THE EFFECTS OF UHT HEATTREATMENT ON THE
MILK NUTRIENTS• Milk is a complete food comprising all the essential
nutrients which is required to nourish the human.
• It contains lactose, protein, fat, vitamin and minerals.
• Milk is sterile at the secretion but it easily can be
spoiled after the milking within 3 to 4 hours if it isstored in the room temperature.
• Milk processing is required to convert the milk into
several other conditions to preserve it and increase
the shelf life.

UHT treatment• It involves several heating conditions• Two types– direct heating system– indirect heating system• It is normally in the range of 135-150oC in
combination with holding times necessary to achievecommercial sterility.

Direct heating systems• The product is heated by direct contact with steamof potable or culinary quality which could beobtained from potable water• The main advantage is that the product is held at theelevated temperature for a shorter period of time
• There are two methods for direct heating, they are;– Injection direct heating system– Infusion direct heating system

Injection direct heating system

Fig 1: Schematic diagram of injection direct heating system

Infusion direct heating system

Fig 2: Schematic diagram of Infusion direct heating system

Indirect heating system• The heating medium and product are not in directcontact, but separated by equipment contact
surfaces. Several types of heat exchangers areapplicable. They are;
– Plate heat exchanger– Tubular heat exchanger

Plat heat exchanger

Fig 3: Schematic diagram of Plate heat exchanger

Tubular heat exchanger

Fig 4: Schematic diagram of tubular heat exchanger

UHT treatment procedure
Raw milk
Preheating and heat regeneration
Homogenization (indirect systems only)
Holding at preheat temperature
Holding to sterilization temperature
Holding at sterilization temperature

Cooling
Homogenization (direct and indirect systems)
Cooling
Aseptic packaging
Storage of package UHT milk
Fig 5: Flow diagram of UHT processing of milk

Time- temperature profileFig 6: Time-temperature profile for direct heating system

Fig 7: Time-temperature profile for indirect heating system

Effects of nutrients during UHT
treatment• Numerous changes in the– chemical composition– physical and organoleptic characteristics of milk even theheating conditions are optimized to obtain higher qualityof milk in the industry• Some, heat induced changes are reversible andothers are not which means the structure and thenutritional values of nutrients will be damaged.

• The reversible heat induced changes occur during
the heat processing are;– lactose mutarotation– ionic equilibrium and protein conformation alterations– casein association– fat globules agglutination– fat crystallization

• The irreversible heat induced changes are;– Whey protein denaturation– Whey protein-casein micelle interactions– Maillard reactions– Fat globule composition changes– Vitamin content changes

Lactose• Main milk carbohydrate (4.8 to 5.2%).
• It is made of D-glucose and D-galactose linked by 1-4
beta glycosidic bond
• Other carbohydrates in milk include– Free monosaccharides (glucose, fructose and galactose inminute quantities)– Aminosugars (glucosamine and galactosamine)– Oligosaccharides.

• Lactose is converted to lactulsoe by isomerization
through UHT treatment.
• Lactulose isomerization is catalyzed by free aminogroup of casein and this isomerization is strictly
depends on time of heating and heating temperatureand pH.
• The lactulsoe formation is little higher in the indirect
heat systems with comparing the direct heating
systems and UHT direct with injection system having
more effect than the UHT direct with infusion
system.

• Other carbohydrates especially– monosaccharides has less heat defect– No significance changes in the initial galactose content of
milk during direct and indirect UHT treatment.
– The content of monosaccharides, aminosugars are ranged
from 2 to 14 mg/100ml in the just processed UHT milk.

Protein• Milk protein can be classified in to two categories;
they are– casein protein (major part, approx. 80%)
• α-casein• β-casein• γ-casein• κ-casein– whey protein (approx. 20%)
• α-lactalbumin,• β-lactoglobulin• immunoglobin.

• Several physical and chemical changes in whey protein
can occur• These changes affect the functional and sensory
properties of milk.
• During the heating process, whey protein containing
sulfyhydryl residues undergo following changes,– A protein complex between beta-lactoglobulin and kappacasein, with consequent modification of rennet coagulation
behavior and heat stability– Typical off flavors– Unusual amino acids• The extent of denaturation of β-lactoglobulin in UHT
milk can vary from as low as 35% in direct plants toclose to 100% in indirect plants• Slight increase in the size of the casein micelle due toits association with denatured whey proteins andcalcium phosphate• Depends on the time and temperature of processing
and the pH of the milk.
• This lead to a chalky or astringent defect in UHT• Milk (especially if heated by steam injection), which
can be eliminated by homogenization after the highheat treatment

• Protein and Nitrogen contents of milk, protein
digestibility were not significantly modified by UHTheat treatment.
• Biological value and net protein utilization of UHT
milk were lower for stored milk than directly used
milk. Lysine loss during UHT is high but notsignificant to affect milk nutritional values.

Fat• Milk fat globule are mostly– triglycerides (98%);– the other lipids amount to less than 2% of thetotal• diacylglycerols and monoacylglycerols - 0.5%
• phospholipids• sterols• free fatty acids• fat-soluble vitamin.

• Fat protects milk components against tested heatinduced changes (lactulose formation, decreased
furosine levels, and whey protein denaturation).
• UHT processing causes virtually no physical orchemical changes in the structure, properties, or
nutritional value of milk fat (Da-wen sun 2006).

Vitamins• Milk contains both water soluble and fat soluble
vitamins.
• The water soluble vitamins are,– vitamin B• thiamin (vitamin B1)• riboflavin (vitamin B2)• niacin (vitamin B3)• panthothenic acid (vitamin B5)• vitamin B6 (pyridoxine)• vitamin B12 (cobalamin)• folate.

• Vitamin C• Fat soluble vitamins are;– Vitamin A (beta-carotene and retinol)– Vitamin D– Vitamin E– Vitamin K

– 20 and 30% losses in vitamin B1 (thiamine) andvitamin B12 can occur during UHT treatment– The levels of Vitamin C (ascorbic acid) and folic acidare markedly reduced in UHT milk containing asignificant level of oxygen during UHT processing andstorage.
– UHT affects the folate binding protein (FBP) at aconsiderable level which is significantly lower withcompared to raw milk. The concentration of FBP,
which might have an impact on folate absorbtion.

• The fat-soluble vitamins (A, D, and E) are largely
unaffected by UHT treatment• They are heat resistant especially beta-carotene isunaffected by UHT processing.
• But in case of retinol, it undergoes some changes

• In retinol stability sometimes are contradictory,• depends on whether the analytic method employed
involved separation of the isomers.
• Here some authors report no significance vitamin A
loss from UHT processing, while others using
chromatographic methods that allow separation ofvitamin isomers reports significance losses in vitaminA.

• Vitamin A in the milk is found in the main form of alltrans retinol and other cis retinol isomers alsopresent.
• If the heat is applied to the milk the predominant
all-trans isomers
cis-isomers• The isomerization of all-trans retinol into cis-retinol
is occurring during the UHT treatment which hassome sort of loss of vitamin A in the UHT milk.

Minerals• The most common cations (positively chargedions) in milk are– potassium (K)– sodium (Na)– calcium (Ca)– magnesium (Mg)

• The most common anions are– chloride (Cl)– inorganic phosphate; citrate, sulfate, carbonate, andbicarbonate (lesser amounts)• K, Na, and Cl are almost entirely diffusible, while Ca,
Mg, inorganic phosphate, and citrate are nondiffusible and associated with the casein micelles.
• Milk salts thus exist in an equilibrium between theliquid and colloidal phase: this equilibrium can beaffected by processing.

• UHT processing transfers minerals from the aqueous
phase to the casein micelle and reduces ionic calcium
levels by 10 to 20%.
• This, in addition to the interaction of whey proteins
with the casein micelle, reduces the susceptibility of
UHT milk to coagulation by rennet.
• Some calcium phosphate is rendered insoluble at thehigh temperatures used in UHT heating and deposits
on the surfaces of the heat exchanger (fouling).

Other effects• Protein- sugar interaction– mainly casein-bound lysine residues and lactose areinteracts and form several chemical compounds which
influence the nutritional quality of milk
– considerable loss of biologically available lysine• Flavor compound production– Cooked or heated flavor (processing)• Volatile sulfur compounds produced mainly from denatured
lactoglobulin– Stale flavor (storage)• Aliphatic aldehydes

Conclusion• The protein especially whey protein has the higher
loss, lactose and vitamins have some marginal loss,
the fat and the minerals have no damages areobserved.