Sample origin and characteristics
Analyses were performed on two lots of pears (Pyrus
communis L. var. S. Bartolomeu), corresponding to two
drying seasons, 2008 and 2009. Each lot was composed by
fresh pear fruits and traditionally dried fruits (direct
exposure to solar radiation) (Traditional). The samples
from 2009 were also processed using three different
methodologies: in a large glass greenhouse with air convection
(GH1), in a small greenhouse with natural convection
(GH2) and using a hot air tunnel in the absence of
light (HAT). All fruits were harvested in an orchard located
638 Eur Food Res Technol (2011) 233:637–646
123
at the village of Ervedal da Beira (Oliveira do Hospital,
Portugal) at the commercial maturity stage (Fig. 1a). On
average, the fresh fruits had a mass of 64 g, with a diameter
of 4.3 cm and height of 6.5 cm. The moisture content was
78%.
For fresh pear analysis, some fruits were frozen just
after harvesting. The remaining fruits were processed
according to the different methodologies under study.
According to the traditional sun-drying process, the
fresh fruits were peeled and allowed to dry in an open
space with sunshine incidence, as described by Ferreira
et al. [5] (Fig. 1b). After being peeled, fresh pears were
also allowed to dry in two greenhouses that differed in their
size, structure and location. GH1 was provided with air
convection, with a flux of 900 m3 h-1, it was located at
ground level and, in comparison to GH2, had the largest
cargo capacity. Its area was 6.3 m2 (3.19 m long by 1.93 m
wide), and the height in the sides was 1.24 m, whereas in
the middle was 1.97 m. The structure was aluminium with
horticulture glass and there were two roof windows for air
extraction. The drying time for GH1 was approximately
7 days (Fig. 1c). The GH2 greenhouse consisted of insulated
glass panels and had the form of a box (1.20 m height
by 1.20 m long and 1.00 m wide). Inside, it was composed
by a U-shaped structure, parallel to the floor, where pears
were let to dry. GH2 was located on a roof of a building
and contained a step structure coated with reflective film,
where pears were allowed to dry. This interior structure
allowed a greater incidence of the light and consequently
promoted the drying process by natural air convection, with
the air entering in the lower level (first step) and leaving in
the higher level, by means of a girandole. The drying time
for GH2 was approximately 5 days (Fig. 1d), 2 days less
that the drying time of GH1.
For hot air tunnel drying (HAT), after peeled, pears were
let to dry at a constant temperature of 40 C and an air flow
of 1.2 m s-1 for about 7 days (Fig. 1e). The drying tunnel
was 2 m long, and the air convection was promoted by a
ventilator placed at the entrance of the tunnel. In this
structure, pears were not exposed to light, although the air
was heated by a solar collector, and therefore the sun was
also the main source of energy.
Independently of the type of processing used, the processed
fruits reached a mass of 10–14 g with a moisture
content of 20% and had a maximum width of 2.5–3.4 cm,
height of 3.9–4.7 cm and thickness of 1.2–1.5 cm. The
sensory descriptive profile of the traditional product, when
evaluated by a sensory panel test, is the following: brown–
red uniform colour (Fig. 1b), sweet and slight acid, with a
not too hard–not too soft texture and presenting elasticity.
Concerning GH1, it was considered very similar to the
traditional product, with the same rate of global appreciation,
but with lower colour uniformity (Fig. 1c), sweetness
and elasticity. GH2 was similar to GH1, although obtaining
a lower global appreciation, possibly due to an even lower
acidity (Fig. 1d). HAT presented the sensory profile close
to the traditional product concerning colour uniformity,
sweetness and toughness but it was not appreciated due to
the colour tonality (yellow-orange) (Fig. 1e) and slight less
acidity. This product, although having the accurate organoleptic
characteristics except the colour, was rejected by
the panellists due to the inaccurate colour when compared
with the traditional product.
Before analysis, the pulp of the fresh and dried pears
was collected, ground and freeze-dried.