Effect of Lactic Acid Bacteria on Color Tone and Anthocyanin Content of Sweet Potato Yoghurt

Abstract

Sweet potato yoghurt (SPY) was produced from colored sweet potato (Ipomoea batatas), skim milk powder and water. The cultivars of sweet potato tested were; purple sweet potato "Yamagawamurasaki (YM)" which contains a large quantity of anthocyanin (AN), orange sweet potato" Benihayato (BH)" which contains a large quantity of β-carotene and normal sweet potato "Kokei No. 14 (K14)". Eleven species of lactic acid bacteria were tested to make a SPY of better color tone. There was no influence of the bacteria species upon the color tone of the SPY made from BH and K14. However, there was a difference in the resolving activity of AN among the bacteria, the amount of AN remaining in the SPY made from YM changed from 97% to 27%. The color tone of the SPY was most favorable in the products containing the high ratio of AN made by IFO13953 (Lactobacillus delbrueckii subsp. bulgaricus) and IFO13957 (Streptococcus salivarius subsp. thermophilus) which hardly resolved AN during the fermentation. These results indicated that IFO13953 and IFO13957 were the most suitable species as a starter for making SPY.