The influence of jostaberry extract active acidity on the color parameters

Abstract

The jostaberry hybrid (Ribes × nidigrolaria) is a fruiting shrub obtained by crossing three original species: the blackcurrant Ribes nigrum, the North American coastal black gooseberry Ribes divaricatum, and the European gooseberry. Jostaberries are rich in flavonoids, especially anthocyanins, a pigment that play a decisive role in the formation of the color of the extracts, which can later be used in the manufacture of food products. The aim of the present work was to analyze the influence of pH (2.5, 3.5, 4.5) on the CIELab parameters (L*, a*, b*, C*, h*) of extracts obtained under ultrasound (UAE, 37 kHz, temperature of 25 ± 1 ⁰C, 20 min) and microwave-assisted (MAE, magnetron power regimes - 100, 180, and 300 W, 6 min) conditions from jostaberries pretreated through freezing, freeze-drying and oven drying processes. The pH value influences the stability of anthocyanidins. At acidic or basic pH, the highly conjugated phenolic groups of anthocyanidins have the ability to protonate or deprotonate, leading to a change in electronic distribution. This process affects the absorption wavelength and the observed color. The extracts of frozen (FJ), freeze-dried (FDJ) and oven dried (DJ) jostaberries were used for the determination of chromatic parameters. It was demonstrated that at pH 2.5 the lowest values of L* were obtained, which vary from 33.31 (FDJ, UAE-20) to 59.29 (DJ, MAE 300-6) demonstrating the color intensity of the extracts, and the highest values of L* were obtained at pH 4.5, ranging from 42.74 (FDJ, MAE-300-6) to 72.86 (DJ, MAE 100-6). The analysis of the a* parameter demonstrated that the highest values were obtained at pH 2.5, followed by pH 3.5 and 4.5. In the case of the b* parameter, it was found that the highest values were obtained in DJ extracts, showing the presence of yellow pigments. It was found that at pH 2.5, C* values are the highest in FJ and FDJ extracts, which denotes the absence of the gray shade. All h* values obtained at pH 2.5, 3.5 and 4.5 are in the first trigonometric quadrant. For FJ and FDJ extracts, the red color predominates and for DJ - the brown color. Jostaberry pretreatment produced significant changes in all color parameters. The red tone predominates in the FJ and FDJ extracts, and the orange tone in the DJ ones. The most stable intense red color is characteristic of jostaberry extracts acidulated at pH 2.5. This is due to the protonated form of the flavylium cation of anthocyanins, characteristic for an acid environment (pH ˂ 3). At pH between 4 and 5, anthocyanins will be in the unprotonated form, chromenol (flavenol), and their red color loses its intensity. Jostaberry extracts obtained under different conditions can provide a wide spectrum of red hues.