Parameters for Milk Quality Analysis

Milk quality analysis involves evaluating a range of parameters to ensure safety, nutritional value, sensory acceptability, and suitability for processing or consumption. These parameters are measured using standardized tests and are often regulated by national or international standards (e.g., U.S. Pasteurized Milk Ordinance, EU regulations). Below is a comprehensive breakdown of the key parameters for milk quality analysis:

1. Microbiological Parameters

• Total Bacterial Count (TBC) / Standard Plate Count (SPC):

  • Purpose: Measures overall microbial load, indicating hygiene and storage conditions.

  • Method: Plate count agar incubation (e.g., 32°C for 48 hours).

  • Standards:

    • Raw milk (Grade A, U.S.): <100,000 CFU/mL.

    • Pasteurized milk: <20,000 CFU/mL.

  • Significance: High counts suggest contamination or inadequate cooling.

• Coliform Count:

  • Purpose: Detects fecal contamination or poor sanitation.

  • Method: Violet Red Bile Agar incubation.

  • Standards: <10 CFU/mL in pasteurized milk.

  • Significance: Indicates potential pathogens like E. coli.

• Pathogen Presence:

  • Purpose: Ensures safety by screening for harmful bacteria.

  • Examples: Salmonella, Listeria monocytogenes, Staphylococcus aureus.

  • Method: Selective media, PCR, or ELISA.

  • Standards: Zero tolerance in finished products.

• Psychrotrophic Bacteria:

  • Purpose: Assesses spoilage potential in cold-stored milk.

  • Method: Incubation at 7°C for 10 days.

  • Significance: Causes bitterness or rancidity over time.

2. Somatic Cell Count (SCC)

• Purpose: Indicates udder health and milk quality (elevated with mastitis).

• Method: Flow cytometry (e.g., Fossomatic) or microscopy.

• Standards:

  • U.S. Grade A: <750,000 cells/mL (often <400,000 for premium).

  • EU: <400,000 cells/mL.

• Significance: High SCC reduces shelf life and cheese yield.

3. Chemical Composition

• Fat Content:

  • Purpose: Affects nutritional value, flavor, and processing (e.g., cream separation).

  • Method: Gerber method, Babcock test, or infrared spectroscopy.

  • Typical Range: 3.5-4% (varies by breed, diet).

  • Significance: Low fat may indicate dilution or poor cow nutrition.

• Protein Content:

  • Purpose: Key for nutrition and dairy product yield (e.g., cheese).

  • Method: Kjeldahl method or infrared analysis.

  • Typical Range: 3.2-3.5%.

  • Significance: Impacts processing efficiency and value.

• Lactose Content:

  • Purpose: Primary sugar, affects sweetness and fermentation.

  • Method: Enzymatic assay or infrared.

  • Typical Range: ~4.8%.

  • Significance: Reduced levels may indicate bacterial breakdown.

• Total Solids:

  • Purpose: Measures all non-water components (fat, protein, lactose, minerals).

  • Method: Gravimetric drying or infrared.

  • Typical Range: 12-13%.

  • Significance: Low solids suggest adulteration with water.

• Solids-Not-Fat (SNF):

  • Purpose: Excludes fat to assess other solids.

  • Typical Range: 8.5-9%.

  • Significance: Used in pricing and standardization.

4. Physical Parameters

• pH:

  • Purpose: Indicates freshness and microbial activity.

  • Method: pH meter.

  • Typical Range: 6.6-6.8 (fresh); drops with lactic acid production.

  • Significance: Below 6.4 suggests spoilage.

• Titratable Acidity:

  • Purpose: Measures acid content (e.g., lactic acid from fermentation).

  • Method: Titration with NaOH.

  • Typical Range: 0.13-0.16% (as lactic acid).

  • Significance: Higher values indicate souring.

• Freezing Point:

  • Purpose: Detects water adulteration.

  • Method: Cryoscopy.

  • Typical Value: -0.520 to -0.550°C (-0.936 to -0.990°F).

  • Significance: Higher values (e.g., -0.4°C) suggest added water.

• Density:

  • Purpose: Assesses composition and adulteration.

  • Method: Hydrometer or densitometer.

  • Typical Range: 1.028-1.033 g/cm³.

  • Significance: Deviations indicate dilution or skimming.

5. Contaminant Parameters

• Antibiotic Residues:

  • Purpose: Ensures milk is free of veterinary drugs.

  • Method: Charm tests, HPLC, or microbial inhibition assays.

  • Standards: Zero tolerance (e.g., U.S. FDA limits for penicillin: <5 ppb).

  • Significance: Residues pose health risks and affect fermentation.

• Aflatoxins:

  • Purpose: Detects mycotoxins from moldy feed.

  • Method: ELISA or LC-MS.

  • Standards: <0.5 ppb (U.S.), <0.05 ppb (EU for M1).

  • Significance: Carcinogenic and regulated tightly.

• Pesticides/Heavy Metals:

  • Purpose: Ensures environmental safety.

  • Method: Gas chromatography or atomic absorption spectroscopy.

  • Standards: Vary by region (e.g., lead <0.02 mg/kg in EU).

  • Significance: Toxic at trace levels.

6. Sensory Parameters

• Flavor:

  • Purpose: Ensures consumer acceptability.

  • Method: Trained sensory panels or informal tasting.

  • Ideal: Clean, slightly sweet, no off-flavors (e.g., rancid, oxidized).

  • Significance: Defects reduce marketability.

• Odor:

  • Purpose: Detects spoilage or contamination.

  • Method: Sensory evaluation.

  • Ideal: Fresh, neutral smell.

  • Significance: Off-odors (e.g., barny, chemical) indicate issues.

• Appearance:

  • Purpose: Assesses visual quality.

  • Method: Visual inspection.

  • Ideal: White to slightly creamy, no clots or discoloration.

  • Significance: Yellowing or curdling signals degradation.

Testing Methods Overview

• Rapid Tests: On-farm kits (e.g., Delvotest for antibiotics).

• Lab-Based: Infrared analyzers (e.g., Milkoscan), microbial culturing, chromatography.

• Frequency: Varies—daily for TBC/SCC at farms, batch-wise at processing plants.