Effect of Roasting on the Phytochemical Properties of Three Varieties of Marble Vine (Dioclea reflexa) Using Response Surface Methodology

This study assessed the optimum roasting conditions on the phytochemical properties of three varieties of Dioclea reflexa seeds using response surface methodology. Roasting conditions were varied using temperature (110°C~200°C) and time (10~40 min). Phytochemical components (phenolics, tannin, flavonoids, cardiac glycoside, and steroids) of the seeds were screened and estimated. The study showed that availability of phytochemical activities was heat-dependent. An increase in roasting temperature beyond 110°C for 10 min resulted in a decrease in total phenolic (TP) and flavonoid (TF) contents. However, prolonged durations of roasting favored increased amounts of TP and TF in dark and light varieties. Total sterol, tannin, and cardiac glycoside contents increased with increasing roasting temperature and time. The desirability of the models were 0.76, 0.74, and 0.72 for black, dark brown, and light brown, respectively. The coefficients of regression (R(2)), ranged from 0.66 to 0.98 signifying accuracy of the model. The following models (cubic, quadratic, and 2 factor interaction) were significant (P≤0.05). We found that roasting time influenced the phytochemical properties of D. reflexa to a greater extent than temperature. The optimum roasting temperature and time was found to beat 110°C, 35 min, 40 min, and 32 min in black, dark brown, and light brown varieties, respectively. Roasting conditions significantly affects the phytochemical contents of three varieties of D. reflexa seed flour (P<0.05). Therefore, D. reflexa holds the potential to be used in development of functional foods and in therapeutic applications to promote health.