Milk Quality

Quality: Any company works for profit which is measured in terms of money earned by company. This success is indicated by 'repeat buys' of the product-means consumer's satisfaction-a measure goal of a manufacturer.

In order to increase 'repeat buys' the manufacturer must identify consumers requirements in terms of characteristics or attributes of the product. This combination of attributes/characteristics that contribute to the acceptability of the product , is defined as 'Quality'.

Milk Quality is a broad concept that encompasses its safety, nutritional value, sensory properties, and suitability for processing or consumption. It’s influenced by factors at every stage—from the cow’s health and diet to milking practices, storage, and processing. Here’s a detailed look at what defines milk quality and how it’s maintained or assessed:

Quality of Milk/Food is the sum of the following kind of desired attributes.

1. Physico-chemical attributes- Nutritive elements, pH, acidity, Boiling point, freezing point etc.

2. Microbiological attributes- Number and types of spoilage causing or pathogenic/toxin producing microorganisms.

3. Sensory attributes- colour, texture, odour, taste

Food/Milk Adulterants are the Substances, addition of which makes the food poorer in quality. Type of adulterants vary according to type of food.

Common Milk Adulterants are 

Water, Benzoic acid and Salicylic acid, Detergents, Urea, Formalin, Ammonium Sulphate, Starch, Carbonates and Bicarbonates.

CONTAMINANTS are Dangerous or disease-carrying substances, addition of which makes the food impure.

Common food/milk contaminants:

Pesticides /Insecticides

Antibiotics

Industrial waste/ chemicals – Heavy metals  (lead, mercury, cadmium, arsenic)

Aflatoxin- from Aspergillus flavus & A. parasiticus

Physical contaminants- metal fragments, glass, stones, dirt, plastics, insects & others.

Parameters for Milk Analysis 

• Lactometer reading

• Fat content

• Total solids content

• SNF content

• Efficiency of pasteurization

• Protein, lactose, lactic acid, citric acid, calcium, chloride, copper, ash contents

• Adulterants and Contaminants : Dirt, added dyes, urea, starch, can sugar, animal (tissue) or vegetable fat, preservatives, detergents, antibiotics and others

• Methyl blue test and bacteriological examination

Key Indicators of Milk Quality

1. Microbial Content

   • Why It Matters: High bacterial counts indicate contamination or poor hygiene, leading to spoilage, off-flavors (e.g., sour, rancid), or health risks (e.g., pathogens like Salmonella or Listeria).

   • Standards:

     • Total bacterial count (TBC) in raw milk is often regulated (e.g., <100,000 CFU/mL in the U.S. for Grade A milk).

     • Pasteurized milk typically has <20,000 CFU/mL.

   • Factors: Cleanliness of udders, milking equipment, and rapid cooling (to <4°C/39°F) reduce microbial growth.

2. Somatic Cell Count (SCC)

   • Why It Matters: Somatic cells (mostly white blood cells) increase with udder infections like mastitis, signaling poor cow health and potentially affecting flavor and shelf life.

   • Standards:

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

     • Lower counts (e.g., <200,000) indicate healthier herds.

   • Impact: High SCC can reduce yield in cheese-making and alter protein stability.

3. Chemical Composition

   • Why It Matters: Milk’s nutritional value and processing potential depend on its fat, protein, lactose, and mineral content.

   • Typical Values (cow’s milk):

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

     • Protein: 3.2-3.5%.

     • Lactose: ~4.8%.

   • Factors: Cow breed (e.g., Jersey vs. Holstein), diet (e.g., high-energy feed boosts fat), and lactation stage affect composition.

   • Adulteration: Watered-down milk or added substances (e.g., urea) degrade quality and are tested for.

4. Sensory Properties

   • Why It Matters: Flavor, odor, and appearance determine consumer acceptance.

   • Ideal: Fresh milk should taste clean, slightly sweet, with no off-odors or discoloration.

   • Defects: See earlier discussion on flavor defects (e.g., rancid, oxidized, feed-related).

   • Factors: Feed, storage conditions (e.g., light exposure), and microbial activity influence sensory quality.

5. Absence of Contaminants

   • Why It Matters: Residues like antibiotics, pesticides, or heavy metals compromise safety and legality.

   • Standards:

     • Antibiotics: Zero tolerance in many regions (e.g., U.S. FDA tests for residues like penicillin).

     • Aflatoxins (from moldy feed): <0.5 ppb in the U.S.

   • Factors: Veterinary drug use, feed quality, and environmental pollution.

6. Physical Properties

   • Why It Matters: Traits like freezing point, pH, and titratable acidity reflect freshness and authenticity.

   • Examples:

     • Freezing point: ~ -0.52°C (-0.94°F); deviation suggests water addition.

     • pH: 6.6-6.8 in fresh milk; drops with bacterial fermentation.

   • Factors: Adulteration or spoilage alters these metrics.

Factors Affecting Milk Quality

• Cow Health: Mastitis, stress, or poor nutrition lowers milk quality (e.g., higher SCC, altered fat content).

• Milking Practices: Dirty equipment or improper cooling introduces bacteria.

• Storage: Temperature abuse (>4°C/39°F) accelerates spoilage; light exposure causes oxidation.

• Processing: Overheating during pasteurization can degrade flavor or nutrients, while insufficient heating leaves microbes.

Quality Control Measures

1. On the Farm:

   • Regular udder cleaning and equipment sanitation.

   • Cooling milk to <4°C within hours of milking.

   • Monitoring cow diet and health (e.g., vet checks, feed analysis).

2. During Processing:

   • Pasteurization (e.g., 72°C/161°F for 15 seconds) eliminates pathogens while preserving quality.

   • Homogenization ensures consistent texture.

   • Packaging (e.g., opaque containers) prevents light-induced defects.

3. Testing:

   • Microbial Tests: Plate counts, coliform tests.

   • SCC: Automated cell counters.

   • Composition: Infrared analyzers for fat/protein.

   • Contaminants: Chromatography or ELISA for residues.

Grading and Standards

• U.S. Example:

  • Grade A: For fluid milk; strict microbial and SCC limits.

  • Grade B: For manufacturing (e.g., cheese); less stringent.

• Global Variations: EU, Canada, and others have similar but distinct standards (e.g., EU’s TBC limit is <100,000 CFU/mL).

Consumer Perspective

• Freshness: High-quality milk lasts longer (e.g., 2-3 weeks refrigerated post-pasteurization).

• Taste: No off-flavors, balanced richness.

• Safety: Free of pathogens and toxins.