Milk Minerals

Milk contains a variety of minerals (often referred to as "ash" in compositional analysis) that contribute to its nutritional value, flavor, and processing properties. These minerals are essential for human health and play a role in milk’s stability and quality. Here’s a detailed breakdown of the minerals present in milk, their concentrations, sources, and significance:

Major Minerals in Milk

1. Calcium (Ca):

   • Concentration: ~1200 mg/L (0.12%) in cow’s milk.

   • Form: Mostly bound to casein micelles (70%) as calcium phosphate; some free or in whey.

   • Source: Derived from cow’s blood, influenced by diet (e.g., forage, supplements).

   • Significance:

     • Nutritional: Key for bone health, muscle function.

     • Processing: Stabilizes casein micelles; excess can affect heat stability (e.g., in UHT milk).

2. Phosphorus (P):

   • Concentration: ~950 mg/L (0.095%).

   • Form: As phosphate (PO₄³⁻), bound to casein or free in solution.

   • Source: From cow’s diet (e.g., grains, pasture).

   • Significance:

     • Nutritional: Supports bone and energy metabolism.

     • Processing: Interacts with calcium to maintain protein structure.

3. Potassium (K):

   • Concentration: ~1500 mg/L (0.15%).

   • Form: Mostly free as K⁺ ions in the serum phase.

   • Source: Cow’s blood, influenced by high-potassium feeds (e.g., grasses).

   • Significance:

     • Nutritional: Regulates fluid balance, nerve function.

     • Processing: Contributes to osmotic balance; rarely affects stability.

4. Sodium (Na):

   • Concentration: ~500 mg/L (0.05%).

   • Form: Free Na⁺ ions in solution.

   • Source: Blood plasma; increases in mastitis milk.

   • Significance:

     • Nutritional: Electrolyte balance.

     • Processing: High levels (e.g., from mastitis) can destabilize proteins.

5. Magnesium (Mg):

   • Concentration: ~100-130 mg/L (0.01-0.013%).

   • Form: Partly bound to casein, partly free as Mg²⁺.

   • Source: Diet (e.g., green forage).

   • Significance:

     • Nutritional: Supports enzyme function, bone health.

     • Processing: Minor role in protein stability; excess linked to coagulation issues.

6. Chloride (Cl):

   • Concentration: ~1000 mg/L (0.1%).

   • Form: Free Cl⁻ ions.

   • Source: Blood; elevated in mastitis or late lactation.

   • Significance:

     • Nutritional: Electrolyte balance.

     • Processing: High chloride can indicate health issues, affecting taste or stability.

Trace Minerals in Milk

1. Iron (Fe):

   • Concentration: ~0.2-0.5 mg/L (trace).

   • Form: Bound to lactoferrin or other proteins.

   • Significance: Nutritional (oxygen transport); low levels limit bacterial growth (e.g., lactoferrin’s antimicrobial effect).

2. Zinc (Zn):

   • Concentration: ~3-4 mg/L.

   • Form: Bound to casein or enzymes (e.g., alkaline phosphatase).

   • Significance: Nutritional (immune function, enzyme activity); stable in milk.

3. Copper (Cu):

   • Concentration: ~0.02-0.1 mg/L.

   • Form: Bound to proteins or free.

   • Significance: Nutritional (enzyme cofactor); excess from equipment can catalyze oxidation (off-flavors).

4. Iodine (I):

   • Concentration: ~0.1-0.6 mg/L (varies widely).

   • Source: Influenced by cow’s diet (e.g., iodized salt) or teat disinfectants.

   • Significance: Nutritional (thyroid function); levels monitored to avoid excess.

5. Selenium (Se):

   • Concentration: ~0.01-0.03 mg/L.

   • Source: Dependent on soil/feed selenium content.

   • Significance: Nutritional (antioxidant); low but bioavailable.

6. Manganese (Mn):

   • Concentration: ~0.02-0.05 mg/L.

   • Significance: Nutritional (metabolism); minimal processing impact.

Total Mineral Content (Ash)

• Concentration: ~0.7-0.8% of milk’s weight (7000-8000 mg/L).

• Measurement: Determined by incinerating milk at 550°C to burn off organic matter, leaving mineral residue (ash).

• Significance: Reflects overall mineral contribution to solids-not-fat (SNF).

Variations

• Breed: Jersey milk often has slightly higher mineral content (~0.8%) than Holstein (~0.7%) due to higher SNF.

• Lactation Stage: Colostrum is richer in minerals (e.g., calcium, sodium) than mature milk.

• Diet: Mineral supplements or forage type (e.g., high-potassium grass) alter levels.

• Health: Mastitis increases sodium and chloride, reducing potassium, affecting mineral balance.

Significance in Milk Quality

1. Nutritional Value:

   • Milk is a key dietary source of calcium, phosphorus, and potassium.

   • Trace minerals (e.g., zinc, iodine) enhance its health benefits.

2. Processing:

   • Heat Stability: Calcium and phosphate balance affects protein coagulation (e.g., in UHT milk).

   • Cheese Making: High calcium aids curd formation; imbalances reduce yield.

   • Flavor: Sodium/chloride spikes (e.g., mastitis) can make milk salty.

3. Adulteration Detection:

   • Low ash content may suggest water addition; confirmed with freezing point or SNF tests.

4. Stability:

   • Excess minerals (e.g., calcium from hard water) can destabilize casein, causing precipitation in heat-treated milk.

Practical Example

• Normal Milk:

  • Calcium 1200 mg/L, Phosphorus 950 mg/L, TS 12.5%, SNF 8.7%.

  • Ash ~0.75%—consistent with fresh, unadulterated milk.

• Mastitis Milk:

  • Sodium 800 mg/L (up from 500), Chloride 1300 mg/L (up from 1000), Potassium 1200 mg/L (down from 1500).

  • Fails stability tests (e.g., COB, alcohol) due to ionic shift.