| dc.description.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: determine the duration of antibacterial effect in camel milk
stored at different temperatures after activation of its LPsystem and 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 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° 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 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 delayinmultiplication 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
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 specifi 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 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 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 0.4 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 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 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 mesophilli 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 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. | en |
