance self with color with cream-coloured shade without eye visible mechanical contaminants Smell fresh, natural without foreign smell in case of doubt smell evaluation should be repeated after heating up to 80 C and next cooling to room temperature Temperature not higher than 8 C by daily reception or not higher than 6 C in other receipt. Not cooled milk can be receipt not later than 2 hours after milking Acidity freshness of milk - titratable acidity from 6,0 to 7,5 SH - ph measure from 6,6 to 6,8 - alizarol test - corresponding brick-red color with lack of precipitates Detailed milk requirements Features Extra grade Density at 20 C not lower than 1,028 g/l Adulteration by watering down - not accepted freezing point not higher 0,520 C than: Bacteria total count in 1 ml Somatic cells, number in 1 ml Antimicrobial substances not accepted REGULATION (EC) No 853/2004 OF THE EUROPEAN PARLIAMENT AND OF THE COUNCIL of 29 April 2004 laying down specific hygiene rules for on the hygiene of foodstuffs

4 MILK ~ 4 ~ REGULATION (EC) No 854/2004 OF THE EUROPEAN PARLIAMENT AND OF THE COUNCIL of 29 April 2004 laying down specific rules for the organisation of official controls on products of animal origin intended for human consumption REGULATION (EC) No 852/2004 OF THE EUROPEAN PARLIAMENT AND OF THE COUNCIL of 29 April 2004 on the hygiene of foodstuffs Milk density Milk is a very complex food with over different molecular species found. There are many factors that affect the composition of raw milk such as breed, age and physical state of the cow and seasonal variations. Therefore only an approximate milk composition of: 87-88% water 12-13% total solids The total solids consist of approx.: 4% fat 9% solids-not-fat (SNF) (proteins, lactose, minerals, vitamins,... ). Milk is an emulsion of milk fat globules in fat-free milk liquid (mainly water). There are up to 4,6 billions fat globules in one milliliter milk. Density of milk The density of raw milk varies between approx and (average 1,031) g/ml at 20 C Milk density is derived from the densities of its components, according to their content. The following densities of milk components (at 20 C) strongly influence the density of milk: Water g/ml Fat g/ml Proteins g/ml (average) Lactose g/ml (average) Minerals g/ml 2.1. Influences on milk density The density of milk and dairy products depends on: Composition The density of milk increases with increasing content of proteins, lactose or minerals and it decreases with increasing fat content. Density of various dairy products as a function of fat and solids-not-fat (SNF) content

5 MILK ~ 5 ~ Temperature The density of milk decreases, if the temperature increases. The higher the fat content of the milk, the bigger the density changes with temperature. The reason is that the volume of fat changes much more with temperature than the volume of water. Density measurement of milk The density is a relationship between the body mass and the volume this body occupies in the space. The density test is performed in order to be used in the detection of adulteration in the milk: since the addition of water only would cause the decrease in density, whereas the skimming (fat removal) would cause an increased density in the milk, besides supplying important information for the determination of the total dry extract. Materials - Thermolactodensimeter (TLD) - Glass cylinder (250 ml) Method The density determination is accomplished by the thermolactodensimeter because the practicability of this method. Place the sample to be analyzed in the clean and dry cylinder by taking the care of inclining the test tube and allowing the liquid to flow down the walls of the glass for avoiding the incorporation of the air which would reduce the density of the milk. Milk temperature should range from 15 C to 25 C Immerse TDL into the test tube and make it rotate slowly on its own axis; Perform the reading of both density and temperature of the milk, as soon as TDL stabilizes; Proceed to the correction of the influence from the temperature, by using an adequate scale. The result will correspond to the corrected milk density.

6 MILK ~ 6 ~ Immersing degrees of Milk density Temperature during measuring C TLD* Milk density in reference temperature 20 C 25 1,0236 1,0237 1,0239 1,0240 1,0242 1,0244 1,0246 1,0248 1,0250 1,0252 1,0254 1,0255 1, ,0245 1,0247 1,0249 1,0250 1,0252 1,0254 1,0256 1,0258 1,0260 1,0262 1,0264 1,0266 1, ,0254 1,0256 1,0257 1,0259 1,0261 1,0263 1,0265 1,0268 1,0270 1,0272 1,0275 1,0277 1, ,0263 1,0265 1,0266 1,0268 1,0270 1,0273 1,0275 1,0278 1,0280 1,0282 1,0285 1,0287 1, ,0273 1,0275 1,0276 1,0278 1,0280 1,0283 1,0285 1,0288 1,0290 1,0292 1,0295 1,0295 1, ,0283 1,0285 1,0286 1,0288 1,0290 1,0293 1,0295 1,0298 1,0300 1,0302 1,0305 1,0307 1, ,0292 1,0294 1,0296 1, ,0301 1,0303 1,0305 1,0308 1,0310 1,0312 1,0315 1,0317 1, ,0302 1,0304 1,0306 1,0307 1,0310 1,0312 1,0315 1,0318 1,0320 1,0323 1,0325 1,0328 1, ,0311 1,0313 1, ,0320 1,0322 1,0325 1,0328 1,0330 1,0333 1,0335 1,0338 1, ,0321 1,0323 1,0325 1,0327 1,0330 1,0332 1,0335 1,0338 1,0340 1,0343 1,0344 1,0348 1, ,0331 1,0333 1,0335 1,0337 1,0340 1,0342 1,0345 1,0347 1,0350 1,0353 1,0355 1,0358 1, ,0340 1,0343 1,0345 1,0347 1,0349 1,0352 1,0356 1,0357 1,0360 1,0362 1,0365 1,0367 1,0370 * - TLD - thermolactodensimeter Determination of acidity The acidity in milk is measured, for example by titration with a 0.1 n NaOH solution, and indicates the consumption of NaOH necessary to shift the ph-value from 6.6 ± 0.1 (corresponding to fresh milk) to a ph-value of (phenolphthalein). Lactic acid is an organic acid with one carboxylic acid, CH 3 -CHOH-COOH, having a molecular weight of 90. One ml 0.1 n NaOH therefore corresponds to: 90 x 0.1 / 1000 = g of lactic acid If the titration requires e.g ml 0.1 n NaOH, the result is often expressed as: 14.5 x % lactic acid The titratable acidity is expressed as % lactic acid and is determined by titration of a known amount of reconstituted milk with 0.1 N NaOH using phenolphthalein as indicator. Acidity Expressed in SH (Soxhlet-Henkel Degrees) Definition: 1 SH = x ml sodium hydroxide 0.25 M based on 100 ml milk sample Acidity of milk SH - Soxlet Henkel degrees: obtained by titrating 100 ml of milk with 0.25N NaOH, using phenolphthalein as the indicator. This method is common in Central Europe. Th - Thorner degrees: obtained by titrating 100 ml of milk thinned with 2 parts distilled water, with 0.1 N NaOH, using phenolphthalein as an indicator; Used mostly in Sweden and the CIS. D - Dornic degrees: obtained by titrating 100 ml of milk thinned with two parts distilled water, with N/9 NaOH, using phenolphthalein as an indicator. Used mostly in the Netherlands and France. % l.a.- percent lactic acid: obtained as D divided by 100. Frequently used in the UK, USA, Canada, Australia and New Zealand. Taking into account the concentration of sodium hydroxide, the results expressed in one value can be easily converted into any other unit value by consulting this convenient chart NaOH concentration (M) SH Th D % l.a. 0,25 0,1 0,111 0, ,5 2,25 0,0225 0,4 1 0,9 0,009 4/9 10/9 1 0,01

7 MILK ~ 7 ~ Titratable acidity METHOD for milk Add to a conical flask 50 ml of yogurt or kefir and 2 ml phenolphthalein solution mix well and titrate with 0.25 M NaOH until a faint pink colour persists for 30 sec. Acidity express in SH (Soxhlet-Henkel degrees) Counting: Acidity is counting according to equation: SH = volume of used 0.25 M NaOH (counted in ml) 2 Acidity Fresh milk 6,5-7,5 o SH (could lower during mastitis) acidity 8-9 o SH slighty acidified acidity o SH stronger acidified acidity o SH coagulate in room temperature METHOD for yogurt or kefir Add to a conical flask 10 ml of yogurt or kefir, add 20 ml water, mix well and titrate with 0.1 M NaOH until a faint pink colour persists for 30 sec using phenolphthalein as indicator. Acidity express in SH (Soxhlet-Henkel degrees) Counting: Acidity is counting according to equation: SH = volume of used 0.1 M NaOH (counted in ml) 2 Acidity of dairy products: Product Raw cow milk Raw goat milk Raw sheep milk UHT milk Drinking and set cow yogurt Drinking and set sheep yogurt Sour Cream Test with alizarol Method reagent: saturated solution of alizarine in 70% ethyl alcohol SH 7.6 SH 7,6 SH 12 SH 7,5 SH 55 SH 65 SH 64 SH Add 1mL of milk and 1mL of saturated solution of alizarol into test tube Mix carefully Evaluate color comparing to pattern. Observe eventually present precipitates

8 MILK ~ 8 ~ Evaluation: Degree I milk with to low acidity (not for reception) ban II fresh milk (could be received) III milk with to high acidity (not for reception) ban ph violet-red ph 6,6-6,8 III violet and brick color over ph 6,8 ph 6,5 brown red to yellow below ph 6,55 presence of precipitates causes milk unsuitable to receipt Determination with ph meters ph Measurements 1. Rinse the electrode in water. Remove water form electrode. 2. Place the electrode in your sample. 3. Wait a while. 4. Read ph from display 5. Record milk ph value in notebook I II ph 6,9 ph 6,6 ph 6,7 ph 6,8 Alcohol test The alcohol test is used on fresh milk to indicate whether it will coagulate on processing. Milk that contains more than 0.21 % acid, or calcium and magnesium compounds in greater than normal amounts, will coagulate when alcohol is added. Apparatus Ordinary 15 cm test tubes. Test-tube stand Reagents - 75% ethyl alcohol solution Procedure 1. Put equal volumes of milk and 75% alcohol in a test tube. The best amount is 2mL 2. Invert the test tube several times with the thumb held tightly over the open end of the tube. 3. Examine the tube to determine whether the milk has coagulated: if it has, fine particles of curd will be visible Interpretation Single test milk : alcohol = 1:1 Fine particles of curd are visible at acidity higher than 10 SH Double test milk : alcohol = 1:2 Fine particles of curd are visible at acidity higher than 8 SH