Phenolic compounds, ubiquitous in plants, are of considerable interest and are increasingly becoming a subject of intensive research due to their bioactive properties such as antioxidant, antimicrobial, anti-mutagenic, anti-viral and anti-inflammatory activity. The objective of this research was to determine the antioxidant activity of extracts from selected plant materials, namely Caesalpinia spinosa, Perilla frutescens, Artemisia annua and Viola wittrockiana Gams. Plant material extracts were studied by in vitro methods, such as Total Phenolic Content, the measurement of scavenging capacity against ABTS cation and 15PH radicals, and the ferric reducing antioxidant power (FRAP). Many in vitro methods, such as ABTS, ORAC or FRAP assay, have been developed to evaluate antioxidant activity. Unfortunately, these methods often correlate poorly with the ability to inhibit oxidative deterioration of foods because the in vitro assays do not account for factors such as the physical location of the antioxidant, its interaction with other food components, and environmental conditions. To evaluate accurately the potential of antioxidants in foods, models must be developed that resemble conditions expected in food products. This study outlines model systems for the evaluation of natural antioxidants in two types of food: oil-in-water emulsions and meat model systems. In addition, in all analyzed samples the content of the main phenolic compounds were determine using techniques such as high performance liquid chromatography (HPLC) or liquid chromatography-mass spectrometry (LC-MS). The extract of Caesalpinia spinosa was tested for its antimicrobial effect against some common microorganisms and for growth promoting properties with respect to probiotic Lactobacillus plantarum strain. The results of this research indicate that extracts from the plants studied may be suitable for use as natural food additives.