During the study, temperature was kept as the independent variable while the pH of the various brand of milk were considered as the dependent variables. The pH of the four brands of milk in the beginning ranged from 6.6 to 5.4 with A2 protein milk having the highest pH of 6.6 and the low fat milk having the lowest pH of 5.4. The standard deviation and the standard errors for the periods between zero hour and 12 hours after the setting of the experiment was constant for all the brands of the milk for both the incubated and the room temperatures. The standard deviation for the mean and the standard error for the four brands at the beginning was 0 while at the 12th hour the standard error was 0.05. Comparison of the standard errors for whole milk indicated that incubated milk was highly sensitive to fluctuations to temperatures compared to the milk kept at the room temperature. The standard error for room temperature remained constant for 24th 36th and 49th hour while it highly varied for the incubated whole milk. Similarly, the incubated organic milk also had a higher sensitivity to temperature changes compared to the sample kept at room temperature. The incubated organic milk further had a higher decline in pH amounting to 3.1 compared to room temperature sample that was 1.25. Subsequently, a similar trend emerged between the four brands of milk.
Samples kept at room temperature were relatively less sensitive to changes in temperature with low fat milk having the least pH changes of 1 over the 48 hour period. Similarly, the incubated low fat milk had constant standard error for 12th 24th 36th and 48th hour intervals. On the other hand, within the 48 hours, the incubated whole milk demonstrated the highest ph fluctuation range of 3.15 followed by incubated organic milk and incubated A2 protein milk that had pH change of 3.1. In the analysis of the accuracy of the results, the standard error for the mean of the pH ranged from 0-0.15 therefore, the recorded pH means had an accuracy of -/+ 0.15 in the higher bounds.
Table 1. Showing the Calculated Mean and Standard Error of the Incubated and Room Temperature Samples
Type of Milk/Elapsed Time 0 12
mean SE Room
mean SE Incubated
mean SE Room
0 6.2 0 4.15 0.05 5.65 0.15
0 6.3 0 4.55 0.05 5.95
A2 Protein Milk 6.6 0 6.6 0 4.95
Low-Fat Milk 5.4 0 5.4 0 3.75
Mean SE Room
Mean SE Incubated
Mean SE Room
A2 Protein Milk 4.05
Low-Fat Milk 3.05
mean SE Room
A2 Protein Milk 3.5
Low-Fat Milk 2.95
Figure 1. Standard Error Bar for Incubated Whole Milk
Figure 2. Standard Error Bar for Incubated Organic Milk
Figure 3. Standard Error Bar for Incubated A2 Protein Milk
Figure 4. Standard Error Bar for Incubated Low Fat Milk
From the analysis of the results and findings from the experiment, it emerged that the whole milk was the most sensitive to changes in temperature by recoding the highest change in pH levels. Similarly, each brand of milk which was incubated indicated a higher fluctuation of pH levels, therefore higher production of lactic acids compared to the samples which were kept at the room temperature. From the results, the primarily ideal condition for the fermentation of milk was identified as incubated environment. However, apart from the incubation process, the nature of the milk which could be identified as the brand also affected the production of the lactic acid (Salminen et al., 2004). From the experiment, the whole milk which was defined by Asteri et al (2010) as comprising of 3.2 % fat had the highest pH change range compared to organic milk, A2 protein milk and low fat milk.
The whole milk majorly comprises of protein, carbohydrate, fat and dietary fibre. The increased reactivity of the whole milk to changes in temperature compared to the other brands of milk could be attributed to the composition of the lactose disaccharide sugar that accounts for 5 % of the dairys whole milk (Walstra, et al., 2006). It is worth noting that it is the level of lactose sugar in the milk which is broken down by the Lactobacillus, Leuconostoc mesenteroides, Pediococcus cerevisiae, Streptococcus lactis and Bifidobacteriumbifidus lactic bacterias. However, consistent with the studies by Walstra (1999), the level of lactose in fermented foods declined with time as the anaerobic process converted it lactic acid.
It was worth noting that the maintenance of a constant temperature resulted to higher production of the lactic acid which could be deduced from the reduced pH levels of milk brands which had been incubated. Toomula (2011) noted that lactic acid producing bacteria such as S. cremoris and L. lactis and L. acidophilus tended to exhibit optimum growth temperatures between 37- 45 0 C . Subsequent fluctuations of the temperatures beyond the 37- 45 0 C range deterred the growth of bacteria and thus lowering the production of the lactic acid. While the incubated samples of milk products were kept at an optimum temperature of 45 0 C, the other set of sample were kept at room temperature that ranged from 19 0 C to 25 0 C. The room temperatures were therefore not optimum for the flourishing growth of lactic producing bacteria.
From analysis and the discussion of the results of the experiment, it emerged that temperature and the nature of the milk plays a significant role in the level of fermentation that takes. In the determination of the suitable conditions for the process of fermentation to take place, it was noted that the whole milk was highly suited compared to the organic milk, A2 protein milk and the low fat milk. Similarly, the study further established that incubated conditions highly favoured the growth of lactic producing bacteria compared to room temperatures. It therefore follows that the whole milk when incubated at 450will sour or create the greatest amount of lactic acid in comparison to the other milks, A2, organic and low fat milks. The significance of this study to the industrial plants is that they should ensure effective control of the temperature fluctuations in the production of yeast related products.
Asteri, I., Kittaki, N., & Tsakalidou, E. (2010). The effect of wild lactic acid bacteria on the production of goats milk soft cheese. International Journal Of Dairy Technology, 63(2), 234-242. doi:10.1111/j.1471-0307.2010.00564.x
Salminen, S., Wright, A., & Ouwehand, A. (2004). Lactic acid bacteria. New York: Marcel Dekker.
Toomula, N. (2011). Bacteriocin Producing Probiotic Lactic acid Bacteria. J Microbial Biochem Technol, 03(05). doi:10.4172/1948-5948.1000062
Walstra, P. (1999). Dairy technology. New York: Marcel Dekker.
Walstra, P., Geurts, T., & Wouters, J. (2006). Dairy science and technology. Boca Raton: CRC/Taylor & Francis.
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