Value addition of Southern African monkey orange(Strychnos spp.) : composition, utilization and quality

Abstract

Monkey orange (Strychnos spp.) is a widely distributed fruit species in Southern Africa commonly consumed by the local population. It has potential to improve the nutritional status of rural populations, being a precious food source in areas with periodic shortages. The present thesis focused on optimization of indigenous processing of S. cocculoides to reduce fruit losses and contribute to food security and livelihoods of vulnerable rural communities in the production areas. Based on an extensive literature review, monkey orange was found to be rich in vitamin C (88 mg/ 100 g), Zn (28 mg/100 g) and Fe (140 mg/100g) and is consumed as fresh or processed as an ingredient to other food products by the local population. A survey conducted in the wet and dry regions of the country showed that most of the fruits and their products are wasted because of limited harvest time, process control and storage conditions, leading to variability in shelf life and sensory quality, thereby impacting nutritional quality. S. cocculoides and S. spinosa juice were used by the majority of respondents as a functional ingredient in maize porridge production. The major constraint to be solved are seed-pulp/juice separation for optimization of juice extraction. Enzymatic treatments were done to improve pulp and juice yield. Prior to treatments, a total of 16 known phenolic compounds predominantly belonging to the phenolic acids, flavonoids and iridoid glucosides classes were tentatively characterized for the first time in S. cocculoides using HRMS and LC/MS/MS to confirm iridoid presence. Overall, the results showed that enzymatic treatments increased pulp yield by 26 % , physicochemical quality (38 % increase in juice clarity), content of phenolic compounds (kaempferol, quercetin, caffeic acid, protocatechuic acid, IGs) and antioxidant activity. The effect of using juice macerated with and without enzyme on the bioaccessibility of main phenolic compounds and micronutrients was assessed during in-vitro digestion together with the kinetic of starch degradation in the maize porridge. Chlorogenic, caffeic and protocatechuic acids had more than 100 % after simulated intestinal digestion phase. Rutin was undetected after the simulated intestinal phase owing to precipitation in the pellet. In vitro bioaccessibility of minerals ranged from 12 – 62 % in monkey orange enriched porridge. A 50-70% decrease of starch hydrolysis was observed at the end of simulated intestinal digestion of monkey orange maize porridge confirming the potential of phenolic compounds to decrease the glycaemic index of starch rich foods. Results suggested monkey orange juice as a suitable ingredient to enrich staple maize porridge thanks to its micronutrients value and the health benefits potential. In addition consumers did recognise the difference in ingredients used for porridge processing though products were equally liked in preference tests. In conclusion, the optimization of juice extraction is essential for reduced juice and pulp losses as well as increase the bioaccessibility of nutrients and phenolic compounds when used as an ingredient in food products. Furthermore, the use of monkey orange fruit in starch based product presents a new direction in future work on reduction of starch hydrolysis for staple food products commonly consumed in Africa. The work from this thesis shows areas of further research on monkey orange potential to improve human health and nutritional problems in Zimbabwe. Thus, improving food use for food security as well as provision of some solutions to nutritional problems in sub-Saharan Africa.