ABSTRACT
Reduced ascorbic acid retention in packaged and nonpackaged broccoli were measured by Barth et al. (1993) as
t (h) Packaged cA (mg/g)
Nonpackaged cA (mg/g)
0 5.6 5.6 24 5.38 4.82 48 4.76 3.86 72 4.59 3.75 96 4.42 3.25
Elementary Reactions and their Rate Expressions
Reaction Differential Rate
Expression Integrated Rate Expression
A k → products dc dt
kA = − c c ktA A= −0
A k → products dc dt
kcA A= − ln lnc c ktA A= −0
A B k+ → products dc dt
dc dt
kc cA B A B= = − dx
x x kc dtA
10 0 0−( ) −( ) =∫ ∫γ where γ = = −c
c x
c c c
,
Without catalyst
A Rk1 →
With catalyst
A Rkc+ → +cat cat
dc dt
kcA A= −
dc dt
k cA c A= −
ln lnc c k tA A c= −0
where
k k k cc = +1 2 cat
A Rk1 →
A Sk2 →
dc dt
k k cA A= − +( )1 2
dc dt
k cR A= 1
dc dt
k cS A= 2
ln lnc c k k tA A= − +( )0 1 2 c c
k k
2 0( )
A R k
→← dc dt
dc dt
k c k cA R A R= − = − +1 2 − − = +
+ ln( )
( ) ( )
1 11x
x k
x tA
γ γ
where xAe = value of xA at equilibrium
Solution: Integrating Equation 3.1 gives: ln lnc c ktA A( ) = ( ) −0 , where cA0 is the initial concentration of the reduced ascorbic acid in broccoli. Substituting the data into the integrated equation gives: ln . .c tA( ) = − × −1 69 5 54 10 3 with r = –0.98 and se = 0.037 with nonpackaged broccoli and ln . .c tA( ) = − × −1 72 2 58 10 3 with r = –0.97 and se = 0.006 with packaged broccoli.