Forecasting and evaluating antioxidant properties of fruit, and vegetable, juices using polarization curves

Abstract

The qualitative and quantitative constituents of antioxidant properties of fruit, and vegetable, juices were studied by volt‐ampere method. The actual redox power of redox systems connected with normal redox potential (qualitative constituents of antioxidant activity) of juices was increased in the line: carrot, pomegranate, cabbage. Reduction current density for carrot juice redox system was proportional to the square root of hydrogen ion concentration, whereas antioxidant properties of cabbage juices were not affected by pH. Redox reactions between phenolic compounds of mixed juices were forecast based on polarization curves of components on Pt. The antioxidant effect of phenolic compounds of cabbage juice' redox system on anthocyans of pomegranate juice influenced the increasing intensity of absorption in 490–510 nm wavelength region in mixed juice compared with the theoretical value calculated as arithmetic means. Thus, polarization curves on Pt electrode can be recommended as criteria for the evaluation of antioxidant properties of juices. Practical applications Polarization curves on Pt can be useful for forecasting the direction of redox reaction in mixed juices. This is vital for color stabilization of products containing anthocyans, and browning decreasing in colorless products. Results obtained in respect of actual reducing power will assist in improving evaluation of antioxidant properties of fruit, and vegetable, products. Results obtained for carrot, cabbage, and pomegranate, juices can be utilized in the area of canned fruit, and vegetable, products.

Electrochemical Basis for Re-evaluating Antioxidant Effect of Redox Substances in Foodstuffs

“…For redox reactions involving hydrogen, the effect of pH level on redox potential obeys the Nernst equation. Redox conversions of cabbage polyphenols were found to be independent of hydrogen concentration . The reduction current density for the carrot juice redox system was proportional to the square root of the hydrogen concentration …”

“…Reducing properties include qualitative (standard redox potential of a redox couple), and quantitative (content of reduced forms), constituents . Indeed, the standard redox potential shows the thermodynamic viability of a reducing agent to reduce oxidized forms of a redox system with a more positive value of the standard redox potential .…”

“…The quantity of reduced forms of redox substances affects only the oxidation current density but not the area of potentials where polarization curves are situated . It was shown that polarization curves on Pt in the region of redox conversions can be used as a visual criterion for evaluating the reducing ability of redox systems …”

“…The pro-oxidant effect of ascorbic acid in certain systems was demonstrated by Gerard et al Previous data show that different polyphenols may act as antioxidants and as pro-oxidants with respect to vitamin C . Indeed, polyphenols of citrus fruit prevent vitamin C and color degradation; , however, apple polyphenols affect color degradation and cause a decrease in ascorbic acid content . Different values of plant polyphenol redox potentials allow the assumption that the reason for the above-mentioned differences may be explained on the basis of the functioning of polyphenols as redox systems, and not as antiradical agents.…”

“…However, the information with respect to antioxidants with the redox mechanism is very controversial and limited, despite the importance of redox reactions in cells of living organisms , as well as in food systems. Antioxidants with a redox mechanism prevent color and ascorbic acid, degradation in foodstuffs of plant origin. − Redox substances were shown to be important in providing a positive effect on milk quality . The effect of redox reactions on color, flavor, texture, and shelf life of fermented food products was demonstrated by Hansen .…”