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Introduction
The production of dairy beverages obtained through the fermentation of whey or lacto-serum has grown significantly worldwide due to the simplicity of its process and, above all, to its excellent consumer acceptance (Boynton & Novakovic, 2014; Janiaski et al., 2016). Whey is a by-product generally obtained in artisanal cheese industries considered a low-value raw material, frequently discarded in water sources or sewers, causing serious pollution problems. Despite possessing lactose in significant quantities as structural carbohydrates that allow the growth and multiplication of lactic acid bacteria, it is mostly used for animal feed (Arce-Méndez et al., 2016; Miranda et al., 2014). Producer ignorance about the nutritional properties of whey and the lack of resources to access adequate technologies for its management and processing leads to the loss of this by-product (Mazorra-Manzano et al., 2019; Poveda, 2013).
In the food industry, Aloe vera L. (Asphodelaceae) and its derivatives (e.i., gel), have several applications due to its wide variety of nutritional properties. Therefore, it has been used as a food supplement in juices, drinks, capsules, and gels, and it is consumed fresh or as an ingredient in culinary preparations (salads and pastry products) due to its content of vitamins and minerals. Thus, it is considered a raw material or main ingredient in the preparation of functional foods (Acevedo et al., 2017; Bonilla & Jiménez, 2016; Sánchez & Caballero, 2020). The by-products of this plant are usually extracted through heating, dehydration, or grinding processes, which can irreversibly affect the bioactive components, including polysaccharides and antioxidant compounds, producing changes in the biochemical properties of the product (Serván, 2018; Villa-Uvidia et al., 2020).
The Passiflora L. genus that belongs to the family Passifloraceae has different species with industrial interest. Granadilla (Passiflora ligularis Juss.), after yellow passion fruit (P. edulis f. flavicarpa Degener), occupies the second place in economic importance due to its participation in national and international markets. It is a fruit that contains multiple seeds surrounded by a sweet aril with great organoleptic attributes that is mostly consumed as fresh fruit (Arias et al., 2016; Gaona-Gonzaga et al., 2020). It is produced mainly in Colombia with a national production in 2018 of 47,458.04 tons, being Huila the main producer department with 23,674.55 tons, followed by Nariño, Cundinamarca and Antioquia, according to the statistics reported by Agronet (2020).
In general, the information obtained allowed establishing a study in which lactose, being of great importance for the industrial sector, could be used as it allows the utilization of this by-product that is typically discarded. This generates, in turn, significant damage to the environment. However, whey can be used together with A. vera crystals, implementing techniques that utilize nutrients from this plant, and those provided by granadilla. This allows obtaining a yogurt-type fermented milk drink with adequate physicochemical, microbiological, bromatological, and sensory parameters for this type of product. For this reason, the aim of this work was to make industrial use of whey in the elaboration of a yogurt-type fermented milk drink with A. vera crystals and P. ligularis pulp.
Materials and methods
Raw material and extraction of Aloe vera crystals and granadilla pulp
Sweet whey was used to make the yogurt-type fermented milk drink obtained from a local cheese company, while the rest of the material was obtained from the local market in the city of Cartagena de Indias (Colombia).
Aloe vera leaves (from 2 or 3-year-old plants) were immersed in a sodium hypochlorite solution and left for 3-5 min to remove any remaining dirt. Then, the aloin content was removed, leaving the leaves in water for 24 h. After this time, the epidermis was removed, and the pulp was cut into cubes of 1.5 ×1.5 × 1.5 cm obtaining what is known in the region as “Aloe vera crystals”.
The granadilla fruits in maturity states 7 and 8, and similar sizes, were washed in the same way as the A. vera leaves. Then, these were scalded in water at 100 °C for 5 min. Subsequently, they were taken to a pulping machine (CI TALSA D1000) to extract the pulp that was not pasteurized.
Formulation and production of a yogurt-type fermented milk drink
The drink formulations assessed can be seen in table 1. The percentages were based on % w/v in relation to sweet whey.
Table 1. Yogurt-type fermented milk drink formulations (F) assessed
Source: Elaborated by the authors
Sweet whey was pasteurized at a temperature of 62 ± 0.5 °C for 30 min. Subsequently, sugar and semi- skimmed milk powder were added until a homogeneous solution was obtained. To the resulting product, the lactic culture (Lactobacillus bulgaricus and Streptococcus thermophilus) attained from a mother culture, was added. The fermentation process took place for 210 min (3.5 h) at 44.5 ± 1.0 °C. The percentages of A. vera crystals and granadilla pulp according to the formulations established (table 1) were added once this process was finished.
Physicochemical and bromatological evaluations
The analyses were made according to the Association of Official Agricultural Chemists (AOAC,1990) as follows: pH (943.02), percentage of titratable acidity (942.15), protein (979.09), moisture (927.05), ash (923.03), fat (920.39), carbohydrates (by difference), Na (985.35), Mg (985.35), K (985.35), Fe (944.02), Ca (944.03), and vitamin C (2,6-dichloroindophenol titrimetric method). Further, 2,2- diphenyl-1-picrylhydrazyl (DPPH) was established according to Repo and Encina (2008).
Microbiological analysis
The microbiological analyses performed on the finished product according to the Colombian Technical Standard 805 (Instituto Colombiano de Normas Técnicas y Certificación [Icontec], 2005) were the following: Total coliforms (Icontec, 2007), and molds and yeasts (Icontec, 1997).
Sensory analysis
A 5-point hedonic test was chosen to determine the sensory acceptability of the four samples or formulations, ranging from "I really dislike it" with a score of 1, to "I really like it" with a score of 5. Fifty persons of both genders between 20 and 30 years of age were chosen to perform this test. The parameters to be evaluated were color, smell, viscosity, acidity, and general acceptability.
Storage behavior
The methodology proposed by Parra (2013) was used for this test with some modifications. Once the sample with the best consumer acceptance was chosen, pH (943.02) and titratable acidity (942.15) tests were performed using the AOAC (1990) methods for 21 days at 4 °C. Measurements were made every seven days in triplicate. In this way, the useful life of the yogurt that obtained the best consumer preference was established.
Statistical analysis
The obtained data were analyzed using standard analysis of variance (ANOVA), and its statistical significance was established utilizing Tukey's test with a confidence level of 95 %, employing the statistics Statgraphic Centurion XVI.I. program. All tests were performed in triplicate.
Results and discussion
Physicochemical properties
The pH behavior during the fermentation process of the yogurt-type fermented milk drink can be seen in figure 1, showing a linear decrease over 210 min. The milk drink recorded a pH value of 7.26 in its initial stage, decreasing its pH slowly during the fermentation process at a temperature of 44.5 ± 1 °C until reaching a pH value of 5.47 at the end of the fermentation period. In this process, the pH did not change abruptly, since the temperature was maintained between the optimal range indicated for this product in other studies for an adequate microorganism development (Adamberg et al., 2003; Hoyos et al., 2010). The pH-decrease phenomenon is due to the lactose fermentation action of lactic acid bacteria (LAB) found in yogurt (L. bulgaricus and S. thermophilus). These act on existing carbohydrates and the production of lactic acid activity that was generated in the fermentation process, whose bacteria can produce acids that eventually increase the H+ concentration in the culture (Østlie et al., 2003; Vahedi et al., 2008; Widyastuti & Febrisiantosa, 2014; Zapata et al., 2015).
Source: Elaborated by the authors
Figure 1. Variation in pH and percentage of titratable acidity during the fermentation process
The increase in the percentage of titratable acidity expressed as the percentage of lactic acid during the fermentation process can be seen in figure 1. The percentage of acidity observed at the end of the fermentation was 0.765, indicating that the lactic acid levels are within the ranges established by the Colombian Technical Standard 805, which stipulates that the minimum percentage of acidity must be 0.60 for dairy products. The results obtained showed the growth of the acidity percentage from 0.45 % at the beginning of fermentation, to 0.765 % at 210 min, finishing at this point, the bacterial incubation phase. This last value is higher than the result obtained by Miranda et al. (2014); these authors elaborated a fermented drink from whey incorporating L. acidophilus and S. thermophilus with a titratable acidity of 0.63 %, and establishing that the content of nutrients and proteins in whey can generate the good behavior of lactic bacteria.
Bromatological properties
The bromatological properties of the four formulations of the yogurt-type fermented milk drink assessed are shown in table 2. Aloe vera and granadilla influenced the parameters evaluated due to the statistical differences (p < 0.05) found between the samples.
Table 2. Bromatological properties of the four formulations (F) of the yogurt-type fermented milk drinkDPPH: 2,2-diphenyl-1-picrylhydrazyl.
Note.Similar letters in the same row indicate a statistically significant difference, according to Tukey's test (p < 0.05); n = 3; average ± standard deviation
Source: Elaborated by the authors
The F2 sample obtained statistically significant differences (p < 0.05) and higher protein percentage, contents of vitamin C, Ca, Fe, and antioxidant capacity (DPPH) compared to the other samples. This is because F2 had the highest percentage of granadilla (12.5 %), and this fruit is rich in macro and micronutrients; moreover, A. vera crystals also possess vitamin C and antioxidants (Cabrera et al., 2014; Carvajal et al., 2014; López et al., 2006; Vega-Gálvez et al., 2011). Sample F4 showed the statistically highest values (p < 0.05) for K, Mg, and Na with respect to the other treatments or formulations. These high percentages are because this sample had the highest percentage of A. vera crystals (12.5 %), providing these minerals to the product (Miranda et al., 2009; Vega et al., 2005; Zhang et al., 2018).
Concerning the moisture content, F1 showed the highest value. Meanwhile, regarding ash content, samples F2, F3, and F4 showed a statistically significant difference (p < 0.05) compared to F1, due to the percentages of ash that granadilla and A. vera have (Carvajal et al., 2014; Miranda et al., 2009). In relation to the percentages of carbohydrates and fat, no statistical differences were found (p > 0.05); these results are, however, similar to those reported by other authors (Miranda et al., 2014; Tirado et al., 2015).
Microbiological properties
The results of the microbiological evaluation carried out are shown in figure 2. The elaborated fermented milk drink complied with the microbiological requirements established in the Colombian Technical Standard 805, since according to the mold and yeast tests (limit of 500 CFU/mL), the samples showed values below the allowed limit. Likewise, for the total coliform tests (limit of 100 CFU/mL), these were within the allowed limit. The samples with higher A. vera content (F2, F3, and F4) had less contamination than the control sample (figure 2); according to Shaaban et al. (2010), this may be due to the antimicrobial properties of A. vera.
Source: Elaborated by the authors
Figure 2. Microbiological properties of the four formulations of the yogurt-type fermented milk drink
The yogurt-type fermented milk drink showed a low quantity of total coliforms, indicating the adequate hygienic quality with which they were elaborated, similar to the results in the coliforms count reported by Mukhekar et al. (2018) in the elaboration of a yogurt product enriched with A. vera.
Sensory properties
The results of the sensory analysis are shown in table 3. F4 obtained the best score in all parameters because it only had statistically significant differences (p < 0.05) over the other samples in smell, acidity, and general acceptability. Concerning color, there were statistically significant differences (p < 0.05) between the white sample (F1) and the rest. Furthermore, no statistically significant differences (p > 0.05) were found in viscosity.
Table 3 Sensory properties of the samples of the four formulations (F) of the yogurt-type fermented milk drink
Nota.Similar letters in the same column symbolize a statistically significant difference, according to Tukey's test (p < 0.05); n = 50; average ± standard deviation.
Source: Elaborated by the authors
When there is a higher A. vera content, the assessment of the panelists was also higher. This coincides with Parra (2014), who indicated that A. vera provides sensory features that yogurt does not possess.
Behavior during storage
The behavior of pH and titratable acidity during storage is shown in figure 3. There was a slow linear decrease in pH, starting from 5.47 and 5.36, and ending with 5.17 and 5.12 during storage for the F1 and F4 formulations, respectively. These results were superior to those reported by Marulanda et al. (2016) and Ruiz and Ramírez (2009). Several authors consider that the acidification during storage may be due to the residual enzymes produced by the initiators during fermentation, remaining active at temperatures between 0-5 °C (Kailasapathy, 2006; Vahedi et al., 2008).
Source: Elaborated by the authors
Figure 3. Variation in pH and percentage of acidity during the storage of the four formulations of the yogurt-type fermented milk drink.
On the contrary, the percentage of acidity showed a linear increase, presenting an initial percentage of lactic acid of 0.765 to 0.864 for F1, and 0.777 to 0.881 for F4, values similar to those found by Londoño et al. (2008) and Londoño et al. (2017), who produced drinks fermented from whey with probiotics, obtaining a percentage of acidity of 0.90 at day 21. The A. vera crystals influenced pH and acidity, since the polysaccharides present in this species had a stimulant effect on the metabolic activity of the microorganisms (Wijesundara & Adikari, 2017; Yadav et al., 2007).
The acidity did not exceed the maximum stipulated in Colombia by Resolution 2310 (1986), which indicates that the maximum percentage of acidity that a fermented milk drink must have is 1.50. At the same time, for pH, there are no regulations in force in Colombia that stipulate a maximum value for this parameter. Therefore, the yogurt-type fermented milk drink had a useful life of more than 21 days at 4 °C.
Conclusions
According to the results obtained, the use of sweet whey, Aloe vera, and granadilla (Passiflora ligularis) as main ingredients in different elaborated products, can be of great industrial value due to the favorability imparted by the different properties that were evaluated in the yogurt-type fermented milk drink elaborated. Regarding the bromatological properties, the F2 and F4 samples showed the best values. The F4 sample obtained the best results in terms of microbiological and sensory properties, also exhibiting good behavior under storage. As shown in all parameters evaluated, F4 (12.5 % of A. vera crystals and 5.5 % of granadilla pulp) was considered the best sample among the ones assessed.
