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 NaHSO<sub>3</sub> (<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.