Evaluation Only. Created with Aspose.PDF. Copyright 2002-2021 Aspose Pty Ltd.
106
E.A. Vlasova et al. / Food Chemistry 190 (2016) 103–109
determined using the Brunauer–Emmett–Teller (BET) equation;
and the pore size distribution and pore volume were calculated
by applying the nonlocal density functional theory (NLDFT)
method. Thermal gravimetric analysis (TGA) was performed in
from terephthalic acid, both in terms of the nature and of the posi-
tion of the main absorption bands (Liu et al., 2013; Loiseau et al.,
2004). In contrast to the free terephthalic acid, the MOF display a
splitting of the bands corresponding to C@O stretching vibrations
air (5 °C minꢁ1
)
(Netzch Sta 449c Jupiter thermal analyzer).
in the region of 1500–1700 cmꢁ1
.
Elemental analysis was performed using a Perkin-Elmer 240 ana-
lyzer Flash EA 1112. IR spectra were registered using a Nicolet
Avatar 360 spectrometer at room temperature in the range of
400–4000 1/cm, with potassium bromide pellets. The content of
metal atoms in vegetable oils before and after extraction of free
fatty acids and peroxide compounds by MOFs was determined by
an atomic absorption spectrometer (AAC BUCK 210 VGP). The mix-
ture of oil and MOFs was stirred using a magnetic stirrer (IKA
C-MAG HS7). The data were analyzed using Origin 7.5.
The structures of the synthesized MOFs is shown in Fig. 1 (Devic
& Serre, 2014; Dikio & Farah, 2013; Ferey & Serre, 2009). XRD data
also confirm the formation of metal–organic framework. Fig. S2
shows XRD patterns of synthesized MOFs (Vlasova, Shalunova,
Makarova, Kudrik, & Makarov, 2014). At small angles (till 11°) all
materials are characterized by two intense peaks, which is typical
for MOFs obtained by the hydrothermal method (Dan-Hardi et al.,
2009; Liu et al., 2013; Yue et al., 2013). All synthesized MOFs have
high thermal stability. Thermal degradation of Zn-MOF and Ti-MOF
starts at temperatures above 410 °C (Fig. S3). Thermal degradation
of Al-MOF starts at temperatures above 500 °C (Fig. S3). Nitrogen
adsorption–desorption isotherms for Al-MOF (Vlasova et al.,
2015), Zn-MOF (Vlasova et al., 2015) and Ti-MOF are shown in
Fig. S4, and the physical properties of these three samples are given
2.8. Determination of acid value
Acid values (AV, mg KOH/g oil) were calculated according to the
equation (Harutyunyan et al., 2004):
in Table S6. The data in Table S6 shows that the surface area (SBET
)
AV ¼ 5:611 ꢂ V ꢂ K=m
where 5.611 is the number of mg of KOH contained in 1 ml of 0.1 N
solution of potassium hydroxide;
ð1Þ
depends on the valence of the cation. At the same time, the micro-
pore volume is much less sensitive to the nature of the metal. By
varying the metal cation, it is also possible to vary the pore size.
As in the case of a SBET, the minimum pore size is seen in the zinc
complex, and the maximum pore size is seen in the titanium one.
The effect of Al-MOF, Zn-MOF and Ti-MOF on basic physico-
chemical parameters (acid value and peroxide value) of unrefined
vegetable oils – sunflower, olive and linseed was studied.
V is the volume of 0.1 N solution of potassium hydroxide con-
sumed for the titration, cm3;
K is correction factor to the titer;
m is the mass of the analyzed oil, g.
Figs. 2–4 show the variations in acid and in peroxides value of
sunflower oil in time, in the presence of Al-MOF, Zn-MOF
2.9. Determination of peroxide value
Peroxide values (PV, mmol of active oxygen/kg) were calculated
as (Harutyunyan et al., 2004):
CTi-MOF = 0.03 wt.%
CTi-MOF = 0.06 wt.%
CTi-MOF = 0.09 wt.%
CTi-MOF = 0.12 wt.%
CTi-MOF = 0.15 wt.%
5,5
5,0
4,5
4,0
3,5
3,0
2,5
2,0
1,5
(a)
PV ¼ ðV1 ꢁ V0Þ ꢂ C ꢂ 1000=m
ð2Þ
where V1, V0 are the volumes of 0.01 M solution of sodium thiosul-
fate consumed for the titration of iodine liberated in the main and
control experiments, respectively, cm3;
C is the concentration of sodium thiosulfate solution, M;
1000 is the coefficient allowing recalculation of the result per kg
fat;
m is the mass of the analyzed oil, g.
2.10. Determination of degree of extraction
The degree of extraction (DE, %) was calculated as:
0,0
0,5
1,0
1,5
2,0
2,5
3,0
DE ¼ ðAV1 ꢁ AV2Þ=AV1 ꢂ 100
ð3Þ
ð4Þ
Time (h)
DE ¼ ðPV1 ꢁ PV2Þ=PV1 ꢂ 100
where AV1, AV2 are acid values based on titrations of the oil prior to
treatment with MOF, and after 0.5 h of contact the sorbent, respec-
tively, in mg ROH per g fat;
CTi-MOF = 0.03 wt.%
CTi-MOF = 0.06 wt.%
CTi-MOF = 0.09 wt.%
CTi-MOF = 0.12 wt.%
CTi-MOF = 0.15 wt.%
(b)
12
11
10
9
PV1, PV2 are peroxide values likewise calculated based on
titrations prior and after exposure to the MOF, in mmol active
oxygen per kg.
8
3. Results and discussion
7
According to the infrared spectra, the synthesized Al-MOF has
intense signals around 1416, 1674, 1613 and 3412 cmꢁ1 relating
to the vibrations of the C@C, coordinated and uncoordinated
C@O and OH, respectively (Fig. S1). In Zn-MOF these bands are at
1390, 1662, 1611 and 3391 cmꢁ1, respectively (Fig. S1) – while
in. Ti-MOF they are at 1401, 1645, 1585 and 3413 cmꢁ1 (Fig. S1).
Overall, these IR spectra are similar to those of other MOFs derived
6
0,0
0,5
1,0
1,5
Time (h)
2,0
2,5
3,0
Fig. 4. Dependence of acid value (a) and peroxide value (b) of sunflower oil on time
in the presence of additives of Ti-MOF.