Abstract:
Milk preservatives can originate from a natural or synthetic source. Incorporation of
synthetic source leads to undesirable effect to consumers. In addition, the tendency of
consumers to use natural preservatives has greatly influenced the food industry. Among
natural preservatives, honey bee propolis was effective in preservation of food. Therefore,
the aim of this research was to evaluate the effectiveness of extracted honey bee propolis
as a natural preservative for raw cow’s milk. The propolis was harvested from three agro
ecologies of Awi zone namely Banja, Dangla and Chagni and extracted using 70 %
ethanol. One hundred millilitres of raw cow’s milk samples collected from injibara
university dairy farm were placed into five pre-sterilized sample bottles in each study
districts and ethanol extracted honey bee propolis from three sources (Banja,Dangla and
Chagni) prepared with a volume of T1 (control), T2 (5ml), T3 (10ml), T4 (15ml) and T5
(20ml) was added in to 100 ml of raw cow’s milk samples. All samples were analyzed for
the physicochemical (protein, fat, ash, solid nonfat, pH, TA clot on boiling, alcohol, and
methylene blue reduction test, microbiological (aerobic plate count (ABC), coliforms
count (CC) and Yeast and mold counts (YMC), and organoleptic properties. The data was
encoded and analyzed by using SAS version 9.4 software. The study shows the Fat, SNF,
Ash, pH, TA and Protein content were significantly (p˂0.05) influenced by propolis
concentration and agro-ecologies of propolis harvested. The interaction has shown a
significant (p˂0.05) effect on protein and fat contents of raw cow’s milk. However, a nonsignificant (p>0.05) interaction effect on SNF,pH and TA contents of raw cow’s milk. In
organoleptic test, both propolis concentration and agro-ecologies were a significantly
(p˂0.05) affected all the sensory values of raw cows milk. However, interaction effects of
propolis concentration and agro-ecologies of propolis collected significant (p˂0.05) only
on color and flavor values of raw cow’s milk. Result revealed that significantly (p˂0.05)
higher preference on sensory parameters of milk was recorded in milks treated with
propolis concentration harvested from Banja than Dangla and Guangua woredas and
lower preference in T4 and T5 concentration treated raw cow’s milk. Agro ecologies and
propolis concentration had highly significant (P < 0.001) effect on the main and
significance (P < 0.05) interaction effect on clot on boiling, alcohol and methylene blue
reduction tests of raw cow’s milk. The shortest coagulation time (2 hour) was recorded in
control group. However, the highest coagulation time was recorded in BT5 9 hour in clot
on boiling, 9:50 hour/minutes in alcohol test, DT5 10 hour both in clot on boiling and
alcohol test and in GT5 12 hour both in clot on boiling and alcohol test and in MBRTs in
GT5 (12 hour), DT5 (10.50 hour/mitutes) and BT5 (9 hour). In microbial test, agro
ecologies of propolis harvested and propolis concentration had a highly significant (P <
0.001) effect on ABC, CF and YM counts of sample raw cow’s milk. In the main effects of
agro-ecologies propolis harvested, a significant lower ABCs,TCFs and YMCs values were
registered in Guangu woredas and the highest was recorded in Banja and Dangla woreds
in decreasing order. Regarding, propolis concentration, the microbial counts significantly
(P<0.05) decreased with the addition of higher concentrations of ethanol extracted
propolis. Finally, it can be concluded that the use of 5ml and 10ml extracted honey bee
propolis concentration harvested from Guangua Woredas (lowland) extends the shelf life
of raw milk for 8–9 hours under ambient temperatures without affecting
organoleptic/sensory characteristics.