Production of yoghurt with Clitoria ternatea flower extract supplementation, and its stability during storage

Abstract

The aim of the present work was to analyse 24 h yoghurt fermentation supplemented with Clitoria ternatea flower (CTF) extracts (0 - 10%); especially elucidating the relationship between antioxidant activity, carbohydrate constituent, and microbial growth which has never been reported. Carbohydrate constituent in the CTF was also investigated for the first time. Colour changes was also assessed during yoghurt production. Furthermore, the stability of yoghurt was studied during the 7 d storage under low temperature (4°C). The supplementation of CTF extracts (0 - 10%) into yoghurt increased the antioxidant activity (up to 46.65 ± 0.29%) and carbohydrate concentration (glucose, up to 9.63 ± 0.3%; sucrose, up to 7.8 ± 0.5%; inulin, up to 5.7 ± 0.8%; and pectin, up to 7.5 ± 0.3%), but decreased dissolved oxygen (DO) down to 0.65 ± 0.023 mg/L in the medium during fermentation. Surprisingly, prebiotic sugars of inulin and pectin were discovered in CTF. The presence of higher carbohydrate concentration and more anaerobic condition enabled Lactobacillus delbrueckii subsp. bulgaricus to grow up to 7.74 ± 0.1 log CFU/mL. In contrast, the final cell concentration of Streptococcus thermophillus decreased up to 8.12 times as the extract concentrations increased. However, the viability of both bacteria still met the international standards (≥ 7 log CFU/mL). The yoghurt colour turned from light turquoise to purple (L* = 69.47 ± 0.2; a* = 14.78 ± 0.15; b* = - 21.77 ± 0.2) as the pH decreased to 4.5 ± 0.11, and the lactic acid concentration increased up to 1.74 ± 0.37%. Furthermore, the quality of yoghurt in all parameters was relatively stable during storage for antioxidant activity, microbial growth, carbohydrate constituent, DO, lactic acid concentration, anthocyanin content, and pH; meanwhile colour changes only decreased 0 - 0.39 times.