Differential scanning calorimetry (DSC) was used to follow changes in
the thermal characteristics
of commercial frying oils (sunflower seed, colza, and groundnut) during
heating at 180 °C for up to
10 h. DSC tracings of oils scanned from 10 to −80 °C were
characterized by a single crystallization
peak (CP) at −43 to −48 °C. Heating of oils resulted in a
progressive shift of the CP to lower
temperatures and reduced enthalpies of crystallization (EC). The
temperature of the CP decreased
as much as 27 °C, and the EC was reduced by almost 90% after heating
for 10 h. These changes
in thermal characteristics correlated well with the appearance of polar
compounds, the increase in
viscosity, and color changes of the oil. DSC is a fast method of
analysis, requires small samples
(15−60 mg) with minimal preparation, and may be implemented directly
in fried products.
Keywords: Differential scanning calorimetry; oil; frying; quality;
enthalpy; viscosity; color
Differential scanning calorimetry (DSC) was used to determine the oil uptake of commercial frozen par-fried potatoes after frying at 180 °C in colza/soybean oil. The enthalpy and temperature range of the crystallization peak for the pure frying oil were 47.2 J/g and -44 to -50 °C, respectively. DSC was performed by cooling samples of crust and core of fried potatoes from 10 to -60 °C at 1 °C/min and the oil content calculated from the peak area. The crust contained almost 6 times as much oil as the central core (23.6% vs 4%, dry weight basis), as visualized by light microscopy. Only 87% of the oil in the intact crust can be removed by solvent extraction, the rest being extractable only after grinding. Deviation between DSC and Soxtec extraction methods was less than 3%. The DSC method is fast, specific, and reliable, does not use solvents, requires smaller samples (<100 mg) than conventional solvent extraction methods, and can also detect freezable water.
High-performance size exclusion chromatography with multiangle laser light scattering detection (HPSEC-MALLS) was used for characterizing complete molecular weight distributions for a range of commercial alginates used as ice cream stabilizers. For the samples investigated, molecular weight averages were found to vary between 115 000 and 321 700 g/mol and polydispersity indexes varied from 1. 53 to 3.25. These samples displayed a high content of low molecular weights. Thus, the weight percentage of material below 100 000 g/mol ranged between 6.9 and 54.4%.
A novel method utilizing 14C palmitic acid for image
analysis and liquid scintillation for quantifying
oil uptake of French fries undergoing deep-fat frying is described.
Radiolabeled computerized image
analysis of the fried product furnished comprehensive visual
information on the distribution and
localization of oil uptake which was limited to the crust. A
significant high linear correlation
(R
2
= 0.977; P < 0.001) was found between oil uptake measured
by liquid scintillation and differential
scanning calorimetry, and between liquid scintillation and radiolabeled
imaging (R
2 = 0.861; P
<
0.001). The high specificity and sensitivity of the method allows
quantifying uptake of very low oil
concentrations ranging from several milligrams. Oil quantification
via liquid scintillation was more
sensitive than image analysis and requires up to 3 order of magnitude
lower concentration of the
radiolabeled marker. The low concentration and inherent stability
of the radiolabeled chemical
make this technique uniquely suitable for studying oil uptake mechanism
during deep-fat frying of
foodstuffs.
Keywords: Deep-fat frying; radiolabeled; liquid scintillation;
image analysis; oil uptake.
Dark chocolate tablets were manufactured using 100% crystalline sucrose, 50% crystalline and 50% amorphous sucrose, and 100% amorphous sucrose. The physical state of sucrose was determined by differential scanning calorimetry (DSC) and X-ray diffraction. DSC scans of dark chocolate samples containing amorphous sucrose were characterized by a glass transition at 63 degrees C, a sucrose crystallization peak at 105 degrees C, and a melting endotherm at 188 degrees C. Independent of the amount of amorphous or crystalline sucrose used for the preparation of dark chocolate, all final chocolate products provided a single melting endotherm at 188 degrees C and a crystalline X-ray diffraction pattern. These results indicated that sucrose crystallized during production of dark chocolate and that no amorphous sucrose was present in the final chocolate products.
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