Dataset on absorption spectra and bulb concentration of phenolic compounds that may interfere with onion pyruvate determinations

We present data on absorption spectra (400–540 nm) and concentration of phenolic compounds quercetin, myricetin, kaempferol, rutin, catechin, epicatechin gallate (ECG) and epigallocatechin gallate (EGCG), in yellow, red and white onions. These data are related to the article entitled “Variability in spectrophotometric pyruvate analyses for predicting onion pungency and nutraceutical value” (Beretta et al., 2017) [1]. Given the relevance of pyruvate determinations for estimating onion pungency and functional value, it is important to identify compounds that can interfere with pyruvate determinations when using two previously published analytical procedures, namely Schwimmer and Weston (1961) (SW) [2] and Anthon and Barret (2002) (AB) [3], which are based on spectrophotometry and light-absorbance at 420 nm and 515 nm, respectively. The data presented in this article are absorption spectra for 7 onion phenolic compounds in the range 400–540 nm, which include wavelengths used by the two pyruvate analytical methods (Schwimmer and Weston, 1961; Anthon and Barret, 2002) [2,3] that were compared in our reference article (Beretta et al., 2017) [1]. Additionally, bulb content data for these 7 phenolic compounds in onion cultivars and F2 progenies with different bulb color were included to allow further analyses.


a b s t r a c t
We present data on absorption spectra (400-540 nm) and concentration of phenolic compounds quercetin, myricetin, kaempferol, rutin, catechin, epicatechin gallate (ECG) and epigallocatechin gallate (EGCG), in yellow, red and white onions. These data are related to the article entitled "Variability in spectrophotometric pyruvate analyses for predicting onion pungency and nutraceutical value" (Beretta et al., 2017) [1]. Given the relevance of pyruvate determinations for estimating onion pungency and functional value, it is important to identify compounds that can interfere with pyruvate determinations when using two previously published analytical procedures, namely Schwimmer and Weston (1961) (SW) [2] and Anthon and Barret (2002) (AB) [3], which are based on spectrophotometry and light-absorbance at 420 nm and 515 nm, respectively. The data presented in this article are absorption spectra for 7 onion phenolic compounds in the range 400-540 nm, which include wavelengths used by the two Contents lists available at ScienceDirect journal homepage: www.elsevier.com/locate/dib pyruvate analytical methods (Schwimmer and Weston, 1961;Anthon and Barret, 2002) [2,3] that were compared in our reference article (Beretta et al., 2017) [1]. Additionally, bulb content data for these 7 phenolic compounds in onion cultivars and F2 progenies with different bulb color were included to allow further analyses. &

Value of the data
The dataset is valuable for the identification of phenolic compounds that may interfere with onion pyruvate determinations when using the spectrophotometry-based methods of Schwimmer and Weston [2] and Anthon and Barret [3].
Characterization of onion germplasm based on their content of seven phenolic compounds; useful for onion breeders and food technologists.
The dataset can serve to compare flavonoids content among onion germplasm from different geographical origins.

Preparation of the standard solutions
Solutions of the authentic standards phenolic compounds were prepared in the range of 0.5-10 mg L À 1 in methanol:water 90:10 (v/v). Equations used for quantification were obtained from a linear regression analysis (r 2 Z0.99).
Bulb contents for the above seven phenolic compounds were estimated, by HPLC analysis, in 5 yellow (Valcatorce, Cobriza, Valuno, Angaco, Navidena) and 3 white (Ancasti, Antartica, Refinta 20) onion cultivars (three replicates of eight bulbs per cultivar were analyzed) developed by INTA La Consulta, Argentina [4], and in 10 yellow-, 16 red-and 11 white-bulb onions from an F 2 population developed by the Argentine onion breeding program, at INTA La Consulta. The onions were grown at the experimental field of INTA La Consulta, Argentina, using conventional agricultural practices for the crop.

HPLC analysis of onion phenolic compounds
Onion phenolic compounds were analyzed according to Insani et al. [5]. Briefly, onion aqueous extracts were prepared in a 1:1 volume (w/v) of distilled water using a blender (Braun MR 400 Plus, Kronberg, Germany), centrifuged and filtered through PTFE membrane filters of 0.45 μm pore size (Agilent Tech., Santa Clara, USA). For each sample, 20 μL of the filtered onion extracts were injected onto the HPLC system and myricetin, rutin, catechin, ECG, and EGCG were determined. For estimation of total quercetin and kaempferol, hydrolysis of the samples was previously performed to release the sugar molecule from the aglycon, prior to injection onto the HPLC system. For the chemical hydrolysis, an aliquot of 1/10 dilution of the onion extract in HCl 0.25 M was heated at 100°C for 2 h in sealed vials. When samples reached ambient temperature they were filtered through PTFE and 20 μL were injected onto the HPLC system. Results were expressed as mg g À 1 fw.