Preparation of Gluten-free Noodles Incorporated of Jabuticaba Peel Flour

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2.3. Physico-chemical Analysis, Bioactive Compounds and Cooking Tests

The determination of proximate composition (moisture, ash, proteins, lipids and carbohydrates), caloric value, pH, titratable acidity, soluble solids, anthocyanins, phenolic compounds, condensed and hydrolyzed tannins and antioxidant potential were carried out both in JPF and in the noodles. The cooking tests (cooking time, weight gain, volume increase and loss of soluble solids into the cooking water) were applied only on noodles. All analyzes were performed in triplicate.

The proximate composition was determined according to the Association of Official Analytical Chemists ^[11]. The moisture was evaluated by weight difference after sample drying, total nitrogen by micro-Kjeldahl method, total lipids using Soxhlet and ash by incineration in muffle furnace. The carbohydrate content was calculated by difference, subtracting from 100 the values of humidity, ashes, proteins and lipids. The energy value was estimated using the ATWATER factors (kcal carbohydrates = 4.0 kcal g^-1; lipid = 9.0 kcal g^-1; protein = 4.0 kcal g^-1) ^[12].

The determination of pH was performed in digital potentiometer (pH Meter HI-9224), total titratable acidity by titrating the sample with 0.1 N NaOH and the total soluble solids content was determined in digital refractometer (Atago N-1E) by reading the Brix of the sample at 20 °C ^[11].

Phenolic compounds in ethereal, ethanol and aqueous extracts was determined using the Folin-Ciocalteu reagent ^[13]. The condensed tannin content was estimated according to the method of Price et al. ^[14], with adjustments made by Barcia et al. ^[15]. The hydrolyzed tannins were determined by the method of Brune, et al. ^[16], with modifications of Barcia et al. ^[15]. The total anthocyanin content was evaluated according to Lee and Francis ^[17], adjusted by Barcia et al. ^[15]. The antioxidant activity was determined by the DPPH method (2,2-diphenyl-1-picrylhydrazyl), according to Brand-Williams et al. ^[18], with modifications of Borguini and Torres ^[19]. Readings for all the aforementioned analyzes of bioactive compounds were performed in spectrophotometer.

The L*, a* and b* (CIELAB) color parameters were determined by reading with a colorimeter (Hunterlab, ColorQuest II), wherein L* represents the lightness (L* = 0 black and L* = 100 white) and a* and b*, chromatic coordinates (+a* red and -a* green, +b* yellow and -b* blue). All of the pasta were subjected to cooking tests according to the AACC 16-50 ^[20] evaluating the cooking time, weight gain, volume increase and loss of soluble solids into the cooking water.

2.4. Statistical Analysis

The evaluations in the noodles were performed using analysis of variance (and when significant, applied the Tukey test or t test, according to the situation), at 5% significance level.

3. Results and Discussion

3.1. Physico-chemical Analysis and Bioactive Compounds of JPF

The JPF has considerable amounts of proteins, lipids and carbohydrates in its composition. Becker et al. ^[21], when preparing flour form the endocarp of buriti fruit, found higher values of humidity (9.93 g. 100 g^-1) and ash (4.59 g. 100 g^-1). The protein and lipid levels (Table 2), were lower and the carbohydrate content was higher than those found by other authors ^{[22, 23]}, when evaluating fruit-derived flours.

The water activity, pH and titratable acidity found in JPF (Table 2) do not favor the enzymatic activities or chemical reactions, once the flour has low water availability and can be considered an acid product according to the pH and acidity value. Ferreira et al. ^[24] when using of sorghum, rice, corn flours with potato starch for the preparation of gluten-free pasta found higher levels of pH to its different formulations with an average value of 5.5. Regarding the total soluble solids, the flour showed 8.814 ^oBrix, which is lower than that found by Aquino and Leão ^[25] in acerola flour (40 ^oBrix). The color analysis (Table 1) showed that JPF has intermediate color value, with a tendency to red.

The anthocyanin contents of JPF were similar to those found in Niagara grapes by Soares et al. ^[26] (47.65 mg of cyanidin-3-glycoside.100 g^-1) and can be used as an alternative source of natural pigments in pasta, as well as other products. The presence of anthocyanins, in addition to improving color attributes of foods, increases its antioxidant potential. The benefits of anthocyanins to human health are related to its antioxidant effect, preventing chronic diseases and various types of cancer.

The levels of condensed tannins were higher than those of hydrolyzed tannins in JPF, an expected result due to the astringency of jabuticaba peel. When comparing the different extracts used for the analysis of antioxidant activity, it was found that the aqueous extract had a higher percentage of DPPH discoloration and consequently greater antioxidant potential.

Table 2. Physico-chemical composition of jabuticaba peel flour

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3.2. Physico-chemical and Bioactive Evaluation of the Pasta

Analyzing the different prepared pasta, some variations were observed as a result from the addition of JPF (Table 3). Regarding the moisture content, the standard samples and those containing 15% of JPF did not differ by the Tukey test (p>0.05), whereas the sample with 30% of JPF was significantly different (p<0.05), with reduced moisture content due to the greater amount of JPF added in the formation and hence the preparation of the pasta. The values found in the moisture determination of all analyzed samples are within the maximum parameter allowed in fresh pasta, 35%, as predetermined by ANVISA in RDC No. 93 of October 31, 2000, which governs the standards of identity and quality of pasta ^[27].

The addition of JPF significantly increased (p <0.05) the protein content of noodles according to the amount added, whereas the ash and carbohydrate contents were higher in the standard formulation. Ash and lipid content showed no significant difference between them (p> 0.05). From the percentage of proteins, lipids and carbohydrates, it was possible to calculate energy values of 299.799 Kcal.100 g^-1 for the standard sample, 298.064 Kcal.100 g^-1 for the sample with 15%, and 307.329 Kcal.100 g^-1 for the sample with 30% of JPF. Therefore, the energy values of noodles did not vary with the addition of jabuticaba flour, once this ingredient only substitutes certain amount of rice flour used in the preparation of the standard sample.

Table 3. Physico-chemical composition of the standard noodles and incorporated of JPF

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The water activity of the pasta was significantly different (p<0.05) among treatments, however, all samples were within pre-established standards, evidencing the stability of this product from a microbiological point of view, once the samples did not show the growth of yeasts, fungi and thermophilic bacteria. The pH and titratable acidity of the samples allow classify them as a low-acid product, a characteristic of pasta.

The color of the pasta is a factor of fundamental importance for marketing, being directly influenced by the raw materials that constitute the sample. The lightness of the standard sample showed significant differences (p>0.05) in relation to others (Table 4), and this difference was explained by the use only of rice flour and pre-gelatinized rice flour. These values are close to that found by Depieri ^[28], in instant noodles, prepared with wheat flour (61.49). Formulations added of JPF had no significant difference (p>0.05) among them, tending to a darker color because of the natural color of jabuticaba peel. As well as the brightness, the chromaticity parameters a* and b* differed only in the standard sample, and the other formulations were influenced by the addition of jabuticaba flour.

Table 4. Color parameters of the standard noodle and noodles added of JPF

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Considering that the standard sample has no added JPF, the analysis of bioactive compounds were carried out only in samples with addition of 15% and 30% JPF, as shown in Table 5.

Anthocyanins are important alternatives for the gradual substitution of synthetic pigments because they are abundant in nature, have a broad spectrum of colors and also due to the beneficial effects to human health. The major limitation to the use of anthocyanins is the greater instability compared to synthetic dyes. The values found for anthocyanins showed significant differences (p <0.05), because of double the amount of JPF added to the sample of 30%.

Table 5. Levels of bioactive compounds in the formulations of gluten-free noodles with JPF

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In the two analyzed formulations, the content of condensed tannins was superior to that of hydrolyzed tannins, and this difference influences positively in the sensory aspect, once the condensed tannins have a lower complexing capacity with proteins, resulting in low astringency ^[15].

Evaluating the contents of phenolic compounds, it was noted that its yield was higher for the aqueous extract. The difference among the extracts can be justified by the differential solubility of phenolic compounds in a given solvent. However, there is no it is not possible to infer the structure of the phenolic responsible for this characteristic, because it has no studies referring to the unique constituents of JPF.

The bioactive compounds are of great importance for the composition of pasta, because it originates color, astringency, aroma and oxidative stability of the final product, besides bringing several benefits to consumer health such as the antimicrobial, neuroprotective, anticance, anti-inflammatory and antioxidant actions.

For the non-conventional pasta prepared without gluten, it is sought the formation of a structure similar to that of gluten, through the use of technologies that exploit the functional properties of the starch present in the raw material or by adding flour rich in proteins or additives, as mentioned by Pagani ^[29].

According to Leitão et al. ^[30], the most interesting characteristics in the cooking test are the degree of cooking, the resistance to welding, water absorption capacity and volume increase. According to these authors, the nature and quality of raw materials, the shape of the final product, the processing system, drying and the cooking system itself can influence this test.

Table 6. Characterization of the quality of noodles from the cooking tests

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