Thesis (MTech (Food Technology))--Cape Technikon, 2004 / Probiotic foods are intended to supply selected viable microorganisms, for
example Lactobacillus acidophilus and Bifidobacterium, to consumers. These
organisms, when consumed at the daily intake of 108
, provide benefits beyond
basic nutrition. Probiotic (AB) foods generally include fermented dairy products
such as yoghurts and cheeses, targeted at the upmarket consumer. However,
due to technical problems associated with the foods and the organism, viable
Bifidobacterium rarely occur in AB foods.
The principle aims of this study were to develop a suitable delivery system for
Bifidobacterium to the consumer, and to supply these living organisms in the
affordable traditional fermented African beverages, amasi and mahewu. This
would provide the benefits of probiotics to the rural African consumer, where
malnutrition and gastrointestinal diseases occur. The organism selected for
this study was Bifidobacterium lactis DSM 10140, commonly associated with AB
starter cultures for yoghurts. The delivery system selected was
microencapsulation of B. lactis using a mixture of the generally recognised as
safe (GRAS) edible gums, gellan and xanthan. Supply vehicles for the
microcapsules to the consumer were amasi and mahewu.
Prior to microencapsulation, rheological studies were undertaken to determine
whether the gellan-xanthan gum mix would provide a suitable support matrix for
microencapsulated B. lactis. This was done using a Paar Physica MGR 300
rotational rheometer with a cone plate 50-2 measuring system. Results
indicated that the hydrated gellan-xanthan gum mix behaved as a
non-Newtonian material, and the flow curve fitted well to the Herschel-Bulkley
model. This demonstrated that the gel was a relatively viscous material with
solid properties. The average yield stress of the gel was 1.515 Pa, indicating
that the gel was stable, and at lower stresses would behave as a solid. The gel
mix would be disrupted by shear stresses associated with mastication and
peristalsis. The minimum viscosity of the gel was constant at temperatures
between 46°C - 61°C. It was concluded from these data that the gel was
suitable for microencapsulation and that microcapsules should only be included
in soft foods, which do not require chewing. Temperatures associated with
microencapsulation, at minimum gel viscosities, were not lethal to B. lactis.
Bifidobacterium lactis cells were incubated under anaerobic conditions (4% H2,
10% CO2, and 86% N2) at 37°C overnight in 250 ml Tryptone-Yeast-Glucose
(TYG) broth, and grown to an 00600 0.9 - 1.1. Cells were harvested and
washed for microencapsulation using centrifugation.
Microencapsulation of the organism was done using a mono-axial extrusion
technique together with a superposed airflow, by manually extruding the
aqueous gum I cell mix through a 27.5 G bevelled needle, fitted on to a 10 ml
syringe. The resultant microdroplets were hardened by free fall into 0.1 M
CaCI2 solution. Microcapsules were separated from the CaCI2 solution by
filtration through Whatman No.1 filter paper. All procedures were carried out in
a laminar flow hood. Results indicated that the method of microencapsulation
used in this study was successful. Using a concentrated inoculum of B. lactis,
high numbers (lOglO 11-12 etu.g-1
) of bacteria were incorporated into the
microcapsules. Therefore the daily intake would be provided by 0.1 g
microcapsules.
The diameter and size distribution of microcapsules were determined by laser
diffractometry. This showed a maximum microcapsule diameter of 2.22 mm
with 50% (w/v) of the microcapsules having a diameter of < 0.637 mm.
Although this represents a considerable size variation, this would not adversely
affect mouthfeel of the beverages, as only 0.1 g microcapsules would be
required to obtain at least 108 B. lactis in any volume of amasi or mahewu.
To enumerate immobilised viable B. lactis, two techniques were compared.
These involved the use of either a pestle and mortar, or high power ultrasound
(HPUS) (20 kHz, 750 W). Results showed that HPUS was superior to the
pestle and mortar technique. A short exposure (15 s) to HPUS disrupted the
matrix releasing all entrapped etus, whereas when using the pestle and mortar
xiii
technique, cells remained partially entrapped in the gel. Therefore the pestle
and mortar technique yielded lower cfu values than expected.
The survival of microencapsulated B. lactis, in 1 M sodium phosphate buffer,
was studied as a possible means of supply of microcapsules to industry for
incorporation into foods. Microcapsules were stored in the buffer for 21 days at
either 4°C or 22°C. Results showed that cell viability was not significantly
reduced (p>0.05) at either temperature after 21 days. Hence this form of
storage could be used to deliver viable immobilised B. lactis to the food
industry.
In order to assess the survival of immobilised B. lactis in the GIT, the
microcapsules were incubated at 37°C over a period of 240 min in simulated
gastric juice (SGJ) (pH 1.5). Viable counts were performed by sampling at
regular intervals. A similar study was done in simulated bile and pancreatic
juices (BPJ) (pH 6.5). In SGJ, it was demonstrated that there was a significant
reduction (3 log cycles) (p<0.05) of free cells after 240 min. However, this
trend was not noted for microencapsulated B. lactis. Therefore, the gellanxanthan
gel matrix protected B. lactis from the lethal effect of SGJ. In BPJ, no
significant difference (p>0.05) was noted for surviving fractions of both
immobilised and free B. lactis.
Commercial pasteurised amasi (pH 4.4) and mahewu (pH 3.5) were selected as
the supply vehicles for the microencapsulated B. lactis. Known numbers of
viable microencapsulated and free B. lactis cells were added to both beverages.
For most samples, incubation was at either 4°C or 22°C for 21 days in the
presence of atmospheric oxygen. In addition, free cells were incubated
anaerobically at 22°C. As oxygen is limiting in the microcapsules, these were
not incubated under anaerobic conditions. The survival I shelf-life studies of
commercial amasi indicated no significant difference (p>0.05) in survival rate
between immobilised and free B. lactis cells. The reduction noted for viable
counts of immobilised or free B. lactis cells was approximately 1.5 log cycles.
Even so, after 21 days viable immobilised B. lactis (1010 0.1 g'l microcapsules)
remained in excess of the daily intake 108
, whereas in the free B. lactis cells,
the viable count declined to 106 mr1
. Statistical analyses showed that
temperature or oxygen presence had little effect on the survival of both
immobilised or free B. lactis cells (p>O.05). In mahewu, decline in viability of
cells was observed for most samples. However microencapsulation enhanced
cell survival at both 4°C and 22°C when compared to free cells. The decrease
in viable B. lactis free cells occurred more rapidly (3 log cycles) in mahewu,
than in amasi, at both 4°C and 22°C. Throughout the shelf-life studies it was
apparent that viable B. lactis cell numbers did not increase. This was
advantageous as metabolites associated with B. lactis growth would have
adversely altered the taste of both amasi and mahewu.
Sensory evaluation of the traditional fermented African beverages, enriched
with either viable immobilised or free B. lactis, was done in order to determine
consumer response to the product. An analytically trained 12-member taste
panel analysed the beverages for colour, texture, and taste. The triangle taste
test procedure was used. No differences were detected with regard to texture,
and colour of the fermented beverages containing immobilised B. lactis.
However, in the fermented beverages containing free cells, a change in
viscosity was noted. There was a significant difference (p<O.05) recorded in
flavour for both amasi and mahewu containing free B. lactis cells. In the two
fermented beverages enriched with immobilised cells, significant (p<O.05)
flavour differences were detected in mahewu. However, this was not observed
in the amasi samples containing immobilised B. lactis. Therefore, in order to
retain the sensory properties of amasi, B. lactis should be supplied in
microcapsules. In mahewu, although flavour differences noted were not
unpleasant to the panellists, results from this study indicate that the use of
commercial flavoured mahewu should be considered as a supply vehicle for
microencapsulated B. lactis.
Overall, this study demonstrated that immobilisation of B. lactis in
gellan-xanthan gum is possible. Microcapsules produced contained high
numbers of viable B. lactis, and were suitable for incorporation into soft foods.
The gel matrix significantly protected viable cells from harsh conditions
associated with SGJ. Although the surviving fraction of immobilised cells,
when compared to free cells, was not improved in amasi samples, it is
recommended that for technological reasons associated with production of
amasi, microencapsulation should be used. In mahewu, microencapsulation
enhanced B. lactis survival at both 4°C and 22°C. Therefore immobilisation of
B. lactis in mahewu is necessary in order to maintain the daily intake.
Immobilised B. lactis should be incorporated into both beverages after
fermentation, and pasteurisation.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:cput/oai:localhost:20.500.11838/824 |
| Date | January 2004 |
| Creators | Kokott, Shaun |
| Contributors | McMaster, L.D., Dr, Truter, E.J., Prof |
| Publisher | Cape Technikon |
| Source Sets | South African National ETD Portal |
| Language | English |
| Detected Language | English |
| Type | Thesis |
| Rights | http://creativecommons.org/licenses/by-nc-sa/3.0/za/ |
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