Natural propolis-based coatings as an effective strategy to control microbial growth and quality losses of kiwifruit during cold storage

Background: this study investigated the effects of ethanol-extracted propolis applications on the quality characteristics, microbial growth, and microstructural changes of kiwifruit (Actinidia deliciosa) during cold storage. Four different application groups were created: control, 70% ethanol application (ETH), 3% propolis coating (PRO1), and 6% propolis coating (PRO2). After dip coating, the fruits were stored for 150 days at 0 ± 0.5 °C and 90 ± 5% relative humidity, and analyses were performed on days 0, 30, 60, 90, 120 and 150. During storage, weight loss, respiration rate, fruit firmness, color, soluble solids content (SSC), titratable acidity (TA), vitamin C, total phenolics, total flavonoids, antioxidant activity (DPPH and FRAP assays), individual phenolic compounds, and microbial growth were determined in fruit samples. In addition, microstructural changes on the fruit surface were examined using scanning electron microscopy (SEM), and the elemental surface composition was determined using energy dispersive X-ray spectroscopy (EDX). Results: propolis coating applications maintained the quality characteristics of kiwifruit during storage. In particular, PRO1 and PRO2 reduced weight loss and respiration rate, better preserved fruit firmness, and maintained more stable color parameters. Propolis coatings also contributed to the preservation of ascorbic acid, total phenolic compounds, and total flavonoids, ensuring that antioxidant activity remained at higher levels throughout the storage period. Microbiological analyses showed that propolis coatings markedly reduced total bacterial counts on the kiwifruit surface, indicating their potential to limit microbial contamination during cold storage. SEM images showed that propolis coatings formed a homogeneous film layer on the fruit surface and limited microbial colonization by sealing surface pores. EDX analyses showed treatment-dependent changes in the surface elemental composition of kiwifruit peel, whereas SEM observations confirmed the formation of a continuous propolis-derived surface layer. Conclusions: overall, ethanol-extracted propolis coatings reduced total bacterial counts and quality losses in kiwifruit during cold storage and may serve as an effective natural preservative for extending cold-storage life. This journal is