| dc.description.abstract | Increased incidence of Non communicable diseases (NCD) such as cardiovascular
diseases, diabetes and cancer has been associated with decreased consumption of
polyunsaturated fatty acids (PUFAs) of the omega-3 series, especially very long
chain eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). These fatty
acids are majorly found in fish and their by-products. Nile perch (Lates niloticus)
is one of the fish that dominates the commercial fish market in Eastern Africa and
its processing results in generation of large amounts of by-products which are of
high nutritional content.
This study aimed to develop functional yoghurts; YFH (yoghurt fortified with
Omega-3 rich Nile perch fish oil and honey) and YFL (yoghurt fortified with
Omega-3 rich Nile perch fish oil and lemon juice) and to evaluate their shelf life
properties. Liberation of fish oil from Nile perch fat pads was done using a food
grade enzyme Alcalase and in the absence of an exogenous enzyme.
Characterization of the fish oil was done by thin layer chromatography and the
quality parameters; PV (peroxide value), AV (anisidine value), TOTOX (total
oxidation) and FFA (free fatty acids content) determined. Three honey samples
and three citrus fruits were analyzed for their antioxidant activity and in both
cases; the honey and citrus fruit with the highest antioxidant activity were used in
development of the functional yoghurt. Four batches of yoghurt were produced,
YFH, YFL, PY (plain yoghurt) and YF (yoghurt fortified with Omega-3 rich Nile
perch fish oil only) where the latter two (PY and YF) were used as controls.
Yoghurt samples were evaluated for sensory characteristics by a random panel of
students. Quality parameters, pH, total acidity and ascorbic acid content were
analyzed over one month storage period at one week’s interval. Triplicate
experiments were conducted and data analyzed using SPSS software.
Hydrolysis of the fish fat pads in the absence of an exogenous enzyme gave a
better yield (60.67% wet weight) compared to Alcalase enzyme hydrolysis
(48.33% wet weight). The quality parameters of the omega-3 rich fish oil were;
Pv (meq/kg) = 4.83 ± 1.75, Av =16.50 ± 2.14, Totox= 26.16 ± 1.09 and FFA (%)
=2.16 ± 0.22. A commercial honey sample (Green forest) and lemon juice which
had the highest Total Antioxidant content (AEAC) of 312± 2.34 and 197± 3.65
mg/L respectively were used for fortification. The sensory evaluation tests
showed that the fortified yoghurt was acceptable to the tasting panel with the best
two most preferred flavors being the strawberry plus honey and strawberry plus
lemon juice samples with ranks of 4.80 and 4.825 respectively in a five point
hedonic scale. During the last week of the one-month storage, the yoghurt honey
sample gave the most reduced peroxide values (9.78± 2.65) followed by lemon
juice (11.54± 2.59) and the sample without antioxidant giving the highest Pv
values (15.54± 0.56). The Av values showed a similar trend. The pH decreased
slightly over time in all the samples. The lemon juice fortified sample had the
highest ascorbic acid content of 28 mg/100g, all the other samples had much
reduced ascorbic acid values below 1 mg/100g.
The study indicates that enough fish oil can be obtained from Nile perch fish pads
by hydrolysis without the need of using an enzyme since enzymatic hydrolysis
decreases oil yield due to the formation of an emulsion. All the quality parameters
of the omega-3 rich fish oil were in the acceptable range of 3-20 meq/kg for Pv
and 4-60 for Av over the one month storage period. In addition, omega-3 rich fish
oil–enriched yoghurt was highly stable to oxidation, with the addition of natural
antioxidants such as honey and vitamin C evident by the low Pv and Av values in
these samples over the one-month storage period.
In conclusion, fortification of yoghurt with the omega-3 rich Nile perch fish oils is
therefore a practical approach towards ensuring a constant intake of EPA and
DHA which is limited due to the low consumption of fish among many
communities in Kenya as well as the high cost of ɷ-3 supplements present in the
market. | en_US |
