Extraction and Identification of the Pigment in the Adductor Muscle Scar of Pacific Oyster Crassostrea gigas

Abstract

In this study, UV (ultraviolet) and IR (infrared radiation) spectral analysis were integrated to identify the pigment in the adductor muscle scar of the Pacific oyster Crassostrea gigas. The pigment was extracted from the adductor muscle scars of cleaned oyster shells that were pulverized, hydrolyzed in hot hydrochloric acid, purified with diethyl ether, and dissolved in 0.01 mL/L NaOH. The maximum absorption of the pigment in the UV absorption spectrum within the range of 190-500 nm was observed between 210-220 nm. The UV absorbance decreased with increasing wavelength which was consistent with the UV spectral absorption characteristics of melanin. In addition, Fourier transform infrared spectroscopy scanning revealed characteristic absorption peaks that emerged near 3440 cm-1 and 1630 cm-1, which was consistent with infrared scanning features of eumelanin (a type of melanin). This study has demonstrated for the first time that the pigment in the adductor muscle scar of the Pacific oyster is melanin, hinting that the adductor muscle could be another organ pigmenting the mollusc shell with melanin other than mantle.

Fig 1. The pigmented and nonpigmented adductor muscle scars of Pacific oyster.

Panel A, the outside surface of the untreated shell with pigmented adductor muscle scar; panel B, the inside surface of the untreated shell with pigmented adductor muscle scar; panel C, the outside surface of the pigmented adductor muscle scar region following treatment; panel D, the inside surface of the pigmented adductor muscle scar region following treatment; panel A’, the outside surface of the untreated shell with nonpigmented adductor muscle scar; panel B’, the inside surface of the untreated shell with nonpigmented adductor muscle scar; panel C’, the outside surface of the nonpigmented adductor muscle scar region following treatment; panel D’, the inside surface of the nonpigmented adductor muscle scar region following treatment.

Fig 2. The extracts from oyster adductor muscle scars with and without pigmentation.

Panel A, the extract from the pigmented adductor muscle scars; panel B, the extract from the nonpigmented adductor muscle scars.

Fig 3. UV absorption spectra of the pigment extracted from the adductor muscle scar of Pacific oyster.

‘Abs’ denotes the absorbance value, ‘Wav’ the wavelength.

Fig 4. IR scanning spectra of the pigment extracted from the adductor muscle scar of Pacific oyster.

‘T’ denotes the transmittance, ‘Wav’ the wavenumber.