Development of a pH indicator for monitoring the freshness of minced pork using a cellulose nanofiber

A cellulose nanofiber (CNF)-based pH-sensitive indicator was developed by mixing CNF with red radish color extract (RRCE) to analyze the freshness of minced pork. Among various mixing conditions of RRCE solutions (0.4–1.6%) and CNF (0.5–1.25%), 0.8% RRCE/1% CNF showing higher mechanical properties, lower response to water, lower leakage of RRCE, and higher sensitivity to ammonia was selected as optimum. Ultraviolet–visible light transmittance and structural properties of the film indicated successful incorporation of RRCE into CNF, with rapid response to changes in pH caused by ammonia solution. The water vapor permeability of the indicator was maintained for 48 h. The fabricated pH-sensitive indicator showed apparent color changes from red color (fresh) to purple color (spoiled) during pork storage at refrigeration temperature. In addition, the deterioration degree was compared by measuring pH, microbial counts, and total volatile base-nitrogen level, confirming the applicability of this CNF-based film as a pH indicator.