Application of the modified Folin-Chocalteu method in the assessing of the antioxidant capacity of emulsified vegetable beverages with the addition of coffee

Recently, plant-based beverages have been introduced into the food market and have been labeled, for commercial and marketing purposes, as “plant milks”, “alternative milks’, «milk substitutes», or even «milk analogues». In this work, we applied the modified Folin-Chocalteu method in assessing the antioxidant capacity (AOE) of “beverages obtained by mixing coffee with vegetable milk substitutes or milk in a ratio of 4:1 by volume. Determination of AOE was performed by the Folin-Chocalteu spectrophotometric method using the original and modified methods of analysis. The results of AOE for oat-based beverages with a fat content from 0.5 to 12 % are presented. In this work, we applied the modified Folin-Ciocalteu method in assessing the antioxidant capacity (AOC) of “plant milk” and its mixture with coffee. The modified and original Folin-Ciocalteu methods correlated with each other in the analysis of oat drinks with different fat content (r = 0,92). Addition of 20 % semi-skimmed milk, oat, almond and soy drinks did not affect the AOE of coffee. Adding a similar amount of rice drink to coffee led to a decrease in the AOE of the latter by 11 %. It has been shown that vitamins B2, B12 and D3 used in plant drinks are not oxidized by the Folin-Ciocalteu reagent and do not contribute to the measured AOE value. Cyanocobalamin at a concentration of 500 mg/l did not give an analytical signal. Cholecalciferol dissolved in sunflower oil (40 mg/l) and pure refined sunflower oil gave the same analytical signal. This study demonstrated that plant-based milk substitutes had no significant effect on the antioxidant properties of coffee. However, additional research is needed using antioxidant methods based on hydrogen atom transfer and metal chelation.