Ecofriendly colorimetric indicators for freshness monitoring of sliced mango fruit ( <i>Mangifera indica</i> L.)

Abstract Due to damage from minimal processing, fresh-cut produce like mango deteriorates more rapidly than an undamaged product. One of the latest cutting-edge packaging technologies, colorimetric intelligent packaging, has the potential to monitor food conditions and alert users to any changes. This study focused on developing and analyzing pH-sensitive freshness indicator labels for packed fresh-cut mango fruit. Three different types of indicators were created using chitosan as a binder, cellulose (filter paper) as a carrier, and anthocyanin [from red cabbage at 100% (RC 100%), butterfly pea flower at 100% (BP 100%), and butterfly pea at 50% (BP7)] as indicators. Sliced ‘Keitt’ mango fruit was stored in polyethylene plastic clamshells with indicator labels at room temperature (20 ± 2 °C and 40 ± 4% relative humidity). Each day, the colour of the indicators, response to pH buffering solution and fruit properties such as pH, color, weight loss, firmness, total soluble solid, total acid content, browning index, microbial load, and total sugar-to-acid ratio were measured. The results showed a significant colour change in the butterfly pea indicator (BP indicator) in relation to the freshness of the sliced mango. By the second day of storage, the fruit quality parameters had deteriorated beyond the spoilage threshold. With this, the total colour difference was measured at 23.12 ± 3.61, transitioning the BP indicator from slightly red to blue. Additionally, there was a significant decline in values for all fruit qualities during this storage day. This study illustrated that the anthocyanin from butterfly pea flowers stabilized in filter paper with chitosan is an easy-to-use and promising indicator for monitoring the freshness of packaged sliced mango fruit. Significance of this study What is already known on this subject? The freshness of fresh meals is currently being tracked using pH-sensitive intelligent indicators. What are the new findings? Sliced mango fruit freshness was tracked using eco-friendly pH intelligent indicator packaging made from butterfly pea flower anthocyanin, stabilized with chitosan and infused into filter paper. What are the expected impacts on horticulture? Eco-friendly pH intelligent indicators could be used by sliced mango fruit users in horticulture sectors to check the fruit’s freshness for food security, safety, and minimizing fruit postharvest loss. Plain language summary Freshness monitoring of sliced mango fruit ( Mangifera indica L.) using eco-friendly, pH-sensitive and colorimetric intelligent indicators. Introduction The highly perishable nature of sliced mango fruit may necessitate the use of intelligent indicator packaging technologies for safety checks. Eco-friendly intelligent indicators could be created using natural dyes and organic biopolymers. Cellulose is a biopolymer with exceptional mechanical properties; cellulose filter paper could be used to carry intelligent indicators; anthocyanins are natural, safe dyes. For instance, red cabbage and butterfly pea can change their clear hue with a change in pH. Therefore, indicators were tested using filter paper, anthocyanins from red cabbage, and butterfly pea to check the freshness of cut mango fruit at 20 ± 2◦C and 40 ± 4% relative humidity. In addition, linkages between indicators and fruit quality parameters were examined. Methods Mangoes cv. ‘Keitt’ used Intelligent indicators Three indicators were developed from filter paper and anthocyanin from butterfly pea flower at 100% (BP), butterfly pea flower at 50% (BP7) and red cabbage at 100% (RC) For sample preparation, 150 g of cut mangoes were kept in polyethylene terephthalate trays with indicators and stored at 20 ± 2 °C and 40 ± 4% relative humidity for 3 days. Measurements The indicators’ and fruit qualities were statistically analysed. Results BP indicator is superior; at low pH, it is red, at 4 slightly red, and between 5 and 6, it shows blue colour. On storage day 2, the BP indicator showed a higher total colour difference of 23.12 ± 3.61, and the colour shifted from slight red to blue and started to spoil. Fruit quality parameters such as pH, total acid, firmness, and weight reduced, while total sugar, microbes, yeast, and mold increased in 1 day. Conclusions Butterfly pea indicator (BP indicator) effectively assessed the freshness of sliced mango fruit. After 1 day of storage, the fruit began to spoil. BP indicator could be further used for fruit freshness monitoring application.