2783 (1982). .8 (1984). ... any previous treatment ( 7 ) . Houever ... 2 s h o u s an e n z y m a t i c b r o u n i n g k i n e t i c a t 2b "C or. an appiè ... the d i f f e r e n c e b e t u e e n t h e 280 nm and 260 nm v a l u e (D.O.D) and ... time considered.
DETECTION
OF
ENZYMATIC
M.C.Nicoli'
BROUNING
I N FRUIT
C.R.Lerici''
R.Massini'
PRODUCTS
and
D . Mas t r o c o i a-'
'
I s t i t u t o d i Tecnologie A1iroentari-University v i a M a r a n g o n i 97 33100 Udine Italy
'
Dipartimento d i Protezione e Valorizzazione Agro-AiIraentare University of Bologna v i a S.Giacomo 7 «H>
Fig. 2. E n z y m a t i c b r o u n i n g k i n e t i c f o l l o u e d b y t h e e v a l u a t i o n o f t h e d i f f e r e n c e b e t u e e n t h e 2 8 0 nm a n d 2 6 0 nm v a l u e ( D . O . D ) a n d t h e m e a s u r e m e n t a t 4 2 0 nm. For f i r s t
the order
Kinetic
range
of
time
considered
both
tuo pararoeters
shou
a
kinetic. rate
constants
are reported
i n table
1.
TA3LE 1 Constant rates of enzymatic brouning r e l a t i v e l y t o s p e c t r o p h o t o m e t r i c m e a s u r e m e n t s a t 4 2 0 nm
t o DOU
index
and
Index
Constant rate k (hours"' )
C o e f f i c i e n t of determination
DOD
0.127
0.9b6
0.035
0.834
420
nm
Froro DOD
i s
observation a more
traditional
of the kinetic
sensitive
index
spectrophotometric
rate
constants
of enzymatic measurement
66
i t appears
brouning
a t 420
nm.
than
that the
ot: a n
appiè
jhotomecric
Heating influence studied.
appiè
of
Flg.Ja
the
ultraviolet
for
a
shou at
blanched as
non
2 8 0 nm
puree
non
and f i g . 3 b region and
a t I i 5 'C
brouning report
depending
f o r d i f t e r e n t tiraes t h e
on
DOù
the variation on
tittie
to first
brouning Maillard
causes
an
reaction
paramet^r
uaa
i n absorbance i n
of heating
e n z y m a t i c a l l y brouned
enzymatic
due
samples
enzymatic
respectlvely
puree.
Ihese
increase
of
fiqures
absorbance
products C l l ) .
I.i. no
tréated
1 Hour 2 Hour8
I.I
u
•luation of C D . 0 . D) a n d
< H
^ters
shou
a » _ IM
9M WAVELENGHT
; index
and F i g . 3a. Changes o f s p e c t r a l b e h a v i o r o f a b l a n c h e d s u b j e c t e d t o one a n d t u o h o u r s t r e a t m e n t s a t 115
.cient of ination
appears ng
than
that the
67
pure* "C.
sample
ili*
n«
«1»
*u
j»
WAVELENGHT F i g . 3b. puree In the
both
broun
causes
Changes o f s p e c t r a l sample s u b j e c t e d t o