Menaquinones (MK’s) are a form of vitamin K, supplementation with which has been shown to provide health benefits by reducing arterial calcification and improving bone density. Fortifying MK’s in foods may provide the health benefits associated with MK’s to the general population. This study aimed to increase the amount of MK’s in yogurt, which typically contains very little MK’s, by co-fermenting milk with both typical yogurt bacteria and bacteria known to produce MK’s in cheese and natto. A LC-MS/MS method was first developed to measure MK’s as well as all other fat-soluble vitamins. The LC-MS/MS method was able to quantify phylloquinone, MK-4, MK-7, MK-9, cholecalciferol, α-tocopherol, and was able to detect MK-8, but was unable to quantify ergocalciferol or retinol due to ionization suppression from the sample matrix. The LC-MS/MS method was used to measure MK’s in non-fat milk samples fermented with either one bacteria ssp. or a combination of S. thermophilus, L. bulgaricus, and one of L. lactis, L. cremoris, P. shermanii, or B. subtilis. Fermentations were carried out at 30 – 45 °C for 36 h to determine the optimal incubation temperature at which to carry out replicate fermentations. The pH was measured throughout fermentation as an indicator of overall growth and the relative amount of each bacteria ssp. after fermentation was measured using qPCR. Only L. cremoris produced MK-8 and MK-9, while all samples, including negative controls, contained high concentrations of MK-7. The qPCR results showed co-fermentations contained over 99 % S. thermophilus, except in co-fermentations with L. lactis which contained 59 % L. lactis, 41 % S. thermophilus, and < 0.1 % L. bulgaricus. Delaying inoculation of S. thermophilus and L. bulgaricus resulted in almost exclusive growth of the first inoculant. Overall, L. cremoris showed the greatest potential for enhancing the MK content of yogurt as it produced up to 234.4 ng/g MK-9, 174.9 ng/g MK-7, and produced MK-8, but further experiments are required to improve the growth of yogurt and MK producing bacteria.Land and Food Systems, Faculty ofGraduat
