1Fisheries Research Division, Mie Prefectural Science and Technology Promotion Center, Suzuka, Mie 510-0243, 2Faculty of Bioresources, Mie University, Tsu, Mie 514-8507, Japan
To quantify the degree of discoloration in faded laver Porphyra yezoensis the levels of tristimulus (L*, a*, b*) were determined using a color difference meter. When the degree of discoloration of the thalli was moderate to severe, a*-values were negative. A negative of a*-value meant that the color of thalli changed from red to green. With increasing decolorization, the a* levels decreased while levels of L* and b* increased beyond normal tristimulus values. When the L*-, a*-, and b*-values were compared with the levels of chlorophyll a, phycoerythrin, and phycocyanin, the a*-values correlated best with these pigments. To restore color in faded laver, thalli were treated with four concentrations of NH4-N (1, 10, 25 and 50mg/L seawater). It was found that seawater enriched with 25mg/L NH4-N promoted the best recovery of moderately or seriously faded laver within 24h. After this treatment, the levels of chlorophyll a, phycoerythrin and phycocyanin increased to 140-186%, 116-153% and 116-157%, respectively (relative to levels in untreated thalli). It is important to note that this treatment was only effective when the laver had a minus a*-value and when cells in the tissue were without granulated cytoplasmic contents. This study demonstrates a rapid method for evaluating the degree of discoloration of harvested Porphyra and offers a simple treatment method to restore thalli color.