Biomedical Engineering Reference
In-Depth Information
common responses to the wounds, and it is considered as an important indicator of
the product shelf life (Surjadinata and Cisneros Zevallos
2003
). Increased rate of
ethylene production in response to cutting may stimulate the respiration and leads
to a faster senescence and deterioration of vegetative tissues (Fonseca et al.
2002
).
The rate of respiration increase in FCFV may range between 1.2 and 7.0, depend-
ing on the produce cutting grade and storage temperature (Ahvenainen
1996
). The
increased respiration after cutting is due to the energized state of all living tissues.
Therefore, after cutting the tissues, the increased respiration provides energy and
carbon skeletons for the anabolic reactions similar to ripening (Helena Gomes
et al.
2010
).
The visual appearance of FCFV has also been reported to be infl uenced by the
increased respiration rate. This process results in a depletion of the carbohydrate
reserve in fruits and vegetables. As the respiration rate increases, an uncontrolled
increase in O
2
consumption occurs, which is often an indication of oxidative brown-
ing (Manvell
1997
). These metabolic reactions use substrate carbohydrates involved
in fruit organoleptic quality such as sugars and organic acids. Hence, as the organic
acids are natural pH indicators involved in fruit color, their decay may lead to
changed color (FAO
1995
). Additionally, the increased respiration, can alter organic
acids (i.e. sugar-to-acid ratio), and may result an insipid taste of the FCFV product
(Manvell
1997
). Some of the effects of the metabolic changes can be diminished by
storing the FCFV product at their optimal storage temperature.
5.3.3
Color Changes (Visual Appeal)
The appearance of FCFV is a decisive factor for customer acceptance, and it strongly
affects the decision to buy the product (Toivonen and Brummell
2008
). After mini-
mal processing of fresh produce, the metabolic reactions that stimulate respiration
and/or ethylene production result in some undesirable effects (discoloration, texture
changes, faster ripening, and senescence) that affect consumer acceptability (Gil
and Allende
2012
). Specifi cally, the browning and discoloration effects are the most
common undesirable changes that affect the color and consequently affect the visual
appearance of fresh produce (Toivonen and Brummell
2008
).
As mentioned before, during minimal processing, fresh produce undergo to dif-
ferent types of stress with the initiation of some decay reactions. For example, the
enzymatic browning in several FCFV starts with cellular disruption, causing the
release of phenolic compounds stored within the vacuoles in cell wall compart-
ments. Once oxygen penetrates the wounded tissue, the phenolic compounds are the
substrate for the enzyme Polyphenol Oxidase (PPO) (Yoruk and Marshall
2003
).
The PPO in the presence of oxygen can catalyse two different reactions: the hydrox-
ylation of monophenols and the oxidation of
o
-diphenolsto o-Quinones. Once the
o
-phenols are oxidized to o-Quinones a non-enzymatic polymerization of quinines
occurs, leading to the formation of melanins that are pigments of high molecular
mass and dark in color (Queiroz et al.
2008
).
