Effects of microwave frying on physicochemical properties of edible oils and quality of potato chips
Microwave frying is an alternative processing method for producing fried food products with the advantages of saving energy and time and improving both the nutritional quality and acceptability of fried foods by consumers. Thus, the effects of microwave frying on the properties of edible oils and...
Saved in:
| Main Author: | |
|---|---|
| Format: | Thesis |
| Language: | English |
| Published: |
2017
|
| Subjects: | |
| Online Access: | http://psasir.upm.edu.my/id/eprint/77128/1/FSTM%202018%2029%20IR.pdf |
| Tags: |
Add Tag
No Tags, Be the first to tag this record!
|
| Summary: | Microwave frying is an alternative processing method for producing fried food
products with the advantages of saving energy and time and improving both the
nutritional quality and acceptability of fried foods by consumers. Thus, the effects of
microwave frying on the properties of edible oils and the quality characteristics of
fried foods should be studied using different techniques to obtain comprehensive
data on the properties of microwave-fried products. In this study, the effects of
microwave frying on the physicochemical properties of frying oils, namely, refined,
bleached and deodorized (RBD) palm olein and corn oil, which have market
acceptability and are widely used in cooking, were evaluated. Changes in
physicochemical properties, including free fatty acids, acid value, peroxide value, panisidine
value, TPM% TOTOX value, color, viscosity, rheological behaviors and
thermal properties, were evaluated to monitor the quality and frying performance of
frying oil. The experimental data highlighted that both studied frying oils exhibited
oil stability against oxidation during the microwave frying process, RBD palm olein
showed a comparatively lower degree as compared to corn oil. The studied oils
exhibited Newtonian behavior, and there was a significant increase (P < 0.05) in the
viscosity of both oils as the extent of frying increased. There was a significant (P <
0.05) difference in the color of the studied edible oils with increased extent of frying.
The thermal properties of the oils were determined by differential scanning
calorimetry (DSC). The melting point of RBD palm olein during the heating curve
was in the range of -3.25 °C, and during the cooling curve it was in the range of 4.35
°C. A comparison of the average melting point values of corn oil revealed values of -
28.0 °C and 26.0 °C during the heating and cooling curves, respectively. The
properties of microwaved potato chips, namely, moisture content, oil uptake, bulk
density, particle density, porosity values, volumetric shrinkage, hardness, and color
development, were also evaluated. The moisture content of potatoes decreased
significantly (P < 0.05), whereas the oil content values of the potatoes increased
significantly (P < 0.05), with increasing frying time and microwave power level. Moreover, the kinetics models gave a good and varied fit for moisture diffusion and
oil transfer. Interestingly, the effective moisture diffusivity for potato chips fried in
corn oil ranged between 6.36x10-9 and 12.68x10-9 m2/s and between 6.64x10-9 and
12.84x10-9 m2/s. The oil transfer rate constant ranged between 2.02x10-2 and
1.94x10-2 s-1 and between 1.89x10-2 and 1.95x10-2 for potato chips fried in RBD
palm olein and in corn oil, respectively. The activation energy obtained from the
Arrhenius plot for the effective moisture diffusivity ranged between 58.17 and 58.84
kJ/mol. Scanning electron microscopy images showed the structural changes at the
surface of microwaved potato chips, revealing detailed and specific information to
elucidate the relation between microwave frying processing conditions and fried
food structure. In addition, confocal laser scanning microcopy (CLSM) images were
obtained to observe the surface morphology and oil distribution of potato chips. The
oil distribution in microwaved potato chips fried under different microwave frying
conditions showed that a crust developed during microwave frying. Oil was trapped
only in intercellular spaces, which was strongly linked to the microstructure (not
only in intercellular spaces but also over some cells). The topographical data
acquired by CLSM in reflective mode confirmed that several cells were broken
during the cutting operation. CLSM image representation of the reconstructed
surface of a microwaved potato chip allowed the oil location on the potato surface to
be observed. The macrostructural properties of microwaved potato chips fried in
RBD palm olein and corn oil were investigated, and the results showed volumetric
shrinkage, thickness expansion and diameter change as a function of the moisture
loss effect by the frying process conditions. Moreover, the hardness showed several
fluctuations at 160, 170, and 180 °C. The texture of fried potato chips was soggy at
160 °C due to the short microwave frying process, which led to incompletely fried
potato chips. The acrylamide content of potato chips was detected during the
microwave frying process. The acrylamide levels in potato chips fried in corn oil
ranged from 380 to 12,301 ppb. Meanwhile, the acrylamide levels in potato chips
fried in RBD palm olein ranged from 282 to 13,230 ppb. Remarkably, 60% of the
potato chips had high levels of acrylamide due to the high thermal process during
microwave frying. It can be concluded that the microwave frying of potato chips
caused the formation of lower amounts of oxidation products in RBD palm olein and
corn oil, indicating a lower extent of oxidative degradation of the studied oils. In
addition, the physical properties of the studied oils were investigated. Moreover, the
quality characteristics of microwaved potato chips were obtained. The levels of
acrylamide in microwaved potato chips were determined. In general, the microwave
frying is an attractive process for food due to its applicability, convenience and low
oxidative degradation. |
|---|