Produce Degradation Pathways and Prevention

Packaging and Produce Degradation 139

resulted in increased pH and better retention of chlorophyll than control samples
stored in air. These effects became more pronounced as the concentration of CO 2
in the atmosphere was increased. The degradation products of chlorophyll in CA-
stored asparagus were exclusively pheophytins. It may be postulated that in spite of
lowering the pH, which expectedly favors pheophytinization, CO 2 has a more pro-
tective effect against other chlorophyll degradation pathways.
Conversely, chlorophyll synthesis in vegetables exposed to light after harvest,
such as white asparagus, endive (chicon), and potatoes is associated with decreasing
quality. Greening of some plant tissues is accompanied by the production of the
poisonous glycoalkaloids solanine and chaconine [132]. It has been demonstrated
that green discoloration can be prevented by maintaining these sensitive commodities
in modified atmosphere containing 15% CO 2 [133,134]. Experiments on endive
(chicon) showed that the oxygen depletion likely plays a major role in greening.
This alteration is prevented by maintaining plant tissues in atmosphere with less
than 1% oxygen. The effects of high CO 2 and low oxygen on the greening and
degreening mechanisms are still unclear.

5.2.2.5.3.2 Enzymatic Browning
Enzymatic browning is the main color deterioration in bruised or injured plant tissues
[135]. The mechanisms of enzymatic browning are detailed in Chapters 2 and 11
of this book. The reactions result in the formation of brown, red, or yellow molecules
that may also degrade the appearance of intact tissues such as litchi and mushroom,
but overall it is one of the main causes of spoilage in fresh-cut processing and
distribution.
One of the most important problems with litchis is the loss of the red coloration
of the peel during storage. Commercialization becomes impossible after browning,
so it is very important to maintain this red color. As an example, Figure 5.14 shows

FIGURE 5.14Effect of gas composition on litchi fruit discoloration assessed by sensory
analysis (the lower the rank, the higher the quality) after 6 weeks at 1°C. (From Varoquaux,
P. et al., Fruits, 57, 313, 2002.)

0

1

2

3

4

5

6

20/0 20/0 5/20 5/15 5/5 2/10

Rank

Atmosphere composition (O 2 /CO 2 )

Low RH

the worst

High RH

the best