140 Produce Degradation: Reaction Pathways and their Prevention
the brown discoloration of litchi fruit estimated by sensory analysis as a function
of atmospheric composition. Results reported in Figure 5.14 show the detrimental
effect of both dehydration and high CO 2 concentrations. A low oxygen concentration
is also beneficial to the external color of litchi fruit. The color of mushroom caps
measured as the L* parameter of the CIE system is well correlated with the visual
appearance of mushroom [136]. White strain cultivars of mushrooms with L values
80 would be acceptable to wholesalers. Those with L < 70 would be rejected by
French consumers. As shown in Figure 5.15, there is a good relationship between
the luminance of the pileus surface after 7 d of storage at 10°C and the CO 2 content
of CA [40]. It is possible that very low percentages of CO 2 (less than 2.5%) improve
color compared to controls kept under normal atmosphere. Oxygen concentrations
from 5 to 20% have no marked effect on external color. This browning phenomenon
not only affects the surface color but also the color of inner tissues. Internal browning
as a function of CA composition follows the same pattern as external browning, but
to a lesser extent. However, CO 2 concentration is not the only factor involved in the
brown discoloration of mushrooms. The availability of O 2 at the intracellular level
and O 2 affinity for other oxidases may play a role in color deterioration. The influence
of O 2 is also significant but much less than that of CO 2. These conclusions confirm
previous results of Smith [137] and Tomkin [138] on external color. Nichols and
Hammond [139] found a linear regression between the internal color of mushrooms
and their respiratory rate in prepacked, overwrapped punnets. These authors also
FIGURE 5.15Changes in the color parameter L of Agaricus bisporus L. as a function of
O 2 and CO 2 concentrations. Color was measured after 7 d of storage at 10°C. Discoloration
was evaluated by measurement of L in the Lab* CIE color system. (From Lopez-Briones,
G. et al., Int. J. Food Sci. Technol., 27, 493, 1992.)
2.5 5(^1015)
20
15
10
5
68
70
72
74
76
78
80
82
84
Luminance L*
CO 2 (kPa)
O 2 (kPa)