Biomedical Engineering Reference
In-Depth Information
geometry, peel thickness, and other characteristics of fruits. This method involves
both chemical and thermal treatments (Barreiro et al.
2007
). In the case of kiwifruit
NaOH concentration of the lye solution led to decreased peeling time and NaOH
concentration above 20 % resulted in excessive softening of fruit. This causes a
complete loss of fi rmness. Furthermore, concentrations below 15 % NaOH were
not suffi cient to properly peel the kiwifruit (Gómez-López et al.
2014
). In contrast,
the immersion in 2.5 % NaOH boiling solution (5 min) showed the best treatment
since it inhibited the enzymatic browning and intensifi ed the natural yellow color of
the cubiu fruit (
Solanum sessilifl orum
Dunal) (Caceres et al.
2012
).
Di Matteo et al. (
2012
) evaluated the lye peeling process at low temperatures for
cuticle removal from different hazelnut varieties. The collected data showed that the
use of the solution with NaOH (0.4 g/100 g) and NaH
2
PO
4
· H
2
O (0.2 g/100 g) at
50 °C was effective in cuticle removal and provided a yield of peeling higher than
90 %. The chemical-physical parameters in unpeeled and peeled hazelnut samples
did not show any differences in texture, sugar, protein and a-tocopherol contents,
while signifi cant changes were observed in colour and total fat. However, these
changes did not infl uence the sensorial parameters of the peeled hazelnut samples,
and the treatment was positively judged by sensory panel (Di Matteo et al.
2012
).
A variant of lye peeling process is the use of KOH instead of NaOH. While KOH
is generally more expensive than NaOH, but half concentration of KOH is needed
to achieve equivalent result. For example, tomato peeling with NaOH at a concen-
tration of 18 % (4.5 N) produced 79 % peeled tomatoes, while equivalent results
with KOH were produced using a concentration between 12 % (2.1 N) and 14 %
(2.5 N) (Das and Barringer
2006
).
4.3.4
Enzymatic Peeling
Enzymatic peeling consists of treatment with a high-activity enzymatic solution
containing polysaccharide hydrolytic enzymes, especially pectinases, cellulases,
and hemicellulases since pectin, cellulose and hemicellulose are the polysaccha-
rides most responsible for the adherence of the peel to the fruit. These enzymatic
preparations were obtained by fermentation of genetically modifi ed fungal micro-
organisms produced by biotechnological industries (Suutarinen et al.
2003
).
Enzymatic peeling is mostly applied in the case of citrus fruits' peeling. The pro-
cess involves manual extraction of fl avedo at oranges' top and bottom poles and its
segmentation through longitudinal and equatorial cuts with sharp knives. These cuts
and segmentations aimed at facilitating enzyme penetration for albedo digestion
inside the fruit (Barrios et al.
2014
). Fruits are later dipped into 1 % pectinase solu-
tion by vacuum infusion. After vacuum, fruits are maintained at 40 °C for 15-40 min
to achieve the most favourable enzymatic activity. The peels are then removed man-
ually and fruits are washed with pressurized water (Barrios et al.
2014
).
The main advantages of enzymatic peeling are its ability to produce good quality
product, requirement of the reduced heat treatment and production of low industrial
