Anggraini 2008 reported that chitosan-coated treatment gave better effects on inhibiting pericarp hardening change, while shelf-life of mangosteen fruit
could be kept as long as 20 days after treatment Ekaputri, 2009. Dangcham et al. 2008 found that when pericarp hardening occurred, pericarp firmness and lignin
contents increased while total phenolics decreased and fruit at the red-brown and red-purple maturity stages stored at 6
o
C had higher lignin contents than of those stored at 12
o
C. Of the phenolic acids predominant in the hardened pericarp, p- coumaric acid declined whereas sinapic acid increased throughout the storage
time. Application of low O
2
0.25 to red-purple fruit during storage at 6
o
C 84 RH, or at room temperature 30
o
C, 71.5 RH following storage at 6
o
C, did not reduce pericarp hardening and there were no significant differences in
firmness, lignin and total free phenolics when compared with fruit in normal air conditions. The results also suggested that increase in pericarp firmness of
mangosteen fruits results from induction of lignin synthesis, associated with an increase in phenylalanine ammonia PAL and peroxydase POD activity and
gene expression. Recent research conducted by Palapol et al. 2009 showed that pericarp firmness of mangosteen fruit decreased from stage 1 to stage 6, 779.3,
201.3, 136.0, 98.4, 66.5 and 46.5 N, respectively when stored at temperature 25
o
C. Increases in pericarp lignin contents are at least part of the reason for the tissue hardening. Bunsiri 2003 found that 3 hours after impact, lignin contents
increased in the damaged pericarp.
2.4. Fruit Ripening and Senescence
Ripening and senescence are the ultimate phases in the developmental events of fruits that result in the expression of the quality characteristics inherent
to the fruit Paliyath et al., 2008 and this phenomenon involves structural, biochemical, and molecular changes that in many cases bear the hallmarks of
programmed cell death Arora, 2008. Degradation of structural elements such as the cell wall and the plasma membrane results in a loss of compartmentalization
of ions and metabolites, leading to the loss of tissue structure and ultimately homeostasis Paliyath et al., 2008.
Fruit ripening is accompanied by a number of biochemical events, including changes in color, sugar, acidity, texture, and aroma volatiles that are crucial for
the sensory quality. At the late stages of ripening, some senescence-related physiological changes occur that lead to membrane deterioration and cell death.
All biochemical and physiological changes that take place during fruit ripening are driven by the coordinated expression of fruit ripening-related genes. These
genes encode enzymes that participate directly in biochemical and physiological changes. They also encode regulatory proteins that participate in the signaling
pathways, and in the transcriptional machinery that regulate gene expression and set in motion the ripening developmental program Bouzayen et al., 2010.
For the consumers and distributors, the process of ripening corresponds to those modifications that allow fruit to become edible and attractive for
consumption Bouzaye et al., 2010. Fruits have classically been categorized based upon their abilities to undergo a program of enhanced ethylene production
and an associated increase in respiration rate at the onset of ripening. Fruits that undergo this transition are referred to as climacteric and include tomato, apple,
peach, and banana, whereas fruits that do not produce elevated levels of ethylene are known as non-climacteric and include citrus, grape, and strawberry Barry and
Giovannoni, 2007. The relationship existing between the climacteric respiration and fruit ripening has been questioned following the discovery that ripening on
the vine of a number of fruit may occur in the absence of any increase in respiration Salveit 1993; Shellie and Salveit 1993. More recently, it has been
reported that the presence or absence of a respiratory climacteric on the vine depends upon prevailing environmental conditions Bower et al. 2002. These
observations indicate that the respiratory climacteric is probably not an absolute trigger of the ripening process, but secondary and consequential to the process of
ripening. An ethylene burst that precedes respiratory climacteric has been shown during the ripening of banana Pathak et al. 2003
.
Senescence of leaves, flowers and fruits can be regulated by an array of external and internal factors. Many environmental stresses such as extreme
temperatures, drought, nutrient deficiency, insufficient lightshade or total darkness and biological insults such as pathogen infection can induce
senescence. Internal factors influencing senescence include age, levels of plant hormones and other growth substances, and developmental processes such as
reproductive growth Gan, 2004. Ethylene plays a key role in promoting senescence of climacteric fruits and flowers although it is less effective in
stimulating non-climacteric fruits and flowers to senesce. Other promotions of senescence process include sugar, jasmonic acid JA, salicylic acid SA,
brassinosteroids BRs, and abscisic acid ABA, while cytokinins CK, Polyamines PAs, Auxin, Gibberellins are considered to delay senescence
process Gan, 2004.
2.5. Ethylene Biosynthesis and its Physiological Effects
