Principales resultados y beneficios esperados

strai ns

•

Thua the finding

.,.

of Cordon

Speck ( 1 96 5a ) that a "bi tter " strai n was mor e

prot eolytic than a "non-bitter " strain in milk cul tur e grown at

ei th er 22° or 32° C was confirmed in th e pr esent investigation

for strains HP and E8 , but could no t be sub stantiated as a general

featur e of all "bi tter " and "non-bi tter " strains.

IV . SURVIVAL A�ffi

ACTIVITY

OF

STARTERS

Tn e d e a th ra t e of star t er bac t er i a in ch e e s e has b e en c o n-

si cl er e c. by s om e au th o r s to i nflu en c e ch e e s er i p ening an d fl avour

d evel opr.: cn t a s o. r e cul t o f th e l ib er a ti on o f j n tr a c el lular e;.z� e s

(?ro.nklin

& Sh arp e , 1 9 6 3 ; R c i t er e t 1 9 67 ) or th e l i mi ta ti on o f th e l evel s o f en zyme form e d

(! ...

n d er s & Jago , 1 96 4 ) .

�n e ext e n d ed survival o f c er tai n s

t

rai ns in th e ch e e s e and th e i r c o n t i nu e d m e tabo l i c ac tivi ti e s

hav�

also been i�pl i ca ted in th e

dev elopm ent o f fl avour defec t s

(

Perry , 1 9 6 1 ; 'le damuthu e t al . ,

1966).

An inves Liga. -: i o n ·..:a s , th er efor e , un·ier taken o f th e bl'O'dh , survival and

proteolytic

activit

y

o f s tar ter s trai ns i n condi ti o n s iia i ch wer e U.esi gr,ed. to simul a t e :;;ome o f tho se encoun t e r e d in

ch e e s cmaking and rr:a turation.

T.u. e fo l l ov;ing s tar ter s ue.r e used:

.§..

cr e�ori s str_ains AM'1 , Al�2 , c 1 3 , E8 , HP , 1viL 1 , R1 , us3 and z8 ; and S . l ac ti s strains _H1 and ML 0 • TI1e fl avour charac t er i s ti c s of ch e e se made wi th the s e

s trains have b e en detailed i n Tabl e I .

S t o ck s ter il e sk i m mi lk cul tur es were tran sferr ed hli c e through pa s t eur i z e d sk im milk

( PSM)

1vi th

1 2 hr incuba tion

a t

30° C

b efore being used as i no cula. Pr evrarmed PSM

( 1 , 000

rnl

)

was

ino culated iri th

2% ( v/v_)

o f th e s e star ter cul tur e s and i ncubated at

35° C

until th e pH' rea.ched

5. 2,

the pH a t which Ch e ddar ch e e s e

.

curd i s normally sal ted. · At thi s point ,

250.

ml amounts o f th e cul tur e uer e aseptically transferr e d to 3 s terile fl ask s . The

47

fi r s t fl a sk co::1.ta.i ned. 2 . 5 g

_{Caco 3}

only , t

:q.

e second fl as1: 2 . 5

g

Caco 3 and

1 0

g Xa. Cl , ancl th e thi r d fl as}c 2 . 5 g Ca co3 an d

1 2. 5

g ra �a .

':bu s

all th e cul tur e s tra�1 sferr e d

to

the se fl

a

_sk

s

con- tai ne\.L

1% (>·/v)

Ca C0 3 '

v;hi l e c_{ul tu}r

e

s i n b e second and th ird fl ctsk .;:; con tai ned

i n

ctddi tion 4 an d 5 %

( v;/v)

!\a Cl

r e np e c ti vely.

':'h e

_{Ca. co3}

hel d the pli con s tant a t cl o s e

to th e

approxi ma te

p H

o f che ese, and th e levels

o f Na Cl

errpl

o

yed

wer e

o f the

order o f

th e " so.l t-in-mo i s tur e " l evel s

commonly found i n

commer c i al Ch eddar

ch e e s e s ( La,.;r e n c e _& _·_{}il l e s}_,

1969 ) .

_·

T'n e

cul ture s

'""e:::- e th en co o l e d to

_{1 3° C}

in

a wat

e

r bo.th

and

h e l d for

1 ·�

day s at thi s

tenp eratur e.

In comiTiercial

pract

i

in

?!e w Zealand , Ch ecldar ch e e s e i s

i

nit

i

.::J.ll

y kep t at

1_{3 C}

fo r

1 4 day s ,

fol l owed by sub s equ ent m a turing a t 7 ° C .

Th e cour s e o f pro t eo lysi s of th e cul tur e s wa s fo ll oHed by

the

m eth

o

d o f

Hull ( 1 911-7 )

a s

d e scri b e d earl

i

(p . 4 1).

Sampl e s , approxi:n :::�. t el y

1 0 ml ,

-...;er e take!"l

a t th e

t i m e of

inocul_a- t i o n , again _{at the s tage}1v-h en th e cul tur e s r ea ch ed pH

5. (

L e . imm e di a t el y b efor e th e a ddi ti on o f lTaCl e.::1d Ca co 3

)

, and at

i nt

ervals duri ng

th e

sub

s_eq

uen

p er i o d a t _{1 3° C. Undi s solved}

Caco 3 i n th e sampl e s wa s

r

o

ved oy

c en tr i fuga ti o n ,

and

p

rote

in

5

ml sa

m

ple o f the su

p

r

natant cul tur e wa s

p

rec

i

tat

ed

by

th @ a�di ti 9n

gf 1 0

ml g f

1 2%

TCA .

In document Memoria de actividades de Red es (página 87-89)