Muscle glycogen: Comparison of iodine binding and enzyme digestion assays and application to meat samples

A rapid assay for tissue glycogen is described. Bovine liver and muscle glycogen were solubilized with perchloric acid (7-10%) and incubated with an iodine (I(2)-KI) solution containing saturated CaCl(2). The optical density of the amber-brown color was determined at 460 nm. Color development was immediate, stable for up to 2 h, and was linear with respect to glycogen concentrations up to 600 μg glycogen/ml. The iodine assay was applied to fresh, frozen, and aged bovine muscle samples and was compared to enzymic (amyloglucosidase) digestion of glycogen followed by glucose determination. The correlation between the iodine and enzyme methods was linear over the range of 0-1400 g glycogen/g tissue (corr = 0·875; P < 0·01; n = 172). The iodine binding assay can be employed with confidence as an indicator of tissue [glycogen] and is faster and more reliable than the enzyme assay. Comparison of the iodine enzyme assays on aged meat samples revealed marked decreases in muscle glycogen during the first 48 h post slaughter. The decreases were identical whether determined by iodine binding or enzyme assay. Regardless of assay method, post-mortem concentrations of glycogen in bovine sternomandibularis muscle were more variable than in longissimus dorsi samples.