Determination of quality indicators and antioxidant activity of various fruit juices

For eight types of juices (apple, orange, pear, pineapple, pink grapefruit, cranberry, blackcurrant and apricot), a range of analytical parameters was analysed in order to use them as primary indicators of juice adulteration. Dry matter, relative density, pulp percentage, ash, pH and titratable acidity, conductivity, total content of proteins, formol number, proline and ascorbic acid were determined in all samples. Antioxidant activity of samples expressed as Trolox equivalent was determined using 2,2-diphenyl-1-picrylhydrazyl (DPPH) assay, 2,2'-azino-bis(3-ethylbenzthiazoline-6-sulphonic acid) (ABTS) assay and ferric reducing antioxidant power (FRAP) assay. The results were in correlation with total phenolic content expressed as gallic acid equivalent. Phenolic compounds chlorogenic acid, caffeic acid, naringin, hesperidin, rutin, quercetin and 5-hydroxymethylfurfural were determined using high performance liquid chromatography. Concentration of these compounds in samples was very variable, mostly in the order of tens of milligrams per litre. Overall, the values of all parameters and the concentration of compounds were the most influenced by the type of fruit from which the juice was produced. The quality control parameters analysis showed that the samples analysed were not adulterated because the results obtained met almost all the requirements given in Czech technical standards.