Produce Degradation Pathways and Prevention

Packaging and Produce Degradation 127

of respiration rate in air is a good index of the physiological condition of the
commodity. Figure 5.7 shows the effect of storage of mushrooms at 10°C for 7 d
in controlled atmosphere containing from 0 to 15% CO 2 on the respiration rate
measured at 10°C under normal atmosphere [40]. There is a good linear relationship
between CO 2 concentration in the CA and the increased respiration rate (regression
coefficient = 0.965), but the respiration after exposure to CA is not significantly
affected by the O 2 concentrations of the CA from 5 to 20%. The temporary inhibition
of mushroom catabolism by CO 2 results in an enhanced respiration when the product
is again placed under normal atmosphere. This increase in respiration may be
considered as a stress response, suggesting that CO 2 concentrations above 5% have
a marked phytotoxic effect on mushrooms.

5.2.2 OPTIMAL GAS COMPOSITION

5.2.2.1 Determination Procedure (Controlled Atmosphere)

The optimal gas composition for MAP is determined using a large range of atmo-
sphere compositions. The CA facilities are based on three different principles:

1. Diffusive membrane
   CA facilities fitted with a diffusive membrane permit the passive equilibration
   of the storage atmosphere to target O 2 and CO 2 composition, depending on
   the diffusive properties of the membrane (area and O 2 and CO 2 permeabil-
   ities). Under commercial conditions only silicone membranes were used,

FIGURE 5.7Respiration rate at 10°C of mushroom (millimoles per kilogram per hour) as a
function of storage atmosphere composition. (From Lopez-Briones, G., Augmentation de la
durée de vie du produit frais: Application au champignon Agaricus bisporus, Ph.D. thesis,
Reims University, France, 1991.)

0

5

10

15

10

15

20

0.00

1.00

2.00

3.00

4.00

5.00

6.00

RR

O^2

(mmol

.kg

−^1

.h

−^1

)

CO 2 (%)

O 2 (%)