Effects of citrus wax coating and brush type on imazalil residue loading, green mould control and fruit quality retention of sweet oranges

• Published in: Postharvest biology and technology Vol. 86; pp. 362 - 371
• Main Authors: Njombolwana, Ncumisa S., Erasmus, Arno, van Zyl, J. Gideon, du Plooy, Wilma, Cronje, Paul J.R., Fourie, Paul H.
• Format: Journal Article
• Language: English
• Published: Kidlington Elsevier B.V 01.12.2013; Elsevier
• Subjects: Biological and medical sciences; Carnauba; Citrus; Citrus sinensis; Food industries; Fruit and vegetable industries; Fundamental and applied biological sciences. Psychology; Fungal plant pathogens; Horsehair; Morpholine-free; Penicillium digitatum; Phytopathology. Animal pests. Plant and forest protection; Polyethylene; Synthetic; Penicillium digitatum; Morpholine-free; Carnauba; Polyethylene; Synthetic; Horsehair; Production quality; Citrus sinensis; Fruit; Rutaceae; Alteration; Retention; Wax; Fungi; Residue; Dicotyledones; Angiospermae; Spermatophyta; Mould; Fungi Imperfecti; Coating
• ISSN: 0925-5214; 1873-2356
• DOI: 10.1016/j.postharvbio.2013.07.017

•Imazalil and coating resulted in residues in sweet oranges that increased with increasing coating load.•Poor curative control and improved protective control was obtained.•Horsehair brushes resulted in less sporulation than synthetic brushes.•Less fruit weight loss and firmness loss was found with carnauba coating and shinier fruit with polyethylene coating.•Scanning electron microscopy showed uncovered stomatal pores in uncoated fruit. Wax application plays an important role in prolonging fruit quality, and the addition of imazalil (IMZ) furthermore protects fruit against green mould caused by Penicillium digitatum. The objectives of this study were to evaluate green mould control and quality preservation effects of carnauba or polyethylene citrus coatings supplemented with IMZ, as well as the effect of synthetic or horsehair brush types used on sweet orange fruit. Single applications of IMZ at 3000μgmL−1 at rates of 0.6, 1.2 and 1.8Lt−1 resulted in residues that increased with increasing coating loads on navel oranges (1.31 to 3.32μgg−1) and Valencia oranges (3.22 to 6.00μgg−1). Coating with IMZ generally provided poorer curative control (≈14%) than protective control (≈58%), with less sporulation in treatments using horsehair (≈59%) than synthetic brushes (≈64%). More fruit weight and firmness losses were found in fruit treated with the polyethylene coating (≈1.18 and ≈0.93 ratios of treated vs. untreated, respectively) and lower in carnauba treated fruit (≈0.76 and ≈0.74 ratios, respectively). However, polyethylene coatings resulted in shinier fruit before (≈10.85 shine ratio) and after storage (11.60), whereas carnauba coatings resulted in lower shine ratios (≈7.45 and 10.15, respectively). Gas (CO2) exchange ratios remained similar for both waxes (≈0.67). Higher polyethylene coating loads (1.8Lt−1) resulted in off-tastes similar to uncoated control fruit (≈2.21 rating on a 5-point scale) and higher than the rating for carnauba coated fruit (≈1.82) at this rate. Scanning electron micrographs showed an amorphous crystallised natural wax layer with uncovered stomatal pores on the surface of uncoated fruit. The thickness of the applied wax layer increased with increasing coating load. A single application of IMZ in wax provided good protective green mould control and sporulation inhibition, with differing effects on some fruit quality parameters due to coating and brush types.