Influence of the addition of acerola residue on the physical characteristics of yougurt

Acerola has acquired great importance due to its high vitamin C content and its potential for industrialization. However, during its processing, a quantity of waste (seed and bagasse) is generated, mainly from pulp processing. These residues can be used as new sources of food with high added value and contribute positively to the reduction of environmental impacts. Therefore, this research aimed to add value to the acerola by-product through the development of a functional yogurt. To develop this research, a complete 2² Factorial Planning and Response Surface Methodology were used. The planning included five different levels, with three central points totaling seven tests. The independent variables were: concentration of acerola by-product (%) and brown sugar (%). The responses analyzed were: water content (g/100g), acidity (g/100g), pH, ascorbic acid (mg/100g), reducing sugars (g/100g), and ash (g/100g). The Statística 7.0 software was used to analyze the results of the adopted planning. It was observed that the acerola by-product concentration factor had the greatest influence on the vast majority of responses studied.


Introduction
The fruit growing sector in Brazil is expanding, where it is estimated that around 53% of production is sold fresh and 47% is destined for the agro-industrial sector for the production of juices, teas, frozen pulps, jellies, and others (Oliveira, 2018).Brazil produces around 45 million tons of fruit annually, making it the third-largest producer in the world.In this production, tropical fruits stand out due to their good adaptation to the Brazilian climate (Embrapa, 2020;Ramadan et al., 2019).
Realizing the potential of acerola, Brazil began to exploit it commercially and established a well-structured production chain, becoming one of the largest producers in the world and exporting large volumes of processed fruits, serving a global market that can reach US$17.5 billion by 2026 (Belwal et al., 2018).In this context, around 40% of the processed volume becomes waste, with 30% being made up of peels and seeds, while 10% is obtained with the clarification of the juice being formed from pulp remains (Poletto et al., 2021).This waste generated is discarded, which represents a waste of raw materials that could be used to obtain energy or other products with greater added value.According to Rezende et al. (2018), there was a growing interest in technologies that generate low environmental impact and promote sustainability, so there is a search for the use of waste from fruit processing industries.
The composition of the residue obtained from acerola bagasse and peels also has a rich phytochemical profile, mainly in total anthocyanins, carotenoids, ascorbic acid, phenolic compounds, and total flavonoids, with a higher proportion when compared to its pulp, showing the importance of its use (Rezende et al., 2018).This byproduct may be interesting as a source of nutrients and other bioactive molecules.The dietary fibers present in by-products can be added to foods with the function of prebiotics and thus guarantee the reprocessing of waste (Albuquerque et al., 2019).Furthermore, they can be added to a functional diet, with the potential for transformation to be added to various foods (Nascimento et al., 2022).
Therefore, the inclusion of fruit residues in yogurt appears as a suggestion for the development of products with functional and nutritious properties (Barboza et al., 2021).According to Gouraji et al. (2019) new yogurt varieties with unique flavors and aromas, which simultaneously offer potential healthcare functions, have shown increased sales and greater consumer satisfaction.Furthermore, it is presented as the product that most arouses consumer desire when launched on the market, being considered a symbol of healthy food, and has the potential to grow even further with innovations that incorporate functionalities into products (Brazil Food Trends, 2020).
The use of acerola juice residue in the production of yogurt could serve as a source of nutrients and bioactive compounds that could increase its nutritional potential and act in a protective and preventive way in the human body and reach an even more diverse audience.
The preparation of the yogurt dough was carried out according to the methodology provided by the Brazilian Technical Response Service -SBRT (2008).
The computer program Statística 7.0 was used to analyze the experimental planning.Table 1 shows the levels of the independent variables.The planning included 5 different levels, totaling 7 tests with three central points.
Table 1 -Planning matrix for preparing yogurts added with acerola residue and brown sugar, with their respective independent variables and their real and coded levels.

Results and Discussion
In Table 2, it is possible to find the characterization data of the pomace from acerola juice.In Table 3, it is observed that the water content value found for the acerola by-product was equal to 89.352 (g/100g), which is close to the value found in the literature by Alves (2019), Nascimento (2018) and Braga et al., (2011) in which they found values equal to 89.65, 93.61 and 89.9 (g/100g), respectively, for acerola residue.
When evaluating the titratable acidity, it is clear that the value obtained in this work is close to the values reported in the literature by Caldas et al., (2010), who found a value equal to 1.39 (g/100g).In work carried out by Sancho et al., (2015) they found a value equal to 3.60, which is above the value reported in the present work.Acidity is a relevant parameter in evaluating the conservation status of a food product (Castro et al., 2015).With the fruit maturation process, acidity is generally reduced, influencing the odor, flavor, color, maintenance of quality, and stability (Pereira et al., 2006).
The average pH value of the fresh acerola by-product found in the present work is close to the values reported in the literature by Sancho et al., (2015) and Mélo et al., (2014), in which they, respectively, showed values equal to 3.45 and 3.54.
The pH can be variable depending on the species of acerola tree, harvest periods, growing regions, and other factors, which cause changes in the pH of the acerola and consequently in the residue (Ferreira, 2020).
In Table 2, the value found for ascorbic acid for the acerola by-product is equal to 1894.097 mg/100g, which is higher than those found in the literature by Alves (2019) and Nascimento (2018) who found values equal to 1116.67 and 1080.11,respectively.It was observed that the vitamin C content in acerola residues was higher than the amount found in some studies, thus showing the nutritional value of the peels that can be used in the production of vitamin C. Therefore, according to Sancho et al. (2015), acerola residue can also be considered an important source of ascorbic acid and should be used in food supplements.
When evaluating the ash content of the acerola by-product, it was observed that the average value found in the present work is close to the value reported by Alves (2019) who found an average ash value equal to 0.44 (g/100g).The percentage of ash found in the acerola residue in this study was 0.302 (g/100g), a lower value than in other studies carried out by Sancho et al. (2015), Silva et al. (2014) and Mélo et al. (2014) with agro-industrial acerola residues, which found values between 2.07 and 2.36 (g/100g).
It was observed that the average value of reducing sugars is close to those reported by Braga et al., (2011)  According to an observation carried out by Sancho et al. (2015), fruits are normally rich in sugars (glucose and fructose), the determination of which is important to evaluate the potential of these residues as raw material for fermentation.
So, those fruits that have a high concentration of sugars would be suitable for fermentation, on the other hand, acerola would be suitable as a food supplement with a low sugar content.The results of the 2² factorial design of the dependent variables, water content (g/100g), acidity (g/100g), pH, ascorbic acid (mg/100g), reducing sugars (g/100g) and ash (g/100g), in the process of making homemade yogurt using a by-product of the acerola juice agroindustry can be seen in Table 3.According to Table 3, about the composition of the yogurt prepared, it can be observed that the water content of the samples decreases as the concentration of brown sugar in the yogurt production increases.It can be seen that in all tests there were high water contents, which were above the values found by Bessa and Silva (2018), who found a value for the water content of tamarind yogurt equal to 83.72 (g/100g).
About acidity, according to the results expressed, the values follow the requirements of the Brazilian Normative Instruction for the product in question, which must be in a range of 0.6g to 1.5g of lactic acid/100g (Brazil, 2007).It can be generally observed that formulations with a lower concentration of acerola pomace presented a lower acidity value.In the work Analyzing the ascorbic acid content, it is clear that all tests presented high values for this parameter.Tests 2 and 4 with high concentrations of acerola residue were those that presented the highest ascorbic acid values and tests 1 and 3 with the lowest concentrations of pomace presented the lowest values.This fact confirms that the value of vitamin C is directly related to the increase in the concentration of the by-product of acerola juice.Data on ascorbic acid in dairy products is scarce, however, it is possible to verify that all formulations had a vitamin C content above 60 mg/100mL, the daily intake value recommended by ANVISA ( 2005), for healthy adult people.The acerola by-product contains a high amount of ascorbic acid, and when added to yogurt, it provides nutritional properties, obtaining a product with a high content of vitamin C.
Concerning the reducing sugars in the yogurt prepared, it was observed that the values found are lower than those found in the yogurt prepared by Borges et al. (2009).However, these values are similar to those found in the study carried out by Batista et al. (2014) for banana cv.terra yogurt.
Regarding the ash content response, it is clear that tests 2 and 4, with the highest concentration of residues, presented the highest values for the ash parameter.However, in general, the ash values found in this research are lower than those found by Januário et al. (2017) who found an ash content equal to 0.9 g/100 g for yogurts flavored with organic beet juice with carrot, cassava, and sweet potato or corn juice.The aforementioned authors observed that variations in the composition of yogurt are in accordance with the composition of the fruits and vegetables used, a similar behavior to that observed in this research, in which the highest ash values were found in tests with higher concentrations of acerola by-product.
With these results in hand, planning analysis was carried out to verify the effects of the independent variables on the responses studied.In Table 4, the analysis of variance (ANOVA) and the F test are presented with 95% (p<0.05)reliability only for the predictive variables, that is, with coefficients of determination greater than 80% in the processing of yogurts added with acerola juice residue.The relationship between Fcalculated and Ftabulated was analyzed at a confidence level of 95%.According to Table 6, it can be seen that the results obtained concerning the parameters of water content, acidity, pH, reducing sugars, and ash were statistically significant, since they presented a Fcalculated value greater than the Ftabulated one, in addition, it was found that the coefficients of determination (R 2 ) of these parameters were greater than 80%, indicating a good fit to the experimental data.
Regarding the individual effects of the independent variables (acerola by-product and brown sugar) as well as the interaction between them on the response variables, they present a statistically significant model (Fc>Ftab).It can be seen in the Pareto diagrams (Figure 1) the factors that had the greatest influence on the preparation of yogurts.It can be seen in Figure 1 that for acidity, the concentrations of the acerola juice byproduct and the concentration of brown sugar were statistically significant, showing a greater influence of these factors on the responses.Regarding the water content, pH, ash, and reducing sugars, it appears that the concentration of acerola juice by-product was a statistically significant factor with greater relevance to the dependent variable.
After analyzing the effects, regression analysis was carried out to extract possible mathematical models coded for each response under study.It was found that for the conditions studied in this work, for the water content and ascorbic acid responses, the increase in the acerola by-product concentration factor promoted an increase in the water and ascorbic acid content response.
However, when the concentration of brown sugar was increased, there was a reduction in the responses in question.Likewise, for the acidity response, it was found that increasing the by-product concentration factor promoted an increase in the acidity response, on the other hand, the response was reduced when the brown sugar concentration factor was increased.Regarding the pH response, it was observed that by increasing the acerola by-product concentration factor, there was a reduction in the pH value.Regarding the responses to reducing sugars and ash, it was found that increasing the concentration factor of the byproduct of acerola juice led to an increase in responses in the present study.
Figure 2 shows the response surfaces obtained for the physical and chemical analyses (response variables) that presented statistically significant models (Fc>Ftab).

Conclusion
Given the results, it is concluded that: The independent variable concentration of acerola by-product had the greatest influence on the responses acidity, pH, ascorbic acid, reducing sugars, and ash.
The variable concentration of brown sugar had a greater influence on the reduction of water content.
Yogurt made with agro-industrial residue from acerola juice is presented as a product in vitamin C (428.55 mg/100g).
The technological use of by-products from the fruit industry can bring benefits such as: reducing environmental impact and providing the development of a good quality product with beneficial properties for the consumer.
In view of the above, despite ongoing research using fruit residues to prepare products, there is still a shortage in the literature regarding the acerola's residue incorporation in yogurt.Therefore, there is a need for future work with more comprehensive studies, aiming to study the product's characteristics, such as: color, texture and aroma, in addition to sensory analyses and in relation to the microbiological safety of the yogurt produced.

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Santos and Ellena (2021), studying the use of yellow passion fruit albedo flour in the formulation of Greek yogurt, the authors found a value of 0.68 and 0.72 g/100g of acidity, values close to those of the present research.Regarding pH, according to IN nº 46 of October 24, 2007, of the Ministry of Agriculture, Livestock, and Supply(BRASIL, 2007), the ideal pH for the identity and quality of yogurt is between 3.6 and 4.5, framing the product of this study is in the recommended range.Research carried out by Bessa e Silva (2018) characterizing tamarind yogurt, found a pH value equal to 3.85.Similar results were described in the research byGonçalves and Leão (2013), who, when studying the addition of fruit flours such as passion fruit, apple, and grape in the production of yogurt, found average values equal to 4.20, 4.54, and 4.60, respectively.According toMartin (2002), andNeres et al. (2015), typically yogurts with average pH values between 4.0 and 4.5 are more accepted by consumers, as they have a less acidic or less bitter flavor.

Figure 1 -
Figure 1 -Response surfaces for the parameters of a) water content; b) acidity; c) pH; d) ash and e) reducing sugars from yogurts, depending on the percentages of acerola by-product and brown sugar.a) b)

Figure 2 -
Figure 2 -Response surfaces for the parameters of: a) water content; b) acidity; c) pH; d) ash; and e) reducing sugars in yogurts, depending on the percentages of acerola by-product and brown sugar.a) b)

Table 2 -
Characterization of acerola by-product.

Table 3 -
Results of the complete experimental design 2² CSA -Concentration of acerola juice by-product; CAM -Brown sugar concentration.Source: Authors.

Table 4 -
Analysis of variance of the coded model for your responses.

Table 5 -
Mathematical models adjusted to yogurt experimental data.