Dairy and product testing

Identification method for dairy products: 1. Normal color milk: fat globules casein colloidal particles - irregular reflection (scattering) of sunlight, appearing white; Fat-soluble carotene and lutein - light yellow; Water-soluble riboflavin, present in whey - fluorescent yellow green. Abnormal milky red - inflammation; Yellow - Colostrum (thick); Turning red or blue - The refractive index of bacterial contaminated milk is 1.344-1.348, which is proportional to the content of milk solids, and can be used to determine whether milk is watered Taste and Flavor Normal Milk Flavor: Contains volatile fatty acids and other volatile substances to form a normal taste. Taste: Fat globules casein colloidal particles, soft and mellow. Taste: Na+, CL - salty, Mg++, Ca++bitter, citric acid -, PO4- sour, lactose sweet, abnormal milk flavor. Weak milk flavor: heat treated cow manure flavor, feed flavor, metal flavor, caramel flavor When the specific gravity (relative density) is 15 ℃, the average specific gravity of normal milk is 1.032, and the relative density of skimmed milk is 1.037. The relative density of milk is the lowest within 1 hour after milking, and gradually increases. The volume changes due to gas escape, protein hydration, and fat coagulation should not be tested immediately after milking. Specific gravity inspection term: specific gravity 32 degrees (1.032) 4 Thermodynamic properties: The freezing point is generally -0.525-0.565 ℃, with an average of -0.540 ℃. Lactose and salts are the main factors leading to the decrease in freezing point. Normal milk has very little change in lactose and salt content. The following formula can be used to calculate the amount of water added based on the change in freezing point: W=(T-T ') * (100-TS)/T, where W - the amount of water added (%); T - Normal milk freezing point; T '- freezing point of the tested milk; TS - percentage of milk solids in the tested milk; For every 10% addition of water, the freezing point of rancid milk will increase by approximately 0.054 degrees Celsius, and the freezing point will decrease. Therefore, the determination of the freezing point must require the acidity of milk to be within 20 ° T. The boiling point of milk at 101.33kPa (1 atmospheric pressure) is 100.55 ℃. The boiling point of milk is affected by its solid content. When concentrated to half the original volume, the boiling point rises to 101.05 ℃. The specific heat of milk is the sum of the ratios of its various components, which is 3.89 milk protein 2.09, milk fat 2.09, lactose 1.25, salts 2.93, and water 4.187. It is commonly used for heating and cooling calculations in dairy production Electrical properties Conductivity: Na+, CL - ↑ (lactose ↓) → Conductivity ↑ Generally ranging from 0.003 to 0.005 S/m, exceeding 0.006 S/m is considered abnormal milk [mastitis milk (high chlorose value), doped with electrolytes] Fat hinders ion movement, skim milk> Whole milk redox potential: Vb2, Vc, Ve, enzymes, microbial metabolites, dissolved oxygen+0.23-0.25VEh ↑: high valent metal ions Eh ↓: heating; Microbial contamination 6. When the surface tension is 0.04-0.06N/cm at 20 ℃, identify whether other additives are mixed in the milk, increase the temperature ↑, and the surface tension ↓; Fat content ↑, surface tension ↓; Homogenization treatment, surface area of fat globules ↑, surface tension ↑; Fat is hydrolyzed by lipase, with surface tension ↓; 7. The viscosity of milk at 20 ℃ is 0.0015-0.0002Pa · s, which is inversely proportional to temperature. Factors affecting viscosity: casein> Fat> Albumin becomes too sticky and thickened; Insufficient viscosity, fat floating, and sugar precipitation. 8. Acidity unit: Jier Niel's degree (° T). Definition of ° T (titration acidity): Using phenolphthalein as an indicator, neutralize the milliliters of 0.1mol/L NaOH solution consumed in 100ml of milk. The acidity of normal milk is usually 16-18 ° T, total acidity. Natural acidity (16-18 ° T). Fermentation acidity: lactose+microorganisms → lactic acid. Other characterizations of lactate (%)=OT × 0.009 [(0.1mol/L NaOH) milliliters × 0.009/gram of titrated milk sample] × 100% pH value: true acidity, hydrogen ion concentration index: normal milk: 6.5-6.7 colostrum, rancid milk:< 6.4 Inflammatory milk and low acid milk:> 6.8 Final milk: 7

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