| dc.description.abstract | 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 levels of thiocyanate inherent in camel milk.
• determine the effect of the LP-system on the keeping quality of
pasteurised camel milk
• determine the effect of the LP-system on the starter culture activity
in heat treated and raw camel milk.
Determination of the duration of antibacterial effect in camel milk was
done by first analyzing camel milk samples from three different
production sites in Kenya (Kajiando, Isiolo and Nanyuki) for
thiocyanate concentration. Changes in total viable counts and titratable
acidity in LP-activated and non-activated camel milk were then
determined during storage at 10, 20 and 30°C. Activation of the LPsystem
was by the addition of sufficient amounts of hydrogen peroxide
to give an initial concentration of 8.5 ppm.
The effect of increasing levels of thiocyanate and hydrogen peroxide
on antibacterial activity of LP-system in raw camel milk at 30°C was
investigated by monitoring changes in total viable counts and lactic
acid development in raw camel milk at NaSCN:H202 concentrations
ratios of 0, 10:I0,20:20.30:30 and 40:40ppms.
The effect of the LP-system on keeping quality in pasteurised camel
milk was assessed by activation of the LP-System in camel milk
followed by pasteurization at after 0, 4, and 8 hours of storage.
Samples were drawn and viable bacteria determined by the standard
plate count method after 3 day and 5 day intervals during storage at 20
. °C and 10°C respectively.
Sensitivity of lactic starter cultures to LP-system was investigated by
monitoring acid production iby mesophillic, thermophillic and Suusac
starter cultures in both LP-system treated and untreated camel milk.
Inoculation with starter was done after 0, 4 and 8 hours of storage of
LP-activated samples.
The effect of heat-treatment on the effect of the LP-system on starter
activity in camel milk was investigated by following a similar protocol
but heating samples at 85° C for 30 minutes prior to inoculation.
Natural concentration of thiocyanate occurring in the camel milk from
the three different sites ranged from 9.7 to 36.4 rng/1. No additional
amount of thiocyanate was therefore used to activate the LP-system.
The average thiocyanate values of camel milk from different sites were
15.8, 32.9 and 9.74 mg/I, and were found to be significantly different
(p<0.001) in the three sampling sites.
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.
Viable counts increased with storage temperature. The difference in
shelf life, as determined by acid production, between LP-system
activated samples and their respective controls were 19 hours at both
10 and 20°C, and 4 hours at 30°C.
Increasing levels of thiocyanate and hydrogen peroxide on
antibacterial activity by LP-system in raw camel milk showed a
significant increase in the 'delay in multiplication of bacteria and acid
production. There was an increase in the delay in multiplication of
bacteria from no lag phase in the control to 4, 6, 11.5 and 9.5 hours
respectively in the NaSCN/H202 concentration ratios of 10:10, 20:20,
30:30 and 40:40 ppm levels. Shelf life of the camel milk as determined
by lactic acid production was 4, 6, 12, 16 and 16 hours at ratios of 0,
10: 10, 20:20, 30:30 and 40:40 ppm dose respectively.
Activation of the LP- System in camel milk followed by pasteurization
extended the shelf-life of camel milk held at both 10° C and 20° C. The
results also showed a significant effect (p<0.001) of storage time prior
to pasteurisation on the effect of the LP-system on the survivmq
microflora at all the 3 times of storage prior to pasteurisation.
Activation of the LP- System in camel milk followed by pasteurization
resulted in a shelf life of 15, 32, 17 and 17 days for the non-activated
control and those pasteurised after 0, 4, and 8 hours of storage of the
LP-System activated raw camel milk respectively during storage of
samples at 10°C. At 20°C, the shelf life was 6, 13, 9 and 7 days for
non-activated control and those pasteurised after 0, 4, and 8 hours of
storage of the LP-System activated raw camel milk respectively. The
number of viable bacteria in untreated sample reached 108 compared
to 105-107 in treated samples after 45 days of storage at 10°C. On
storage at 20°C, the viable bacterial counts increased to 108 and 107
106 in untreated in and treated milk samples respectively after 15 days
only. The mean specific growth rates at 10°C storage temperature
were 0.51, 0.2, 0.41 and 0.5 for the non-activated control, activated
and pasteurized after 0, 4, and 8 hours respectively. Values for the LPtreated
samples were significantly lower than in the control (p<0.001).
At 20°C storage temperature, the mean specific growth rates were
1.46, 0.27, 0.69 and 1 for the inactivated control, activated and
pasteurized milk samples after 0, 4, and 8 hours respectively. These
were also significantly lower in the LP-treated camel milk samples than
in the control (p<0.001)
The study on inhibition of mesophillic, thermophillic and Suusac starter
cultures by LP-system activation showed a significant slow down in
acid development in the raw camel milk inoculated immediately after
inoculation in all the three starter cultures. For the thermophillic starter
culture, the mean lactic acid produced in the non-activated sample,
and those activated and inoculated after 0, 4, and 8 hours were 0.41,
0.32, 0.35 and 0.36 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>005) at the
inoculation times 0, 4 and [3 respectively. For the Suusac starter,
mean lactic acid produced was 0.67, 0.62,' 0.67 and 0.52 for the nonactivated
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 the
mesophillic starter culture the mean values of lactic acid produced
were 0.53, 0.48, 0.42 and 0.54 for the 'non-activated control and
samples activated samples inoculated after 0, 4, and 8 hours
respectively, The differences in means between the control and
activated samples were significant (p<0.01) for samples inoculated
after 0 and 4 hours and non-significant (p>0.05) when inoculated after
8 hours.
The investigation on the effect of the LP-system on starter activity in
heat-treated camel milk showed that heat treatment reduced starter
inhibition by the LP-system for the mesophillic and thermophillic starter
cultures. This was however so when LP-system activation, heat
treatment and inoculation followed each other sequentially. For the
mesophillic starter, the mean lactic acid values for the non-activated
control samples and those activated and then inoculated after 0, 4 and
8 hours were 0.52, 0.52, 0.54 and 0.40 respectively. The differences
between mean lactic acid values of the control and activated samples
were not significant (p>0.05), when immediately inoculated but were
significant after 4 hours (p<0.05), and (p<0.001) 8 hours. Mean lactic
acid values for the thermophillic starter for the non-activated 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 zero to significant on
inoculation after 4 (p<0.05) and 8 (p<0.01) hours storage of the LPSystem
activated raw camel milk prior to heat treatment and
inoculation. However, with suusac starter, the mean lactic acid values
for non-activated 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. Inhibition by LP-System for inactivated control samples,
those activated and inoculated after 0 and 4 hours was significant
(p<0.005), but non-significant for those inoculated after 8 hours.
The present investigation therefore shows that by activating the LPsystem
it is possible to extend the storage period of raw camel milk
and that the inhibition by the LP-system on the microbes present varies
with temperature of storage. Increasing levels of thiocyanate and
hydrogen peroxide on antibacterial activity of LP-system in raw camel
milk significantly increases delay in multiplication of bacteria and acid
production.
Activation of the LP- System in camel milk followed by pasteurization
results in an extension in the shelf-life of camel milk. This extension
however reduces with increase in time of storage of the LP- System
activated camel milk prior to pasteurisation.
Camel milk preserved using this method could still support satisfactory
mesophillic and thermophillic starter culture activity if the raw camel
milk is held for upto 8 hours during storage at 30°C prior to processing.
Heat treatment reduces i starter inhibition by the LP-system for the
mesophillic and thermophillic starter cultures when LP-system
activation, heat treatment and inoculation follow each other
sequentially. However, 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 the
raw milk by LP-system. | en |
