Abstract
Following the previous works on the safe storage of ascorbic acid in hoshi-nori (dried laver, Porphyra yezoensis), we tried to find the cause of the destruction of ascorbic acid; which reaction does occur in hoshi-nori during storage, an enzymatic or a chemical oxidation? I. Ascorbic acid was decomposed with both aqueous extracts of hoshi-nori and yaki-nori (toasted laver) as much as an enzyme free control at 37°C. II. A reducing velocity of ascorbic acid in hoshi-nori agreed with that in yaki-nori at each moisture condition (aw0.1-0.6) at 20°C. III. Hoshi-nori was stored at 10, 20, 30 (±0.5)°C under the conditions ofaw≈0 to 0.6 for 8 weeks. The destruction of ascorbic acid could be treated as a first order reaction. The ratio of the rate constants (k) every 10°C corresponded to 2 or 3 at each aw's. ARRHENIUS plots (ln k vs. T-1) gave essentially straight lines. Apparent activation energy for the destruction of ascorbic acid (Ea) was no change below a monolayer moisture content (nearly aw 0.2) and 78kj/mol of Ea at aw 0.6 was the same order as the case of the destruction in an enzyme free model system reported by LEE or LABUZA. Therefore, we concluded from the experiments described above that ascorbic acid in hoshinori, possibly in yaki-nori, during storage was destroyed mainly by a chemical or non-enzymatic oxidation.
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