Pineapple juice : phenolic composition and enzymatic browning inhibition Public Deposited

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  • The phenolic profile of pineapple juice was analyzed by reverse-phase HPLC/Diode Array Detector, and 9 major peaks accounting for 70% of total peak area were characterized. None of these peaks are represented by the pineapple phenolics reported to be present by previous workers. Most of the major peaks are not typically considered as phenolic compounds by the commonly accepted definition, and these peaks are: two aromatic amino acids -- tyrosine and tryptophan, dimethylhydroxylfuranone (DMHF) and its fi-glucoside, and serotonin. One of the major peaks is characterized as a p-coumaric acid-like compound because they have very similar 'UV spectra and retention times. This is possibly why p-coumaric acid has been reported in the literature. The other three peaks are sinapyl derivatives with amino acid or peptides, and they are: S-sinapyl-L-cysteine, N-L-y-glutamyl-S-sinapyl-L-cysteine, and S-sinapyl glutathione. This is the first time to report their existence in nature. Their structures were elucidated from UV spectra, acid hydrolysis and subsequent amino acid analysis, mass spectrometry, and 1D/2D NMR Spectroscopy. These sinapyl derivatives are possibly unique to pineapple, and may serve as marker compounds for pineapple juice. A phenolic compositional database of these 9 major peaks have been created from 54 commercial authentic pineapple juice concentrates, which consist of major commercial varieties and have been collected over 3 consecutive years from the most significant growing regions around the world. Means and standard deviations were as follows (mg/l00 mL single-strength juice, normalized to 12.8 °Brix): tyrosine, 3.6(1.4); serotonin, 1.8(0.8); dimethylhydroxylfuranone, 1.4(0.7); dimethylhydroxylfuranone glucoside, 6.2(3.0); tryptophan, 2.2(0.9); S-sinapyl-L-cysteine, 1.1(0.6); N-y-L-glutamyl- S-sinapyl-L-cysteine, 2.3(1.1); S-sinapyl glutathione, 5.4(1.4); and a p-coumaric acidlike phenolic compound (calculated as p-coumaric acid), 0.5(0.4). This information will be useful for evaluation of authenticity and quality. Pineapple juice has been demonstrated to have enzymatic browning inhibition activity, but the information about the nature of the inhibitor(s) is very limited. In order to characterize the major inhibitor(s) in pineapple juice, three different pineapple juices, fresh, canned, and frozen concentrate, were investigated by using a combination of fractionation methods. It was found: The inhibition activity could be mainly contributed by protease in fresh juice, by artificially added ascorbic acid in canned juice, and possibly by a possibly very polar organic acid (neither ascorbic acid nor citric acid) in frozen concentrate.
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