Chemistry Reference
In-Depth Information
bacteria after spray drying remained low, these microparticles showed good cell pro-
tection in gastric juice and controlled release of probiotic bacteria under simulated
intestinal conditions. To improve the survival of probiotics, a few approaches used
are the incorporation of thermoprotectants, such as trehlose, nonfat milk solids,
adnitol, granular starch, and so forth. Spherical polymer beads with diameters
ranging from 0.3 to 3.0 mm and immobilizing active biomass are produced using
extrusion or emulsification technique, by thermal (κ-carrageenan, gellan, agrose,
gelatin) or ionotropic (alginate, chitosan) gelation of the droplets. The conventional
encapsulation method, with sodium alginate in calcium chloride (CaCl
2
),
has been
used to encapsulate
Lactobacillus acidophilus
to protect this organism from the
harsh acidic conditions in gastric fluid. Studies have shown that calcium-alginate-
immobilized cell cultures are better protected, shown by an increase in the survival
of bacteria under different conditions; than they are in the nonencapsulated state.
The results from these studies indicate that the viability of encapsulated bacteria
in simulated gastric fluid increases with an increase in capsular size.
171,172
However,
although promising on a laboratory scale, the developed technologies for producing
gel beads still present serious difficulties for large-scale production of microencap-
sulated organisms. The use of microencapsulated probiotics for controlled-release
applications is a promising alternative to solving the major problems of these organ-
isms that are faced by industry. Even so, the challenges are to select the appropriate
microencapsulation technique and encapsulating materials. To date, the research on
the encapsulation of probiotics has been focused mainly on maintaining the viability
of probiotic bacterial cell at low pH and high bile concentration.
171
Very recently
we
have developed floating beads of proboitics (
L. acidophilus
) using alginate-HPMC
and studied their survival and effectiveness against ethanol-induced ulcers in rats.
173
The formulated beads showed good viability and significantly better gastro protec-
tion compared to the unformulated probiotic.
The survival of probiotics in oral solid dosage forms, such as tablets, pellets,
and capsules, have also been investigated in an attempt to formulate a stable oral
dosage forms. A range of compaction forces (1 to 300 MPa) were employed to inves-
tigate the susceptibility of
L. acidophilus
incorporated into lactose and a micro-
crystalline formulation mixture, to forces produced during tablet compression. A
strong negative correlation between bacterial survival and compaction pressure was
observed, suggesting that survival decreased with the increase in tablet compaction
forces. However, stability testing of
L. acidophilus
formulation showed that bacteria
do not remain viable after 8 to 9 days in a mixture with lactose and microcrystal-
line cellulose, respectively. While for extrusion, survival of Gram-positive probiotic
organisms after extrusion, spheronization, and drying were significantly higher than
Gram-negative organisms. The level of mortality was not affected by extrusion speed
or the ratio of die length to radius. However, survival was found to be inversely pro-
portional to extrusion pressure over the range of 1 to 8,000 kPa. Capsule filling with
the
L. acidophilus
/lactose mixture was proved to be the most successful approach, as
the lethal effects of drying and pressure were kept to a minimum. Furthermore, these
capsules were successfully coated with an ethylcelluose/amylase colon-specific coat,
without loss of bacteria viability.
169
To stabilize the lyophilized cell and to target the
