The Feasibility of Using the Degree of Aspartic Acid Racemization as an Indicator to Improve the Evaluation of Fish Meal Protein Freshness

Fish meal is the main protein source in aquatic feed. However, L-amino acids of fish meal protein are easily racemised into D-amino acids during processing. Isomer formation often is caused in fish meal by acid, alkali or heat treatments commonly used in the manufacturing process. Many kinds of D-amino acids are adverse or toxic for animal nutrition. They can damage cell function or reduce animal growth capacity and are hazardous to the reproductive health of the fish. In heat or alkali treatments, aspartic acid is one of the most sensitive of amino acids to racemize. So, an effective evaluation index of fish meal protein nutritive value can be the content of D-Asp in the fish meal. This paper introduces conventional fish meal freshness indicators and their existing problems. The degree of aspartic acid racemization is expounded as a method of evaluating fish meal protein freshness. The paper presents an innovative freshness evaluation index; and then summarizes the relationship between D-Asp content and fish meal nutritional value in order to set forth the feasibility that a valuation of the freshness of fish meal can be established by the degree of aspartic acid racemization.