Fruits and vegetables are a major source of antioxidants. The aim of current research was to study and compare the antiradical activity, the total polyphenol content (TPC) and the total flavonoid content (TFC) in dried carrots (Daucus carota), pumpkins (Cucurbita maxima), leeks (Allium ampeloprasum var. porrum) and black radish (Raphamussativus) using a traditional convective drier and a microwave-vacuum drier. For each vegetable steaming as pre-treatment was used. Vegetables were harvested in Latvia in 2012, gathered when ripe and then dried. Analyses were made in Latvia University of Agriculture, Faculty of Food Technology laboratories. The total polyphenol content was determined by the Folin- Ciocalteu method and the total flavonoid content - using spectrophotometric method. The antiradical activity was analyzed by the 2,2-diphenyl-1-picrilhydrazyl (DPPH) assay. The results of experiments demonstrate that the total amount of polyphenols ranged from 98.97 to 623.70 mg gallic acid equivalent (GAE) 100 gE-1 in dry weight and the total amount of flavonoids ranged from 40.32 to 100.23 mg catechin equivalent (CE) 100 gE-1 in dry weight. The value of DPPH antiradical activity for vegetable samples ranged from 6.10 to 45.14 percents.

Vegetable processing in food industry results in significant number of by-products – peel, mark, bark, seeds still rich in bioactive compounds. The objective of this study was to investigate the stability of total phenolic content (TPC) and antioxidant activity after high temperature short time (HTST) extrusion cooking of a rye and oat- based matrix with addition of apple, carrot and pumpkin by-product flour (BPF) in various amounts (5%, 10%, 15% and 20%). Extrusion was performed with co-rotating twin-screw extruder (compression ratio 8:1) at Ltd MILZU. The main drive of extruder was provided with a 7.5 HP motor (400 V, 3 HP, 50 cycles). Temperatures for extrusion zones were 125 °C /135 °C /145 °C. TPC was determined using the Folin Ciocalteu method. Antioxidant activity was evaluated by free radical 2, 2-diphenyl-1-picrylhydrazyl (DPPH) antioxidant scavenging activity. TPC in cereal-based crispbread was 62.03 ± 0.15 mg GAE gE-1 DW before extrusion and 37.73 ± 1.96 mg GAE gE-1 DW after extrusion. Addition 20% of apple BPF increased TPC in crispbread to 193.92 ± 1.37, carrot BPF 171.36 ± 6.97 and pumpkin BPF to 195.09 ± 4.68 mg GAE gE-1 DW after extrusion. Antioxidant activity of control (20% oats, 80% rye flour blends) sample was 0.516 ± 0.192 mg TE gE-1 DW but in samples with addition of 20% by-products, it was significantly higher reaching 0.926 ± 0.05 TE gE-1 DW in samples with pumpkin by-products after extrusion.