Optimisation of Baobab (Adansonia digitata) fruit processing and handling techniques for increased human nutrition and commercialisation in Malawi

The influence of thermal processing and preservation techniques on selected bioactive compounds of baobab fruit pulp and juice from Malawi were analysed using RP-HPLC whereas total phenol content (TPC) and antioxidant activity were measured by spectrophotometry. 1H NMR-based metabolomics was used to compare the metabolic profile of untreated (UT), high temperature short time (HTST) pasteurised and high temperature short time pasteurised with added citric acid (CAHTST) baobab juice samples and to analyse the temporal changes upon different storage conditions. Malawi baobab pulp contains high levels of procyanidin B2 (533.3 ± 22.6 mg/100 g FW), vitamin C (465.8 ± 2.5 mg/100 g FW), gallic acid (68.5 ± 12.4 mg/100 g FW) and (-)-epicatechin (43.0 ± 3.0 mg/100 g FW) and showed high TPC and antioxidant activity. Vitamin C content of dry baobab pulp and 10% juice (w/v) was retained during heat treatment by microwaving and pasteurisation (72 °C, 15 s) respectively. However vitamin C level in pasteurised juice significantly decreased during storage compared to untreated control, suggesting the demand for advanced processing methods including non-thermal pasteurisation. Seed liquor enhanced phenolic compounds in the juice but its influence on vitamin C needs further investigation. Principal Component Analysis (PCA) of 1H NMR data produced distinct clusters separated according to treatment and storage conditions. For HTST and CAHTST juice samples, the most important accumulating metabolites were fructose, glucose and galacturonic acid, while sucrose decreased over time. The more rapid production of ethanol in UT juice is a clear indication that pasteurisation of juice alone or in combination with the addition of citric acid can minimise fermentation in baobab juice. Results from this study will enhance understanding of composition of baobab fruit products and promote development of quality novel functional foods to tackle malnutrition as well as expand market opportunities for Malawi.