Integrating hypoxanthine and K value for reliable and rapid freshness assessment in marine fish

This study aimed to explore the relationship between hypoxanthine (Hx) levels and freshness indicators in three kinds of fish samples during storage for 7 days at 4 °C to determine the Hx levels indicating freshness. The total volatile basic nitrogen (TVBN) was tested using the semi-micro Kjeldahl method, and Hx level and K value were measured using high-performance liquid chromatography (HPLC). During storage, Hx levels, TVBN, and K values increased, and distinct patterns were observed between Hx and TVBN in three fish samples. The Hx level highly correlated with K value (Adj-R² = 0.998, 0.986, and 0.986) when K value was below 40 %. A paper biosensor was applied for Hx determination, the color of which correlated well with the K value, offering an easy, rapid and visual tool for predicting fish freshness. Thus, Hx can be used to predict K value and indicate freshness in some application scenario prior to spoilage.