Total Content of Phenolics and Antioxidant Activity in Crispbreads with Plant By-product addition

Vegetable processing in food industry results in significant amount of by-products – peel, mark, bark, seeds still rich in bioactive compounds. Apple, carrot and pumpkin peel and mark may be used for production of crispbreads as functional ingredients. The objective of this study is to investigate the stability of total phenolic content (TPC) and antioxidant activity after high temperature and short time (HTST) extrusion cooking of a wheat and rice-based crispbreads with addition of apple, carrot and pumpkin by-products obtained after juice extraxtion and dried. Raw materials for crispbread production were wheat flour, rice flour, wheat bran (72%, 24% and 4% respectively) with addition of microwave–vacuum dried by-product powder in different amount (5%, 10%, 15%, 20%). Extrusion process was performed by using a laboratory singlescrew extruder GÖTTFERT 1 screw Extrusiometer L series (Germany). Total phenolic content (TPC) was determined using the Folin Ciocalteu method. Antioxidant activity was evaluated by free radical 2, 2-diphenyl-1-picrylhydrazyl (DPPH) antioxidant scavenging activity using a modified colorimetric method. Comparing different raw formulations, it was observed that the TPC of the apple by-product flour was significantly higher (p < 0.05) than in carrot and pumpkin flour. TPC in cereal-based crispbread was 36.06±1.15 before extrusion and 13.90±1.01 mg GAEg-1 DW (milligram Gallic acid equivalent per 100 g of dry weight (mg GAE 100 g⁻¹ DW) after extrusion. Addition of apple BPF increased TPC in crispbreads to 106.25±2.08, carrot BPF 84.73±3.45 and pumpkin BPF to 108.82±1.04 mg GAEg⁻¹ DW. Antioxidant activity of control sample was 1.07±0.01mg TE (Trolox equivalents) g⁻¹ DW but in samples with addition of 20% apple by-products, it reached 3.77±0.02 TE g⁻¹ DW for samples wih 20% carrot by-products reached 2.52±0.03TE g⁻¹ DW and for samples wih 20% pumpkin by-products reached 3.77±0.02 TE g⁻¹ DW.