Guava - Tropical and Subtropical Fruits: Postharvest Physiology, Processing and Packaging - page 202

slices. In these processes, a careful selection of guava is
required and damaged, defective and/or nonstandard fruits
(size, flesh thickness, pulp color) are discarded and/or des-
tined to the processing of other products. Generally, fruits
with a consistent, firm flesh are preferred for these products.
All the fruits must have a similar size and flesh thickness to
cook/dehydrate similarly. Specifically, for red guava, an in-
tense color is also desired, which is usually obtained during
thermal processing (Sato et al., 2006).
After grading, the fruits should be properly washed and
sanitized, according to the steps described in the 'Minimal
Processing Section'. Likewise, peeling must be carried out.
In this case, the mechanical techniques are preferred, and
chemical peeling may also be used since the products will
undergo further processing. Chemical peeling is usually
done using a hot solution of sodium hydroxide (lye peeling)
(

consists of immersing the fruits in vessels containing
highly concentrated solutions that usually vary from 40 ◦ to
60 ◦ Brix (Sanjinez-Argando na et al., 2005; Vieira, 2012).
Sucrose solutions are typically used in the osmotic pro-
cess for guavas (Sanjinez-Argandona et al., 2005; Panades
et al., 2008; Correa et al., 2010; Vieira, 2012), however,
other compounds can be used as dehydrating agents such
as maltose, honey, or sucralose (Pereira et al., 2006; Queiroz
et al., 2007; Duangmal and Khachonsakmetee, 2009).
The processing temperature and time are highly relevant
parameters in the OD process since they have a direct influ-
ence on the process kinetics and on the characteristics of the
final product. The process time varies from 2 to 3 hours, pe-
riod in which the highest rate of mass transfer occurs, result-
ing in pretreated guava with good sensory characteristics
(Pereira et al., 2009; Vieira, 2012). The process temperature
varies from 20 ◦ to 50 ◦ C (Sanjinez-Argando na et al., 2005;
Pereira et al., 2006; Panades et al., 2008); higher temper-
atures can cook the fruit, thereby compromising the OD
process. Generally the rate of mass transfer increases sig-
nificantly with increasing temperature due to an expansion
and plasticizing of the cell membranes, causing a faster and
more intense flow of water loss and weight reduction of the
product (Lazarides et al., 1997). Conversely, although the
increase in temperature causes an increase in the osmotic
rate, temperatures higher than 45 ◦ C can cause changes in
the color characteristics, flavor, aroma, and cell walls of the
product (Torreggiani, 1993).
The process of OD of the guava can be performed at
atmospheric pressure or by applying a vacuum pulse at the
beginning of the process. The application of pulsed vacuum
contributes to relatively higher water loss when compared
to the osmotic treatment performed at atmospheric pressure
(Souza et al., 2003; Panades et al., 2008; Correa et al., 2010;
Vieira, 2012).
The addition of calcium salts to the osmotic solutions
has been evaluated to preserve the structural integrity of
fruits and vegetables (Jackman and Stanley, 1995; Pereira
et al., 2009; Mastrangelo et al., 2000). The osmotic process
for guava promotes softening of the tissues, which can re-
sult in rejection of fruit by the consumers. The addition of
calcium salts to the osmotic solutions has a strong influ-
ence on the texture and structure of the processed guava,
resulting in maintenance of the tissue structure when cal-
cium lactate was used at concentrations of up to 1.5%
and calcium chloride was used at 0.5%. Good sensory ac-
ceptance of these osmotically dehydrated guavas was ob-
served, indicating that the sensory properties of OD guava
were not influenced by the addition of calcium (Pereira
et al., 2007).

70 ◦ C and 2% NaOH), in which the product is immersed ∼

for 50 sec (Barreiro et al., 1995; Sanjinez-Argandona

et al., 2005). The sodium hydroxide acts by dissolving the
natural epicuticular and cuticular waxes, subsequently dif-
fusing into the fruit, where it reacts and breaks the epider-
mal and hypodermal cell walls down, dissolving the middle
lamella and finally resulting in separation of the skin (Floros
and Chinnan, 1987). To maintain fruit firmness, excessive
time/temperatures must be avoided in this procedure. The
lye and peel residues are removed by washing, followed
by neutralization with an acid solution based on an organic
acid such as citric acid. After peeling, depending on the
product for which the guavas are destined, the stem ends
are carefully cut and the fruit is halved or sliced, and the
fruit may have their seeds removed before further process-
ing. However, in some products, such as in some canned
guavas, the fruit may be processed in its whole form.

∼

Osmotic dehydration
Osmotic dehydration (OD) is a useful technique for con-
servation, maintaining the nutritional quality of the guava,
and allowing for a longer shelf life as compared with the
nonprocessed guava. This technique enables partial water
removal with low energy consumption and with the use
of only mild heat treatment. The OD process also allows
for the incorporation of additives such as antimicrobials,
nutrients, and firming agents. When combined with other
treatments, such as drying and freezing, OD provides
stable products with high nutritional and sensory quality
and characteristics similar to those of the fresh fruit (Torres
et al., 2006; Falade et al., 2007; Pereira et al., 2007; Pino
et al., 2008).
For the OD process, the fruits should be processed in
slices or halves with their seeds removed. The process