Characterization of a red-purple extract from alternanthera sp. by HPLC-ESI-MS-QTOF

Abstract

[Introduction]: The use of natural pigments and antioxidants instead of synthetic ones is receiving increasing interest in the food industry due to the health promoting effects of natural substances. Recently, in response to this trend, healthy functional foods and cosmetic products for human health and safety have been gradually expanded. The aim of this work was to investigate the diversity of compounds present in Alternanthera brasiliana and Alternanthera tenella, including betalains and polyphenols. Both species of native plants could be a source of suitable material for functional food production, specifically for acting as natural food additives. [Materials and Methods]: Experiments were carried out with two different species, Alternantera brasiliana and Alternanthera tenella maintained in greenhouse. The vegetal material (0.1 g of leaf or stem) was extracted at 4 ºC. The supernatant was filtered and them was used for betalains and polyphenols analysis. Aliquots of each sample were injected into the HPLC-DAD-ESI-QTOF. The analysis was performed on an Agilent 1200 series HPLC (Agilent Technologies, Waldbroon, Germany), comprised of a quaternary pump (G1311A) with integrated degasser (G1322A), an autosampler (G1367B), a thermo stated column compartment (G1316A) a diode array detector (DAD) (G1315B) and a hybrid mass spectrometer quadrupole-time of flight via an electrospray ionization source (ESI) with JetStream technology (Agilent Accurate Mass QTOF LC-MS, Waldbronn, Germany) in series in the same chromatographic line. The compounds were monitored at 280 nm (polyphenols) and 538 nm (betalains), while mass spectra were acquire with electrospray ionization and the TOF mass analyzer in both positive (betalains) and negative (polyphenols) mode over the range m/z: 100-1000. Total polyphenol content was determined by Folin-Ciocalteau method (Schlesier, Harwat, Böhm, & Bitsch, 2002). FRAP assay was carried out to determine the iron-reducing capacity of each extract (Benzie & Strain, 1996). [Results]: When working in positive mode, a number of compounds was separated from the leaf and stems identified as betalains. A. tenella showed the same betalain profile than A. brasiliana, both for leaf and stem. When working in negative mode, a number of polyphenolic compounds were found; hydroxibenzoic acids, hydroxycinnamic acids, flavones and flavonols were identified and characterized on the basis of their accurate MS and MS/MS information. [Conclusions]: The betalains found in the extracts showed a relatively simple and well defined pigment profile. Polyphenols were diverse with presence of different groups and multiplicity of derivatives in both plants, which may be an indication of a highly promising antioxidant and bioactive potential.