Non-destructive sensing of the freshness of packed cod fish using conductivity and pH electrodes

The use of pH and conductivity electrodes as non-destructive methods for monitoring changes in the freshness status of packed fish is explored. The electrodes monitor changes in the electrical properties of an aqueous phase positioned in the headspace of the fish package. Volatile compounds produced in/ on the packed fish and released in the headspace dissolve into this aqueous phase. Several compounds affect the electrode signals. The signals of the electrodes were compared with the volatile amines content of fresh cod fillets stored at 0–15 degrees C. The changes in the pH signal were strongly temperature dependent and not suitable as quality indication for practical storage temperatures. The conductivity signal showed a characteristic pattern, that correlated with the increasing volatile amines content at all temperatures. The non-destructive measurement of conductivity establishes the proof of principles for monitoring the freshness of packed fish and paths the way towards new developments of intelligent packaging concepts