Evaluation of the effect of manihot esculenta edible coating incorporated with ocimum gratissimum essential oil on the shelf-life of fresh mangifera indica

Abstract

Fresh produce often suffers from post-harvest spoilage losses. From the 2020 post-harvest losses report in Kenya, about 512,000 metric tons of mangoes were lost. Continued use of chemical preservatives for regulation of postharvest deterioration and prolonged shelf- life has led to pathogen-resistant strains, harmful effects on human health and the environment. The general objective of this study was to evaluate the antibacterial and antioxidant efficacy of M. esculenta (CS) edible coating modified with O. gratissimum (African basil) leaves essential oil for the improvement of the shelf-life of fresh Mangifera indica (mango) fruit. The specific objectives of the study were to: investigate the phytochemical composition of Manihot esculenta tubers and O. gratissimum leaves crude extracts; prepare and modify M. esculenta edible coating using 0.5%, 1%, and 1.5% O. gratissimum essential oil; characterize the modified and unmodified coating; determine the antioxidant and antibacterial activity of the modified coating, and establish the shelf-life of coated mango at room temperature (23 ± 2 °C). Serial maceration method using hexane, ethyl acetate, acetone, and methanol as solvents were used for extraction. Standard methods were used to determine the phytochemical components. Preparation and modification of the coating were homogenized at 70 ± 2 °C. Ultraviolet-Visible (UV- Vis) Spectrophotometry, Fourier Transform Infrared (FT-IR) Spectroscopy, and Gas Chromatography-Mass Spectrometry (GC-MS) were used for characterization. Physico- chemical parameters including weight loss, titratable acidity (TA), Vitamin C concentration, total soluble solids (TSS), and pH were used to establish the fruits’ shelf- life. The antibacterial activity of the modified coating and antioxidant activity were determined by the agar disc diffusion method and a 2,2-diphenyl-1-picrylhydrazyl (DPPH) assay respectively. Phytochemical screening results indicated the presence of alkaloids, flavonoids, terpenoids, phenols, and tannins. The UV-Vis spectra of the coatings showed absorbance in the spectral range between 300 nm and 600 nm, while the FT-IR spectra showed peaks at 3400 cm -1 (OH), 2929 cm -1 (C-H stretch), 1586 cm -1 (C=C stretch), and 1150 cm -1 (C-O stretch). GC-MS analysis of O. gratissimum oil identified a total of 22 compounds with 2-Octen-1-ol, (Z) (26.66%) as the major compound. The % DPPH inhibition of the modified coating at 0.5%, 1.0%, and 1.5% were 24.73 ± 1.2, 39.74 ± 0.4, and 51.72 ± 0.8% respectively. The antibacterial activity of the modified coating (1.5%) showed the most significant (P<0.05) inhibitory effect of 22.22 ± 0.03 and 17.53 ± 0.28 mm on Staphylococcus aureus and Escherichia coli respectively. The modified coating (1.5%) maintained TA (0.66%), reduced weight loss by 27.81%, delayed the increase of TSS (7.50%) and pH 5.20 while retaining the vitamins C (8.13 mg/100g concentration) up to 18 days of storage at room temperature (23 ± 2 °C). The distilled water treatment (control) reduced TA to 0.11%, increased weight loss to 47.12%, TSS to 20.22%, and to pH 8.21 while retaining the vitamin C to 3.74 mg/100g concentration. In conclusion, modified M. esculenta coating showed remarkable antibacterial and antioxidant activities with a shelf-life of 18 days for coated fruit as compared to 9 days for the uncoated one. Modified M. esculenta edible coating is recommended for preserving fresh produce while maintaining their physico-chemical qualities during storage.