Pineapple - Crop Post-Harvest: Science and Technology - page 152

proteins and other phenolic compounds to form complex
brown polymers. The brown or black colour of the affected
tissue is due to the formation of these compounds. The
phenolic substrates for PPO are located in the vacuole, and
therefore the enzymic browning reaction only occurs when
sub-cellular compartmentalization is altered. The
p -coumaric acid, ferulic acid, caffeic acid and sinapic acid
are identified as the major phenolic compounds in
pineapple (Van Lelyveld & De Bruynm 1977) and it has
been confirmed that the concentration of coumaric acid
and sinapic acid and the activity of polyphenol oxidase are
higher in the tissue undergoing internal browning (Teisson
et al . 1979). In fruit affected by the chill-induced internal
browning disorder, PPO activity was tenfold higher than in
unaffected fruit, and there was a direct correlation between
PPO activity and the severity of internal browning
symptoms (Stewart et al . 2001). Southern blot analysis
suggested the presence of at least four PPO genes in
pineapple. The chilling induces the de novo synthesis of
PPO in Smooth Cayenne pineapples (Stewart et al . 2001).
PPO activity of pineapple cv. Mauritius (Queen) under
prolonged cold (10°C) storage increases progressively in
parallel to the increase in the intensity of internal browning.
The increase of PPO activity coincided with the initiation of
internal browning. The level of PPO activity in relatively
resistant cultivars (e.g. 'Kew') was low throughout the
period of cold storage (Weerahewa & Adikaram 2005a). An
increase of PPO activity in pineapple fruit Smooth Cayenne
was related to the incidence of internal browning symptoms
both temporally and spatially (Zhou et al . 2003). The effect
of maturity on susceptibility to internal browning was
highly correlated to the response of PPO activity to chilling.
Weerahewa and Adikaram (2005a) studied physico-
chemical and biochemical differences between two
varieties having varied responses to chilling injury by
internal browning development. The study revealed greater
increase in rate of respiration, higher total soluble solids,
build-up of acidity and higher PPO and peroxidase activity
in the more susceptible variety 'Mauritius' (Queen) during
cold storage than 'Kew' (Smooth Cayenne). Graham et al .
(1998), however, found that peroxidase activity remained
unaltered during the induction of internal browning while
PPO activity increased tenfold.
Numerous factors affect the development of internal
browning disorder in pineapple. Fruits harvested at more
mature stage are more susceptible to chilling injury and inter-
nal browning than less mature fruit (Wang 1982; Weerahewa &
Adikaram 2005a). Fruit size (Hoffman & Smith 1993), crown
size and ascorbic acid content (Teisson et al . 1979) affect the
expression of internal browning. Relative to Smooth Cayenne

Queensland clone13, the intergroup hybrids 73-50 and
53-116 have been found to show some level of field resist-
ance to internal browning after storage at 10°C for 14 days
followed by 20°C for 8 days. The ascorbic acid levels were
not consistent with relative resistance suggesting that factors
other than ascorbic acid play a role in resistance to internal
browning (Sanewski & Giles 1997).

Control
Field application of certain fertilizers has been found
effective in reducing internal browning. Application of
CaCl 2 and fused magnesium phosphate (Selvarajah et al .
1998) to soil reduced internal browning of harvested
pineapple. Combined treatment of pre-harvest CaCl 2 fruit
spray (1.3 g per fruit) followed by post-harvest wax
treatment showed 80% good fruit with no black heart
symptoms after low-temperature storage at 10°C for 17
days followed by 2 days at ambient temperature of 28 ±
2°C. Both core and flesh regions of pineapples subjected to
pre-harvest fruit spray treatment showed higher total
calcium levels compared to controls (Hewajulige et al .
2006). There is a correlation between the calcium content
in the pineapple tissue and incidence of internal browning
(Hewajulige et al . 2003). The calcium concentrations in
the fruit were significantly higher in variety Kew (Smooth
Cayenne) than Mauritius (Queen) pineapple. The difference
corresponded to a significantly lower incidence of chilling
injury in the former. The calcium concentration in both
cultivars was significantly higher in the shell than the core.
Internal browning symptoms are associated with the core
and the flesh adjacent to the core, where the calcium
content is low (Hewajulige et al . 2003).
Harvesting fruits at immature, green stage tends to limit
the development of internal browning, but this fruit is gen-
erally of poorer eating quality than fully ripe fruit. While
the above methods have been used with some success, they
are not completely effective in reducing the incidence of
the disorder (Stewart et al . 2002). Fruits containing high
ascorbic acid developed only slight browning, but fruits
containing low ascorbic acid showed severe browning.
Post-harvest attempts to control internal browning
include waxing of fruit to restrict the availability of oxygen
(Rohrbach & Paull 1982), storing fruit in modified
atmospheres (Abdullah et al . 1985) and rapid marketing
strategies designed to deliver the fruit to the consumer
before browning symptoms become evident (Swete-
kelly & Bagshaw 1993). Waxing the fruit and the crown of
fresh pineapple with a 20% v/v paraffin-polyethylene:water
mixture reduced the incidence and severity of internal
browning (Rohrbach & Paull 1982).