Evaluation of a glucose oxidase/peroxidase method for indirect measurementof glycogen content in oysters (Crassostrea virginica)

A colorimetric method for indirect measurement of glycogen concentrations i n tissue homogenates of eastern oysters (Crassostrea virginica) was evaluat ed. This method uses a conversion of glycogen to glucose by amyloglucosidas e. The procedure was optimized Fur extracting buffer pH (5.0) and amylogluc osidase concentration (5 mg/mL). Coefficients of variation(n = 10) for oyst er homogenates with mean glycogen concentrations of 84 and 242 mg/dL had wi thin-run Values of 3.29 and 3.66%, and between-run results of 4.46 and 3.15 %, respectively. When mean glycogen concentrations of thawed oyster homogen ates were compared with those of initial fresh homogenates, no significant (P less than or equal to 0.05) differences were detected in samples thawed after 1 h, 1 day, 1 wk, or 1 mo. Glycogen recovery percentages of 104.1, 10 3.7, and 104.5% were obtained with mixed solutions containing 111, 94, and 19 mg/dL glycogen, respectively. The lower limit of sensitivity for the pro cedure was approximately 14 mL/dL. The assay was considered to be linear to 436 mg/dL. Lyophilized samples appeared to provide the most reliable deter mination of glycogen concentrations per gram of tissue by avoiding variable water content in oyster tissues. Initial laboratory ranges for tissue glyc ogen based on wet (mean +/- 2 SD: 7-43 mg/g) and dry (mean +/- 2 SD: 19-145 mg/g) weights were determined with 49 second-year growth oysters obtained during July 1998 (Covehead, Prince Edward Island, Canada). It was concluded that the colorimetric assay offered a reliable indication of tissue concen trations of glycogen in eastern oysters (C. virginica).