Effects of Water Activity on the Lipid Oxidation and Antioxidants of Dried Laver (Porphyra) During Storage in the Dark

Lipid oxidation and antioxidant degradation in dried laver (Porphyra) were determined during storage at water activities (A(w)) of 0.11, 0.30, 0.51, 0.75, or 0.89 in the dark at 40 degrees C for 15 d. Lipid oxidation was evaluated by measuring peroxide value (POV) and conjugated dienoic acid (CDA) contents, and fatty acid composition was analyzed by gas chromatography. Contents of polyphenols, tocopherols, and porphyran were determined by spectrophotometry, HPLC, and gravimetry, respectively. The POV and CDA contents of the dried laver lipids increased during storage as A(w) increased from 0.11 to 0.30, 0.51, 0.75, and 0.89, whereas the relative content of eicosapentaenoic acid was decreased; however, the contents of polyphenols, -tocopherol, and porphyran in dried laver showed the reverse phenomena. Lipid oxidation and antioxidant degradation in dried laver sharply increased at an A(w) of 0.51. Polyphenols, -tocopherol, and porphyran contributed to reduction of lipid oxidation in dried laver. The degree of lipid oxidation of dried laver was more dependent on the concentration of -tocopherol than that of either polyphenols or porphyran during storage in the dark. The results strongly suggest that the quality of dried laver can be improved by preserving tocopherols as much as possible while decreasing A(w) during storage.