Selection of folate-producing lactic acid bacteria for improving fermented goat milk

Goat milk is a complete food but its low level of folic acid diminishes its nutritional efficacy. In this study, Streptococcus thermophilus, Lactobacillus delbrueckii subsp. bulgaricus, Lb. delbrueckii subsp. lactis and Lb. helveticus strains were selected for folate production in goat milk to improve its quality. A suitable HPLC method was developed to directly determine both total folate and its biologically active derivatives such as 5-methyl-tetrahydrofolate (5-CH3-H-4-PteGlu), tetrahydrofolate (H-4-PteGlu) and 5-formyl-tetrahydrofolate (5-CHO-H-4-PteGlu). Results showed that S. thermophilus, Lb. delbrueckii subsp. lactis and Lb. helveticus strains produced higher amounts of total folate than Lb. delbrueckii subsp. bulgaricus, especially 5-CH3-H-4-PteGlu and H-4-PteGlu. Moreover the use of selected S. thermophilus strains in association with Lb. delbrueckii subsp. bulgaricus resulted in yoghurt with a significant quantity of folate and good organoleptic features.