共查询到8条相似文献,搜索用时 15 毫秒
1.
Salwa Bornaz Jacques Fanni Michel Parmentier 《Journal of the American Oil Chemists' Society》1995,72(10):1139-1142
The oils and fats industry needs well-identified fractions with well-defined physical properties for its final formulated
products. In view of future applications, a triglyceride partition phenomenon of butter oil on a hydrophobic membrane is investigated
by crossflow filtration. Triglycerides are separated into four groups according to their molecular weight and unsaturation
index, leading to behavior that can be interpreted in terms of consistent stereochemical parameters. 相似文献
2.
Isothermal crystallization of plam oil was studied by means of differential scanning calorimetry (DSC) as well as by nuclear
magnetic resonance spectrometry to monitor its solid fat content (SFC). The temperature of crystallization (Tc) varied from
0 to 30°C, depending on the method used. The plot of %SFC vs. time at 25°C was sigmoidal in shape. However, at lower temperatures,
two consecutive curves were clearly visible. Results from DSC experiments showed the following interesting features. At each
Tc, the crystals produced were of different compositions. From 0 to 8°C, the thermogram showed three peaks, with the first
two peaks (I and II) sharp, and the third (III) rather broad. At elevated temperatures up to 20°C, peak II disappeared totally
while peak III tended to shift toward peak I. Above 20°C, both peaks shifted downward to longer times. Peak I continued to
be broadened, and then suddenly disappeared at Tc above 24°C. The melting thermograms of the crystals obtained above and below
this cut-off point were distinctly different. Kinetic studies on isothermal crystallization based on the data of SFC measurements
showed that the data fit well into the Avrami-Erofeev equation with n=3 over the first 70% of the crystallization. 相似文献
3.
Dorota Johansson Björn Bergenståhl Eva Lundgren 《Journal of the American Oil Chemists' Society》1995,72(8):921-931
Wetting of fat crystals has been extensively examined in this work by contact angle (θ) measurements of fat crystal, oil,
and water in three-phase contact. Contact angle was measured in oil. The crystals were nonpolar and wetted by oil for a contact
angle equal to 0°, and polar and wetted by water for an angle equal to 180°. Fat crystals are expected to contribute to the
stability of margarine emulsions if they are preferentially wetted by the oil phase (0°<θ<90°), but result in instability
if they are preferentially wetted by the water phase (90°<θ<180°). In the absence of oil and water additives, fat crystals
in α and β' polymorphs were introduced to the oil/water interface from the oil side (contact angle θ ∼ 30°). β Polymorphs
were completely wetted by oil (θ ≈ 0°). The contact angle for β' crystals decreased with increasing temperature and was slightly
lower in butter oil than in soybean oil. Emulsifiers in the oil phase (lecithins, monoglycerides and their esters, ethoxylated
emulsifiers) and surface-active proteins in the water phase (milk proteins) made the crystals more polar (higher θ). Nonsurface-active
proteins, sugar, and citric acid had no significant effect, although concentrations of salt lowered θ. Contact angle increased
with temperature for emulsifiers of limited solubility in the oil, e.g., saturated monoglyceride. 相似文献
4.
M. L. Herrera C. Falabella M. Melgarejo M. C. Añón 《Journal of the American Oil Chemists' Society》1999,76(1):1-6
Isothermal crystallization of sunflower seed oil hydrogenated under two different conditions was studied by means of pulse
nuclear magnetic resonance (pNMR) and optical microscopy. Solid fat content (SFC) curves showed two different shapes depending
on supercooling. When supercooling was high, hyperbolic curves were found, whereas with low supercooling sigmoidal curves
were obtained. Curves were interpreted with the modified Avrami equation. Photographs of the crystals were taken from the
beginning of crystallization, every 15 s until 15 min and every 5 min until 60 min. Samples which exhibited hyperbolic curves
showed a slight increase in crystal number, and crystals were needle-shaped in all cases. Samples which had sigmoidal crystallization
curves showed a marked increase in crystal number with time, and crystals were spherical in shape. Crystallization behavior
was also in agreement with the chemical composition of the samples. Samples which had the highest content of high-melting
triacylglycerols (especially trielaidin) showed only hyperbolic curves. Supercooling is a very important parameter that defines
the way nucleation occurs. Depending on the initial number of nuclei, two different growth mechanisms were found: a uniform
linear growth of the nuclei for a small initial number (sigmoidal curves) and an aggregate of the nuclei for a high initial
number (hyperbolic curves). 相似文献
5.
Dorota Johansson Björn Bergenståhl 《Journal of the American Oil Chemists' Society》1995,72(8):933-938
Fat crystals influence the stability of food emulsions, such as margarine, butter, or cream, if adsorbed to the oil/water
interface. During the adsorption process, a new fat crystal/water interface is created, while the oil/water interface is lost.
The driving force for adsorption is therefore the difference between the interactions between fat crystal/water and oil/water.
In this work, we have estimated this interaction difference and compared it to the displacement energy for fat crystals from
the oil/water interface to the oil. Our calculations have shown that fat crystal adsorption to the oil/water interface (expressed
by contact angle ϑ) is determined by polar energy, excess of fat crystal/water over oil/water (I
sw
-I
ow
). The interfacial tension constitutes the resistance force for crystal adsorption to the interface. Polar interaction energy
for fat crystal/water is stronger than the polar interaction energy for oil/water in all cases examined (I
sw
-I
ow
>0). The difference corresponds to about 104–106 hydrogen bonds for a hypothetical fat crystal with a diameter of 1 μm. The displacement energy for fat crystals to oil is
lower than the polar energy excess in most cases examined. Thus, an additional interaction between fat crystals and oil makes
it easy to displace the crystals to the oil. There is also a relationship between the adhesion tension (-γ
ow
• cos ϑ) for the crystals at the oil/water interface and the interfacial tension γ
ow
. A straight line of slope -1 is achieved for systems with low interfacial tensions (γ
ow
) and low polar energy excess (I
sw
-I
ow
). 相似文献
6.
Milad El Riachy MSc Feliciano Priego‐Capote Lorenzo León Luis Rallo María Dolores Luque de Castro 《European Journal of Lipid Science and Technology》2011,113(6):692-707
The biosynthesis of the phenolic fraction of olive fruits during ripening and the transformations occurring in this moiety during virgin olive oil (VOO) extraction are discussed in this paper. The influence of agronomical factors that can significantly affect the phenolic profile of VOO is also discussed. Particularly, it is worth emphasizing the role of genetic factors, cultivation and climatic conditions such as water availability, atmospheric temperature, altitude, health status of the fruits, alternate bearing in the olive, and some processing factors such as crushing, malaxation time and temperature or volume of water added during milling. Among these parameters, special attention has been paid to genetic factors due to the high variability observed among Olea europaea genotypes for all recorded traits. In this context, interesting experimental results have been obtained with cultivated and wild olive trees, and also with segregating populations resulting from olive breeding programs. To the authors' knowledge, reviews evaluating the influence of the main factors that contribute to the profile of hydrophilic phenols have not been previously published. The discussion concerning olive breeding programs is a major and novel aspect to be emphasized considering recent trends to obtain new olive cultivars that confer better organoleptic properties and better quality to VOO. 相似文献
7.
8.
Roberta Di Monte Paolo Fornasiero Jan Ka
par Paolo Rumori Giuseppe Gubitosa Mauro Graziani 《Applied catalysis. B, Environmental》2000,24(3-4):157-167
Pd-loaded Ce0.6Zr0.4O2 solid solutions supported on Al2O3 are investigated as catalysts for the reduction of NO by CO. The attention is focused on the role of the Ce0.6Zr0.4O2 and of the Pd dispersion on the catalytic activity. The system shows a very high activity below 500 K, which is almost independent on the Pd dispersion. The high activity is attributed to a promoting effect of the Ce0.6Zr0.4O2 on the NO conversion. Investigation of the influence of high temperature treatments disclosed a thermal stabilisation of both Ce0.6Zr0.4O2 and Al2O3 in the Ce0.6Zr0.4O2/Al2O3 system. 相似文献