Factors Affecting the Stability of Supplemental Ascorbic Acid in Practical Trout Diets

Abstract

The stability of L-ascorbic acid in practical trout diets that had been processed by several different methods was investigated. Coated ascorbic acid was more stable to autoclaving than the fine-powdered form, but losses due to water addition, "cold" pelleting, and drying were approximately 90% with or without first autoclaving the diet. Increasing the level of supplemental coated ascorbic acid increased absolute losses but permitted retention of a significant level in the feed for a longer period of time. The shelf life of processed trout diets is dependent on the type of processing, storage temperature, and moisture content of the diet. Laboratory-processed diets stored at room temperature lost all the supplemental ascorbic acid within 6 wk. Commercially processed diets had less processing losses than the laboratory-processed diets, but storage losses were still severe. Freezer-stored diets had minimal losses while diets stored at room temperature were below NRC requirements after 5 wk (steam-pelleted diet) and below this level after 8 wk (extruded diet) when both were initially supplemented with 400 mg/kg feed. Key Words: ascorbic acid, trout diets, vitamin stability, processing stability, storage stability, vitamin requirements trout