Hydroxymethylfurfural

The 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) diammonium salt, hydroxymethylfurfural, potassium persulfate, 2,4,6-tris(2-pyridyl)-s-triazine, and Trolox^® were purchased from Sigma-Aldrich (Buchs, Switzerland). Maltodextrin and Amberlite XAD-16 resin were supplied by Brenntag (Kędzierzyn-Koźle, Poland). Cyanidin-3-O-glucoside, peonidin-3-O-rutinoside, quercetin-3-O-glucoside, quercetin-3-O-rutinoside, p-coumaric, and ferulic acid were obtained from Extrasynthese (Lyon, France). Chlorogenic and neochlorogenic acids were from TRANS MIT GmbH (Giessen, Germany). Acetonitrile for UPLC (gradient grade) and ascorbic acid were from Merck (Darmstadt, Germany). UPLC grade water prepared using the HLP SMART 1000s system (Hydrolab, Gdańsk, Poland) was additionally filtrated through a PTFE 0.22 µm membrane filter (Millex Samplicity Filter, Merck, Darmstadt, Germany) before use.

Avocado seed (AS), from the Hass variety, was gathered from a local restaurant in Ourense (Northwest Spain). Firstly, the seed was washed with tap water with the purpose of removing the remaining pulp and the layer covering the seed was removed. Before drying it at room temperature, AS was powdered using a laboratory mill with sieve to a smaller size than 1 mm. AS was collected into zip bags and stored at −20 °C.
The chemicals used in this work were 2,2′-azino-di(3-ethyl- benzo-thia-zoline-6-sulfonic acid (ABTS), 2,4,6-tri(2-pyridyl)-s-triazine (TPTZ), 6-hydroxy-2,5,7,8-etra-methylcrhoman-2-carboxylic acid (Trolox), arabinose, choline chloride, ethanol, Folin–Ciocalteu reagent, furfural, gallic acid, glucose, glycerol, hydrochloric acid, hydroxymethylfurfural, iron (III) chloride hexahydrate, methanol, potassium persulfate, rutin, sodium acetate trihydrate, sodium carbonate, sulfuric acid and xylose, that were purchased from Sigma-Aldrich (Barcelona, Spain).

1,1-Diphenyl-2-picrylhydrazyl radical (DPPH^•), 6-hydroxy-2,5,7,8-tetramethylchroman-2-carboxylic acid (Trolox), 2,4,6-tri(2-pyridyl)-s-triazine (TPTZ), dimethyl sulfoxide (DMSO), FeCl₃, acetonitrile, formic acid, sulfuric acid, sodium hydroxide, and hydroxymethylfurfural (HMF) were acquired from Sigma-Aldrich (Taufkirchen, Germany). Acetic acid was obtained from Chempur (Piekary Śląskie, Poland). acetonitrile for HPLC was purchased from POCh (Gliwice, Poland). Loganic acid (LA), loganin (Lo), Sweroside (S), gallic acid (GA), ellagic acid (EA), 5-O-caffeoylquinic acid (5-CQA, chlorogenic acid), p-coumaric acid (p-CuA), quercetin 3-O-glucoside (Q glc), kaempferol 3-O-glucoside (Kf glc), cyanidin 3-O-glucoside (Cy glc) were purchased from Extrasynthese (Lyon Nord, France). All reagents were of analytical grade.