**1. Introduction**

With the development of functional foods having beneficial effects for the health, the interest of scientists, consumers and industrialists in raw materials rich in antioxidants has increased considerably over last few years. Moreover, consumers require more accurate information on the composition of the food which they eat. Natural antioxidants such as phenolic compounds have been reported to possess beneficial bioactivities due to their capacity to act as antioxidant; anticarcinogenic, antibacterial, antimutagenic, anti-inflammatory, and antiallergic. These activities contribute to bringing a feeling of well-being to consumers. In fact, it was observed that the consumption of foods rich in antioxidants leads to the decrease of some diseases such as diabetes, cancer, cardiovascular or neuronal diseases [1]. To evaluate the antioxidant activity of raw materials several methods were investigated. These methods go through two steps. The first one is the extraction of the antioxidant compounds from the matrix of raw material and the second one consists in the determination of the antioxidant activity. For each step several alternatives are described in the bibliography. The data obtained showed a large variability depending on the method used. This renders the choice of an appropriate method a very sensitive task. The objective of this chapter is to make a critical study of the various methods of evaluation of the antioxidant activity of food raw materials. For this, in the first part, we will underline the different sources of variability from several examples of food raw materials. Then in the second part the different methods used for the extraction of antioxidants will be detailed. The third part will bring a complete view of the existing methods to measure antioxidant activity. The last part will deal with a general discussion on the meaning of the different values of antioxidant activity.

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