Crystalline Precipitates in Bay Scallops (Argopecten irradians) Imported from China

Abstract

Macroscopic evaluations documented uncharacterized white spots in bay scallops (Argopecten irradians) to be a surface phenomenon, occupying scallop tissue only to a depth demarcated by translucent tissue, which is associated with salt solution penetration. Light microscopy characterized the white material to be crystalline in nature. Scanning electron microscopy and energy dispersive X-ray spectroscopy (EDS) identified two types of crystals, the crystal presents in scallops as imported from China, and a second precipitate resulting form reprocessing scallops with sodium tripolyphosphate (STP). The crystal present in scallops as imported were largely water insoluble, did not dissociate upon heating, and contained phosphorous and magnesium as major elements with sodium present only in trace amounts. Crystals resulting form STP reprocessing contained P, Mg, and Na as major or minor elements. This slight compositional alteration affected crystal stability, producing a more water soluble crystal which dissociated upon heating. Both crystals share similar attributes with struvite crystals (Magnesium ammonium phosphate) but are considered to be different precipitates. Dissociation of crystalline precipitates in imported bay scallops was demonstrated during phosphate processing using alternatives to the alkaline STP. Sodium hexametaphosphate (SHMP, pH 7.0) provided total dissociation of scallop precipitates during processing, while a phosphate blend (pH 7.2) containing STP, SHMP, and acid pyrophosphate provided partial precipitate dissociation. STP solutions with pH adjusted to 5.0, 6.3, and 7.0, had no effect on precipitate dissociation.