Improvement of sensory characteristics of Barangan banana (Musa acuminata Linn.) slices as a stirred yogurt topping

This study aimed to improve the sensory characteristics of bananas (Musa acuminata Linn.) slices as a stirred yogurt topping. Ascorbic acid was used in three different concentrations (C; 1%, 2%, and 3%) at three different soaking times (T; 4 mins, 5 mins, and 6 mins). Samples without soaking in ascorbic acid were used as a control. The sliced bananas were analyzed for color (brightness, L*; redness, a*; and yellowness, b*) and hedonic test (taste, aroma, and color) of 30 semi-trained panelists. The most preferred sample was then analyzed by descriptive test (taste, aroma, and color). The results showed that panelists mostly liked the slices banana soaked in 2% of ascorbic acid for 4 minutes. It had a strong sour taste, yogurt aroma, and brownish yellow color. The color values of the preferred sample of L*, a*, and b* were 98.1, -13.9, and +47.3 respectively. On the other hand, the control sample had sour taste, banana aroma, and blackish yellow color. The color values of the control sample of L*, a*, and b* were 94.2, -10.03, and 37.9 respectively. These results indicate that ascorbic acid could increase the appearance of Barangan banana as a stirred yogurt topping.


Introduction
Yogurt is a dairy product made from fermentation with addition of lactic acid bacteria (LAB; Streptococcus thermophilus and Lactobacillus bulgaricus).According to market surveys, yogurt usually comes in one of two types: with or without added flavors [1].Meanwhile, based on the production method, there are three types of yogurts, which are stirred yogurt, set yogurt, and drink yogurt.Stirred yogurt has a thick and slightly runny texture.The yogurt texture becomes liquid due to the stirring process that is carried out after the incubation process so that the clumping or coagulation of proteins is hampered before the cooling process.The production of stirred yogurt is in a big container and is transferred into a small cup once the fermentation process is done [2].Set yogurt has a thick and dense texture, made by adding yogurt culture directly into the package so that the fermentation process occurs inside the package [3].Drink yogurt has a liquid texture and is made with a solution of sugar, thickening agents, and flavors [4].
IOP Publishing doi:10.1088/1755-1315/1297/1/012077 2 Yogurt with added flavor can be obtained naturally from the addition of fruits.Banana (Musa acuminate Linn) is a local fruit originating from North Sumatra, Indonesia that can be added in the production of fruit yogurt.This fruit is between 10-18 cm long, 2.5-4.5 in diameter and has a crooked shape with a tapered end like the neck of a bottle.Ripe fruit has a black spot, sweet taste, soft texture, brass white color, no seeds, and a fragrant aroma [5].Bananas contain 0.5 mg of iron and 37 mg of vitamin C per 100 grams [6].In addition, this type of banana has a higher level of sweetness than other types of bananas, so the slices of bananas can be used as a natural flavoring as well as a topping for stirred yogurt.
Bananas are a climacteric fruit that is prone to discoloration and decay.This is because bananas contain a fairly high phenolic component, which is 181 mhGAE/kg [7].The process of color changing in bananas into brown is included in enzymatic browning which occurs due to the presence of phenolic compound in foodstuffs that react with the polyphenol oxidase (PPO) enzyme with the help of oxygen to form quinones.Quinones quickly undergo polymerization to produce brown pigments, namely melanin [8].The occurrence of browning reactions is also influenced by several factors such as oxygen, temperature, moisture content, and time.If these four factors increase, the change in color to brown will also continue to increase.
Color changing of the banana slices as a yogurt topping can affect the physical form of the stirred yogurt, thereby reducing consumer acceptance of the product.The soaking method is one of the best ways that can be used to prevent browning reactions on fresh fruit slices [9].The use of types of acid to prevent browning varies widely.Ascorbic acid, which dissolves in water, is safe to consume in sufficient quantities and can inhibit polyphenolase enzyme activity, so it is widely used as a compound to inhibit enzymatic browning in fruit.Previous research showed that ascorbic acid acts as an antioxidant which will bind to oxygen, thereby preventing the activity of polyphenol oxidase enzymes and inhibiting the formation of brown melanin compounds in an apple [10].Therefore, the purpose of this study was to determine the exact concentration of ascorbic acid and soaking time in inhibiting the browning of banana slices so that they can be used as a yogurt topping.

Sample preparation and experimental design
The main ingredient in this study was ripe Barangan bananas (Musa acuminate Linn) and UHT (Ultra High Temperature) milk obtained from Ulee Kareng traditional market, Banda Aceh, Indonesia.Bananas were peeled and cut into slices measuring 3 mm in thickness.Another main ingredient was powdered ascorbic acid which is obtained from an online shop.In the preparation of ascorbic acid solution, water was added.
The study was conducted using a randomized block design consisting of two factors and 3 replications.The first factor was the concentration of ascorbic acid (C; 1%, 2%, and 3%).The second factor was the soaking time (T; 4 minutes, 5 minutes, and 6 minutes).

Production of plain stirred yogurt
UHT milk was heated in a water bath until it reached 43°C and was cooled in cold water until the temperature was 38°C.Starter cultures (3 grams) were added into the milk and was stirred until well distributed.The mixture was put into a stainless-steel container and was incubated at 38°C for 8 hours.The resulting yogurt was put into a sterile glass jar.Slices of bananas that had been soaked in ascorbic acid solution according to the experimental unit were then used as toppings for stirred yogurt [11].

Sample analysis
Banana slices soaked in ascorbic acid and used as a yogurt topping were analyzed for color (L*, a*, and b*).Color analysis was performed using a color analysis application version 7.0.0 offered by Lab Tools from Brazil which includes L*, a*, and b* colors.The L* notation indicates the brightness level [L*= 100 (brightest) and L*=0 (darkest)].The a* (redness level) notation indicates the red-green color ranging from 0 to +100 for red (+a values) and from 0 to -80 for green (-a values).The b* (yellowness level) notation indicates the yellow-blue color ranging from 0 to +70 for yellow (+b values) and from 0 to -70 for blue (-b values) [12].
The sliced bananas were also analyzed for hedonic test (taste, aroma, and color).The hedonic test was carried out with five assessment criteria (totally dislike, dislike, neutral, like, and really like) by 30 yogurt consumers as the panelists.Selection of the best treatment was carried out using a ranking test.
The best treatment sample was then analyzed for descriptive test of color (yellow, brownish yellow, yellow-black, brown, and dark brown), taste (banana, sweet milk, typical sour yogurt, very sour, and bitter), and aroma (banana, sour yogurt, milk, and alcohol) with five assessment criteria (1: very weak, 2: weak, 3: normal, 4: strong, and 5: very strong).The panelists used in this test were 25 yogurt consumers [13].

Data analysis
All mean data from color analysis was analyzed by standard error.The data obtained from hedonic test was analyzed using Analysis of Variance (ANOVA).If there is a significant effect on the concentration of ascorbic acid and the soaking time on the banana slices, the test was continued with the Duncan's Multiple Test (DMRT) method.Then, data obtained from the descriptive test were analyzed by descriptive statistics.

Color of banana slices soaked in ascorbic acid
Color is one of the parameters in determining the quality of a product.Color can affect the value of a product from consumers or panelists.The results of the calculation of the color of a product obtained are very dependent on the method of measurement and the surface condition of the object being analyzed.In this study, color was seen from the L*, a*, and b* values, where the higher the L*, a*, and b* values obtained, the higher the product color degradation.Figure 1 shows a comparison of the discoloration of the control banana slices and the banana slices soaked in ascorbic acid.
The brightness level (L*) of the control banana slices was 94.2, while the L* value of the banana slices after soaking ranged from 96.36 to 98.43 with an average of 97.8.The highest L* value was found in the C2T3 treatment where this value was greater than that of the control bananas.Changing in the control banana slices was faster than the treated banana slices due to oxygen permeability which can cause fruit tissue to be easily oxidized, causing a faster browning reaction [14].The values of all treatment are close to 100 which indicates the brightness level of treated bananas slices remained bright.These results also showed that ascorbic acid could reduce the browning of banana slices so that it could be applied as a yogurt topping.
The redness level (a*) value indicates the red-green color level.The redness value of soaking banana slices ranged from -9.1 to -15.6 with an average of -13.57.Soaking bananas in 1% of ascorbic acid could increase the a* values.However, in other concentrations, the highest a* value was reached at 5 mins.According to Abbasi et al. [15], the use of ascorbic acid as an anti-browning agent depends on the concentration used.Ascorbic acid is a compound that is easily oxidized to dehydro ascorbic acid which no longer has activity as a reducing agent.When ascorbic acid is oxidized, cells from reactive oxygen compounds cannot be protected, resulting in cell death in bananas which causes brownish-red pigments on the surface of bananas [16].Compared with the control bananas (a*; -10.3), treatment with 3% of ascorbic acid and 5 minutes of soaking time (C3T2) was able to increase the a* value to 15.63.
The yellowness level (b*) value indicates a chromatic mixture of yellow to blue.The yellowness level obtained from soaking the banana slices ranged from 27.32 -56.53 with an average of 47.79.The b* values had a similar trend with the a* values where increasing yellowness level because of increasing soaking time only applied at 1% ascorbic acid treatment.In other concentrations, the highest b* value was also reached at 5 mins.This is due to the use of high concentrations and long soaking time which makes ascorbic acid more quickly oxidize.When oxidation occurs, the role of ascorbic acid as a reducing agent is unable to reduce the o-quinone back into phenolic compounds resulting from an enzymatic browning reaction so that the color pigment on the fruit slices turns brown [17].Compared with the control bananas (b*; +37.93), treatment with 3% of ascorbic acid and 5 minutes of soaking time (C3T2) was able to maintain the yellow color on the banana slices.Notes: Data are presented as the means of three replications ± standard deviation.
Overall, the L* a* and b* values of 3% ascorbic acid concentration with 5 minutes of soaking time were better able to maintain the color (prevent browning) of banana slices than the control.This shows that ascorbic acid is effective as an anti-browning agent in banana slices.Different from previous research, soaking poor apples with 3% concentration of ascorbic acid and a soaking time of 2 minutes was able to inhibit the browning reaction more.The addition of ascorbic acid can prevent the enzymatic browning reaction of the cut banana tissue, so that the degradation of the anthocyanin color pigment which functions as an antioxidant can be broken down.Anthocyanins are antioxidant compounds that can be maintained in quantity by adding ascorbic acid to bind to the anthocyanins of the material so that they are not easily degraded.[18].

The panelists' preference on yogurt with banana slices topping soaked in ascorbic acid
The hedonic test was conducted to determine the level of panelists' preference for stirred yogurt topped with banana slices which was soaked in ascorbic acid.The results showed that the preference level for the taste of stirred yogurt topped with banana slices ranged from 2.65 to 2.98 (average) with an average of 3 (average).The results of ANOVA showed that the ascorbic acid concentration and soaking time and the interaction between the two had no effect (P>0.05).Also, the results of the hedonic test of aroma ranged from 3.16 to 3.44 (average) with an average of 3.28 (average) showed that both treatments and the interactions had no effect (P>0.05) on the level of preference.This is due to the ascorbic acid is a type of acid that dissolves in water and does not have a flavor, so it does not affect the taste of the final product.
Furthermore, the hedonic test on the color showed that the concentration of ascorbic acid had an effect on the panelists' preference.Panelists' preference for the color of stirred yogurt topped with bananas ranged from 3.15 to 3.46 with an average of 3.30 (neutral).The results of ANOVA showed that the ascorbic acid concentration had a significant effect on the color hedonic test (P≤0.05).From Figure 2, panelist preferred stirred yogurt topped with bananas which were soaked in ascorbic acid up to 2% even the value is slightly different with the 3% treatment.A similar result was also shown by previous research on the addition of Ambon banana (Musa paradisiaca) extract in the yogurt production [19].This suggests that the browning reaction still occurs during banana processing, where the browning enzymes can still interact with the substrate in the form of amino acids tyrosine and phenolic components so that they can be oxidized and cause an increasingly concentrated banana color change [20].Further research on the preferred organoleptic characteristics of yogurt with sliced bananas topping needs to be conducted.

Descriptive analysis of selected yogurt with banana slices topping soaked in ascorbic acid
The descriptive test was examined from the ranking test of the hedonic results.From Table 2, the most preferred samples chosen by the panelists were C2T1 treatment (2% ascorbic acid with 4 minutes soaking) and C2T3 treatment (2% ascorbic acid with 6 minutes).Therefore, the selection was continued based on the shortest soaking time which is C2T1.From Figure 3, it can be seen that panelists describe that stirred yogurt topped with banana slices which were soaked in 2% of ascorbic acid for 4 mins had a normal yogurt aroma, a normal banana yogurt taste, and a weak yellow color.From Table 1 and Figure 4, this result had a brightness level (L*) of 98.1, a redness level (a*) of -13.9 and a yellowness level (b*) of +47.3.Compared to other studies, yogurt with the addition of 15% skim milk and 12 hours fermentation has a sour taste, slightly thick texture, typical of yogurt aroma, and slightly yellowish color [21].

Conclusion
Based on color analysis, the control banana slices have an L* value of 97.3, a* value of -10.03, b* value of +37.93.The expected of redness level (a*) is found in the 3% of ascorbic acid with 5 mins soaking (C3T2) treatment with a value of -15.63 indicating that the color of the banana slices is green and is not turned to red.Also, the expected of yellowness level (b*) is found in the C3T2 treatment with a value of +56.53 indicating that the banana slices have yellow color.Based on the preference level of stirred yogurt topped with banana slices, the most preferred sample and selected for descriptive analysis was obtained from C2T1 treatment.It had a strong sour taste, yogurt aroma, and brownish yellow color.

Figure 2 .
Figure 2. The effect of ascorbic acid concentration on the level of color preference in the DMRT 0.05 follow-up test (values followed by the same letter show no significant difference; coefficient of variation = 4.02%).Hedonic scale of color; 1: totally dislike, 2: dislike, 3: neutral, 4: like, and 5: really like.

Figure 4 .
Figure 4. Color analysis of stirred yogurt with banana slices topping soaked in 2% of ascorbic acid for 4 mins using color analysis application version 7.0.0(Lab Tools, Brazil).

Table 1 .
Color value of banana slices at various concentrations and soaking times in ascorbic acid

Table 2 .
Ranking test of hedonic characteristics of stirred yogurt with banana slices topping 6