Use of freshness indicators containing red beetroot and red cabbage extracts in monitoring shrimp freshness

This study aimed to develop natural extract-based freshness indicators for real-time monitoring of shrimp spoilage during refrigerated storage (4°C) for up to nine days. The indicators were composed of 1% (w/v) red cabbage or red beetroot extract, 2% (w/v) sodium alginate, and 10% (v/v) glycerol, and were incorporated into packaging materials. To assess shrimp quality and spoilage, pH, total volatile basic nitrogen (TVB-N), total mesophilic aerobic bacteria (TMAB), and total psychrophilic aerobic bacteria (TPAB) counts were monitored. The results showed significant increases in pH (from 7.52 to 7.88), TVB-N (from 20.3 mg/100 g to 44.80 mg/100 g), TMAB (from 3.72 log CFU/g to 7.29 log CFU/g), and TPAB (from 6.30 log CFU/g to 8.21 log CFU/g) confirming microbial spoilage. The spoilage threshold for TVB-N (35 mg/100 g) was exceeded on the fifth day, indicating the end of shrimp shelf life. Accordingly, the color change (ΔE) values of the indicators changed markedly over time: the ΔE value increased from 0 to 11.34 for the red cabbage-based indicator, while it decreased from 8.53 to 3.51 for the red beetroot-based indicator. The red cabbage-based indicator exhibited strong and statistically significant correlations with pH (r = 0.86, p = 0.029) and TVB-N (r = 0.83, p = 0.040), indicating high potential for freshness detection. In contrast, the red beetroot-based indicator showed weaker and statistically insignificant correlations. These findings suggest that natural extract-based freshness indicators, particularly those containing red cabbage extract, offer a promising and non-invasive alternative to conventional methods for monitoring shrimp spoilage and enhancing food packaging systems.