Optical properties and antioxidant effect for juices of Raspberry (Rubus idaeus)

This investigation concerns juices obtained from raspberry (Rubus idaeus) by pressing and adding 1 g, 2 g, 3 g of inulin or lactulose with different concentrations-0.5, 1, 1.5 ml. Total content of polyphenols, anthocyanins, β-carotene, color parameters in SIE Lab colorimetric system and antioxidant activity of the samples are determined by using two methods-DPPH and ABTS. The fluorescence intensities for juices with inulin determined by the methods of applied photonics are observed in the following spectral regions at cited excitation wavelength: 1. for excitation wavelength λ=295 nm- the peak connects with content of anthocyanins. 2. for excitation wavelength λ=265 nm- the peak connects with content of phenolic acids. 3. for excitation wavelength λ=295 nm-the peak connects with different types of pigments. The following conclusions can be made: Strong correlation dependences between the second fluorescence maximum and the total phenolic content and between the first fluorescence maximum and content of anthocyanins have been observed. The negative linear dependences are determined between lightness and the anthocyanins, β-carotene and color parameters. The antioxidant activity of the samples decreases when the content of lactulose increases. The similar dependence is not observed for samples with inulin. Тhe antioxidant activity obtained by the ABTS method is always higher than this, which is obtained using the DPPH method. The linear dependences between intensity of the first or the second fluorescence peak with antioxidant activity determined by DPPH or ABTS are obtained.