Effect of Parinari curatellifolia Peel Flour on the Nutritional, Physical and Antioxidant Properties of Biscuits

Abstract

This study investigated the impact of Parinari curatellifolia peel flour on the nutritional, physical and antioxidant properties of formulated biscuits. Biscuits enriched with 5%, 10%, 15% and 20% of Parinari (P). curatellifolia peel flour were formulated and characterised. Thermal, physicochemical, polyphenolic compounds and antioxidant properties of flour and biscuits were determined. The incorporation of P. curatellifolia peel flour significantly increased (p < 0.05) thermal properties (onset, peak and conclusion temperatures) of flour. However, enthalpy of gelatinisation, viscosity and pH of flour samples decreased. Nutritional analysis revealed an increase in ash (0.74% to 2.23%) and crude fibre contents (0.39% to 2.95%) along with an increase of P. curatellifolia peel flour levels. Protein content and carbohydrates decreased while moisture content was insignificantly affected by the addition of P. curatellifolia peel flour. The L*, b* values and whiteness index of formulated biscuits decreased while parameter a* value (10.76 to 21.89) and yellowness index (69.84 to 102.71) decreased. Physical properties such as diameter (3.57 mm to 3.97 mm), spread ratio (2.67 to 3.45) and hardness (1188.13 g to 2432.60 g) increased with the inclusion levels of peel flour while weight and thickness decreased. The inclusion of P. curatellifolia improved the polyphenolic compounds and antioxidant activity of biscuits with values of total flavonoids content ranging from 0.028 to 0.104 mg CE/g, total phenolic content increasing from 20.01 mg to 48.51 mg GAE/g, ferric reducing antioxidant power (FRAP) increasing from 108.33 mg to 162.67 mg GAE/g and DPPH (2,2-diphenyl-1-picrylhydrazyl) from 48.70% to 94.72%. These results lead to the recommendation of the utilisation of P. curatellifolia peel flour to enhance the nutritional value, polyphenolic compounds and antioxidant activity of bakery products such as biscuits.