Guwahati: Mandarin oranges, with their vibrant hue and sweet citrus aroma, are among the widely cultivated fruits in India. Their popularity extends beyond domestic markets, reaching global consumers who prize their juiciness and nutritional benefits. However, these delicate fruits face a major challenge—rapid post-harvest deterioration.
Within one to two weeks of harvest, mandarins suffer significant weight loss, fungal infections, and a decline in overall quality, making them difficult to store and transport. This results in substantial financial losses for farmers and exporters, as nearly 60% of mandarins can spoil before reaching consumers.
Mandarin orange (Citrus reticulata) is the most common citrus fruit grown in India. It occupies nearly 40% of the total area under citrus cultivation in India. The maximum genetic diversity is seen in the Northeast part of the country.
Determined to address this issue, a team of researchers from the Central Institute of Technology, Kokrajhar, led by Dr. Santosh Kumar, Assistant Professor in the Department of Food Engineering & Technology set out to develop an effective and natural solution to extend the shelf life of mandarins while maintaining their freshness and glossy appeal. Their study published in Food Chemistry: X, an Elsevier Journal, focused on edible coatings—thin, protective layers applied to fruit surfaces to slow down moisture loss and prevent microbial decay.
“Postharvest deterioration in mandarins causes huge economic losses to farmers and growers, which can be minimised using edible coatings, a sustainable alternative to petroleum/paraffin waxed-based coatings causing adverse impacts on human health and environment,” Dr Santosh Kumar, Assistant Professor in the Department of Food Engineering & Technology at Central Institute of Technology Kokrajhar who is the corresponding author of the study told EastMojo.
The team turned to two natural waxes: carnauba wax and shellac. Carnauba wax, derived from the leaves of the Brazilian palm tree, is known for its water-resistant and glossy properties, often used to coat fruits like apples and mangoes. Shellac, a resin secreted by the lac insect, creates a firm barrier that reduces oxygen exposure, slowing down senescence and preserving texture.
“Carnauba wax and shellac-based fruit coatings serve a dual purpose, they not only act as a protective barrier, preventing water evaporation and fungal decay, but also enhancing the visual glossy appeal of the fruits”, Kumar said.
While these waxes alone offer some level of protection, the researchers sought to enhance their effectiveness by incorporating carvacrol nanoemulsion (CNE)- a plant-based antimicrobial agent derived from oregano essential oil, recognised for its strong antifungal and antibacterial properties.
“Carvacrol, a compound in oregano essential oil, is recognized for its strong antimicrobial and antioxidant properties. However, carvacrol faces challenges such as instability, poor solubility in water, and is susceptible to degradation upon exposure to light, oxygen, humidity, or higher temperatures, which limits their use as antifungal, antibacterial and antioxidant agents,” Kumar said, adding that to address these limitations, as well as to make it more effective antimicrobial agents, the nano-emulsions of carvacrol has been prepared using ultrasonication method.
The study involved the formulation of five different coatings, each containing varying concentrations of waxes and carvacrol nanoemulsion. Freshly harvested mandarins were carefully dip-coated with these solutions and stored at ambient conditions for 30 days, mimicking real-world storage and transport scenarios.
The obtained results were remarkable. The mandarins coated with a blend of carnauba wax, shellac, and 2% carvacrol nanoemulsion (CNE) exhibited the best preservation. After a month, these coated mandarins retained their firmness (12.06 N) and experienced only 19.23% weight loss, a drastic improvement compared to the 51.93% loss in uncoated fruits. They also maintained a desirable total soluble solids content of 16.1°Brix, ensuring the fruit remained sweet and flavorful. Additionally, titratable acidity remained at 1.56%, preventing the mandarins from turning bland or overly soft.
Beyond physical attributes, the coating also proved highly effective in preventing fungal decay. While uncoated mandarins exhibited severe spoilage by day 15, with a decay index of nearly 5%, the coated fruits remained largely unaffected, with only a 1.13% decay index after 30 days. Microbial tests further confirmed that yeast and mould counts were significantly lower in the coated samples, showcasing the protective power of carvacrol-infused wax.
The impact of this innovation was further validated through sensory evaluations. Trained panellists assessed the coated mandarins for appearance, texture, and overall acceptability. The fruits treated with the optimized coating maintained a high sensory score of 5.83 even after 30 days, indicating that the natural coating preserved not only shelf life but also the fruit’s consumer appeal.
Kumar said this breakthrough is a game-changer for citrus farmers and exporters. By using a natural, cost-effective alternative to synthetic preservatives, they can significantly reduce postharvest losses while meeting global consumer demand for chemical-free, sustainable produce. The study also highlights the potential for large-scale adoption, as carnauba wax, shellac, and carvacrol are already recognized as safe for food applications by the US FDA.
With further refinement and commercialization, this natural wax-based coating could transform postharvest management in the citrus industry, improving supply chain efficiency and increasing profitability. The research not only provides a scientific solution to a longstanding problem but also offers hope to farmers seeking practical, eco-friendly ways to extend the market life of their produce.
“This method is scalable and cost-effective. It is a cost-effective method; it will cost about 50 paise to coat 1 kg of mandarins” he said.
By harnessing the power of nature, this innovative edible coating could redefine fruit preservation, ensuring that more mandarins reach consumers in their freshest, most flavorful state—one golden fruit at a time.
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