Moringa-Based Coating Preserves Organic Acids and Antioxidant Compounds of ‘Ester’ Granadilla Fruit Exocarps During Storage

The marketability of fresh granadilla (Passiflora edulis) fruit is significantly reduced by oxidation reactions occurring in its exocarp, which is not directly linked to the organoleptic quality of its arils. However, organic means of mitigating this are not topical in research. This study investigated the potency of moringa (Moringa oleifera)-based coating to preserve antioxidant compounds in granadilla. Physiologically mature fruit of equal size were assigned to a completely randomized design experiment at the North-West University Farm Laboratory. The fruit samples were coated with 2% xanthan gum (commercial coating), 2% moringa, or 2% rosemary coating and kept at shelf-life conditions (25 ± 2 °C; 40 ± 5%RH) for 5 weeks while sampling at weekly intervals. Correlations between the measured parameters were confirmed prior to regression analysis. Significant (p < 0.05) differences were observed in weekly changes in the exocarp pH, total antioxidant compounds (TAO), tartaric acid (TA), malic acid (MA), and citric acid (CA). At the end of storage, the moringa- and xanthan-coated fruit had the highest exocarp pH (7.8) and TAO (0.87 mg/g). Moringa-coated fruit had higher TA and MA (6.0 and 5.36 µg/g, respectively) as well as a significantly higher CA (0.51 µg/g) preserved than the other coatings. Strong correlations between MA and TAO (r > 0.82), as well as TA and TAO (r > 0.86), indicated the potency of developing TAO estimation models using multivariate data from the organic acids. Pre-processed data regression models were developed but were limited by the amount of data collected. Models developed similarly can be used for sustainable TAO assessment as a latent variable to minimize toxic waste that results from wet chemistry analyses.