Improved sensitivity of freshness indicator based on purple sweet potato anthocyanins through pH optimization and its application in flesh food monitoring during logistics

Abstract

The practical application of freshness indicator has been greatly limited by complicated fabrication process and insufficient sensitivity. In this study, a novel pH colorimetric label was prepared by simple impregnation of non-woven fabrics in a solution composed of polyvinyl alcohol and purple sweet potato anthocyanins. The pH value of the impregnation solution was firstly optimized, and when the pH was 3.5, the label (3.5-PNP) showed the highest sensitivity towards volatile amines and stability. When applied in the shrimp packaging, 3.5-PNP label also displayed the Specialty highest total color difference (ΔE = 22.01) to indicate the spoilage of shrimp. The ΔE values of 3.5-PNP exhibited smaller variations in the packaging of fresh fish and pork (ΔE = 11.1 and 9.2) due to the reduced release rate of volatile amines from meat, indicating the considerate influence of the micro-environment inside the packaging on label sensitivity. However, the color changes of the label were still significant enough to be visible. The impact of transportation on the shrimp packaging was further investigated, revealing that the shelf life of the shrimp was shortened by 8 h after being transported for 150 min, while maintaining label sensitivity. A distinguishable color change (ΔE = 28.32) of 3.5-PNP label was observed when the shrimp spoiled. Therefore, this study developed a novel colorimetric label with simple preparation technique and promising sensitivity, and revealed the impact of the packaging micro-environment and road transportation on the sensitivity of indication label, offering valuable guidelines for practical application.