Effect of selected plant extracts on phytochemical, antioxidant, physicochemical and sensory properties of yoghurt

Abstract

Health conscious consumers are investing in food products containing functional ingredients. The study investigates the effect of addition of selected plant extracts on phytochemical, antioxidant activity, physicochemical and consumer acceptability of yoghurt. Yoghurts were produced from 70% raw cow milk and 30% skimmed milk powder with 10% (v/v) of Cymbopogon citratus leaf, Carica papaya leaf, Sorghum bicolour stalk or Ocimum gratisimum infusion added before the fermentation stage. The yoghurt sample without the infusion served as the control. The yoghurt samples were analysed 1 day after production for phytochemical and antioxidant properties and after 1, 7, 14 and 21 days of refrigeration at 4°C for titratable acidity, pH, syneresis, colour and sensorial quality using standard methods. Total polyphenol content ranged from 0.04 to 0.12 mg GAE/100mL and alkaloid content ranged from 1.25% to 3.36% with the least value reported in the control sample, respectively. Similarly, antioxidant activity ranged from 13.88% to 45.74% with the highest value in yoghurt with the pawpaw leaf extract. The addition of various plant extracts resulted in lower pH, increased syneresis but no effect on the titratable acidity during storage period. The colour attributes (L∗, a∗, b∗) showed significant differences (p≤0.05) among the samples over the storage period. Considering overall consumer acceptability, the control sample was most preferred. Functional milk product has potential to expand the application of endangered species of plant food material in the dairy industry.