286 Produce Degradation: Reaction Pathways and their Prevention
(absence of chemical residues and microbial contamination) (Thompson, 1996;
Piagentini et al., 2002).
9.8.1 APPEARANCE AND COLOR
The initial attraction leading to the purchase of any fresh produce by consumers is
based on its appearance. The consumer’s perception of visual quality is influenced
by size, shape, color, uniformity, surface texture, consistency, and visible defects
and blemishes of the produce. Many physical defects of fresh produce result from
water loss after harvest and during storage; some of these defects include shriveling,
wilting, wrinkling, and internal drying (Hruschka, 1977; Grierson and Wardowski,
1978; Kader, 2002). Considerable loss of water from fresh produce leads to a
shriveled appearance; the skin’s elasticity can no longer accommodate the reduction
in volume associated with weight loss. Thompson et al. (2001) reported that the two
most noticeable effects of delays in cooling of produce are shriveling and the loss
of fresh, glossy appearance of commodities that lose water and quickly show visible
symptoms at low levels of water loss, such as leafy vegetables. They recommended
a loss of no more than 1% to prevent consumers from seeing the effect of shrivelling
due to water loss. Izumi et al. (1996) noted that zucchini slices stored under 0.25%
O 2 lost less weight and had less browning/decay and greater shear force than those
stored in air. Gonzalez-Aguilar et al. (2000) found that a combination of antibrown-
ing agents and modified atmosphere packaging reduced browning and deterioration
of fresh-cut mangoes stored at 10°C. They concluded that the high humidity created
in the in-package atmosphere alleviated tissue dryness and was an important factor
in the ability of the antibrowning solutions to prevent browning and decay. Baldwin
et al. (1996) reported reduced weight loss and browning of cut apples treated with
Nature SealTM or ascorbic acid added to edible coating in vacuum-packed trays
compared to overwrapped tray storage. Barth et al. (1992) found misting of broccoli
during cabinet display resulted in significant retention of chlorophyll and green color
as measured by hue angle.
9.8.2 TEXTURE
Consumers’ expectation of the texture of produce is key in determining the quality
of the produce being purchased. Consumers’ perception of texture quality varies
depending on the produce; some produce is expected to be high quality if it is firm,
while others are judged to be of optimum quality if it is soft. The texture quality of
fresh produce is judged by feel and sound, both of which reflect crispness and
crunchiness. Plant cell constituents that are important in texture are the parenchymal
cells, which have the ability to absorb water and generate hydrostatic pressure called
turgor pressure. It is this turgor pressure that gives fresh produce its characteristic
crispness and firm texture. Loss of water from cells of fresh produce results in loss
of crispness and texture, which is accompanied by breakdown of cell wall compo-
nents. Harker et al. (1997) in their review reported that turgor has a major function
in determining tissue strength and that it is related to water loss and has a profound
influence on produce’s texture. Texture evaluation is also used to indicate freshness