5.1 Physicochemical Properties of Banana Stirred Yogurt
Being an acidic food, pH and titratable acidity are two of the major parameters of physicochemical properties of our developed value added yogurt with banana. pH is inversely related with acidity, thus lower pH indicates higher acidity in the yogurt, inferring microbial activity and a higher fermentation rate results indicates that the yogurt is becoming more acidic faster. So, it’s very important factor is this issue. From our study, it was found that sample 6 had the highest pH (4.06±0.057) and control had the lowest (3.53±0.057) and pH value increased with the increase of banana puree. It was observed that addition of banana affects the microbial activity and retards the fermentation rate with the time goes. There was higher difference in pH in control fresh sample and the sample after 7 days, with least difference for the yogurt with 8% of banana puree. According to EI- Bialy et al. (2014), fresh sample of control had less pH than the sample with added banana pure, but after 7 days, it reversed. Moreover, a slight change was also observed with the work from EI-Bialy et al. (2014), where the pH range was 4-4.5 and out obtained result was around 3.5-4.
On the other way, there was a bit of ups and downs in the titratable acidity of our developed product. Highest percentage of acidity (1.05±0.03%) was found in yogurt with 7% of banana puree, whereas 3% (0.92±0.03%) was the lowest. Both of the value exceeded the acidity range (0.64-0.96) from EI-Bialy et al. (2014), but within the acidity range (0.88- 1.22) done by Islam et al. (2013). So, the result of present findings agreed with the study of Islam et al., that our acidity of the developed product had increased with the increment of banana concentration.
Now, here comes the total soluble solids(TSS), that increases with the addition of banana concentration as the TSS content of banana stirred yogurt ranged between 19-23%, whereas EI-Bialy et al. found the range of TSS of their developed yogurt was 14.50-20% and Islam et al. described the range between 20.50-22.50%. So, no such difference was observed from the data of Islam et al. TSS increased gradually due the increase of banana in every next consecutive samples and addition of sugar and the heating, that reduced the volume of milk to around 65-70%.
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Addition of banana in yogurt made remarkable changes in proximate composition namely moisture, ash, fiber, protein & fat. Variation in concentration of banana made changes in yogurt sample in such compositions.
Among the samples, Control had the least (78.94 ±0.31%) amount of moisture content, and sample 4 had the highest (80.93±0.04%). Islam et al. found that moisture of banana stirred yogurt was (77.00-79.33%) and the moisture content decrease with the increase of banana puree. Although the moisture content was around the range, but, it minimally differed from our findings. According to shiga et al., increment of moisture content of the yogurt sample comes from the soluble fiber of banana, which has moisture absorbing ability. And there was significant different among the yogurt sample of 0, 5% and 8% banana puree.
Considering the fat, yogurt with 5% & 7% banana puree were significantly difference than the others. Yogurt with 3% and 8% banana puree had the highest percentage of fat with 5.06±0.06% and lowest (4.83±0.06%) in the yogurt with 7% banana puree, which was a bit high (4.5-4.7) compared to previous study (Islam et al., 2013). In this study, Fat percentage increased to a certain concentration and then decreased. It was happened due to the addition of fruit puree that might have decrease the fat percentage of yogurt in some extent. (Islam et al., 2013), and the lipolytic activity of micro flora (EI-Bialy, et al.)
(Abdalla et al.,2019) stated that the fiber increased with the increasing amount of banana puree comparing the control. Our study agreed with that as the control had 3.93±0.00% of fiber and 5.64±0.03% was present in the yogurt of 8% banana puree. Significant difference was also present in all samples.
Significant difference was found in ash content among the samples namely the yogurt from 5% banana puree and control, with the remaining samples. Highest (3.62±0.04%) and lowest (2.97±0.11%) ash found in the yogurt from 7% and 5% banana puree respectively.
Gradual increase was seen among most of the samples as banana contains good amount of minerals. But the amount of the ash content was a bit lower than the findings done by (Islam et al., 2013), as they gave the value between (3.33-4.44%).
The protein content of yogurt significantly increased with the increase of the added banana puree. The highest and lowest values of protein content of this value added yogurts were 4.37±0.00%& 4.23±0.05% for the treatments of 8% banana puree and control respectively,
33 | P a g e which was higher than the findings of (Islam et al., 2013), which can be attributed to the higher protein content in banana puree. No such significant difference was found among the samples except the control & the yogurt from 8% of banana puree.
5.3 Microbial Analysis
A gradual decrease was obtained with the increment of the banana concentration. The values are 95.33±3.51×105, 88.67±3.21×105, 61.00±2.65×105, 40.6±2.52×105, 26.33±3.06×105, 13.67±1.52×105 for the concentration of 0, 1, 3, 5, 7 & 8% of banana puree respectively. Among the samples, control demonstrated the highest number of colony forming unit/gm with 95.33±3.51×105 and sample 6 contained the lowest (13.67±1.52
×105), which was much lower than the TVC count by EI-Bialy et al. (2014). There was no significant difference between control and sample 1 regarding to TVC, but except the pair, all the remaining samples were significant different.
On the other hand, no coliform was identified in the samples after 7 days of storage period, 5.4 Mineral Contents
Mineral is the essential components of every foodstuffs and plays a vital role in maintain the body function. We also incorporate banana in yogurt in order to make some fortifications in mineral compositions. From the table, we have seen that a gradual increase in the amount of iron that comes from the incorporation of banana, whereas the value ranged from (105-187 µg/dl). On the other hand, magnesium didn’t show a sequential approach, as it went high (1.51±0.07 mg/dl) for the yogurt from 1% of banana puree and became low for the control (0.26±0.02 mg/dl), and the magnesium content was somehow decreased due to the addition of banana puree. For potassium, it was highest for the sample with 3% (7.33±0.57 mmole/dl) and lowest for the sample with 8% banana puree (5.00±0.00 mmole/dl).
5.5 Sensory Analysis
Sensory analysis of the produced banana stirred yogurt samples was done in two consecutive times based on concentration of banana puree. In first phase, control got the best score in every segment followed by the yogurt with 2% banana puree. Then we made a second trial for the samples which had an average score of greater than 5.5.
In the second & final phase of sensory analysis, control yet liked (8.00±0.70) most by the panelists, while the 7.80±0.44, 6.80±0.83, 7.00±0.70, 7.00±0.70, 6.80±0.83 were the score
34 | P a g e of the yogurt from 1, 3, 5, 7 and 8% respectively. Statistically, no significant difference was present considering the appearance No significant difference was also found in terms of taste. Same as before, control was preferred mostly (7.20±0.44), while 8% got the minimum score (5.40±1.95). The preference of the control was followed by 1%(7.00±0.00), 3% (6.80±0.83), 5% (7.80±0.83), 7% (6.80±1.92) yogurt from banana puree. In terms of smell, yogurt from 5% banana got the highest (7.80±1.30) preference, while 8% was the sluggish (5.80±1.79). A sweet aroma was created by the particular amount of banana puree, mainly 5% which was preferred much more than the control. Here, no significance difference was found among the samples. Same as smell, texture of 5% had the highest preference (8.00±1.00) and 8% was the lowest (5.80±1.09). Same as before, yogurt from 5% of banana puree preferred more than the control. Moreover, significant difference was found between the samples of 8% with 3% & 5%. Considering the overall acceptability, Control and yogurt from 8% banana puree got the highest (8.00±0.70) and lowest (5.80±1.09) preferences. Yogurt from 8% banana puree has a bitter taste and pungent smell compared to the variations. Moreover, significant differences were found between the control & yogurt from 5% banana puree with the sample containing 8% banana puree.
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