Agriculture Reference
In-Depth Information
Disadvantages of storage in a control-
led atmosphere include: (i) irregular ripen-
ing in some cases; (ii) the modification
of the organoleptic characteristics (as a
result of anaerobic respiration); and (iii) the
increase, sometimes, of physiological
disorders and chilling damage (Mir and
Beaudry, 2003).
When the aim is to accelerate the ripen-
ing of a product, such as tomato, ripening
chambers may be used, adding ethylene and
keeping a proper temperature. These cham-
bers are often used in ripening citrus
(degreening).
MAP (modified atmosphere packag-
ing) of fresh vegetables allows for isolating
fresh products, with active respiration, in
plastic film packages to modify the O
2
and
CO
2
levels in the atmosphere inside the
package. At the time of packaging, levels of
2-3% of O
2
and 5% of CO
2
are usual (Kader
et al
., 1989).
In addition, MAP decreases the dehy-
dration of the product and insulates it from
the external environment, limiting its expo-
sure to pathogens and contaminants, which
contributes to maintaining its quality. It is
often used in fresh cut products.
The modification of the atmosphere in
MAP requires active respiration of the
plant tissues, on one side, and the exist-
ence of a barrier that prevents the gas
exchange, on the other side. The creation
of such barriers is achieved by using plas-
tic films of a characteristic permeability
(that controls the entrance and exit of O
2
and CO
2
into/from the package) and by
means of micro-perforated plastic films
(Mir and Beaudry, 2003).
In MAP, the control of temperature is
essential. The decrease of water losses
prevents the product becoming desic-
cated but in some cases may increase how
much it wilts. Not all products are suit-
able for MAP.
A variant of MAP is partial vacuum
packaging, which keeps the normal com-
position of the atmosphere, but at a lower
than normal pressure in impermeable
packages, at low temperature (Gorris
et al
.,
1994). This system stabilizes the quality,
decreasing the metabolic activity of the
products avoiding the increase of unde-
sired microorganisms.
15.6
Quality
The notion of a food product's quality is,
simultaneously, complex and relative; it is
complex because the quality of a product
cannot be determined by a single property,
but from the combination of all its physical,
chemical and sensorial properties; and it is
relative because this combination of factors
that define it must be such that determines
acceptance by the consumer (MartÃnez-
Madrid
et al
., 2000). Fresh vegetable prod-
ucts maintain, after their harvest, a metabolic
activity that is essential for the preservation
of their quality. In Chapter 16, other aspects
of quality will be discussed. In this section
sensorial quality aspects are described.
The sensorial quality is dictated by a
number of external and internal factors.
The external factors include the attributes
related to the appearance, such as colour,
form, size and firmness, and are subject to
physical and visual properties, being
appreciated by the consumer through the
senses of sight and touch, whereas the
attributes related to flavour, aroma and tex-
ture, which are sensed by the taste and
smell, are included among the internal fac-
tors of sensorial quality (MartÃnez-Madrid
et al
., 2000).
The essential criteria to evaluate the
sensorial quality in fruits and vegetables
are the colour, flavour, aroma and texture
(Photo 15.4). The flavour and the aroma
are the most subjective and difficult to eval-
uate qualitative aspects. The flavour can be
evaluated by taste and smell, and is mainly
composed of sweetness, acidity and aroma,
that correspond to the sugars, acids and vol-
atiles, respectively (Baldwin, 2003). Other
components of the flavour are bitterness,
salinity and astringency. The acidity and
the aroma modify the perception of sweet-
ness, one of the most important components
of the flavour in fruits and vegetables. The
perception of the non-volatile components
of flavour (sweet, acid, salty and bitter)
takes place on the tongue and the aromas
