Biomedical Engineering Reference
In-Depth Information
polysaccharide, followed by drying of the emulsions. Spray-drying is commonly used to
prepare the microcapsules [69]. Application of acyl ascorbate for microencapsulation of a
lipid was examined to propose the example for the effective use of acyl ascorbate.
Linoleic acid mixed with various acyl ascorbates was microencapsulated with
maltodextrin or gum arabic by spray-drying, and its oxidation process was evaluated to
examine the antioxidative ability of the ascorbates toward the encapsulated linoleic acid [28].
The oxidation process of the encapsulated linoleic acid mixed with methyl palmitate or
unmodified ascorbic acid and then encapsulated with maltodextrin was also measured for
comparison. A specific amount of maltodextrin or gum arabic was dissolved in distilled
water, and linoleic acid was mixed with the wall material solution. Methyl palmitate, ascorbic
acid or acyl ascorbates, such as octanoyl, decanoyl, lauroyl and palmitoyl ascorbates, was
then added to the solution. The mixture was emulsified with a rotor/stator homogenizer for 1
min at power control 8. The particle size distribution of the oil droplets in the emulsion was
measured using a centrifugal particle size analyzer or a laser diffraction particle size analyzer.
The emulsion was fed into a spray-dryer at a flow rate of 3.0 kg/h and was atomized by a
centrifugal atomizer operated at
ca.
3 x 10
4
rpm. The emulsion in the reservoir was gently
magnetically-stirred to prevent flotation of the emulsion droplets. The temperatures of air at
the inlet and the outlet were 200
o
C and 100 - 110
o
C, respectively. The flow rate of air was
ca
.
7.5 m
3
/min. The microcapsules prepared were collected in a cyclone. Because spray-drying
was completed within 3 or 6 min, no significant change in the size of oil droplets would occur
during the drying. Spray-dried microcapsules were weighed into a flat-bottom glass cup, and
the cups were placed in a plastic container in which a Petri dish filled with a saturated lithium
chloride solution to regulate the relative humidity at 12%. The container was tightly closed
and stored in the dark at 37
o
C. At appropriate intervals, a cup was removed from the
container. The unoxidized linoleic acid in the microcapsules was extracted and determined by
a GC analysis.
The oxidation processes of linoleic acid to which palmitoyl ascorbate was added at
various molar ratios of the ascorbate to the acid and which was encapsulated with
maltodextrin or gum arabic were measured. Because linoleic acid encapsulated without the
addition of the ascorbate was oxidized relatively fast, there was a possibility that oxidation of
the acid partially proceeded during emulsification and spray-drying although the peroxide
values of the acid before and after microencapsulation were not measured. Therefore, the
present results are overall estimate of the antioxidative ability of the ascorbate for all the steps
of emulsification, spray-drying and storage. The oxidative stabilities of the linoleic acid in
both the maltodextrin- and gum arabic-based microcapsules were higher at the higher molar
ratios. The induction period for oxidation of the encapsulated linoleic acid was elongated by
the addition of palmitoyl ascorbate at high molar ratios due to its radical scavenging ability.
Oxidation of the encapsulated linoleic acid quickly proceeded after the induction period and
then reached a level where further oxidation seemed to proceed very slowly or to cease. The
level was higher for the microcapsules with the higher ratios. The molar ratio would affect the
particle size of the oil droplets in the O/W emulsion because of the emulsification ability of
palmitoyl ascorbate. Therefore, the distribution of the particle size was measured using the
centrifugal particle size analyzer. The dependence of the median diameter of the oil droplet
on the molar ratio was evaluated. As expected, the median diameter decreased with an
increase in the ratio. We reported that the oxidative stability of linoleic acid in the
microcapsule prepared from an emulsion with a smaller median diameter of oil droplets was
