Effects of processing techniques on the glucosinolate and isothiocyanate content of malunggay (moringa oleifera) and determination of its antioxidant activity

Glucosinolate (GSL) and isothiocyanate (ITC) are biologically active compounds of malunggay (Moringa oleifera), known for their chemotherapeutic potential. This research determined the effect of boiling, steaming, blanching, microwaving, and stir-frying on the glucosinolate and isothiocyanate concentrations, as well as their effect on the antioxidizing properties of malunggay leaves and seeds. The glucosinolate concentration of the desulfated raw and processed. oleifera leaves and seeds were quantified using an HPLC. Overall, malunggay seeds (48.63-335.28 µmol/g) were shown to contain a greater glucosinolate concentration than malunggay leaves (03.06-76.41 µmol/g), with steamed malunggay seeds and raw malunggay leaves having the most GSL retention, respectively. This can be attributed to the outer protective cover of a malunggay seed that prevents the GSL from leaching or being affected by heat. Additionally, boiling and blanching exhibited a significant decrease in glucosinolate concentration. Myrosinase inhibition could have aided the retention of the compounds, especially in seeds. Using the Bradford Assay, the protein concentration of malunggay seeds was evaluated to be 1.631 mg/mL, which could verify the presence of the myrosinase enzyme in the sample. Similar to glucosinolates, the isothiocyanate concentration of samples that underwent cyclocondensation was quantified through HPLC. It was identified that initializing hydrolysis can increase the detection of ITCs in the instrument. Hence, the presence of ITC was significantly higher in hydrolyzed leaves (0.7548-1.5646 µM) and seeds (0.7075-1.3571 µM) than in the unhydrolyzed leaves (0.7075-1.0242 µM) and seeds (0.7075-0.9545 µM). It was hydrolyzed microwaved leaves and unhydrolyzed blanched leaves, as well as hydrolyzed and unhydrolyzed fried seeds with the highest ITC concentration. Factors that could have affected the hydrolysis product include myrosinase inactivation, thermal degradation of GSLs and ITCs, and the presence of specifier proteins. The isothiocyanate was qualitatively analyzed further through GC-MS; however, limitations in the instrument hindered the identification of ITC. Lastly, the antioxidant activity of M. oleifera was determined using the DPPH assay. Stronger antioxidant activity was observed in malunggay leaves as opposed to malunggay seeds. Moreover, boiled and stir-fried leaves, as well as blanched seeds, exhibited a greater response than their raw counterparts