Edible Coatings of Calcium Chloride and Carrageenan Mitigate Chilling Injury and Maintain Quality of Red-Fleshed Pitaya (Hylocereus polyrhizus) during Cold Storage

Abstract

Red-fleshed pitaya (Hylocereus polyrhizus), is a non-climacteric fruit esteemed due to its vivid red-purple colouration and high antioxidant content. This fruit is prone to rapid deterioration and chilling injury during low-temperature storage. Thus, the study evaluated the efficacy of three edible coating treatments: calcium chloride (CaCl₂, 3% w/v), carrageenan (0.5% w/v) and a combined formulation consisting of 1% CaCl₂ + 0.5% carrageenan on the visual quality and phytochemical attributes of H. polyrhizus stored at 10°C and 85-90% relative humidity for 20 days. Fruits were assessed at five-day intervals for visual quality, total betacyanin content, total phenolic content (TPC) and antioxidant activity using 2,2-diphenyl-1-picrylhydrazyl (DPPH) and 2,2’-azino-bis (3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) assays. The combined CaCl₂-carrageenan coating most effectively maintained peel integrity and reduced chilling injury exhibited through minimal scale browning and dehydration up to day 20 in comparison with the control. In contrast, fruits coated with 3% calcium chloride (CaCl₂) retained significantly higher (P≤0.05) betacyanin levels (0.72-0.85 mg/g) during mid-storage than those coated with carrageenan or the combined formulation (0.47-0.54 mg/g), indicating the more prominent role of calcium in pigment stabilization. TPC was also better preserved in coated fruits (0.013-0.016 mg GAE/g), whereas uncoated fruits exhibited a significant decline (0.009-0.010 mg GAE/g) by days 5 and 10, demonstrating rapid phenolic degradation without protective coatings. Antioxidant activity (DPPH) was highest (P≤0.05) in fruits coated with carrageenan (53.47%) and CaCl₂ (48.95%), while carrageenan also produced greater ABTS inhibition (16.58%) when compared with uncoated fruits (13.92%). However, the combined coating showed reduced antioxidant retention, this was possibly due to antagonistic interactions in the composite coating. Overall, single component coatings (CaCl₂ or carrageenan) were more effective for preserving antioxidant properties, whereas the combined formulations better maintained external visual quality and chilling-injury resistance during prolonged cold storage. Edible coatings thus represent a sustainable postharvest strategy for extending the shelf life and nutritional quality of pitaya during cold chain distribution.