Bilayer goat ’ s milk yogurt with tamarind ( Tamarindus indica L . ) and wild passion fruit ( Passiflora cincinnata Mast ) jam : Characterization and acceptability

The aim of this study was to develop a goat's milk-based yogurt with a layer of tamarind and passion fruit jelly on the bottom of the package (bilayer yogurt) as well as to carry out the physical-chemical, microbiological and sensory characterization of product. For comparison purposes, goat's milk products were compared with the same cow's milk product. The Research, Society and Development, v. 9, n. 9, e46996139, 2020 (CC BY 4.0) | ISSN 2525-3409 | DOI: http://dx.doi.org/10.33448/rsd-v9i9.6139 3 physicochemical analyzes showed that the samples are within the standards of the legislation, both for yogurts and jams. Regarding microbiological analyzes, there was no microbial growth in any of the samples evaluated. Sensory tests were carried out with 60 tasters that were aged between 14 and 32 years. Sensory attributes related to “appearance”, “color”, “aroma”, “consistency” and “flavor” were evaluated, among them only consistency showed a significant difference due to the chemical characteristics of goat's milk, however, in percentage values goat's milk yogurt was rated with the highest grades. In the global impression and purchase intention, the analysis of the data obtained showed that the values attributed by the tasters are located in the highest scores of the hedonic scale. Thus, for bilayer goat's milk yogurts with tamarind or wild passion fruit jams, the results are favorable and highly acceptable. These results denote the possibility of insertion of these new products in the regional market in view of the acceptance of the product by the tasters as well as the intention to purchase, in addition to the appreciation of the regional fruits present in the jams elaborated.

According to Mayer & Fiechter (2012), goat's dairy products (yogurt and different varieties of cheese) can provide a profitable alternative to cow's milk products, due to their specific flavor and the natural and healthy image to consumers. Thus, goat's milk is an excellent matrix for the development of a wide variety of innovative products and functional foods (Silanikove et al., 2010;Silveira et al., 2015), such as that added with endemic fruits from Brazilian regions.
Due to the territorial extension, geographical position, soil and climatic conditions Brazil stand out as one of the largest fruit producers on the world (Pereira et al., 2012;Verruck et al., 2020). The unique properties of tropical fruits, mainly its sensorial characteristics, has shown great consumer interest in these fruits (Duarte et al., 2010). Thus, several fruit species not widely studied have been evaluated more recently, as an alternative to traditional species (Pereira et al., 2012;Verruck et al., 2020). The addition of pulp of citrus fruits endemic in the Brazilian semiarid region, such as tamarind (Tamarindus indica L.) and wild passion fruit (Passiflora cincinnata Mast), in food products being studied with a view to the insertion of new products and the valorization of native fruits (Silva et al., 2020). In addition, consumers and their acceptance are the most important agents in this perspective. Thus, to assess the acceptance of a food, sensory analysis with untrained tasters who habitually consume the product in question is an alternative.
Sensory tests are included as a guarantee of quality as they are an integrated multidimensional measure, in which the consumer will determine the parameters of interest related to the sensory quality of the food (Minim, 2018). Therefore, the objective of this study was to develop a goat's milk-based yogurt with a layer of tamarind and passion fruit jelly on the bottom of the package (bilayer yogurt) as well as to carry out the physical-chemical, microbiological and sensory characterization of product. For comparison purposes, goat's milk products were compared with the same cow's milk product.

Jams manufacture
Extra jams (50% fruit: 50% sugar) were made in the following flavors: passion fruit (Passiflora cincinnata Mast) and tamarind (Tamarindus indica L.). For processing, 300g of frozen pulp (Salifrutas, Brazil) were previously thawed in a domestic refrigerator (≈4 ° C) and mixed with purified water to a total volume of 1 liter. Then, the pH was corrected to around 3.30 with sodium bicarbonate (NaHCO3), with the objective of reaching the ideal pH for gelation. Development, v. 9, n. 9, e46996139, 2020 (CC BY 4.0) | ISSN 2525-3409 | DOI: http://dx.doi.org/10.33448/rsd-v9i9.6139 6 The pulps diluted in water were subjected to heating (± 100 ° C), then they were added with the sugar and pectin mixture and homogenized until complete dilution. Sugar was quantified based on the total weight of the diluted pulp and the pectin was measured based on the amount of sugar in the proportion of 1.5g of pectin for each 100g of sugar.
According to the specific legislation, the final soluble solids content of the jams must be at least 63 ºBrix. The ideal point for the produced jelly was determined using the refractive index at 68 ºBrix and this was verified with the use of a digital refractometer (Reichert, AR200, Buffalo, USA). After the passion fruit and tamarind jams were ready, they were cooled to ± 40 °C. Thus, 10 grams of each jam were added in polypropylene packaging, with a capacity of 30 grams with a lid.

Yogurt manufacture
Two formulations of yogurt were produced. One was produced from goat's milk and another with cow's milk to be used as control in the study. The first yogurt was prepared with 1 liter of goat's milk treated by Low Temperature Long Time (LTLT) pasteurization (65 ºC for 30 minutes), 8% sucrose, 4% powdered milk and lactic culture composed of Lactobacillus delbrueckii subsp.bulgaricus and Streptococcus thermophilus (Yoflex®, Chr.Hansen, Hønsholm, Denmark), according to manufacturer's instructions. This mixture was homogenized and 20g were placed in the packages containing the tamarind or passion fruit jam at the bottom. The mixture was incubated at 44 ± 1 °C in Biochemical Oxygen Demand oven -DBO (EL101/4, Eletrolab, Brazil), until reaching a pH of 4.6, followed by cooling and storage at 4 ± 1 °C for 24 h. The control sample with cow's milk was prepared following the same instructions, however, it was used 1 liter of UHT cow's milk and full-fat cow's milk powder (Nestlé ® , Rio de Janeiro, Brazil) for this purpose. Therefore, it was obtained four yogurts samples: goat's yogurt with tamarind jam; goat's yogurt with passion fruit jam; cow's yogurt with tamarind jam; and cow's yogurt with passion fruit jam.

Physicochemical analysis
The pH was analyzed using the potentiometric method using a pH meter (mPA, Tecnopon, Piracicaba, Brazil) (Brasil, 2005). The total soluble solids content of the jams were determined by direct reading on a refractometer (AR200, Reichert, Buffalo, USA), with a scale in Brix degrees (ºBrix), according to the methodology of the Adolfo Lutz Institute Research, Society and Development, v. 9, n. 9, e46996139, 2020 (CC BY 4.0) | ISSN 2525-3409 | DOI: http://dx.doi.org/10.33448/rsd-v9i9.6139 (Brasil, 2005). The determination of total titratable acidity of the samples was performed using the acidimetric method in which the samples were titrated with 0.1M NaOH solution and 0.1% phenophthalein solution as indicators and the results were expressed in % of lactic acid for yogurts, according to the methodology described by Normative Instruction No. 68 of MAPA (Brasil, 2006).

Microbiological analysis
Microbiological analyzes were performed according to the methodology described by APHA (2015), and the total count of coliforms at 30 °C and 45 °C, and molds and yeasts was determined as required by RDC 12/2001, which establishes microbiological standards for food (Brasil, 2015). The results were expressed in Colony Forming Unit per gram (CFU/g) for mold and yeast product and Most Probable Number (MPN) per mL of product for coliforms.

Sensory analysis
The sensory analysis was approved by the Ethics Committee with the number 51211015.0000.5588. Hedonic tests were carried out to evaluate the acceptance of bilayer goat's or cow's milk yogurt samples flavored with regional fruits of tamarind and passion fruit according to Dutcosky (2013). For the test, the samples were coded with random numbers of three digits, using the experimental model of complete randomized blocks. The tests were applied in individual booths, using white light and the samples served monadically in disposable 30 mL pots with a lid, at a temperature of 15 ± 1 ° C during approximately 15 minutes for each person. Samples of yogurt based on each type of milk (goat and cow) in the two types of flavors (tamarind and passion fruit) were served separately in two blocks. The consumers were not informed about samples composition, i.e. samples made with goat's or cow's milk yogurt. Tasters familiar with the testing procedures and consumers of yogurt were used.
Sixty judges participated in the test and the data analysis followed the standards required by ABNT NBR ISO 11136 (2016), for sensory evaluation of food and beverages using a hedonic scale. To assess acceptability, cards with a hedonic scale of nine points were used, ranging from "I disliked extremely" (score 1) to "I liked it extremely" (score 9), for the tasters to express the acceptance of the samples in relation to the color, aroma, flavor, global impression attributes and buying attitude (Minim, 2018). Research, Society and Development, v. 9, n. 9, e46996139, 2020 (CC BY 4.0) | ISSN 2525-3409 | DOI: http://dx.doi.org/10.33448/rsd-v9i9.6139 8

Statistical analysis
The results were evaluated by analysis of variance (ANOVA) and the means compared by the Tukey test at p ≤ 0.05 using the Excel software version 2010.

Results and Discussion
To obtain a jam with an optimum point for gelation, pH values and total soluble solids content present in the product are decisive. These physical-chemical parameters of the maracujá-do-mato and tamarind jams were evaluated and are listed in Table 1.  Research, Society and Development, v. 9, n. 9, e46996139, 2020 (CC BY 4.0) | ISSN 2525-3409 | DOI: http://dx.doi.org/10.33448/rsd-v9i9.6139 9 Brazilian legislation does not establish specific parameters for yogurt made with goat's milk, therefore, the standards established by Normative Instruction No. 46 of October 23, 2007 of MAPA dealing with cow's milk were considered for comparison purposes (Brasil, 2007). The results of the physicochemical analyzes of pH and titratable acidity of goat's milk and cow's milk yoghurts were obtained from the average values of three repetitions and are shown in Table 2.   (2013), that working with goat's milk yogurt and semi-arid fruits, found values from 2.93 to 3.20 for the same product, results that are inferior to those presented in the present work For the titratable acidity parameter, also observed in Table 2 Possibly, these results differed from the present study due to the fact that most authors incorporate the fruit pulp to the yogurt (stirred yogurt), unlike the bilayer yogurt elaborated in this work (separate layers), in which the fruit jam, responsible for the flavor, was added to the bottom of the container in which the sample was served and analyzed separately.
The microbiological results of bilayer goat's or cow's milk yogurts with tamarind or wild passion fruit jams, for analysis of coliforms at 30 °C and 45 °C, did not show turbidity or Research, Society and Development, v. 9, n. 9, e46996139, 2020 (CC BY 4.0) | ISSN 2525-3409 | DOI: http://dx.doi.org/10.33448/rsd-v9i9.6139 gas formation in any of the evaluated samples (<3 MPN/mL), which indicates the absence of these microorganisms. Colony growth was also not observed for the analysis of molds and yeasts (<10 CFU/g). Regarding coliforms at 30 °C and 45 °C, their presence is indicative of unsatisfactory sanitary practices in the production process (APHA, 2015). Likewise, the determination of molds and yeasts is related to the shelf life of the product, and a high count of them affects the quality of the product, considering that yogurt with sugar or added fruits are especially susceptible to the growth of fungi, as Moreira et al., (1999) (Brasil, 2007), which regulates the Fermented Milk Identity and Quality standards, the product evaluated is in accordance with the current parameters, showing that the production process was carried out responsibly in accordance with Good Manufacturing Practices -GMP.
The judges who participated in the sensory analysis showed the following profile: 67% male and 33% female, 14 to 32 years old that consume yogurt frequently. The sensory attributes "appearance", "color", "aroma", "consistency" and "flavor" of the bilayer goat's or cow's milk yogurts with tamarind or wild passion fruit jams samples were evaluated and the results are shown in Table 3 and Figure 1. In none of the samples of bilayer goat's and cow's milk yogurts with tamarind or wild passion fruit jams there was observed a significant difference for the evaluated attributes, except for consistency. In addition, the average values of the scores assigned to the attributes were situated from "I liked it slightly" and "I liked it regularly". Regarding the characteristic of flavor and aroma, no difference was observed between goat's and cow's milk yogurt in the present study. However, Silva (2013) when evaluating goat's milk yogurt with umbu cajá pulp, reported that the tasters identified the very strong aroma and flavor of goat's milk, as well as Galdino et al., (2010) also observed rejection of the goat's milk in yogurt samples with forage palm pulp, which was not observed in the present study. This result is favorable in relation to the product developed in our study because it states that, unlike other studies, bilayer yogurt made with goat's milk did not show any perceptive difference in flavor and aroma when compared to that developed with cow's milk. This behavior could be explained by Vedran et al. (2010) that reported that during fermentation of goat's milk its characteristic 'goaty' taste becomes less noticeable.   Paccard, Guillet, & Chilliard, 2008). The casein micelles in goat's milk are also smaller when compared to cow's milk and consequently more friable (Miocinovic et al., 2016;Clark & García, 2017). Therefore, the proportion of small-sized casein micelles is higher in goat's milk than that of cow's milk, which could be related to the lower consistency index of goat's milk and its dairy products (Verruck et al., 2019). However, despite this already known characteristic, researchers are continually seeking to further improve texture and viscosity parameters of goat's milk products, such as added heat-denatured whey protein to the milk, Development, v. 9, n. 9, e46996139, 2020 (CC BY 4.0) | ISSN 2525-3409 | DOI: http://dx.doi.org/10.33448/rsd-v9i9.6139 13 which aggregates to caseins through S-S bridges causing greater water holding capacity in the product and consequently greater consistency/viscosity (Verruck et al., 2019).
As mentioned by Bezerra (2010), this difference in consistency can be predicted since this product has low viscosity and a fragile structural network, the formation of fragile clots, characteristic of goat's milk products, constitutes barriers to the production of this type of derivative. For this author, the nature of the milk used becomes a decisive factor for flavor and aroma attributes, among others, and can be valued with the addition of elements that favor sensory characteristics, such as fruits, special preparations, dairy solids and not dairy solids.
For global impression test, the data obtained showed that the values attributed by the tasters are situated on the hedonic scale between "I liked it regularly" and "I liked it very much". For goat milk bilayer yogurt the averages were 6.77 for tamarind and 6.97 for wild passion fruit and for yogurt made with cow's milk 6.65 for tamarind and 6.90 for wild passion fruit. These values did not indicate a significant difference at p ≤ 0.05 by the Tukey test.  As a percentage of the grades related to the global impression of tamarind flavored yogurt, both for goat's and cow's yogurt, 68.3% of the tasters chose goat's milk yogurt and 65% for cow's milk yogurt. In addition, 28.3% of the tasters attributed the maximum value of the scale for yogurt with goat's milk against 18% for yogurt with cow's milk, which shows that the goat's milk yogurt flavored with tamarind presented the highest scores of the tasters and their consequent acceptance. This corroborates with the study of Queiroga et al. (2011) that in research involving the production of natural yogurt and tropical fruits from goat's milk, concluded that this product represents a viable alternative for the increase of the goat dairy sector, being able to contribute to the strengthening of this segment in the dairy industry. In view of the acceptability of goat's bilayer yogurt with regional fruit jam, there is another option for goat's milk derivatives to add value to this raw material yet, which already has proven market growth. An example in addition to milk production are goat's milk cheeses, which already have high added value (Bomfim et al., 2013).
The evaluation of the overall impression of goat's and cow's milk bilayer yogurts flavored with wild passion fruit jam is shown in Figure 3. It can be seen that goat's and cow's milk bilayer yogurts with wild passion fruit jam were accepted with values assigned between "I liked it regularly" and "I liked it a lot", i.e.
75% for goat's milk yogurt and 65% for cow's milk yogurt. Also, it was observed that of this total, 30% rated goat's milk yogurt as "I liked it a lot", against 23.3% for cow's milk yogurt.