The Effect of Freezing and Thawing During Storage on the Retinyl Ester: Retinol Ratio in Rat Liver

Abstract

The effect on rat liver vitamin A of repeated freezing and thawing and of continuous storage at −15 °C over a 7-week period was studied. Conversion of retinyl ester (RE) to retinol (ROH) began within 1 week in minced liver tissue held under either condition of storage. With intermittent freezing and thawing, the level of ROH reached a peak after 3 weeks of storage, after which time an apparent reesterification of the accumulated ROH to RE took place. In samples that were stored at −15 °C without interruption, the rise in ROH was even more pronounced. Reesterification was also noted in these samples only if they were allowed to thaw for 5 h before assaying for vitamin A.No artefact, analogous with that reported in stored plasma, and which reacts with trifluoroacetic acid to produce spuriously high vitamin A levels, appeared in stored liver tissue.