Lac dye-based intelligent colorimetric indicator for real-time freshness monitoring of packaged white button mushrooms (Agaricus bisporus)

The study aimed to develop an intelligent real-time freshness indicator for white button mushrooms by immobilizing the lac dye, a natural anthraquinone dye on filter paper. The indicator was characterized for its pH responsiveness; structural, mechanical, thermal properties; and color stability. During the freshness test, mushrooms were packed in punnet with an indicator placed in the package headspace and stored at two different temperatures (4 °C and 25 °C). Mushroom spoilage was monitored concurrently by indicator's color change, physicochemical indices, and volatile organic compounds (VOC) generated during storage. The FTIR results revealed that dye was immobilized on matrix via hydrogen bonding. A slight reduction in matrix crystallinity post dye immobilization was observed. However, the thermal and mechanical properties remained unaffected. Indicator showed good color stability during one month storage at 4 °C and 25 °C. The indicator changed its color from orange-red (at acidic pH) to purple (at alkaline pH) due to the inherent properties of lac dye. In the freshness test, the visual color change of indicator distinguished mushrooms into three stages: ' fresh', 'medium fresh', and 'spoiled'. Principle Component Analysis (PCA) validated the synchronization between color change of indicator and quality parameters. Partial Least Square (PLS) regression models derived from indicator's color parameter data successfully predicted the physicochemical indices of mushrooms stored at 4 °C. The lac dye-based indicators emerged as a novel and potential solution for non-destructive freshness monitoring of white button mushrooms.