physchem prpty of milk

8/16/2019 Physchem Prpty of Milk

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The specific gravity of milk is lowered by addition of water and cream and

increased by addition of skim milk or removal of fat. 6pecific gravity can be determined

by lactometer and is e)ual to8

"!!!

&0!

"

! F at reading Lactometer

gravitySpecific +=

The percent total solid and solid9not9fat in the milk can be calculated by the

following formula.

.%

.-!

&""!!!,

1-.!--.!-'.!%

1-.!--."-'.!.%

!

samplemilk theof Fat F

C at milk of densityd

d DWhere

F DSNF

F DS T

=

=

−=

++=

++=

Recknagel phenomenon

The specific gravity of milk increases gradually after milking up to certain time.

(uring milking - or other gas are mi+ed and this phenomenon proceed until the gas

comes out. This process continues at "'o for " to - days. He found this phenomenon

during "22#. 6o this phenomenon is called :ecknagel’s phenomenon. The causes of

increase in specific gravity are due to casein hydration and slow solidification of fat.

Freezing point of milk

4ilk free;es at temperature slightly lower than water due to the presence of soluble

constituents such as lactose, soluble salts etc. The free;ing point of water is ! o but due

to the solutes, for cow milk it becomes lower 9 !.'''o&, and for buffalo milk 9!.'0!o

and addition of water will raise the value below 9!.'#o&. The instrument measuring the

free;ing point is ryoscope.


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4ilk is heavier than water. 4ilk boils at some higher temperature due to the reason that

the boiling point depends on the specific gravity. The water boils at "!!o at sea level but

milk boils at "!!."1o. >hen water is added to milk, the boiling point also lowers due to

decrease in the concentration of solutes.

Specific heat

6pecific heat is the ratio of heat necessary to raise the temperature of some substances

and the heat to raise the temperature up to some e+tent of water having same weight. The

unit is ?calorie’. The specific heat of milk in average is !.5$'1, whereas pure water is

".!! at 6T@. It depends on the physical and chemical condition. 4ilk boils faster or

temperature rises faster than water but the boiling point of milk is higher than water. It is

because milk dissolves more soluble solids but water do not dissolves it.

Color of milk

4ilk seems as white nontransparent color. The white color is due to Acalcium9casienateB

in the form of colloidal. *enerally the color is a blend of the individual effects produced

by

• the colloidal casein particles and the dispersed fat globules, both of which

scatter light, and

• the carotene to some e+tent +anthophylls& which imparts the yellowish tint.

4ilk ranges in color from yellowish creamery white cow milk& to creamery white

buffalo milk&. The greater the intakes of green feed, the deeper yellow the color of cow

milk. The larger the fat globules and higher the fat percentage, the greater the intensity of

the yellow color. 6kim milk has a bluish and whey a greenish yellow color. The greenish

of whey is due to riboflavin Lactoflavin&.

The color of foods is an important aspect of their marketability. olor has # aspects that

are tint, intensity and uniformity.

Flavor

This is composed of smell odor& and taste. The flavor of milk is a blend of the sweet

taste of lactose and salty taste of minerals, both of which are damped down by proteins.

The phospholipids, fatty acids and fats of milk also contribute the flavor.

The sulfahydryl compounds significantly contribute to the cooked flavor of heated milk

and milk products. 6ometimes the cowy flavor appears. In late lactation milk and milk of


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mastitis animal, the increase amount of chloride cause salty flavor. Late lactation milk

has been found bitterness due to the action of lipase en;yme splitting the fat to fatty

acids, so bitterness causes. 4icroorganisms may enter and cause sourness due to lactic

acids. 6imilarly various chemical changes causes o+idi;ed, metallic or fishy odor.

Viscosity Plasticity

It is measured by stwald Ciscometer. It is the measurements of resistant flowing the

li)uid. >ater flows simply than milk. 3 -!o water has viscosity ".!!' c@ but milk has

".' to -.! p, skim milk ".', whey ".!!1, >hole milk -.! c@. The value decreases both

with an increase of temperature and with the removal of fat. @asteuri;ation does not

appreciably alter the viscosity of milk. hen a droplet of li)uid is free flowing in a gas or in another li)uid with which it doesn’t

mi+, the droplet tends to pull itself into a spherical shape, or into that shape which has the

smallest surface area per unit of volume. The force pulling the droplet into this shape is

the surface tension of the li)uid. The surface tension of milk is about $' to '! dynesDcm

but water has 1-.' dynesDcm. It is mainly affected by fat, temperature and ageing also.

Homogeni;ation increases the surface tension. (u 7uoy Tensinometer is used.

Action of milk on metals

4ilk acts on certain metals, so that a small amount of the metal is dissolved in it. The

metallic salts thus formed may give rise to a metallic taste in the milk. 6ome salts acts as

catalysts, thus hastening the o+idation of fat and producing an o+idi;ed flavor. These

metals are said to taint milks.

The factors which influence the degree of action by milk in the metal are8


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". Temperature of the milk.

-. @eriod of contact.

#. leanliness and polish of metals.

$. 3mount of free air in milk, and

'. 3cidity of the milk.

The metals used for the milk contact surfaces must, as far as possible, meet the

following re)uirements.

". 7on to+ic,

-. 7on tainting,

#. Insoluble in milk and milk products,

$. Highly resistant to corrosion,

'. Easy to clean and keep bright

0. Light and strong,

1. *ood agents of heat transfer

2. *ood in appearance throughout life,

5. Low in cost.

"!. 7on absorbent.

"". (urable.

7o single metal or alloy meets all these re)uirements. However, "282 stainless steel alloy

are the most satisfactory at present. orrosion can’t be entirely prevented in dairy

e)uipments but its rate can be controlled to a large e+tent. To prevent corrosion of

stainless steel surface the following measures should be taken.

". The surface should be clean.

-. 6urface air dry, whenever possible.

#. leaners and saniti;ers use in the lowest concentration and for shortest

duration.

3n invisible film of chromium o+ide forms on stainless steel surface when it is dry

and e+posed to the atmosphere. This film protects it from being corrosion.

hloride and its compounds are very corrosive. E)uipments should be saniti;ed with

chloride solutions. @referably =ust before it is to be used, so as to avoid prolonged contact

and thus corrosion pitting&.


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"efractive inde#

r

i

sin

sin= µ

>hen light passes through from dense to rare medium, it deflects from its path. The

measurement of this deflection is refractive inde+. 3t -!!, water has refractive inde+ of

".### but normal milk has ".#$$ to ".#$$'. The instrument measuring the refractive

inde+ is 3bbe refractometer.

$#idation%red!ction potential

+idation means loss of electron and reduction means gain of electron. :edo+ potential

means the potential of o+idation and reduction. The redo+ potential of milk is Eh /!.- to

!.# volts. Two methods of measuring the redo+ potential is electrometric and

colorimetric. This potential decreases when boiling the milk. The growth of microorganisms also decreases the redo+ potential.

Adhesiveness of milk

The adhesiveness is due to casein so casein is used to make gums in the industry.

&ffect of heat on milk

The ob=ectives of heating the milk are

". the destruction of pathogenic and other microorganisms.

-. for the concentration of the milk.

#. for inactivation’s of milk en;ymes.

$. to mi+ other constituents simply.

In factory the milk is heated during pasteuri;ation, fore warming, condensation, drying

etc. The effect may cause carameli;ation, cooked flavors and loss of some nutrients. This

depends on the temperature of heating.

Significance of physical properties of milk

". Helps in detection of the adulteration.

-. Helps in manufacture of dairy products fermented and unfermented&.

#. Helps in the fabrication of dairy e)uipments.

3ssessment of physical and chemical changes in milk and milk products duringmanufacture

'ilk components


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i. Water: Free, Bound and Crystallized water

>ater acts as a suspending, dispersing and dissolving media for the other components of

milk. It occupies 21 % per cent of fresh milk. It e+ists in three forms such as free water,

bound water and crystalli;ed water. 3ny variations in the amount of other constituents

also reflected upon the water percentage.

a( Free )ater* Largest portion of water e+ists in this form. This is the one which act as

dispersing and dissolving media for other constituents. It free;es at ! o and evaporates at

"!!o. It can dissolve soluble substances. It can be removed easily while processing of

milk. It is also supportive to microbial growth.

+( Bo!nd ,ater* It e+ists in milk as binding with protein through hydrogen bond&, fat

globules and hydrophobic radical of milk constituents. In fresh milk, #."2 % of the total

water e+ists in this form. It is very hard to remove while processing milk. This can be

neither free;e at !o nor can evaporate at "!!o and it cannot act as a solvent. It cannot

support microbial growth.

c( Crystallized ,ater* This water e+ists within chemical structure of any of the milk

constituents e.g. 9lactose hydrate "-H--"".H-&. This is most stable and hence hardest

to remove. It also cannot support microbial growth.

In various milk products, high e+tent of water makes it liable to microbial growth. Hence,

it is essential to remove water up to re)uired level.


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present in milk as true solution. This usually amounts to '!9'- % of the total solids in

skim milk. >hen it crystalli;es from water, it forms hard gritty crystals, which have one

molecule of water of crystalli;ation "-H--"".H-&. These gritty crystals sometimes

appear in certain milk products under certain circumstances under which these crystals

are allowed to grow in si;e. These crystals appear in ice cream when the mi+ contains a

high proportion of milk solids. The lactose content of milk is increased slightly by the

over feeding of carbohydrates, especially soluble carbohydrates or decreased by mastitis

infection of the udder.

Lactose is the ma=or carbohydrate in milk. 4ilk contains traces of other carbohydrates

but no polysaccharides. The glucide compounds like he+osamines and 79

acetylneuraminic acid occurs in milk, but these are largely associated with proteins and

cerebrocides. Lactose solution in water has reducing properties and reduces fehling

solution and ammonical silver nitrate.The reducing power of lactose is doubled by

hydrolysis as both the sugars formed as a result of hydrolysis have one active aldehy9de

group each. Lactose is insoluble in alcohol and ether but is soluble in hot acetic acid. +i9

dation of lactose in slightly acid condition yields formic acid and finally laevulinic acid,

but o+idation by concentrated nitric acid breaks lactose into o+alic acid and carbonic

acid. >hen lactose is heated between ""!9"#!o, the lactose hydrate crystals loose the

water of crystalli;ation and above "'!o they turn yellow and at at "1'o they turn

brown and form caramel. The slight burning and characteristic colour of cooked milk is

due to the formation of caramel, though the milk and milk products are never treated to

such high temperatures under ordinary processes. Lactose, when gently warmed with

nitrogeneous bases like ammo9nia, certain amines, amino acid, any of which may be

present in heated milk, forms brown coloured comple+es. Thus, the e+tent of these

changes will depend upon the severity of the heat treatment and the time of holding.

@asteuri;ed milk is only slightly effected, while steri9li;ed milk or evaporated milk have

more effect. Lactose is a valuable product and is used for the preparation of infant,

weaned food products invalids. This is the main source of galac9tose, present in brain

nerve tissues of human body. Lactose helps in assimilation of calci9um and phosphate

from intestines has a tonning effect on the aliment9ary canal. >hey is the main sourse for

its manufacture.


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Physical properties of lactose

Lactose is normally found in two crystalline forms i.e. 9hydrate and 9anhydrous.

". 9hydrate8

ommercial lactose is 9lactose monohydrate "-H--"".H-& or 9hydrate. It is prepared

by concentrating an a)ueous lactose solution to super saturation and allowing

crystalli;ation to take place at a moderate rate below 5#.'o. It is stable solid form at

ordinary temperature because it forms hydrate below 5#.'o.

6pecific rotation in water [ ]-!

D

α J 25.$ melting point J -!".0o.

K9may form a number of crystal shapes, depending on the conditions of crystalli;ation,

the most familiar forms being prism and tomahawk shapes. 3s the crystals are hard and

not very soluble, they feel gritty in mouth as sand particles may arise problems in ice

cream, condensed milk or at cheese depends on si;e and number of crystals&.

6i;e 9"! μ or small 9undetectable.

3bove "0 μ or below #! μ 9 tolerated without effect.

#! μ or large 9 sandiness

Chemical properties of lactose

Lactose is a disaccharide composed of (9glucose and (9galactose. The aldehyde group of

galactose is linked to the 9$ group of glucose through a 9", $9 glycosidic linkage fig

"&.


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group is converted to a carbonyl group. 6omewhat more vigorous o+idation ruptures the

glycosidic linkage and produces carbonyl groups in the remaining sugars. *entle

reduction of lactose converts the aldehyde group to an alcohol group. 4ore intence

reduction of cleaves the glycosidic linkage and results in the formation of alcohol groups

in the remaining sugars.

9form

galactose& glucose&

9L3T6E

@yranose form furanose form

*alactose& Fructose&

L3TML6E

Fig( " hemical structure of lactose and lactulose.

Hydrolysis of lactose by acid does not occur easily. If it occurs at high temperature, low

pH, many reactions takes place as well. Lactose can, however, simply be hydrolysed

using the en;yme lactase 9(9galactosidase&. This en;yme is highly specific for the 9

",$ linkage of a galactopyranose residue.


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Hydro+ymethylfurfural Furfuryl alcohol

3cetol H#.H.H-H Formic acid HH 3cetic acid H#.H

4ethylglyo+al H#..H @yruvic acid H#..H

Formaldehyde HH Levulinic acid H#..H-.H-.

The proportion of the products formed depends on concentration of sugar, pH, heating

time, and temperature. The very important maillard reaction occurs in the presence of

amino compounds in milk mainly concerns the N9amino groups of the lysine residue in

milk proteins&. It involves formation of a 6chiff base between the amino group and the

aldehyde group of lactose. The initial reaction product undergoes a series of

rearrangements, yielding nitrogeneous reaction products in addition to such products as

mentioned above for carameli;ation. Further reactions lead to brown color, loss of

nutritive value, and off flavors. 3ll these changes occur on prolonged storage, and

especially during heating.

Lactose is≈ !.# times as sweet as sucrose. The sweet taste in milk is somewhat masked

by the protein, primarily the casein. >hey has a sweeter than milk. The mi+ture of

glucose and galactose formed by hydrolysis tastes much sweeter than lactose.

Physiochemical aspects of lactose

-( &.!ili+ri!m in sol!tion /'!tarotation0

Lactose e+ists in two forms, and .


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3lso, important besides the variables of the e)uation, are temperature of the solution,

wave9length of the light source, and concentration of the solution. The standard light

source used to measure optical rotation has been the bright yellow ( lines of the sodium

spectrum, but the single mercury lines, O '$0" 3o is now used fre)uently for precision

measurements. *enerally the specific rotation is reported at -!o and e+pressed as8

[ ] -! Dα or [ ]-!

Hg α .

The following formulas e+press variations in specific rotation in terms of these variables8

[ ] t Dα J '0.1' !.!"19 !.!'2 T ( line, O J '25 Pm&

For pure 9lactose 8 ( J 5"." at -!o and For pure 9lactose 8 ( J ##.- at -!

o.

>here, c J is gm anhydrous lactose D"!! ml solution&

T J is degree centigrade.

[ ] t Hg α J 00.-' !.!!1 !.!'$ T. Hg line, O J '$0 Pm&

>here, J is gm of lactose monohydrate D"!! mil solution.

>hen either of and lactose is dissolve in water, however there is a gradual change

over of one form to other until e)uilibrium is established. :egardless of one form used in

preparing a solution, the rotation will change mutarotation& until [ ] -! Dα J ''.#, at

e)uilibrium anhydrous weight basis&. This is e)uivalent to #1.# % in 9form and 0-.1 %

in the 9formQ since the e)uilibrium rotation is the sum of the individual rotations of the

and forms. The e)uilibrium ratio of to at -!o, therefore, is#.#1

1.0-J".02.

4utarotation has been shown to be a first order reaction, the velocity constant being

independent of reaction time and concentration of the reactant.

In solution, conversion of 9 to 9 lactose and vice versa occurs.

9lactose 9 lactose, reaction constant k "

9lactose 9lactose, reaction constant k -

4utarotation e)uilibrium ratio,-

"

k

k R = Q

[ ]

[ ]α

β = R

The rate of mutarotation reaction has the constant RJ k "/ k -

If we dissolve, for instance, lactose and if we define[ ]

[ ] me!ili"ri! #

α

α =


13/37

kt

e

=

−"

ln

α

α α

β

or, t k e

e =

−×

α α

α

α

β ln or, >e have,

( ) kt

#

R=

−"ln

( t k e−−= "α β

if time is very large the term e9kt becomes too small so it is neglected, then it should be,

t J o e9k t or, t J oe

9k t

In other words, the proportion of the mutarotation reaction that has been completed at

time t is given by "9e9kt

The same holds for conversion of 9lactose. The changes may be observed by using

polarimeter. The rotation of plane of polari;ation then is found to change to mutate& with

time because 9 9lactose differ in specific rotation. Hence the term called

AmutarotationB.

%

T h&

pH

Fig. 2 $!tarotation of lactose sol!tion% &'( Co!rse of the reaction &) finished( against time t% &*(

$!tarotation reaction constant k &h+, ( as a f!nction of pH &appro#% -. oC(%

4utarotation rate k depends closely on temperature. 3t -!o

and pH 0.1, k≈

!.#1 h9"

, itincreases by a factor of # or more per "!o rise in temperature. 3t room temperature it

takes many hours before mutarotation e)uilibrium is reachedQ at 1!o a few minutes.

Fig. -


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The mutarotation e)uilibrium likewise depends on temperature8 : J ".0$─!.!!-1 T,

where, T is degrees elsius. Thus the change in temperature causes mutarotation.

4utarotation depends on lactose concentration. >ith increasing concentration, k

decreases : changes as well. If other sugar such as sucrose present in high concentration,

k decreases considerably. 3t very high lactose concentration, i.e., in amorphous lactose as

, for e+ample, occurs in spray9dried milk powder, after e)uilibration : ≈ ".-',

independent of temperatureQ mutarotation may occur, but e+tremely slowly.

Table 1 Some properties of lactose

". Sol!"ility in /ater ), in g D"!! g water& as a function of temperature T, o&Q9lactose8 log )≈ !.0"# / !.!"-2 T 9lactose8 log )≈ ".0$ / !.!!# T

E)ulibrium solutionQ )≈"-.$2 / !.-2!1 T / '.!01×"!9#T- / $."02×"!90 T# / "."$1×"!90

T$

-% Density0 viscosity0 and refractive inde# as a f!nction of concentration%Conc%of lactose Density of 'pparent density 1iscosity of Ref% inde#

of

&g 2,33g /ater( sol!tion at -3o of lactose dissolved sol!tion&m%4a%s( sol n at -.oC

kg2m5 in /ater &kg2m5 ( -3oC 63oC 7 = .89 :m

! 552.- ─ ".!! !.$1 ".##-'

"! "!$# "1'! ".#2 !.1! ".#$2$

-! "!2- "0-5 -.!$ !.5! ".#0'5 #! ""-$ "'5- #.$- ".-5 ─

$! ""1# "'5" 1.!" -."5 ─

c. 6pecific rotation 8

is e+pressed in degrees of arc of rotation per cm path length in a hypothetical solution

of " g anhydrous lactose solution. The rotation depends on temperature T, o&, on the

wave length of light 7&, and somewhat on concentration , g D"!! mL solution&, etc.The

e)uations are given above.

Different crystal forms of lactose

-( 1%lactose

a( "eg!lar /!nsta+le0 anhydro!s 1%lactose * It has melting point of ---.2o. It is stable

in dry air, but highly hygroscopic and unstable under normal atmospheric conditions.


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+( Sta+le anhydro!s 1%lactose * The new crystalline structure reduces tendency of the

product to take up water of crystalli;ation, so thus anhydrous form remains stable even in

an environment of '! % :H.

2( %lactose

It is not very hygroscopic, and dissolves )uicklyQ its solubility is good. >hen lactose

crystalli;ation occurs above 5#.'o the crystals formed are anhydrous and have a specific

rotation of [ ] -! Dα J #'.!, and melting point J -'-.-o. They are composed of anhydrous

9lactose, which is sweeter and considerably more soluble than 9hydrate. The common

form of crystals is an un9even sided diamond when crystalli;ed from water and curved

needle like prisms when from alcohol.

3( Anhydro!s lactose glass /Amorpho!s non%crystalline glass0

>hen a lactose solution is dried rapidly, as in spray drier, the viscosity increases so

)uickly that crystalli;ation cannot take place. The dry lactose is essentially in the same

condition as it was in solution e+cept for removal of the water. This is spoken of as

concentrated syrup or an amorphous non9crystalline& glass. Lactose in milk powder is

non9crystalline and e+ists in the same e)uilibrium mi+ture of and lactose as e+isted in

the milk prior to drying. 3morphous lactose contains at least a few percent of water and

can )uickly dissolve on addition of water.


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hydrate soon starts to crystalli;e. 69lactose is very hygroscopic. The unstable anhydrous

9form, however, is hygroscopic, accordingly, its transition to 9hydrate occurs easily,

and the sugar dissolves faster, though not better, than 9hydrate.

Fig( 4 The different forms of lactose. T J Temperature o&

4( Crystallization of 1%lactose hydrate

rystalli;ation is of great practical importance. e usually

have to add numerous tiny seed crystals to ensure the rapid formation of sufficient, hence small

si;ed crystals.To prevent segregation and development of AsandinessB in milk products, the

>

a t e r u p t a k e

(issolve,TS 5#.'

TS 5#.'

>

a t e r u p t a k e

, H # H

/ H , l

>

a t e r u p t a k e

( i s s o l v e

T S

5 # . ' o ,

T

5 # . ' o ,

T 5 # . ' o ,

6 u p e r s a t u r a t i o n

T S 5 # . ' o ,

6 u p e r s a t u r a t i o n

Lactose in solution,

9hydrate" mol H

-&

9anhydrous

3nhydrous9unstable

3nhydrous9stable

6upersaturationin ethanolompound crystal

'

#

anhydrous

3morphous lactose

TU "!!, presenceof water vapor

TU "!! in vacuowater uptake

TS 5#.'

(issolve,TS 5#.'

TU "'!, presenceof water vapour


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largest crystals formed should be no more than "! μg in si;e. This implies that at least "!"!

crystals per gram of crystalline lactose should be present. The 9lactose hydrate crystals can have

many geometrical form but the crystal lattice is always the same&. The commonest shape is the A

tomahawkB fig. below&.

Msually, the crystals does not grow in the direction of the ?b’ a+is, i.e., the crystal faces oVo and k

or "'!. Likewise, lateral faces do not grow at all. onse)uently, the Aape+B of the crystal is also

the point where the crystal started to grow. Furthermore, crystal growth is slow, far slower thanmay be accounted for by the combined effect of mutarotation and diffusion of 9lactose to thecrystal.

@resumably, there is some difficulty of fitting molecules into the crystal lattice.


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*rowth μm.h9"& of face

6upersaturation %& :emarks oWo WWo Woo WVo

'' 9

'' /"! ppm gelatin #.2 #.# ".# !.#

'' /"!! ppm riboflavin ".- ".! ".! !.$'' / "! ppm T4(3Y -.1 !.! !.! !.!

"-! 9 $# #$ -" "-'' wn pH #.- -.1 ".0 !.$

'' pH 1 0.0 '.! -.1 ".-

'' # × recrystalli;ed !.- !.1 ".# !.'

'' 7onionicY Y "5." 5." #." ".-'' 7onionic / Inhibitor Y Y Y !.! !.! !.5 !.'

Y Trimethyloctadecylamonium chloride.YY 6olution passed through an anion e+changer.YYY Lactose 4onohydrate.

6actic Acid Fermentation

Lactose is the main source of energy for most of the bacteria growing in milk.

ommonly, the organisms attack lactose by hydroly;ing it to form galactose and glucose.

The latter molecules are each fermented into lactic acid H#HHH&, but part of

the galactose may not metaboli;ed. Lactic acid bacteria are of two types. The one, which

can produced only lactic acid, is called homofermentative and those produce lactic acid

as well as -, acetic acid and ethanol.

*lucose / -3(@ / -H#@$ - lactate / -3T@ / -H-

Lactic acid is an essential component of many milk products. 4ost bacteria produce

about " % lactic acid in milk, but some of these can reach as much as - %. 6uch high

lactic acid concentration inhibits growth of most microorganisms.

Sol!+ility

The solubility of and lactose differ considerably and it depends on the temperature. If

9lactose is brought in water, much less dissolves at the beginning than later. This is

because of mutarotation8 9lactose is converted to , hence the9 concentration diminishes

and more can dissolve. If 9lactose is brought in water, more dissolves at the beginning

than later at least below 1!o&8 n mutarotation more 9lactose forms that can stay

dissolved, and 9lactose starts to crystalli;e.


19/37

-!!

"!! -." ".0 "

$!

-!

"!

' -! $! 0! 2! "!! T o&

Fig( 3 6olubilities of 9 and 9 lactose, final solubility of lactose curve "&, and

supersaturation by a factor of ".0 and -." as a function of temperature.

The solubility thus depends partly on the mutarotation e)uilibrium, the rate of dissolution

on the mutarotation rate. The so9called final solubility is identical whether we dissolve 9

or 9 lactose. It is : / " times the solubility of 9lactose. This applies below 5#.' o

because above this temperature 9lactose determines the final solubility. 3t lower

temperature, it takes a long time to reach e)uilibrium.

>hen 9lactose hydrate is added in e+cess to water, with agitation, a definite amount

dissolves rapidly, after which an additional amount dissolves slowly until final solubility

is attained. Its solubility in water is only "1.2% at 11oF -'o&.

Z9lactose at room temperature is about 1 times more soluble than 9form. The initial

solubility is the true solubility of 9form. The increasing solubility with time is due to

muta9rotation. 6ince the solution was already saturated with , formed by mutarotation

will crys9talli;e to reestablish e)uilibrium. 6ince 9lactose is much more soluble and

mutarotation is slow, it is possible to form more highly concentrated solutions by

dissolving 9rather than 9lactose hydrate. The increase solubility makes it appear sweet

to taste and favors the use of it in dietary and baby foods.

The overall rate of lactose crystalli;ation can be summari;ed by the reaction.

7ot saturatedintermediate

4etastable

liable


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Z9lactose 9lactose 9lactose hydrate crystals.

Lactose solution can be supersaturated easily and to a considerable e+tent. 3t

concentrations over -." times the saturation concentration, spontaneous crystalli;ation

occurs rapidly, probably because of homogeneous nucleation i.e., formation of nuclei in

a pure li)uid&. 3t less than ".0 times the saturation concentration, seeding with crystals

usually is needed to induce crystalli;ation, unless we wait a very long time, the solution

is thus metastable. In the intermediate region, crystalli;ation depends on several factors,

such as time.

$ther physical properties

a. (ensity 8 Carious lactose crystals differ slightly.

9hydrate J ".'$! 9 anhydride J ".'$$ from dehydration&

9anhydrate J ".'25 9 anhydride J ".'1' from crystalli;ation by alcohol&

(ensities of lactose solutions are not straight line function of concentrations.

b. :elative sweetness8 9lactose is sweeter than and is appreciably sweeter than the

e)uilibrium mi+ture e+cept when the concentration of lactose solution e)uals or greater

than 1 %. 6ince there is appro+imately 0# % in the e)uilibrium mi+ture, a 9lactose

solution differs less in sweetness from a solution in e)uilibrium than does 9lactose

solution. However, for practical purposes there is little advantage in using for sweetness

in preference to an e)uilibrium solution at these concentrations, since the small difference

is )uickly eliminated by mutarotation.

7ses of lactose

The large amount of lactose is consumed in the form of milk products but the sugar itself

has only few industrial applications.

• 3s a constituents of infant foods and medical products.

• In the early stages of brain formation, galactose is needed, which is found in lactose.

• For the manufacture of tablets and capsules and general fillers.

• Mse in fondants and tablets like candies.

• use in baking industries to produce a desirable brown color in pie, crusts, cookies

and other baked goods.

• to improve the flavor and body of the product like chocolate milk, butter milk, and

modified 64@


21/37

• Msed as substitute for cream in coffee as a dry mi+tures.

• Msed for the formation of penicillin due to its slow rate of fermentation properties.

• Lactobacillus spp. of bacteria only utili;ed lactose sugar and produce lactic acid

which is used as substitute for acetic acid and citric acid in food stuffs.

• Msed as ingredients of the medicine in which mold is grown.

• Msed as a reducing agent in silvering of mirrors.

• 4inor use of lactose include use of it military technology for making of smoke

screen and signal and target candles.

For the manufacture of several dairy products like sweetened condensed milk, instant

milk powder, stabili;ed whey powders and lactose ice cream etc., the process of

crystalli;ation is important. The control of lactose crystalli;ation becomes important for

various products like ie cream etc.

8!tritional and physiological effect of lactose 9 6actose intolerance

4ilk and its derivatives contribute lactose to the diet. In the digestive tract, lactose may

be fermented by bacteriaQ in the intestine it may be absorbed directly or hydrolysed by 9

(9galactosidase Lactose& and its components absorbed. Z9(9galactosidase is an

intracellular en;yme which in man is found within the cells of the intestinal mucous

membrane hydrolysis, therefore, occurs during transport through the intestinal wall.

3 great deal of interest has recently centered in the en;yme lactose because it bringsabout certain diarrheal syndromes in infants, but also because of its wide spread

deficiency in adults who normally consume little or no milk after weaning. ALactose

intoleranceB causing abdominal cramps, gaseous distention or diarrhoea in severe cases,

is atributed to a deficiency of lactase in the intestinal mucosa. Lactose deficiency is

detected by a biopsy of the mucosa or by feeding lactose to the sub=ect after a period of

fasting and measuring the rate of increase in A blood sugarB level.

The significance of this sub=ect is obvious because of its implications on the suitability of

milk as a food after weaning in countries whose there is a high incidence of lactase

deficiency in the population.

Lactase may also be transferred to the blood or urine lactosuria& without being

hydrolysed, particularly after consumption of a large )uantity of lactose or during

lactation.


22/37

Proteins

hemistry of proteins

Definition @roteins are high molecular weight polymers, generally over "!!!! 4>, of amino

acids covalently linked by the peptide bond. 4ost of the milk proteins contain more than "'!

amino acids. The properties of the various proteins are dictated by the amino acids in the

molecule and by their se)uence in the polypeptide chains&, which regulates the

molecular configuration of the protein molecule and the surface electrical charge.

@roteins can e+ist in helical coils, random coils, pleated sheets or in a combination of

these forms. These properties relate to the stability of the proteins in the food system and

influence processing of the products. 4ilk proteins generally possess several of theseforms in a single protein molecule.

@rotein is one of the most essential nutrients of milk present in about #.' %. 4ilk

protein contains almost all of the essential amino acids and hence high nutritive value.

arbon, Hydrogen, 7itrogen, +ygen, 6ulphur, and phosphorus are the elements present

in protein. In milk among the total protein, casein contributes -.5 % and whey protein !.0

%. 4ilk protein may be divided into two main groups8 asein and whey proteins

lactalbumin, lactoglobulin&.

Casein

The caseins are characteri;ed by their relatively high phosphorus content. asein is a

generic term for a class of proteins that are synthesi;ed in the mammary gland and make

@eptide bond

: "

: -

H

H

: "

H

H

7H-

/

H

H

7H-

: -

7H-

7

3mino acid - (ipeptide

3mino acid "


23/37

up about 2!92' % of the total milk protein. It is present in the form of micelles or

particles of macromolecular si;es.

asein is composed of four recogni;ed components called s, , [, \ on the basis of

differences in their electrical charge. hemically the casein system is defined as a

glucophosphoprotein, since it contains both carbohydrate glycol group& and phosphorus

as integral parts of the protein. In milk, casein e+ists as its calcium salts, namely, calcium

caseinate, in distinct globular particles, ranging from $!9#!! mµ in diameter. These

particles are called micellesQ each micelle contains all the component casein held together

in part by calcium phosphate.

ommercial casein is obtained from fat9free skim milk by precipitation either by

addition of an acid, or by the addition of rennet e+tract containing the en;yme rennin&.

aseins are high molecular weight 25,!!!& compounds. They are the charged

particles having IE@ $.0. The elementary composition of casein indicates carbon '# %&,

hydrogen 1.!1 %&, sulfur !.10 %& and phosphorus !.2' %&. The factor used for

determination of protein is 0.#2. This is because 7- content in milk is taken as "'.0'

instead of normal value "0 %&. 4ilk and milk products provide food proteins of

e+cellent )uality for the nutrition of man and animals. asein, the dominant protein of

milk, is a good source of amino acids, which are the indispensable for human nutrition.

The milk protein differs considerably from each other in amino acid compositionhowever they all contain considerable amount of dietary essential amino acid. The 9

lactalbumin contains very high amount of tryptophan, while all milk proteins are rich in

aspartic acid and glutamic acid. The essential amino acids such as tryptophan, threonine,

isoleucine, leucine, lysine, methionine, cystine, phenylalanine, tyrosine and valine, all are

found in milk.

The peptide chain obtained after en;ymatic hydrolysis found to have phosphorus

bound to the peptide. Hence, they are also called phosphopeptides or phosphopeptone.

@rotein is present as a phosphoric ester of serine in which the hydro+yl group reacts with

one of the #9 hydrogen atom of phosphoric acid.

H

H @ HHH-H7H-H

@hosphoric acids

6erine


24/37


25/37

casein, together with other milk constituents including fat, forms a thin layer over the

surface of the milk. The application of heat to milk that is slightly acidic will cause the

precipitation of casein.

ne to two molecules of serine combines with " phosphoric acid molecule a

diphosphoric ester is formed. Therefore, phosphoric acid may form a cross link between

polypeptide chain. asein has acidic nature, as compared to other proteins, is )uite

distinctive as it has considerable base binding properties and can even liberate - from

carbonates.

alciumhydrogen9caseinate / Lactic acid 3cid casein precipitates / alcium

lactate solution&

The protein is precipitated only after pH $.0. The progressible removal of a starts at pH

$.0, when lactic acid develops.

a9caseinate / a#@$&- / $H#HH aH-@$&- /

-H#HH&-a/asein]

oncentration and dry form of milk when left for a long time gradually developed a

brown color. The browning in milk is caused by a maillard type of reaction between

amino group of milk protein and aldehyde group of lactose. 6uch products are unfit for

human consumption.

3s lactic acid develops, calcium from colloidal solution of protein moves to soluble

condition and this process continuous till the milk curdling. The calcium removes from

calcium hydrogen carbonate to form calcium lactate. The protein is precipitated or

progressible removal of calcium starts& only after pH $.0. The concentrated and dry form

of milk, when left for a long time gradually develops a brown color. The browning in

milk is caused by a maillard type of reaction between amino group of milk protein and

aldehyde group of lactose. 6uch products are unfit for human consumption.

It is known that casein is the macromolecule in the form of micelles and each micellecomposed of about "!!! casein molecules. asein is a mi+ture of different fractions and

is heterogeneous in nature. The different fractions are differing in composition, solubility

and rennet coagulation.

It has been found that in electric field, casein separates into three separate components

moving at different speeds. Those components are , and \ casein which are arranged in


26/37

descending order of mobility. The and casein are phosphoprotein of high )uality

where \9casein contain very little phosphorus. n the basis of electrophoretic analysis,

whole casein contains about 1' % of 9casein, -- % of 9casein and # % of \9casein.

3lpha casein is responsible for the stabili;ation of the micelle in the milk and it is the

component where readily attack. It is composed of two sub9fractions of 9s casein or

calcium sensitive casein& and κ 9casein or calcium insensitive casein&.

P"&C:P:5A5:$8 $F CAS&:8

*enerally, casein can be precipitated by the following methods.

,% 'cid coag!lation of casein

The pH value of normal milk often ranges from 0.0 to 0.1. >hen acid is added, the pH

will be lowered and pH $.0, i.e., IE@ will be obtained in which casein will be precipitated.

The casein precipitated with weak acids is free of calcium or free casein at pH $.

(epending upon the acid used, the product is termed sulphuric, muriatichydrochloric&, or

lactic acid casein.

3fter the addition of acid, first of all reaction will be taken place between a // D 4g//

salts and acid. The added acid should be in e+cess amount to remove calcium ion ca //&

from calcium caseinate. The a//creates metallic odor in processed product like cheese.

a9caseinate / Hl asein / al-

alcium phosphate ^a#@$&-_ alcium hydrogen phosphate aH-@$&-


27/37

The principle of alcoholic precipitation is the dehydration of adsorbed layer of micelle

and e+posure of [9casein and ultimately action of developed acidity due to microbial

contamination upon the milk.

Hence alcoholic precipitation of milk will be only possible if the milk is contaminated by

microbes and acidity is developed. This method is used to )uick check for freshness of

milk. If the milk is immediately precipitated out on adding alcohol, it is not fresh and vice

versa.

5% hen en;yme like renin and pepsin are added in milk,

precipitation of casein takes place with the formation of para9casein or para9casein. The

reaction is as follows.

[9casein of micelle para9[9caseinate / *lycomacropeptide

Hydrophobic Hydrophillic

insoluble in water& soluble in water&3ctually [9casein has "05 amino acids molecules. In the position of "!' th , there is

phenylalanine and on the position of "!0th there is methionine. The link between these

amino acids "!'9999"!0 & is the most weakest for en;yme action, thus it is more

favourable for proteolysis. Thus almost all the proteolytic en;yme acts upon this link.

hain "```.to``."!' para9[9caseinate insoluble&

hain "!0``.to``."05 *lycomacropeptide soluble&

In the above reaction, para9[9caseinate remains in micelle with s and casein.


28/37

In this phase, splitting [9casein into para9[9caseinate and macro9peptide take place.

b. 4hase -2 Secondary phase2 4recipitation phase

In this phase, calcium bridge form where para9[9caseinate is not present and their

synthesis occurs and finally precipitation occurs.

; a//

>% Heat precipitation of casein

@ure casein is not precipitated by heat, but in fresh milk prolonged heating at high

temperatures "!!o for "- or more hours or "-!o under pressure will cause the precipitation of casein. n boiling fresh milk, a thin layer of finely precipitated casein,

together with other milk constituents including fat, forms a thin layer over the surface of

the milk. The application of heat to milk that slightly acid will cause the precipitation of casein.

>hen milk is heated at "#!o for several hours " hrs& hydrogen bond rupture and 9

dimensional structure of casein disruption causes ultimately governing the proteindenaturation and finally precipitation occurs. The cooked curd casein is less soluble and

contain more ash than the other caseins.

En;ymes

3n en;yme is a biological catalyst elaborated by a living cell, milk en;ymes being

elaborated by the cells of the mammary tissue. The en;ymes produced by bacteria in milk

:ennet

[

s

s

/ *lycomacropeptide

@ara9[9caseinate

@ara9[9caseinate

s

a

s

s

s

s

a

a a

a

alcium9caseinate ppted&


29/37

can not be controlled as inactivated by high temperatures, they posses a pH of optimum

activity, and they e+hibit specificity for certain substrates.

4ilk contains numbers of en;ymes. The native en;ymes, i.e., those known to be

e+creted by mammary gland, may include several present in the leukocytes, e.g., catalase.

In addition, en;ymes of microbial origin may be involved. The latter may be present in

microorganisms, secreted by the organisms e.g., proteinases and lipases&, or released

after lysis. The native en;ymes can be present at different locations in the milk. 4any of

them are associated with the fat globule membrane. 4ost of the membrane originates

from the apical cell membrane, which contains several en;ymes. ther en;ymes are in

solution, i.e., dispersed in the serum, but some of these e.g., lipoprotein lipase& are partly

associated with the casein micelles.

Table " 6ome En;ymes in 4ilk

7ameptimum 3ctivity"

>here in milk Inactivation- pH Temp o& @otential 3ctual

anthine o+idase

6ulfhydryl o+idase

atalase

Lactopero+idase6upero+ide dismutase

Lipoprotein lipase

3lkaline phosphatase

:ibonuclease@lasmin

X2

X1

1

0.'

X5

X5

1.'2

#1

$'

#1

-!

##

#1

#1#1

$!

X-!!!

#!!!

'!!

#&#

$!

#!!

--!!!

!.#

SS'!!

!.!'

Fat globule membrane

@lasma

Leukocytes

6erum@lasma

asein micelles

Fat globule membrane

6erumasein micelles

1min 1#o

# min 1#o

- min 1#o

"! min 1#o1!min 10o

#! s 1#o

-! s 1#o

$! min 1#o

"

mol.min9"

.L9"

-Heat treatment needed to reduce activity to appro+imately " %.#""9-' mg en;ymeDkg milk.

4ost of the milk en;ymes seem to have no biological function in milk, even if they are

present in high concentrations e.g., ribonuclease&. ften, they do not significantly alter

the milk. 6ome milk en;ymes have an antimicrobial function or play other beneficial

roles. 3 few of the en;ymes may facilitate resorption of milk constituents into the blood if

and when milking is stopped. It presumably concerns plasma and lipoprotein lipase,

which are not very active in fresh milk through they are present in high concentrations

Table "&.

These, as well as some other en;ymes, can cause spoilage of milk during storage. 6ome

en;ymes are used for analytical purposes. Formerly, catalase was applied to detect

mastitis, but the correlation is too weak. Furthermore, particular en;ymes are used to

monitor pasteuri;ation.


30/37

&nzyme Activity

The properties of a solution are governed by activities rather than by concentrations, and

this certainly holds for en;ymes. The ma+imum rate of catalysis is e+pressed as k cat or

turnover number for the en;yme, i.e., the number of molecules of substrate converted per

en;yme molecule per second if the substrate is in e+cess and the conditions for the

en;yme pH, temperature, ionic strength, and other factors affecting en;yme activity& are

ideal. The total turnover rate is defined by Cma+ J k cat ^E_, where ^E_ J en;yme

concentration. 3ccording to 4ichaelis and 4enten, the velocity of reaction as a function

of the substrate concentration ^6_ is

vi J vma+ ^6_ D R m / ^6_& "

The 4ichaelis constant R m is a measure of the affinity of an en;yme for its substrate the

lower R m, the greater the affinity&. It depends on the type of substrate used and is thus a

variable ne+t to k cat , ? m e)uals the substrate concentration when vi J Cma+ D -Q only applies

to the initial velocity of reaction vi because reaction products may inhibit the reaction

product inhibition&Q moreover, the substrate concentration decreases during the reaction.

The following are the additional factors that can affect en;yme activity.

a. In addition are the above9mentioned reaction products, several

substances may inhibit the reaction products, several substances may inhibit

en;yme activity, e.g., because these substances also bind to the en;yme

competitive inhibition& or because they affect the conformation of the en;yme

molecule.

b. The above e)uation does not apply to so9called allosteric en;ymes.

c. 4any en;ymes need a AcofactorB. 3n e+ample is apoprotein -,

which is essential for lipoprotein lipase action. The concentration of cofactors in

milk varies.

d. There may be other stimulators that inactivate an inhibitor.

e. The substrate can be inaccessible. 37 e+ample is the triglycerides,

which are screened from en;ymes in milk by the fat globule membrane.

! - $

!

-

Cma+

D-

3ppro+imate;eroth9

order kinetics

3ppro+imate firstorder kinetics

#C

ma+

^6_

v i

"


31/37

Fig( 2 Effect of substrate concentration ^6_ on initial reaction rate vi of an en;yme reaction, according

to e)uation ". 3rbitrary scale.

f. The en;yme can be adsorbed onto particles, thereby becoming less

active. 6ome en;ymes lipases, proteinases& are adsorbed onto casein micelles.

g. The en;yme may be present in a nonactive form, a so9called

;ymogen, and slowly be activated. 3n e+ample is plasmin, largely occurring in

milk as the inactive plasminogen.

h. The en;yme may be slowly& inactivated. For instance, lipoprotein

lipase in milk loses activity, presumably caused by an o+idative reaction.

Some 'ilk &nzymes

". 'nti"acterial here the substrate H3 can include several compounds8aromatic amines, phenols,

vitamin , and so on. The en;yme can also cataly;e o+idation of thiocynate ^76 9_ by

H-- to an unidentified product that inhibits most bacteria. If the bacteria themselves

produce H--, as most lactic acid bacteria do, they are inhibited. In milk, H--

decomposition by catalase, is too to prevent this.


32/37

Lysosome is another bactericidal en;yme, it hydrolyses polysaccharides of bacterial cell

walls, eventually causing lysis of the bacteria. In cows’ milk the lysosome activity is

weakQ in human milk it is much stronger.

-% @#idored!ctases

a. Aanthine o#idase 4ilk is the best known source of the en;yme +anthine o+idase. 3n

o+idase is an en;yme which cataly;es the addition of o+ygen to a substance or the

removal of hydrogen from it. For the removal of hydrogen, the dehydrogenase is

sometimes usedQ for the donor of o+ygen, the term reductance is applied. The en;yme can

reduce nitratetrace amount in milk& to nitrite. This property is use in the manufacture of

cheeses, where nitrate is added to milk to prevent the proliferation of the detrimental

butyric acid bacteria. 7itrate inhibits these bacteria. If nitrate has been added to the milk,

nitrite is present in sufficient amounts in cheese, though it is fairly rapidly decomposed.

ows’ milk has a relatively high +anthine o+idase content. 4ost of the en;yme is

associated with the fat globule membrane.


33/37

# 4hosphatases 6everal phosphatases occur in milk.


34/37

The Aplasma lipaseB re)uires an activation treatment homogeni;ation or agitation& before

it produces rancidity. >hereas the ?membrane lipase’ re)uires cooling to place it in

contact with the substrate. ows late in lactation and on dry feed contain more of this

?membrane lipase’, and the milk is sub=ect to spontaneous lipolysisQ but many

investigators do not agree that lipolytic activity increases toward the end of lactation.

Lipase has not yet been crystlli;ed or obtained in pure form, and the percentage in milk is

still in doubt. The effect of heat treatment on lipase activity in milk and noted a decrease

as the temperature was increased. However, complete inactivation did not occur at 1#.5 or

2'o for #! min.

'. 4roteinases In milk at least two trypsin9like endopeptidases occurs. ne of these is

the so called alkaline milk proteinase, which is identical to the plasmin of blood. 4ost of

the alkaline proteinase in milk is present as the inactive plasminogen. The en;yme is

largely associated with the casein micelles. Its activity in milk varies widely, partly

because of a variable ratio of plasmin to plasminogen. Msually, the activity increases with

time as well as by heating, e.g., pasteuri;ation. 4ilk contains one or more promoters that

cataly;e the hydrolysis of plasminogen to yield plasmin. 4oreover, milk contains at least

one substance that inhibits the promoters&. The inhibitor is inactivated by heat treatment.

It also appears that leucocytes contain a promotor, and milk by heat treatment. It also

appears that leukocytes contain a promotor, and milk of a high somatic cell count

generally shows enhanced plasmin activity.

@lasmin can hydroly;e proteins to yield large degredation products and is responsible

for production of \9casein and protease9peptone from 9casein. The en;yme causes

proteolysis in some products, e.g., in cheese. In MHT milk products its proteolytic action

causes a bitter flavor and eventually can solubili;e the casein micellesQ in some cases,

gelatin has been obserbed. This is because the en;yme is very heat resistant. 3ccordingly,

appropriate MHT treatment e.g., "$!o for "' s& should be applied to prevent this

problems. In milk an acid milk proteinase also occurs, though with a lower activity. This

en;yme is less heat resistant than plasmin.

For whole raw milk, proteolytic activity showed a range of $9"-0 μgD 'ml with an

average of '1.!. The protease activity of milk was not serious affect in milk processing.


35/37

0. Lactopero#idase; It catalyses the transfer of o+ygen from pero+ides, especially

H--, other substances. 3ll milk contains pero+idase. 4ilk pero+idase is known as

lactopero+idase , it is a heme protein with an iron content of about !.!1 %. 4olecular

weight of about 2-!!!. Its optimum pH is 0.2, and pasteuri;ation temperature do not

inactivate it.

The average pero+idase activity of milk as --,!!! IM, colostrum -5-!! IM.

1. 'mylases8 It catalyses the hydrolysis of starch to de+trin or maltose. 3n amylases that

catalyses the hydrolysis of central glucosidic linkases in the starch molecule, thus

producing de+trini;ation, is designated as 9amylase, one that catalyses saccharafication

is called 9amylase.

ows milk contain both , and 9amylases. K9amylases is inactivated by heating milk at

''o for #! minQ 9amylase withstands 0'o for #! min without loss of activity.

9amylase, a normal , native constituent of cow’s milk. The amylase activity of the milk

was "!-5 IM μ4DminD"!!! ml D#1o&. 6ome milk contain low percentage of 9amylase.

2. 3ldolase8 The en;yme aldolase reversely splits fructose ",09diphosphate into

dihydro+yacetate phosphate and phosphoglyceric aldehyde. @resent in fresh milk in the

same concentation range as in blood serum. It is present in greater concentration in cream

than in milk. It is unstable when in milk, stability is enhanced by purification. It is

completely inactivated in milk by heating at $'

o

for -! mins.5. :ibonuclease8 This en;yme hydroly;es nucleic acid to its component nucleotides. It is

present in milk in relatively large amounts. The en;yme is )uite heat stable, there being

little loss when heated to 5!o for -! min at pH #.'Q however, under the same conditions

at pH 1, all the activity is lost. The optimum activity at pH 0.5 and 0! o. Its activity is

not reduced by pasteuri;ation. It content in milk about ""!! μ/"!!ml.

"!. Lysoome; It content of milk "# μgD"!!ml. For human milk it is $! !!! μgD"!!ml.

The average lysosome content in brown 6wiss, *uernsey, Holstein and ersey milks were

-", "' and ' μgD"!! ml, respectively. The stage of lactation or milk yield did not affect

lysosome secretion.

"!. Car"onic anhydrase8 The en;yme catalyses the hydration of - and the reverse

reaction, the dehydration of carbonic acid. It is a ink9containing protein associated


36/37

with the :


37/37

Fig( Timet’& and temperature T& of heating milk needed to inactivate some

en;ymes i.e., reduce the activity by about 55 %& and to prevent cold agglutination.

physchem prpty of milk

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