Quantitative Fate of Chlorogenic Acid during Enzymatic Browning of Potato Juice

The quantitative fate of chlorogenic acid (ChA) during enzymatic browning of potato juice was investigated. Potato juice was prepared in water without the use of any antibrowning agent (<i>OX</i> treatment). As a control, a potato juice was prepared in the presence of NaHSO₃ (<i>S</i> control). To study the composition of phenolic compounds in potato in their native states, also a potato extract was made with 50% (v/v) methanol containing 0.5% (v/v) acetic acid (<i>MeOH</i> control). Water-soluble low molecular weight fractions (LMWFs) and high molecular weight fractions (HMWFs) from <i>S</i> and <i>OX</i> extracts were obtained by ultrafiltration and dialysis, respectively. Pellets obtained after the <i>OX</i> treatment and the <i>S</i> and <i>MeOH</i> controls were also analyzed for ChA content. Whereas in the <i>S-</i>LMWF all ChA was converted to sulfonic acid adducts, no free ChA was found in the <i>OX-</i>LMWF, indicating its high reactivity upon enzymatic browning. Analysis of protein in the HMWFs showed a higher content of “reacted” ChA in <i>OX</i> (49.8 ± 7.1 mg ChA/100 g potato DW) than in <i>S</i> (14.4 ± 1.5 mg ChA/100 g potato DW), as evidenced by quinic acid release upon alkaline hydrolysis. The presence of quinic acid in <i>S</i>-HMWF was unexpected, but a mass balance incorporating the ChA content of LMWF, HMWF, and pellet for the three extractions suggested that ChA might have been attached to polymeric material, soluble in the aqueous environment of <i>S</i> but not in that of <i>MeOH</i>. Size exclusion chromatography, combined with proteolysis, revealed that ChA reacted with patatin and protease inhibitors to produce brown soluble complexes

Green and Black Tea Phenolics: Bioavailability, Transformation by Colonic Microbiota, and Modulation of Colonic Microbiota

Monomeric green tea catechin (GTC) and oligomeric, oxidized black tea phenolic (BTP) have shown promising health benefits, although GTC has been more extensively studied than BTP. We review the current knowledge on bioavailability, colonic transformation, and gut microbiota modulatory effects of GTC and BTP. As a result of their similar poor bioavailability in the small intestine and potentially similar metabolites upon colonic fermentation, it seems as if GTC and BTP have similar health effects, although it cannot be excluded that they have different gut microbiota modulatory effects and that BTP gives a poorer yield of bioactive phenolic metabolites upon colonic fermentation than GTC

Analysis of Palmitoyl Apo-astaxanthinals, Apo-astaxanthinones, and their Epoxides by UHPLC-PDA-ESI-MS

Food products enriched with fatty acid-esterified xanthophylls may result in deviating dietary apo-carotenoids. Therefore, free astaxanthin and its mono- and dipalmitate esters were subjected to two degradation processes in a methanolic model system: light-accelerated autoxidation and hypochlorous acid/hypochlorite (HOCl/OCl^–) bleaching. Reversed phase ultrahigh-performance liquid chromatography photodiode array with in-line electrospray ionization mass spectrometry (RP-UHPLC-PDA-ESI-MS) was used for assessment of degradation products. Apo-astaxanthinals and -astaxanthinones containing 3 (apo-9) to 10 (apo-8′) conjugated double bonds were found upon autoxidation for all three types of astaxanthin (except free apo-8′-astaxanthinal). Fragmentation of [M + H]⁺ and [M + Na]⁺ parent masses of apo-astaxanthins from dipalmitate astaxanthin indicated palmitate esterification. Astaxanthin monopalmitate degradation resulted in a mixture of free and palmitate apo-astaxanthins. HOCl/OCl^– rapidly converted the astaxanthins into a mixture of epoxy-apo-9- and epoxy-apo-13-astaxanthinones. The palmitate ester bond was hardly affected by autoxidation, whereas for HOCl/OCl^– the ester bond of the apo-astaxanthin palmitoyl esters was degraded

Modification of Prenylated Stilbenoids in Peanut (<i>Arachis hypogaea</i>) Seedlings by the Same Fungi That Elicited Them: The Fungus Strikes Back

<i>Aspergillus oryzae</i> and <i>Rhizopus oryzae</i> were compared for inducing the production of prenylated stilbenoids in peanut seedlings. The fungus was applied at two different time points: directly after soaking (day 1) or after 2 days of germination (day 3). <i>Aspergillus</i>- and <i>Rhizopus</i>-elicited peanut seedlings accumulated an array of prenylated stilbenoids, with overlap in compounds induced, but also with compounds specific to the fungal treatment. The differences were confirmed to be due to modification of prenylated stilbenoids by the fungus itself. Each fungus appeared to deploy different strategies for modification. The content of prenylated stilbenoids modified by fungi accounted for around 8% to 49% (w/w) of total stilbenoids. The contents of modified prenylated stilbenoids were higher when the fungus was applied on day 1 instead of day 3. Altogether, type of fungus and time point of inoculation appeared to be crucial parameters for optimizing accumulation of prenylated stilbenoids in peanut seedlings

Mass Spectrometric Characterization of Benzoxazinoid Glycosides from Rhizopus-Elicited Wheat (Triticum aestivum) Seedlings

Benzoxazinoids function as defense compounds and have been suggested to possess health-promoting effects. In this work, the mass spectrometric behavior of benzoxazinoids from the classes benzoxazin-3-ones (with subclasses lactams, hydroxamic acids, and methyl derivatives) and benzoxazolinones was studied. Wheat seeds were germinated with simultaneous elicitation by Rhizopus. The seedling extract was screened for the presence of benzoxazinoid (glycosides) using reversed-phase ultra-high-performance liquid chromatography with photodiode array detection coupled in line to multiple-stage mass spectrometry (RP-UHPLC–PDA–MSⁿ). Benzoxazin-3-ones from the different subclasses showed distinctly different ionization and fragmentation behaviors. These features were incorporated into a newly proposed decision guideline to aid the classification of benzoxazinoids. Glycosides of the methyl derivative 2-hydroxy-4-methoxy-1,4-benzoxazin-3-one were tentatively identified for the first time in wheat. We conclude that wheat seedlings germinated with simultaneous fungal elicitation contain a diverse array of benzoxazinoids, mainly constituted by benzoxazin-3-one glycosides

<i>Sr</i>CloQ reaction products tentatively annotated by RP-UHPLC-UV-MSⁿ.

<p><i>Sr</i>CloQ reaction products tentatively annotated by RP-UHPLC-UV-MSⁿ.</p

Aromatic acceptor substrates and their percentage of conversion (molar %) by <i>Sr</i>CloQ.

<p>The atoms shared with the genuine substrate are highlighted in blue colour. Phenolic substrates with green label represent the best acceptor substrates, whereas those with red labels were not utilized by the enzyme.</p

Efficacy of Food Proteins as Carriers for Flavonoids

Enrichment of flavonoids in food is often limited by their off-tastes, which might be counteracted by the use of food proteins as carriers of flavonoids. Various milk proteins, egg proteins, and gelatin hydrolysates were compared for their binding characteristics to two flavan-3-ols. Among the proteins tested for their affinities toward epigallocatechin gallate (EGCG), β-casein and gelatin hydrolysates, in particular fish gelatin, were found to be the most promising carriers with an affinity on the order of 10⁴ M^–1. A flexible open structure of proteins, as present in random coil proteins, was found to be important. The saturation of binding observed at high flavonoid/protein ratios was used to estimate the maximal binding capacity of each protein. To reach a daily intake of EGCG that has been associated with positive health effects, only 519 mg of gelatin B and 787 mg of β-casein were required to complex EGCG on the basis of their maximal binding capacity. When the absence of turbidity is taken into account, β-casein prevails as carrier. Three selected proteins were further investigated for their binding potential of representative flavonoids differing in their C-ring structure. An increase in hydrophobicity of flavonoids was related to a higher affinity for proteins, and the presence of a gallic acid ester on the C-ring showed an overall higher affinity

Resolubilization of Protein from Water-Insoluble Phlorotannin–Protein Complexes upon Acidification

Marine phlorotannins (PhT) from Laminaria digitata might protect feed proteins from ruminal digestion by formation of insoluble non-covalent tannin–protein complexes at rumen pH (6–7). Formation and disintegration of PhT–protein complexes was studied with β-casein (random coil) and bovine serum albumin (BSA, globular) at various pH. PhT had similar binding affinity for β-casein and BSA as pentagalloyl glucose, as studied by fluorescence quenching. The affinity of PhT for both proteins was independent of pH (3.0, 6.0, and 8.0). In the presence of PhT, the pH range for precipitation of tannin–protein complexes widened to 0.5–1.5 pH units around the isoelectric point (pI) of the protein. Complete protein resolubilization from insoluble PhT–protein complexes was achieved at pH 7 and 2 for β-casein and BSA, respectively. It was demonstrated that PhT modulate the solubility of proteins at neutral pH and that resolubilization of PhT–protein complexes at pH deviating from pI is mainly governed by the charge state of the protein

Structural basis for non-genuine phenolic acceptor substrate specificity of <i>Streptomyces roseochromogenes</i> prenyltransferase CloQ from the ABBA/PT-barrel superfamily

<div><p>Acceptor substrate specificity of <i>Streptomyces roseochromogenes</i> prenyltransferase SrCloQ was investigated using different non-genuine phenolic compounds. RP-UHPLC-UV-MSn was used for the tentative annotation and quantification of the prenylated products. Flavonoids, isoflavonoids and stilbenoids with different types of substitution were prenylated by SrCloQ, although with less efficiency than the genuine substrate 4-hydroxyphenylpyruvate. The isoflavan equol, followed by the flavone 7,4’-dihydroxyflavone, were the best non-genuine acceptor substrates. B-ring <i>C</i>-prenylation was in general preferred over A-ring <i>C</i>-prenylation (ratio 5:1). Docking studies of non-genuine acceptor substrates with the B-ring oriented towards the donor substrate dimethylallyl pyrophosphate, showed that the carbonyl group of the C-ring was able to make stabilizing interactions with the residue Arg160, which might determine the preference observed for B-ring prenylation. No reaction products were formed when the acceptor substrate had no phenolic hydroxyl groups. This preference can be explained by the essential hydrogen bond needed between a phenolic hydroxyl group and the residue Glu281. Acceptor substrates with an additional hydroxyl group at the <i>C</i>3’ position (B-ring), were mainly <i>O</i>3’-prenylated (> 80% of the reaction products). This can be explained by the proximity of the C3’ hydroxyl group to the donor substrate at the catalytic site. Flavones were preferred over isoflavones by SrCloQ. Docking studies suggested that the orientation of the B-ring and of the phenolic hydroxyl group at position <i>C</i>7 (A-ring) of flavones towards the residue Tyr233 plays an important role in this observed preference. Finally, the insights obtained on acceptor substrate specificity and regioselectivity for SrCloQ were extended to other prenyltransferases from the CloQ/NhpB family.</p></div