Antioxidant and Antimicrobial Properties Determination of two Varieties of Malanga: White Malanga (Xanthosoma sagittifolium) and Purple Malanga (Xanthosoma violaceum) Cultivated in Ecuador

RESULTS AND DISCUSSION

Volume and mass of extracts obtained: Soxhlet and supercritical fluid (FSC) methods were analyzed from malanga samples, whereby Soxhlet a larger volume was obtained in purple malanga with 10.7 mL and only 3.3 mL in white malanga in Table 2. This difference is due to its state of maturation and the numerous volatile compounds. Díaz et al.¹³, in their research, obtained 1.1 mL of hexanic extract from the species Xanthosoma maximiliani Schott. While Guadalupe and Magali¹⁴, in his study of Andean tubers obtained 55 mL of ethanolic extract in melloco and 21 mL of ethanolic extract in mashua. These comparisons were made because no bibliographical references to malanga extracts were found. On the other hand, concerning the extracts obtained utilizing FCS, greater mass was given by purple malanga with 1.24 g and white with 1.08 g, as can be seen in Table 2, this difference can be attributed to the starch, the variety of the tuber, to the state of maturation of the same. Regarding the extraction of the extracts by SCF of the malanga, no bibliographical references were found, therefore, the current study was the first to carry out extractions of said tubers by the mentioned method.

Analysis of antioxidant activity, radical capture (DPPH): This method is used to determine the antioxidant capacity of foods and synthetic compounds, the DPPH radical, this free radical is capable of reacting with antioxidant compounds through a process characterized by the transfer of a hydrogen atom provided by the antioxidant agent.

After the analysis of antioxidant activity, a greater DPPH radical scavenging effect was evidenced by the SCF method with values of 207.8 μmoL of trolox g^–1 sample in white malanga and 167.6 in purple malanga, being much higher than those obtained by the Soxhlet method in Table 3.

Moncayo et al.¹⁵, analyzed the antioxidant capacity of ethanolic extract from leaves of 18 species of plants native to western Ecuador, in which Xanthosoma sagittifolium presents a percentage of 44.99 I% of antioxidant activity by the DPPH method. On the other hand, Kim et al.¹⁶, carried out a study on the antioxidant capacity with the DPPH method of extract of Colocasia esculenta and identified a value of 4.52 μmoL of trolox g^–1 sample, a value that was considerably lower than that obtained in this work, where the higher the value the higher the antioxidant capacity. The results obtained in this research differ significantly for each variety of tuber, this can be attributed to the extraction method, the analysis performed on starch, the type of tuber and the climatic conditions.

As no previous work on the antioxidant activity of malanga was found, it was contrasted with work carried out on tubers of the same order and family.

Analysis of antimicrobial activity
Antimicrobial activity against Escherichia coli : The results obtained from the antimicrobial activity of the extracts obtained were expressed by measuring the diameter of the inhibition halo in mm against E. coli strains. Where in Table 4 inhibition halos of malanga extracts by supercritical fluids can be seen ranging from 2-4.3 mm in halo size, these values are much lower than those recommended by Ponce et al.¹⁷, since this author considers that there is an antimicrobial effect of extracts and vegetable oils, this must be greater than or equal to 8 mm, however it is important to consider that the extract of the purple malanga at a dilution of 1:2 presented a greater inhibitory effect against the Cer3C1 strain with a value of 4.3 mm, concerning the control antibiotic (levofloxacin), the inhibition halo being considerably greater compared to the extracts. On the other hand, Sánchez-Bautista et al.¹⁸, in the interpretation of sensitivity, considered the percentage of levofloxacin antibiotic sensitivity of 67.8% in E. coli bacteria. Pérez-Delgado et al.¹⁹, in its antibiogram manual, discloses the inhibitory halos of E. coli against levofloxacin from 27-33 mm in diameter. It is important to emphasize that this is the first work on the antimicrobial activity of malanga extracts.

Antimicrobial activity against Salmonella sp.: The following table details the antimicrobial action against the extracts obtained by SCF, at different concentrations. After this analysis, Table 5 shows a poor antimicrobial effect of the extracts obtained against Salmonella strains, with halo size values of 0-1 mm.

However, the Minimum Inhibitory Concentration (MIC), according to the Clinical Laboratory Standard Institute (CLSI) mentioned by Humphries et al.²⁰ considers that the Enterobacteriaceae family was resistant to the antibiotic levofloxacin when the inhibition halo is <16 mm in diameter. Similarly, Sfeir²¹ considers levofloxacin resistant if the inhibition halo is <13 mm in diameter against the Enterobacteriaceae family, in such a way that it can be defined that the S7 and 5M3 strains were resistant to the drug.

Antimicrobial activity against Arcobacter sp.: In Table 6, the results of the inhibition halos were presented and low antimicrobial activity against Arcobacter can be observed, where halo size values of 1-3.3 mm are evidenced, being the 1:2 dilution the one that showed the greatest effect against the Q1BC1 strain, however, these values are very low compared to what is recommended by Ponce et al.¹⁷. On the other hand, works such as the one developed by Goyes²², in his research on the susceptibility of the different Arcobacter strains, reveal the resistance of the bacteria to levofloxacin with a halo <14 mm in diameter, Humphries et al.²⁰, in the table of cut-off points for the interpretation of MICs and zone diameters, it mentions that the genus Campylobacter is susceptible with a halo >26 mm to the group of fluoroquinolone antibiotics in which levofloxacin is immersed. The interpretation of the results was carried out using the recommendations of the European Committee for Susceptibility Testing according to EUCAST and the CLSI²⁰. In this sense, the Q1NC1 strain showed resistance to the reference antibiotic.

Antimicrobial activity against Staphyloccocus aureus: The results obtained from the antimicrobial action of the extracts of the two varieties of the tuber against the gram+S. aureus bacteria were expressed by measuring the diameter of the inhibition halo. In this analysis, the 1:2 dilution of the purple malanga extract presented the best effect with a halo size of 7 mm, followed by the white malanga extract in the 1:2 dilution with a 6.7 mm halo in Table 7, these results were quite close to the 8 mm recommended by Ponce et al.¹⁷.

The extract of the white malanga in the different dilutions presents values greater than 5 mm in halo size. EUCAST for S. aureus reports that the halo <22 mm in diameter is resistant to the antibiotic levofloxacin and is susceptible when the inhibition halo is ≥50 mm, while CLSI, reported that inhibitory halos of S. aureus are 25-30 mm in diameter compared to levofloxacin. Concerning the antimicrobial activity of malanga, no reports were found in the literature, so it is the first investigation of the antimicrobial action of these tubers against the S. aureus bacteria. In short, the extracts of the purple and white malanga have low antimicrobial action compared to the control antibiotic used.

Identification of compounds present by gas chromatography (GC-MSD) in purple malanga extract obtained by SCF: After the chromatographic analysis of the obtained extracts, it is important to highlight that some beneficial compounds for health were identified in this work, among these we have: it is, Phthalic acids, bis (2-Ethylhexyl) ester with an area of 36.96% being an acid Phthalic, continuously with the Linoleic acid 13.31% being an essential fatty acid type compound, the Palmitic acid with an area 9.75% forming part of the essential fatty acid, the Linolein, 2-mono with an area 6.65% forming part of the fatty acids and finally Furfural with an area of 0.375 forming an aldehyde-type compound.

The Pyranone compound, which was identified in the extract of the white malanga, was also identified by Zakaria et al.²³, in the ethanolic extract of the fresh leaves of Pandanus amaryllifolius, a tropical plant from Southeast Asia, the aforementioned compound has a high capacity to act as an antioxidant in volatile substances and has been much discussed in recent years. The Linoleic acid compound was identified by Jiménez et al.²⁴, in the mashua Tropaeolum tuberosum, whose function is to be anti-inflammatory, in addition, it helps prevent coronary diseases, inhibiting angiogenesis, developing a cytotoxic activity in tumour cells. The Furfural compound was also identified by van der Maas et al.²⁵, this allows to inhibit microbial growth.

CONCLUSION

After this investigation, conclude that the extracts of purple malanga obtained by supercritical fluids can be used as a natural food additive, especially for its antioxidant and antibacterial effect, especially in the Gram-positive group, demonstrated especially by the presence of Furfural, Linoleic acid and Pyranone.

SIGNIFICANCE STATEMENT

This study determines the parallel antioxidant and antimicrobial effect of white and purple malanga extracts, they can be a natural alternative to treat bacterial infections, as well as their broad antioxidant benefit, in such a way that it will be possible in the future to obtain biopharmaceuticals.