Storage Fungi Occurrence in Roselle (Hibiscus sabdariffa) Calyx and Effects on it’s Composition

Abstract

Roselle (Hibiscus sabdariffa) is a tropical plant grown mainly for its vibrant red calyces used in making herbal teas and beverages rich in antioxidants and vitamin C. However, global production of roselle is greatly hampered by severe fungi attack especially at post-harvest stage. This study therefore, investigated the incidence, pathogenicity, and effects of various fungal species on the quality of Hibiscus sabdariffa (zobo) calyx. Samples of infected roselle calyx were collected from Ubani and Ndoro markets located in Umuahia and Ikwuano LGA, respectively in Abia State. Fungi isolation from the infected samples was done using standard procedures. Proximate, mineral and vitamin composition of fungi inoculated roselle samples were done using AOAC procedures. Experiments were laid out in CRD in triplicates. Data were analysed using ANOVA at α0.05. Fungi species including Aspergillus (A. flavus, A. niger), Rhizopus sp., and Fusarium sp. were isolated from zobo samples. Among these, A. niger exhibited the highest incidence (51.39 %), followed by Fusarium sp (28.01%), A. flavus (17.13 %), and Rhizopus sp. (3.47 %). Pathogenicity tests revealed that A. niger and Rhizopus caused 100 % rot in the zobo samples, while A. flavus and Fusarium sp caused 90 % rot. Zobo samples inoculated with sterile water (control) had significantly higher minerals: than those inoculated with fungi. The control samples exhibited the highest concentrations of iron (0.0046 mg/100g), Β-carotene (0.0058 mg/100g), K (1.5250 mg/100g), Ca (0.2600 mg/100g) and vitamin A (4.2800 mg/100g), Vitamin C (2.3550 mg/100g), while fungal-inoculated samples had reduced nutrient levels iron (0.0300-0.0415 mg/100g), Β-carotene (0.0035-0.0051 mg/100g), K (0.9650-1.1300 mg/100g), Ca (0.1400-0.2200 mg/100g), C (1.1650-1.1800 mg/100g) and Vit A (2.4750-3.1400 mg/100g). The proximate composition of zobo calyx was influenced by fungal contamination. Control had the higher ash (1.76 %) and crude fibre (2.68 %) contents than the fungi inoculated samples. Control had the least moisture (12.27 %) content compared to the fungi inoculated roselle (12.68-14.06 %). This study highlights the negative impact of fungal contamination on the nutritional and proximate composition of zobo calyx, emphasizing the need for their control.