Lecture 23/3 - Lactos

Question 1

Var hittas lactos? Hur stora mängder?

Answer 1

• Unique for milk
– High concentrations only found in
milk (exception - seals)
– Highest levels found in the milk of
some primates (100 g/L)

Question 2

Hur påverkas lactos innehållet beroende på art?

Answer 2

Djur som lämnar sina ungar längre perioder (eller mindre di tid) har ofta fett som näringskälla istället.

Om diar oftare kommer energin oftare från carbs - laktos

Question 3

Hur mycket av kolhydrater i mjölk är lactos?

Vad finns det för andra kolhydrater?

Answer 3

99,8%
Glucos, galactos, aminosocker mm

Glycolipider, glycoproteins

Question 4

Vad består lactos av?

Hur är dessa delar ihopbundna?

Answer 4

• Disaccharide
– 2 monosaccharide molecules
– D-glucose + D-galactose
• Coupled via ß-1,4-glucosidic bond

Question 5

Hur bildas lactos?

3 steg

Answer 5

1. Uridine diphosphate+Glc-1-P
   blir
   UDP-Glc + P-P
2. UDP-Glc
   blir
   UDP-Gal
3. UDP-Gal + Glc
   blir (va lactos synthase
   Glc-Gal (Lactose) + UDP

Question 6

Lactose synthetase subunits

Vilka finns?

Answer 6

• Subunit A (basic unit): galactosyltransferase (GT)

* Subunit B: a-lactalbumin (whey protein)

Question 7

Hur degraderas laktos?

Vad blir komponenterna?

Answer 7

Mainly by being decomposed by isomerization and
degradation

• Formation of lactulose in large quantities
  (galactose and fructose)
• Degradation of fructose into formic acid. Formic acid cause lower pH in sterilised milk.

Question 8

Vad ger den bruna färgen till lactos?
Vad reagerar?
Vad heter det som ger färgen?
Vad kan va dåligt med detta?

Answer 8

• In milk, Maillard products between sugar aldehydes
and protein amino groups
• lactose + free NH2-group of casein (lysine residue)
• Discolouring + taste defects due to polymerization
between amino compounds and melanoidins
• Certain loss in nutritive value (lysine blir unavailable for absorption)

Question 9

Hur söt är laktos jämfört med andra socker?

Answer 9

Den har låg relativ söthet

Question 10

Vilka två anemerers finns av laktos?
Hur påverkas Equilibrium av temp?
När uppnås jämnvikt

Answer 10

• Equilibrium between 2 anomers, a- and b-lactose, in milk
• Free aldehyde form (ring open) always present, increases at higher temperature
• Equilibrium at 20°C (room temp) a: 37% and b: 63%
• Equilibrium is temperature dependant, a (%) increases with temperature

Question 11

Hur påverkas lösligheten beroende på vilken typ av laktos formation man har?
Hur stor är lösligheten?

Answer 11

• True solubility of a-lactose approximately 70 g/l
water

• Final solubility of a-lactose approximately 170 g/l
water

Question 12

Laktos och kristallisering.
Hur påbörjas det och hur kan det påverkas?
När sker det?

Answer 12

• Formation of nuclei (start punkt, första kristallen)

• particles with an excess of surface energy form new, more stable forms
• addition of crystals, “seeding”, for control of crystal growth (tillsätter små, får små kristaller)

• Crystal growth takes place in oversaturated solutions

Question 13

Vilken är den vanligaste kristallformen för laktos?

Hur beter/känns de?

Answer 13

• α-lactose crystals most common form, most stable at room temperature
• a -lactose-monohydrate crystals are
hard and brittle : “sandy” taste in mouth if too big (>10 μm) (problem i produktion)

Question 14

Vad inhiberar bildandet av kristaller?

Answer 14

• crystal formation in dairy products is
inhibited by for example riboflavin and
lactose mono-phosphate

Question 15

Whey products:

Vilka pulver finns?

Answer 15

Whey powder
Lactose powder
WPC - Whey Protein Concentrate

Question 16

Hur kan laktos användas utanför mjölken?

Answer 16

• Pharmaceutical industry; as a filler or binder in the manufacture of coated pills
• Fermentation industry (substrate for LAB)
• Infant formulae
• Food additive
• Sweets, jam, marmalade, canned fruits
• Bakery goods and bread
• Brewery
• Sausages
• Spices and flavourings
• Dry soups and sauces

Question 17

Vad gör Subunit A i lactose synthase?

Answer 17

• Subunit A (basic unit): galactosyltransferase (GT)

-transition of Gal from UDP-Gal to N-acetyl glucose amine (NAG) in oligosaccharides bound to glycoproteins

Question 18

Vad gör Subunit b i lactose synthase?

Answer 18

• Subunit B: a-lactalbumin
-modifies specificity of GT to add free Glc-molecules to Galmolecules
(in membranes of Golgi vesicles)
-rate of lactogenesis is determined by a-lactalbumin
concentration in mammary glands

Question 19

Hur mycket laktos innehåller skim milk powder och hel mjölks pulver?

Answer 19

• Skim milk powder contains 50% lactose

* Whole milk powder 37% lactose

Question 20

Vad innehåller whey milk powder?

Hur påverkar det dess eg

Answer 20

Whey powder
• 70% lactose
• Lactose in non-crystalline form –easily absorbs water
• Instantizing needed for soluble product

Question 21

Hur får man laktos powder?

Hur är lösligheten?

Answer 21

Lactose powder
• Ultra filtration – lactose separated from whey proteins, concentrated and dried
• Poor solubility without instantizing