Effect of moringa oleifera leaf powder extracts on the browning, nutritional and storage qualities of dried granny smith apple slices

Abstract

This study aimed to determine the effect of the Moringa oleifera leaf powder (MOLP) extracts on the browning, nutritional, and storage qualities of dried granny smith apple slices. The MOLP extracts were prepared by maceration with the assistance of ultrasound extraction to ensure maximum bioactive compounds using methanol (MOME), ethanol (MOET), water (MOAQ) and acetone (MOAC). The obtained extracts were freeze-dried and subjected to bioactive compound profiling using liquid chromatography-mass spectrometry (LC-MS). The extracts were also evaluated for antioxidant activity in terms of FRAP, DPPH, ORAC and ABTS. Thereafter, the anti-tyrosinase activity of MOLP extracts with PEG-6000 as a hydrophilic carrier was examined for IC50 . The IC50 of all MOLP extracts was used to determine the concentration of the treatment complex for the dried apple slices. For the anti-browning treatments, each extract (MOME, MOET, MOAQ, MOAC) was separately prepared at upper (0.3%), mid (0.03%) and low (0.003%) concentrations in combination with 2% citric acid to determine the effectiveness of each extract on the colour attributes of the dried apple slices. Thereafter, the pre-treatment solution with a strong IC50 effect on the colour of the dried apple slices was selected for treatment of the dried apple slices to determine its impact on the proximate composition, and physicochemical properties. The storage stability of the dried apple slices treated with the 0.003% MOAQ anti-browning mixture was investigated through the analysis of physicochemical properties such as water activity, moisture, extensibility, and colour. The pre-treated dried apple slices were subjected to 35°C accelerated conditions and the first order reaction kinetics was used to determine the shelf-life with an assumed Q10 of 3. The MOLP extracts showed 23 bioactive compounds such as phenolic compounds, flavonoids, amino acids, quinones and fatty acids. The MOME extract showed a higher number of phenolic compounds, especially flavonoids than other MOLP extracts. A dose-dependent antioxidant activity was observed for all the extracts; however, the MOME and MOET extracts had a significantly (p = 0.001) higher antioxidant activity than the MOAQ and MOAC extracts. Furthermore, 34.66 (MOAQ) to 71.29 μg/ml (MOET) was observed for IC50 of all the MOLP extracts against tyrosinase. The MOAQ was significantly (p = 0.001) stronger (IC50 = 34.66 μg/ml). Moreover, the samples treated with the 0.003% MOAQ anti-browning mixture were significantly (p = 0.001) lighter, yellower, and greener than the control and other MOLP anti-browning mixtures. The ash, vitamin C and total fat content of the MOAQ-treated samples was higher than the control. The MOAQ-treated apple slices demonstrated an increase in extensibility (p = 0.001). Furthermore, the estimated shelf life of MOAQ-treated apple slices was 153 days compared to the control (126 days) at 25oC.The finding of this study suggest that the Moringa oleifera leaf powder aqueous extract (MOAQ) is a promising preservative in dried fruits by highlighting its potential for reducing browning, maintaining acceptable colour attributes, and preserving the dried apple slices.