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.