Effect of thermization and storage on the nutrition properties and shelf-stability of yoghurt from blends of cowmilk and coconut milk.

Project Abstract

<p> Yoghurts were produced by blending reconstituted powdered cow milk (100 g of powdered<br>cow milk (CM) 0.5 litres of water) with 25 % and 50 % coconut milk (CCM) and a control<br>(100 % cow milk) before fermentation. After fermentation for 16 h at room temperature, the<br>yoghurts were subjected to two heat treatments (thermization) namely, 75 0C thermization<br>and 80 0C thermization and a control (unthermized). The proximate, physicochemical,<br>vitamin and microbiological quality of yoghurt samples were investigated during storage at<br>room temperature for 5 weeks. The results obtained, revealed that in each of the three<br>formulations of yoghurt, proximate composition, titratable acidity (TTA), total solids, free<br>fatty acids (FFA), viscosity, microbial load and vitamins decreased as the temperature of<br>thermization increased.<br>The pH and moisture increased from 4.30 and 82.36 %, respectively<br>with increase in thermization temperature to 4.59 and 83.39 %, respectively. Yoghurts<br>samples from 50 % cow milk (CM) + 50 % coconut milk (CCM) had the highest moisture<br>content (83.39 %) and lowest total solid content (17.84 %) compared to 82.98 % and 18.16<br>%, respectively from 75 % cow milk (CM) + 25 % coconut milk (CCM) and 82.92 % and<br>18.28 %, respectively from 100 % cow milk (CM). Titratable acidity increased significantly<br>(p &lt; 0.05) with increase in percentage coconut milk ( 0.77 for 100 % cow milk (CM), 0.82 for<br>75 % cow milk (CM) + 25 % coconut milk (CCM) and 0.87 for 50 % cow milk (CM) + 50 %<br>coconut milk (CCM)). There was significant (p &lt; 0.05) decrease in pH as the percent coconut<br>milk increased (4.48 for 100 % cow milk (CM), 4.40 for 75 % cow milk (CM) + 25 %<br>coconut milk (CCM) and 4.30 for 50 % cow milk (CM) + 50 % coconut milk (CCM)). The<br>highest viscosity of 282.59 ± 2.46 cPs was obtained for unthermized 100 % cow milk which<br>also had the highest protein content of 3.84 ± 0.11 %. Free fatty acid increased significantly<br>(p &lt; 0.05) with increase in percent coconut milk and during storage. B-complex vitamins (B1,<br>B2 and B3) increased significantly (p&lt;0.05) as the storage time increased while the<br>antioxidant vitamins (vitamin C and E) decreased significantly (p &lt; 0.05). Vitamin A was not<br>detected in any of the samples. Total bacterial count increased significantly (p &lt; 0.05) from<br>2.27 x 102 cfu/ml ± 0.14 to 6.77 x 102 cfu/ml ± 0.10 on storage within 3 weeks. Thereafter,<br>their numbers reduced. Fungi were detected in all the yoghurt samples but they reduced after<br>one week of storage. Sensory results indicated that yoghurts with coconut milk (CCM) and<br>those thermized at 80 0C had significant (p &lt; 0.05) lower consumer preferences. <br></p>

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