Effects of lactoperoxidase system in camel milk for preservation and fermentation purposes

Citation:
undefined. Effects of lactoperoxidase system in camel milk for preservation and fermentation purposes. Wangoh J, Lamuka PO, eds. University of Nairobi; 2007.

Thesis Type:

MSc Thesis

Abstract:

Summary
This study was conducted to investigate preservative effect of the LPsystem
on both raw and pasteurized camel milk. The effect of the LPsystem
on selected starter cultures in the raw and pasteurized camel
milk was also investigated. Experiments were therefore conducted to:
 evaluate the effect of LP-system activation on shelf-life of raw
camel milk with the underlying activities being to:
o determine the duration of antibacterial effect in camel milk
stored at different temperatures after activation of its LPsystem
and
o monitor effect on keeping quality of increasing
concentrations of sodium thiocyanate and hydrogen
peroxide within physiological limits.
 determine the effect of the LP-system on keeping quality in
pasteurised camel milk
 determine the effect of the LP-system on starter culture activity in
camel heat treated and raw camel milk.
The concentration of thiocyanate occurring naturally in the milk used in
the present investigations ranged from 9.7 to 36.4 mg/l. No addition of
thiocyanate was therefore necessary to activate the LP-system. The
average thiocyanate values of camel milk from different sites were
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15.8, 32.9 and 9.74 mg/l and were significantly different (p<0.001)
across the three sampling sites in this study.
Changes in total viable counts between LP-activated and LPinactivated
camel milk were determined during storage at 10, 20 and
30°C. Viable counts increased with storage temperature. Microbial
growth was halted for 15, 17 and 76 hours at 30, 20 and 10°C
respectively by activation of the LP-system in raw camel milk. At 30°C
the effect was mainly bacteriostatic and at 20°C, there was an initial
bactericidal effect in the first 15 hours. At 10°C, the bactericidal effect
was noted throughout the period of 76 hours.
The titratable acidity between LP-activated and LP-inactivated camel
milk was determined during storage at 10, 20 and 30°C. There lag in
acid production of 14, 23, and 10 hours at 10, 20 and 30°C
respectively as compared to the controls and was significantly different
(p>0.05) across the three incubation temperatures. Shelf life difference
between LP-system activated samples and their respective controls
was 19 hours at both 10 and 20°C and 4 hours at 30°C.
The differences in mean acid produced between the control samples
and the activated samples, however, were 0.12, 0.61 and 0.49 for 10,
20 and 30°C respectively. Inhibition of acid production by the LPsystem
increased from significant (p<0.05) during storage at 10°C to
highly significant (p<0.01) during storage at 20 and 30°C. The present
investigation therefore shows that by activating the LP-system it is
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possible to extend the storage period of raw camel milk and that the
effect of the LP-system on the microbes present varies with
temperature of storage.
The effect of increasing levels of thiocyanate and hydrogen peroxide
on antibacterial activity of LP-system in raw camel milk at 30ºC was
investigated. Changes in total viable counts and lactic acid
development in raw camel milk at concentrations of 0, 10:10, 20:20,
30:30 and 40:40ppms, NaSCN
-
:H2O2 were monitored. The delay in
multiplication of bacteria increased significantly with an increase in the
LP-system components from no lag phase in the control to 4, 6, 11.5
and 9.5 hours in the 10:10, 20:20, 30:30 and 40:40 ppm levels of
NaSCN/H2O2 respectively.. The lag in acid production was 0, 4.8, 6, 12
and 8 hours for 0, 10:10, 20:20, 30:30 and 40:40 ppm dose of
NaSCN:H2O2, respectively. The shelf life of the camel milk was 4, 6,
12, 16 and 16 hours, respectively, for 0, 10:10, 20:20, 30:30 and 40:40
ppm dose of NaSCN:H2O2.
Lactoperoxidase system (LPS) was activated in camel milk followed by
pasteurization after 0, 4, and 8 hours after of storage.
This resulted in a shelf life of 15, 32, 17 and 17 days for the nonactivated
control and those activated after 0, 4, and 8 hours of storage
respectively during storage of samples at 10ºC. At 20°C, the shelf life
was 6, 13, 9 and 7 days for non-activated control and those activated
after 0, 4, and 8 hours of storage respectively. These results showed
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a significant effect of storage time prior to pasteurisation on the effect
of the LP-system on the surviving microflora between the control and
activated samples at all the 3 times of storage prior to pasteurisation
(p<0.001). The number of viable bacteria in untreated sample reached
108 after 45 days compared to 105-107 in treated samples during
storage at 10ºC and 108 after 15 days in untreated compared to 107-
106 in treated samples under storage at 20ºC. The mean specific
growth rates at 10ºC storage temperature were 0.51, 0.2, 0.41 and 0.5
for the inactivated control, activated and pasteurized after 0, 4, and 8
hours respectively and were significantly lower in the LP-treated camel
milk samples than in the control (p<0.001). At 20ºC storage
temperature, the mean specific growth rates were 1,46, 0.27, 0.69 and
1 for the inactivated control, activated and pasteurized after 0, 4, and 8
hours respectively. These were also significantly lower in the LPtreated
camel milk samples than in the control (p<0.001)
Sensitivity of lactic starter cultures to LP-system was investigated by
monitoring acid production by mesophillic, thermophillic and Suusac
starter cultures in both LP-system treated and untreated camel milk.
Inoculation with starter was done after zero, 4 and 8 hours of storage
of LP-activated samples.
In all the three starters, LP-system activation resulted in a significant
slow down in acid development in raw camel milk activated and
inoculated immediately. For the thermophillic starter mean lactic acid
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was 0.41, 0.32, 0.35 and 0.36 for the inactivated control sample and
those activated then inoculated with starter after 0, 4, and 8 hours
respectively. The differences in means between the control and the
activated samples were very highly significant (p<0.001), highly
significant (p<0.01) and not significant (p>0.05) at the inoculation times
o, 4 and 8 respectively. For the Suusac starter, mean lactic acid was
0.67, 0.62, 0.67 and 0.52 for the inactivated control sample and those
activated then inoculated with starter after 0, 4, and 8 hours
respectively. The differences in means between the control and
activated samples were highly significant (p<0.01) at all the inoculation
times after activation. However, for mesophillic starter culture the mean
values of lactic acid produced were 0.53, 0.48, 0.42 and 0.54 for the
inactivated control and activated then inoculated with starter after 0, 4,
and 8 hours respectively. The differences in means between the
control and activated samples were significant (p<0.01) at 0 and 4
hours and non-significant (p>0.05) at 8 hours. This implied that camel
milk preserved using this method could support satisfactory mesophillic
and thermophillic starter culture activity if the milk is held prior to
processing.
The investigation on the effect of the LP-system on starter activity in
camel milk heat-treated prior to inoculation showed that heat treatment
reduced starter inhibition by the LP-system for the mesophillic and
thermophillic starter cultures for samples LP-system activated, heat
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treated and inoculated at immediately. For the mesophillic starter mean
lactic acid values for the inactivated control sample, activated and then
inoculated after 0, 4 and 8 hours were 0.52, 0.52, 0.54 and 0.40
respectively. The differences in mean lactic acid values between the
control and activated samples showed that a non-significant effect of
inoculation time at time 0 (p>0.05), a significant effect after 4 hours
(p<0.05), and a very highly significant effect (p<0.001) after 8 hours.
Mean lactic acid values for the thermophillic starter for the inactivated
control sample and those activated and then inoculated after 0, 4 and 8
hours were 0.52, 0.52, 0.54 and 0.40 respectively. The inhibition
changed from insignificant (p>0.05) on inoculation at time 0 and 4
hours (p<0.05) and was highly significant (p<0.01) on inoculation after
8 hours. Thus the inhibitory effect of the LP-system on mesophillic
and thermophillic starter culture activity in heat treated camel milk
apparently is reactivated and increases with time of preservation of raw
milk by LP-system. However with suusac starter, the mean lactic acid
values inactivated control sample and those activated and then
inoculated after 0, 4 and 8 hours respectively were 0.69, 0.58, 0.64
and 0.71. At zero and four hours after activation inhibition was
significant (p<0.05) compared to a non-significantly different inhibition
(p>0.05) on inoculation after 8 hours of storage.
The use of the LP-system might therefore have a significant influence
on the time taken to reach the desired pH in the vat, which is a critical
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factor for the manufacturer of fermented camel milk and this influence
is dependent on the time of preservation of raw camel milk prior to
processing of fermented products.

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