EFFECT OF THERMIZATION AND STORAGE ON THE NUTRITION PROPERTIES AND SHELF-STABILITY OF YOGHURT FROM BLENDS OF COWMILK AND COCONUT MILK

ABSTRACT 
Yoghurts were produced by blending reconstituted powdered cow milk (100 g of powdered 
cow milk (CM) : 0.5 litres of water) with 25 % and 50 % coconut milk (CCM) and a control 
(100 % cow milk) before fermentation. After fermentation for 16 h at room temperature, the 
yoghurts were subjected to two heat treatments (thermization) namely, 75 0C thermization 
and 80 0C thermization and a control (unthermized). The proximate, physicochemical, 
vitamin and microbiological quality of yoghurt samples were investigated during storage at 
room temperature for 5 weeks. The results obtained, revealed that in each of the three 
formulations of yoghurt, proximate composition, titratable acidity (TTA), total solids, free 
fatty acids (FFA), viscosity, microbial load and vitamins decreased as the temperature of 
thermization increased.

The pH and moisture increased from 4.30 and 82.36 %, respectively 
with increase in thermization temperature to 4.59 and 83.39 %, respectively. Yoghurts 
samples from 50 % cow milk (CM) + 50 % coconut milk (CCM) had the highest moisture 
content (83.39 %) and lowest total solid content (17.84 %) compared to 82.98 % and 18.16 
%, respectively from 75 % cow milk (CM) + 25 % coconut milk (CCM) and 82.92 % and 
18.28 %, respectively from 100 % cow milk (CM). Titratable acidity increased significantly 
(p < 0.05) with increase in percentage coconut milk ( 0.77 for 100 % cow milk (CM), 0.82 for 
75 % cow milk (CM) + 25 % coconut milk (CCM) and 0.87 for 50 % cow milk (CM) + 50 % 
coconut milk (CCM)). There was significant (p < 0.05) decrease in pH as the percent coconut 
milk increased (4.48 for 100 % cow milk (CM), 4.40 for 75 % cow milk (CM) + 25 % 
coconut milk (CCM) and 4.30 for 50 % cow milk (CM) + 50 % coconut milk (CCM)). The 
highest viscosity of 282.59 Â� 2.46 cPs was obtained for unthermized 100 % cow milk which 
also had the highest protein content of 3.84 Â� 0.11 %. Free fatty acid increased significantly 
(p < 0.05) with increase in percent coconut milk and during storage. B-complex vitamins (B1, 
B2 and B3) increased significantly (p<0.05) as the storage time increased while the 
antioxidant vitamins (vitamin C and E) decreased significantly (p < 0.05). Vitamin A was not 
detected in any of the samples. Total bacterial count increased significantly (p < 0.05) from 
2.27 x 102 cfu/ml Â� 0.14 to 6.77 x 102 cfu/ml Â� 0.10 on storage within 3 weeks. Thereafter, 
their numbers reduced. Fungi were detected in all the yoghurt samples but they reduced after 
one week of storage. Sensory results indicated that yoghurts with coconut milk (CCM) and 
those thermized at 80 0C had significant (p < 0.05) lower consumer preferences.