Colorimetric hydrogel indicators based on polyvinyl alcohol/sodium alginate for visual food spoilage monitoring

A colorimetric pH-sensitive hydrogel indicator integrated with the smartphone for real-time and visual food spoilage monitoring was developed. Herein, the poly(vinyl alcohol)/sodium alginate (PVA/SA) hydrogel was used as the carriers for the pH-sensitive mixed-dye methyl red/bromothymol blue (MR/BB), which can be employed as an amine indicator. The functional hydrogel was prepared by a simple freezing/thawing process that mainly performed in PVA and calcium cross-linking in SA. The optimal condition for the sensitivity of hydrogel towards ammonia and the structure of the hydrogel were investigated. The potential applications of the hydrogels in beef, fish, chicken and pork were evaluated under different storage conditions. Sigmoidal fitting results indicated that the RGB model with a smartphone can form a strong correlation with the total volatile basic nitrogen (TVB-N) values in common meat products. The hydrogel indicators with sensitive and stable properties have proven to be promising materials for use in food spoilage monitoring.