Eco‐Sustainable Spearmint Essential Oil Nanoemulsion–Chitosan Coating Enhances Postharvest Quality and Phytonutrient Retention of “Tango” Mandarins ( Citrus reticulata )

Development of edible coating from a combination of chitosan (CH) polymer and nano (S) essential oil (EO) has gained commercial recognition for its safe and effective impact on fruit quality preservation over conventional chemical fungicides. Conventional chemical fungicides used for postharvest quality extension pose health and environmental concerns, driving the search for safer green alternatives. Hence, this study investigated the efficacy of an eco‐friendly CH‐based coating incorporated with spearmint (S) ( Mentha spicata ) EO nanoemulsion in maintaining postharvest quality and bioactive compounds of “Tango” mandarins ( Citrus reticulata) during cold storage. Five treatments, (i) uncoated control, (ii) chemical fungicide (imazalil, 250 g/L), (iii) CH (0.8%), (iv) (S)EO nanoemulsion (2%), and (v) combined CH (0.8%) loaded with (S)EO (2%) nanoemulsion coating were evaluated. Fruits were stored at 10°C and 85% RH for 28 days following a completely randomized design, with quality attributes and natural decaying ( Penicillium digitatum and Penicillium italicum ) assessed at 7‐day intervals. The combined CH + EO nanoemulsion treatment significantly ( p < 0.05) showed commercially acceptable weight loss (5%) and maintained higher firmness (12.5 N) compared to the control. Coating reduced the decay incidence of P. digitatum and P. italicum incidence with CH + EO nanoemulsion showing comparable efficacy to imazalil. Total carotenoid levels in the CH (0.8%) + (S)EO (2%) nanoemulsion treatment were significantly higher ( p < 0.05) between Days 14 and 28 compared with all other groups. This treatment also better preserved total soluble solids, titratable acidity, phenolic compounds (gallic, caffeic, protocatechuic acids, naringenin, and hesperidin), and antioxidant activity. These findings demonstrate the potential of CH–S nanoemulsion coatings as an eco‐sustainable postharvest strategy to extend shelf life and preserve nutritional quality of soft citrus (mandarins).