Heat- and light-treatment change the visible fluorescence of Akoya cultured pearls

• Published in: Fisheries science 2013-11, Vol.79 (6), p.959-966
• Main Authors: Hiramatsu, Junichi, Iwahashi, Yasunori, Nagai, Kiyohito
• Format: Article
• Language: English
• Subjects: Aquaculture; Biomedical and Life Sciences; Experiments; Fish & Wildlife Biology & Management; Fluorescence; Food Science; Freshwater & Marine Ecology; Heat; Heat treating; Heat treatment; Life Sciences; Light; Original Article; Pearls; Studies; Temperature
• ISSN: 0919-9268; 1444-2906
• DOI: 10.1007/s12562-013-0663-0

We exposed Akoya cultured pearls separately to heat (60–120 °C) and artificial light to investigate changes to fluorescence in the visible range and yellowing. We found that for both heat-treated and light-treated pearls, the fluorescence peak shifted from 480 to 430 nm with an increase in fluorescence intensity. This change in intensity was more prominent in heat-treated pearls, with the initial speed of increase rising with treatment temperature; treatment at 100 °C caused the greatest increase in fluorescence intensity. However, aminoguanidine suppressed the heat-induced change in the fluorescence of an ethylenediaminetetraacetic acid–soluble nacreous layer matrix. These results suggest that the heated-induced changes in the fluorescence of Akoya cultured pearls were caused largely by a buildup of fluorescent advanced glycation end products through the Maillard reaction. Although heat treatment led to a large increase in fluorescence intensity of the peak at approximately 430 nm in a deoxygenized environment, hardly any change in fluorescence intensity was observed after light treatment in this environment. Moreover, a new shoulder peak appeared at about 460 nm after light treatment. These results suggest that the Maillard reaction was not a major factor in the light-induced changes in the fluorescence of Akoya cultured pearls.