Abstract
Marula (Sclerocarya birrea) grows well in the Sub-Saharan regions of Africa. It is among the most commercially utilized indigenous fruits in South Africa, mostly in the beverage manufacturing sector. During the production of secondary products such as jam, juice and alcoholic beverages, the by-products (peels) are discarded making them an underutilized part of the fruit. Orange (Citrus sinensis) on the other end is a citrus fruit making up approximately 60% of the total citrus world production and it is commercially grown worldwide. The Orange peels are commonly discarded during both domestic and industrial processing. These fruit peels have been reported to contain essential phenolic compounds such as flavonoids and phenolic acids. Phenolic compounds in the peels, have been found to assist in lowering the incidence of cardiovascular diseases and cancer. Thus, demonstration their potential as antioxidants even for food application, diabetes, cancer, hypertension, obesity and cardiovascular diseases. These compounds are highly affected by extraction methods, thus close attention was also given to the method of extraction used to extract polyphenolic compounds which were used to stabilize salad dressing samples.
The Marula and Orange peels were extracted by soxhlet extraction (making use of methanol as a solvent) and fractionation (using water as a solvent). The extracts were then analysed for their Total Phenolic Content (TPC), Total Flavonoid Content (TFC), antioxidant activity, phenolic composition as well as their molecular fingerprint (organic and inorganic molecules) through Fourier Transform Infrared Spectroscopy (FTIR). The study found significant differences (p < 0.05) in the TPC, TFC and antioxidant activity between soxhlet and water extracted Marula and Orange peel samples. Generally, water extraction resulted in the lowest TPC of 473.66 mg GAE /100 g whereas soxhlet extraction resulted in the highest TPC of 625.00 mg GAE/100 g. Marula peel (751.00 mg GAE /100 g) had a TPC significantly (p < 0.05) higher than that of Orange Peel (348.17 mg GAE /100 g). For the characterization and quantification of the polyphenolic profile of the extracts UPLC–MS was used. UPLC-MS data on the different polyphenol classes were therefore recorded for both Marula and Orange peel extracts. The Marula peel consisted of polyphenolic compounds not only made of phenolic acids but also of flavonoids (Procyanidin dimer B1 and Procyanidin dimer B2) and non-phenolic organic acids such as quinic, and citric...
M.Tech. (Food Technology)