The effects of Maillard reaction products (MRPs) on apple and potato polyphenol oxidase (PPO) were estimated spectrophotometrically. Model systems of glucose and amino acids [lysine (lys), tyrosine (tyr), proline (pro), cysteine (cys), glumatic acid (glu), aspartic acid (asp), and histidine (his)] were heated at 90°C for 3 h. The MRPs showed inhibitory effects on PPO extracted from apple and potato. These effects depend on the type of MRP and origin of PPO. The antioxidant activity of MRPs was evaluated. It was found that MRPs exhibit different free radical scavenging activity and these effects were significant. The colour intensity of MRPs was estimated. Browning was not directly related to the antioxidant activity.

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Different plant seeds extracts of Citrus sinensis, Hordeum sativum, Triticum sativum, Canna indica, Citrullus vulgaris and Capsicum annuum were evaluated for their antioxidant activity by the following methods: 2,2-diphenyl-1-pycril-hydrazyl (DPPH) radical scavenging, reducing power, RBCs hemolysis and linoleic acid oxidation, a long with the determination of total phenolic and flavonoids contents. All the methanolic extracts showed high antioxidant activity and have high contents of phenolic and flavonoid. The Canna indica extract exhibited strong antioxidant as a reducing power and as DPPH radical-scavenging (3.61 absorbance, 87.12%, respectively), while the Hordeum sativum extract exhibited highest inhibitory effect on RBCs hemolysis (59.55%) and the Capsicum annuum extract has highest inhibitory effect on linoleic acid peroxidation (65.06%).

Cumin (Cuminum cyminum L.) and caraway (Carum carvi L.) are aromatic plants within the Apiaceae family. They have a variety of purposes and demonstrate antioxidant and antimicrobial properties. Methanolic and acetonic seed extracts of both plants were able to neutralize free radicals and carried antioxidant properties. Both seed extracts were able to protect erythrocytes from hemolysis. The methanolic cumin extract showed a higher percentage of protection than both extracts of caraway. Seed extracts of cumin showed slightly higher neutralization ability than caraway seed extracts (57.0 and 52.4% vs. 44.7 and 39.5%, respectively). Antioxidant properties of both seed plants may be useful in pharmacologic preparations.

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