Effect of milk preservation by activation of lactoperoxidase system on the quality and shelf life of pasteurised and fermented milk products
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Date
2001
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Publisher
Sokoine University of Agriculture
Abstract
The study was conducted to investigate the effect of milk preservation by the use of
activated Lactoperoxidase system (LPS) on fresh, pasteurised and fermented milk
quality. Fieldwork was done at Mwakaleli, Mbeya region, while the laboratory work
was conducted at Sokoine University of Agriculture. After collection, milk LPS was
activated by addition of sufficient amount of thiocyanate and hydrogen peroxide
followed by milk shelf life determination under different storage conditions. The
best LPS holding time before pasteurisation was found to be 3 hours followed by 6
hours, whereas the holding time above 6 hours performed poorly. The effect of LPS
activation on fermented milk quality was also investigated. No significant (P>0.05)
difference in pH between treated and untreated milk was observed on the milk that had
a holding time of less than 9 hours, above this period milk recorded significantly
(P<0.05) low pH. Likewise was the pH of the yoghurt with more or less similar trend.
The analysed natural Thiocyanate content of the test milk was within normal range
(4.09±l・l ppm). This indicates the test milk could accommodate recommended
external addition of thiocyanate for LPS activation without raising SCN- content above
the physiological limits. The LPS carry over effect on milk inocula could not be
detected due to the LPS inactivation by pasteurisation (80° C/1 min.). This explains the
absence of any noticeable physical, chemical or organoleptic abnormality on milk
and milk products final quality. In the field, activated LPS prolonged morning raw
milk shelf life for more than 15 hours as compared to less than 12 hours registered by
the untreated milk, whereas throughout the experiment under all storage conditions
LPS treated pasteurised milk performed significantly (P<0.001) better than the control.
In order to solve the problem of raw milk short shelf life in the remote rural tropical
environment a cheap and convenient charcoal cooler box was designed, constructed
and tested with encouraging results in the storage of raw milk. The cooler
performance was 8.94° C and 5.45° C below the environmental maximum and
minimum temperatures respectively. When compared to the room temperature
storage conditions, the cooler performed significantly (P<0.001) better than the
room temperature. Therefore, under any tropical environmental condition
accompanied with the absence refrigeration or cold room facilities, the application
of both activated LPS and charcoal cooler box for raw milk storage is strongly
recommended for the fresh milk shelf life extension to enable the marketing
functions to operate.
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Thesis
Keywords
Lactoperoxidase system, Milk products