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 (OX treatment). As a control, a potato juice was prepared in the presence of NaHSO3 (S 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 (MeOH control). Water-soluble low molecular weight fractions (LMWFs) and high molecular weight fractions (HMWFs) from S and OX extracts were obtained by ultrafiltration and dialysis, respectively. Pellets obtained after the OX treatment and the S and MeOH controls were also analyzed for ChA content. Whereas in the S-LMWF all ChA was converted to sulfonic acid adducts, no free ChA was found in the OX-LMWF, indicating its high reactivity upon enzymatic browning. Analysis of protein in the HMWFs showed a higher content of “reacted” ChA in OX (49.8 ± 7.1 mg ChA/100 g potato DW) than in S (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 S-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 S but not in that of MeOH. Size exclusion chromatography, combined with proteolysis, revealed that ChA reacted with patatin and protease inhibitors to produce brown soluble complexes

Identification and quantification of (dihydro) hydroxycinnamic acids and their conjugates in potato by UHPLC–DAD–ESI-MSn

Hydroxycinnamic acid conjugates (HCAcs) and dihydrohydroxycinamic acid conjugates (DHCAcs) were identified and quantified in potato tuber extracts by UHPLC–DAD–ESI-MSn. The HCAcs and DHCAcs identification took place by screening for product ions and neutral losses in combination with UV spectra. Thirty-nine HCAcs/DHCAcs were detected, including 17 previously reported in potato. HCAs were found unconjugated, linked to hydroxyl-containing compounds including hexose, quinic acid and malic acid, to amino-containing compounds, such as putrescine and octopamine, and to unknown compounds. DHCAs were present linked to spermine, spermidine and to still unidentified compounds. Chlorogenic acid was the most abundant compound (25.43 ± 0.49 mg/g DW) followed by cryptochlorogenic acid (7.31 ± 0.38 mg/g DW), a non-hydrolyzable sinapic acid conjugate (2.80 ± 0.06 mg/g DW) and neochlorogenic acid (2.41 ± 0.10 mg/g DW), in total accounting for 83% (w/w) of the total concentration of HCAs/DHCAs-containing compounds. Quantifications of HCAs released after alkaline hydrolysis matched well with the quantification of the unhydrolyzed molecules. The UHPLC–DAD–ESI-MSn method showed a larger diversity of HCAcs and DHCAcs in potato than described before

Diversity of (dihydro) hydroxycinnamic acid conjugates in Colombian potato tubers

In potato tuber, caffeic acid (the predominant hydroxycinnamic acid (HCA)), its conjugates (HCAcs; i.e. chlorogenic acid (ChA), crypto-ChA, and neo-ChA), and anthocyanin-linked HCAs have been extensively described in the literature. In contrast, only little information is available on the occurrence of other HCAcs and didydrohydroxycinnamic acid conjugates (DHCAcs). Fifteen Colombian potato cultivars were screened for these less commonly described conjugates by reversed-phase ultrahigh performance liquid chromatography coupled to a diode array detector and a heated electrospray ionisation mass spectrometer. A total of 62 HCAs/HCAcs/DHCAcs were found in extracts from peel and flesh. Among them, only twelve compounds were common to all cultivars in both peel and flesh. The less commonly described compounds accounted for 7.1–20.1% w/w of the total amount of HCAs/HCAcs/DHCAcs in whole tubers, highlighting their contribution to the total phenolic profile of potato tubers. Among all cultivars, the abundance (mg/100 g DW whole tuber) of neo-ChA (0.8–7.4) ranged in similar quantities as the less commonly reported feruloyl octopamine (1.2–5.2), 5-O-feruloyl quinic acid (0.1–7.5), cis-ChA (1.1–2.2), caffeoyl putrescine (0.6–2.5), sinapoyl hexose (0.1–1.8), N1,N14-bis-(dihydrocaffeoyl) spermine (0.2–1.7), N1,N10-bis-(dihydrocaffeoyl) spermidine (1.1–2.6), and N1,N5,N14-tris-(dihydrocaffeoyl) spermine (trace – 11.1)

New Insights into an Ancient Antibrowning Agent: Formation of Sulfophenolics in Sodium Hydrogen Sulfite-Treated Potato Extracts

The effect of sodium hydrogen sulfite (S), used as antibrowning agent, on the phenolic profile of potato extracts was investigated. This extract was compared to one obtained in the presence of ascorbic acid (A). In the presence of A, two major compounds were obtained, 5-O-caffeoylquinic acid (5-CQA) and 4-O-caffeoyl quinic acid. With S, their 2'-sulfo-adducts were found instead, the structures of which were confirmed by nuclear magnetic resonance spectroscopy and mass spectrometry. Also, for minor caffeoyl derivatives and quercetin glycosides, the corresponding sulfo-adducts were observed. Feruloyl and sinapoyl derivatives were not chemically affected by the presence of S. Polyphenol oxidase (PPO) was thought to be responsible for the formation of the sulfo-adducts. This was confirmed by preparing 2'-sulfo-5-O-caffeoyl quinic acid in a model system using 5-CQA, sodium hydrogen sulfite, and PPO. This sulfo-adduct exhibited a small bathochromic shift (¿max 329 nm) as compared to 5-CQA (¿max 325 nm) and a strong hypochromic shift with an extinction coefficient of 9357 ± 395 M–1 cm–1 as compared to 18494 ± 196 M–1 cm–1, respectively. The results suggest that whenever S is used as an antibrowning agent, the O-quinone formed with PPO reacts with S to produce sulfo-O-diphenol, which does not participate in browning reactions

Inhibition of Enzymatic Browning of Chlorogenic Acid by Sulfur-Containing Compounds

The antibrowning activity of sodium hydrogen sulfite (NaHSO3) was compared to that of other sulfur-containing compounds. Inhibition of enzymatic browning was investigated using a model browning system consisting of mushroom tyrosinase and chlorogenic acid (5-CQA). Development of brown color (spectral analysis), oxygen consumption, and reaction product formation (RP-UHPLC–PDA–MS) were monitored in time. It was found that the compounds showing antibrowning activity either prevented browning by forming colorless addition products with o-quinones of 5-CQA (NaHSO3, cysteine, and glutathione) or inhibiting the enzymatic activity of tyrosinase (NaHSO3 and dithiothreitol). NaHSO3 was different from the other sulfur-containing compounds investigated, because it showed a dual inhibitory effect on browning. Initial browning was prevented by trapping the o-quinones formed in colorless addition products (sulfochlorogenic acid), while at the same time, tyrosinase activity was inhibited in a time-dependent way, as shown by pre-incubation experiments of tyrosinase with NaHSO3. Furthermore, it was demonstrated that sulfochlorogenic and cysteinylchlorogenic acids were not inhibitors of mushroom tyrosinase