Críticas a la concepción lineal del transporte sobre el territorio

patt erns were s c anned \vi th a densitomet er and the

p eak areas o f the c as e ins c ompared with thos e from

th e gel patt erns for the milks .

as

�

I

Fig . 5 . 1 :

-.. . l · i.• ..

2 3 4 5 6 7 8

9

1 0 1 1 1 2 13

G e l e l ec trophores i s ( pH 8 . 4 ) o f the cas e ins pres ent in the ultrac entrifuge s era , ob tained by s edim ent ing c aprin e , ovine and b ovine cas e in mic e l l e s at differ ent t emperatures . 1 , who l e c aprin e c a s ein ; 5 , who l e ovine c as e in ; 9, who l e bovine cas ein ; 2 , 6 , 1 0 , 1 1 , 4°0 s erum � 1 has twic e as much s ampl e as 1 �; 3 , 7 , 1 2 , 2000

s erum ;

4 ,

8 , 1 3 , 30 °0 s erum . _{The dire c t i on of elec trophores is is indicat ed .} (,.) ₀₀

l

39 I t i s evident ( Fi � . 5. 1 , Table 5 . 1 ) , that a c ons i der­ ab l e amount of th e p-c as ein in mi lks from the thr e e s p ec i e s was s o }.ub l e a t 4°C . Only a t rac e of (3- c as ein was s o lub l e at 20°C in b ovine milk , with none evid ent at 30°C . C aprine and ovine mi lks had 15% and 21 % r e s p ectively , of th eir �-cas ein frac t i on s o lub l e a t L�°C , c ompar e d with 1 0% for b ovine mi lk.

A numb er of minor c as e in ' c omponents wi th e l e c trophor etic mob i l i t i es l e s s than tl:ie (3-c as eins an d which were s o lub l e in c aprine and ovine mi lks at 20°C , remained s o lub l e in c aprine milk at 30°C . Th e s o lubility of the ovine nnd c aprine

"p- c as eins" at high t emp erature c an largely b e a ttribut ed t o

th e minor c as eins evid ent in th e (3-c as ein region .

O ' C onnor and Fox ( 1 9 73 ) , in a simi lar s tudy , found 1 0% and 1%, res p ec tively o f the (3 - and as -cas e ins in b ovine mi lk were s o lub l e at 5°C , s imilar t o the J,-res ent r e s ult s ( Tab l e 5 . 1 ) . Their values for t3-cas e in in c gprine milk a t 5°C and 20°C were higher than thos e in ·rabl e 5 . 1 , b eing 2570 and 1 0�5 , r e s p e c tively . Th e proport i on of s o lub l e �-c as ein in ovine milk was s imilar at 5°C and 20°C to the r e sult s in Tab l e 5.1 , b eing 1 5';v and 2;b , res pec t i vely . Furth ermore , 0 ' C onnor and Fo�c ( 1 973 ) obs erved minor c omponents in ovine and c aprine milks , s imilar to tho s e in Pig . 5 . 1 , that Here s o lub l e at 5°C and 20°C wit h e l ec trophore tic m ob i lities in alkalin e gels

l e s s than the (3 -c as eins . O ' C onnor and Fox ( 1 973 ) des i gna t e d th e s e c omponents as . "minor (3 -c as eins " , s inc e they were not r eadily hydr o lys ed by r ennin and were s o lub l e at 5°C and 20°C . D e t ails of a pr eliminary att empt made in this s tudy t o

e s t ab l ish the ident i t y o f th e s e c a s eins are outl ined in Chapt er 1 2 . 2 .

and Solvat i on of C �s ein Mic el les

The vo luminos i t y and s o lvat ion of c as ein mic e l l e s fr om c aprine , ovine and b ovine milks were measur ed at 4°C and 30°C from their intrins ic vis c o s it i e s .

'

...

IJ.'he r e lative dens ities o f the milks and s era , ob tained · ·

b y pycnometry , ar� c ompar ed with value s obtained by Ne j im

( 1 96 3 ) for ovine milk and thos e r e port ed by Macy et al . (1953 ) for c aprine and bovine mi lks ( Tabl e 5. 2) . The value obt ained -

by N e j im

(

'1 96 3 ) f o r the r e l �J t i ve d ens i t y o f ovine m i l k Has c ons i d erably l o\j er tho.n tl1n t ob t a ined in this s tudy.

'r ab l e �) . 2

H e l n t iv e D e n: J i t i es o f I'Ji lks and

U l () era

/1 "

()vin e I C a prir..e

'1

Bovine c..

l'"lilk '1 • ()ll6'1 30°C S e i'llJ'Il 1 • 027LJ- 1+ oc _{s e rum 1 . 0 3 22} I"J i lk '1 . 0 3 663 '1 . Me as ur e d at 25°C 2. Measur e d a t 20°C 1 . 03 3 '1 1 . 034 1 e 0 �04 1 . 0 25 1 . 0 280 1 . 0 27 '1 . 0 3 34 1 • 0 3 21� � Va l u e obtained by t e j im ( 1 963 ) at 1 5 °C . 4. V cJ.lues r e port e d b y Hac y et al . ( '1 9 53 ) .

Lj.J

Th e r e duc ed viscosities o f the mi lks and di luted m i lk fracti ons ( r E: l a t iv e t o u.ltrac entr i fuge s erwn ) v·.r ere us e d t o d e t ermine t h e intri ns i c vi s c o s i t i e s o f th e casein mic e l l e s at 4°C and 30°C . The intrins i c v i s c o s �_ t i e s o f the mic e l l e s from

c apr in e , ovine and b ovin e m i lk were ob t a in e d bj l in e ar l e a s t s quar e s analysis o f the r e du c e d viscosity pl o t s , s ome o f

whi c h are shown i n Figs . 5 . 2 , 5 . 3 and

5 . 4 .

Th e val u e s

ob t ained for the int rins i c vi s c o s i t i es , vo lw;1ino s i t i e s ,

Huggin ' s c ons t an t , k ' , and the c onc en tra t i o n o f c a s e i n tn the

mice lles ar e p r e s ent ed in T ab l e 5 . 3 .

B orne variation in th e int rinsic v i s c o s i ty , and h enc e v o lumino s i ty va

l

ues w e r e appar ent b e twe en the di fferent sample s of mi lk . It is evid en t from T ab l e 5 . 3 that w i th t wo exce

p

ti ons t h e r e w e r e no appr ec i ab l e d i f f e r enc e s b e tw e en the intrins i c vis c o s it y a n d vo lwninos i ty values a t 4°C and 30°C for the s am e s a�p l e o f mi lk . The r e s ul t s for ovine m ilk ( 1 2/ 1 2/72 ) may b e un:c e l i ab l e since this was :--r: end o f

l ac t at i on m i l k s ampl e wh i c h conta ine

d

an abnormally hi gh c onc entrat i on o f pr o t e in .

c w u

15

� 5

_w a::

0

1

2 CO NCE NTRAT I O N

(. 102 gfm

I

)

Fig . 5 . 2 : Plots o f r educ ed vis c o s i ty for caprine c as ein mic e l l e s agains t c onc entra t i on of mic e l l ar c as e in

at 4°C

(•)

and 30 °C

(e) .

Ul trac entri fuge s era

prepared at 4°C and 3 0°C were us ed as refer enc e

s o lvents .

15

-

ep

_-

�10

8

c 14.1 u ::;) c w

0::: 5

0

2 3 ·coNCE NTRATI O N

(•102 g/ml)

Fi g . 5 . 3 : Plots of reduc ed vi s c o s i ty for ovine c as ein

mic e l l e s agains t c onc entrat i on of mic e l lar c as ein at 4°C

(•)

and 30 °C

(e) .

Ul trac entrifuge s era pr epar e d at 4°C and 30 °C were us ed as referenc e s o lvent s .

2 0

0 2

CONCENTRAT I O N

(e.102gfin1)

Fi g . 5 . 4 : f l o t s o f reduc ed v i s c o s ity for bovine c as ein mic e l l es agains t c onc entra t i on of mic e l l ar

c as ein at 4°C

(•)

and 30 °C

(e) .

U ltrac entri fuge s era prepared at 4°C and 3Q °C wer e us ed as

ref erenc e s o lvent s .

Tab l e

I nt rins ic Vis c o s i t � c s and Voluminos i t i e s o f Ovine and Bovine Cas ein Mic e l l es

I ntrins ic Cas ein

vis c o s i t y , Vo luminc s i ty ( V ) Huggin ' s c onc entrat i on

Dat e

[77 ]

ml/g ml/g C ons tant

(k ' )

g/ml

30°C 4°C 30 °C 4°C 30°C 4°C A00 ,..., ./ v 4°C Ovine milk 1 /1 2/7 2 6 . 20 - 2 . L�8 - 0 . 9 - 0 . 0474 1 2/1 2/72 5 . 63 6 . 55 2 . 25 2 . 62 0 . 5 1 . 0 0 . 0 5_94 0 . 0 587 1 9/ 9/73 7 . 25 7 - 53 2 .. 90 3 . 01 0 . 6 1 . 1 0.0453 0 . 0442 27/ 9/73 6 . 43 6 . 30 2 . 57 2 . 52 0 . 9 1 . 9 0.0450 .. 0 . 0400 4/1 0/73 7 - 73 7 . 1 2 3 . 09 2 . 87 0 . 7 2 . 4 0 . 0456 0 . 0385 -- Mean 2 . 66 2 . 80 G aprine milk 25/ 9/73 7 - 3 5 7 . 88 2 . 94 3 . 1 5 0 . 7 2 . 2 0 . 021 4 0 . 01 83 1 /1 0/73 6 . 53 8 . 90 2 . 61 3 . 56 0 . 6 1 . 2 0 . 0255 0 . 021 2 1 8/1 0/73 6 . 01 - 2 . 40 - 4 . 4 - 0 . 01 92 -- Mea:a. 2 . 65 3 - 3 5 Bovine milk 9/1 0/7 3 - 8 . 40 - 3 . 36 - 1 . 6 - O e 021 6 1 6/1 0/73 7 - 9 5 7 - 25 2 . 96 2 . 90 1 . 2 4 . 1 0 . 0235 0 . 01 93 -- Mean 2 . 96 3 . 1 3 +:­ +:-

45 I t is appar ent from th e vo lumino s ities o .f . the c a s e in mic e l l e s from c aprine , ovine and b ovine milks ( Tabl e 5 . 3 ) ,

that the mic e l l es did not appr eciably change th8ir hydro­ dynamic s i z e as the t emperature was decreas e d from 30°C t o 4°C . Furth ermor e , th ere was l e s s c as e in in t h e mic e l l e s a t 4°C than at 30°C ( Tab l e 5 . 3 ) , c ons is t ent with di s s ociation of cas e ins from the mi c el l es at low t emp eratur e .

The value of Huggin ' s c ons tant , k ' , c a lculated from the gradi ent of the grap� of reduc ed vi s c os i ty agains t c on­ c entrati on and the intrins i c vis c os it� is generally c ons idered to be related to the int erac t i on b etween s o lut e mol ecul e s

( Bradbury , 1 970 ) ( Chapt er 3 . 1 1 ) . At 30°C , values of k ' range fr om 0 . 6 t o 1 . 2 , with one exc eption (' rab l e 5 . 3 ) . At 4°C , values of k ' were c ons i d erably higher , and with one

exc ept ion , range from 1 . 1 to 2 . 4 . Values o f k ' at 4°C wer e a lways great er than thos e at 30°C . This was du e t o the

s l ope of the r educ ed vis c o s i t y plots ( Fi gs . 5 . 2 , 5 . 3 and 5 . 4 ) , s inc e the intrins ic vis c os ity values were s imi lar at 4°C and 3 0°C . The inc reas e d value o f k ' at 4°C , c ompar ed with 30°C may b e du e to inc r eas ed int erac tion b et1:1 e en the dis s o c iat ed c as eins and �he c as e in mic e l l e s , as wel l as inc r e as ed inter­ action b etwe en the mic e l l e s .

From the average voluminosities o f the c as ein mic e l l es ( Tab l e 5 . 3 ) , values were obtained for the s o lva t i on of c as e in �ic e l l es from c aprine , ovine and b ovine milks a t 4°C and

30°C ( Tab l 6 5 . 4) . Thes e c as e in mic e l l e s o lva t i on values , obtained by vis c os i ty measur em ents , are c ompar e d in T ab l e 5 . 4 with c as e in-p e l l et s o lvat i on val ue s , obtained by ul tra­

c entrifugat i on of mi lk samp l e s at 30°C ( Tabl e 4 . 3 ) and at 4°C . C as e in-pe l l et s o lvati on values were obt ained at 4°C by c entrifuging mi lk samples for 1 h at 1 02 000 g . The

c entrifugal forc e us ed to s ediment th e mic e l l e s was l e s s than that us e d at 30°C ( 3 26 000 g for 20 min t o 1 80 min ) .

The mic e l l e p e llets ob t aine d at l ow t emp eratur e s were very " s o ft " , c ompare d to the "hard rubb er- lik e " t extur e of the p e l l et s at 30°C . C ons equent ly , difficulty was

experi enc ed in s eparat ing th e mic e l l e and s. ert,m phas e s o f p e l l ets s ediment ed a t l ow t emperatures .

Tc.1b l e ·

S o lva t i on o f C a s e i n Mi ce lles water

Ovine C aprine bovine

V i s c o s i t y I�easur em en t s 1

3 0 °C 1 . 96 1 . 9 5 2 . 26

4°C 2 . 1 0 2 . 6 5 2 . 43

U l trac ent r i fuga t i on c_ ')

3 0°C 2 . 0-1 . 6

1

• 97-1 •

5L�

2 . 1 2-1 . 57 4°C 2 . 29 2 . 83 3 . 1 6 7 D e v.Jan et ;{ l .

( 1 973 ) /

3 . 67 1_1homp s on e t a l . ( '1 969 a ) 4. '1 . 60 1 . 90 1 . S o lva t i on values f or c a s e in micel les w e r e c a l c u l a t e d from t h e avera g e v o l umino s i t i e s i n T ab l e 5 . 3 us ing the expr e s s i on :

V =

- 0

v 2 + o'1 v1 ( Chapt er 3 . '1 1 )

� C as ein- p e l l e t s o lvat i on va l u e s ( g wa t er per g dry mic e l l e p e l l e t ) at 30°0 w e r e ob t a ined from Tab le 4 . 3 . Values a t 4°C w e r e obt ain e d b y cent r i fuging mi lk

s ampl e s for 1 h at 1 0 2 000 g .

3. 0b t a i n e d a t 25°C from vi s c o s 1 ty m e as ur ement s .

4. C as ein-p e l l e t s o lvat i on va l u e s ob t a i n e d a t 3 7°0 b y u l t rac ent r i fugat i on of m i l k s ampl e s a t 6 8 0 0 0 g for 3 5 m in .

46

C as e in mic e l l e s o lva t i on values m e as ur e d at 4°C from

vi s c o s ity m e asur em ent s ( Tab l e 5 . 3 ) were s l i gh t l y h i gh er than

tho s e obt ai n e d at 30 °0 ( T ab l e

5 . 4 ) .

C a s e in-p e l l e t s o lva­

t i o n va lues ( ob t ained by ult rac ent r i fugat i on ) at 3 0°C w e r e

s im i lar t o tho s e ob t a ined fr o m vi s c o s i t y m e a s ur em en t s a t

3 0°C . Likewis e , wi th th e p o s s ib l e exc ep t i on o f b ovin e m i l k ,

t h e cas e in- p e l l e t s o lvat i on va l ue s at 4°C wer e s i�i l ar t o

Th e value o f c a s e in mic e l l e s o lvat i on ob t a in e d for b ovine mi lk by D ewun e t al . ( 1 97 3 ) from vi s c os i ty measur e­ ment s at 2 5°C , wa s c ons iderab l y h i gher than tho s e ob tained

in t h i s s tudy by u l t rac entri fugat i on or vi s c o s i t y m e a s ur e­

In document Estrategias de comunicación y cambio del sistema ferroviario en España (1992 2012) (página 113-116)