This study was aimed to enhance the flavor and some microbial, physiochemical and sensorial properties of yogurt by threonine and glycine. This study included the estimation (acetaldehyde, acetone and ethanol), acetaldehyde content was 13.46, 13.9, 19.52, 13.99, 28.76, 27.31 and 18.52 mg L-1 for (A) control treatment, (B) glycine 1g /L , (C) threonine 1 g/ L, (D) glycine 3 g/ L, (E) threonine 3 g/ L, (F) threonine 3g + glycine 1g / L and (G) glycine 3g + threonine 1g / L treatments respectively. Acetone content was 8.38, 8.26, 5.71, 8.12, 3.84, 3.11 and 5.49 mg L-1 for A, B, C, D, E, F and G treatments respectively. Ethanol content was 10.25, 10.17, 6.39, 10.16, 4.56, 4.16 and 6.21 mg L-1 for A, B, C, D, E, F and G treatments respectively. Lactobacillus bulgaricus count after the first day of manufacture were 7.38, 7.34, 7.49, 7.39, 7.70, 7.68 and 7.50 cfu mL-1 for A, B, C, D, E, F and G treatments respectively, after 28 days of manufacture was 6.25, 6.23, 6.32, 6.27, 6.51, 6.47 and 6.38 cfu mL-1 for A, B, C, D, E, F and G treatments respectively. Streptococcus thermophilus count after the first day of manufacture were 9.20, 9.14, 9.38, 9.30, 10.62, 10.53 and 9.47 cfu mL-1 for A, B, C, D, E, F and G treatments respectively, after 28 days of manufacture were 8.25, 8.11, 8.34, 8.27, 9.17, 9.11 and 8.36 cfu mL-1 for A, B, C, D, E, F and G treatments respectively after 28 days. The chemical composition did not change, there were no significant differences compared with treatments. Sensory evaluation score showed significant differences (P≤0.05) among the treatments.

Debaryomyces hansenii yeast was grown in Malt Extract Broth medium at 30 °C for 5 days until the total count reached 5.6 ×108 colony forming units/ milliliter, Monterey cheese was made from cow's milk and adding of starter bacteria Lactococcus lactis subsp. lactis and Lactococcus lactis subsp.cremoris with D.hansenii yeast as adjunct starter in 2% for each treatment included M1 (100% starter bacteria), M2 (50% starter bacteria + 50% live D.hansenii) and M3 (50% starter bacteria + 50% dead D.hansenii),the ripening of Monterey cheese was done at 15°C and (85% relative humidity) for 56 days. The highest count of starter bacteria was 9.7 ×108 cfu/g in M1 treatment after 3 days of ripening, the lowest number of starter bacteria was 6.9 ×108 cfu/g in M2 treatment. The highest count of D.hansenii yeast was 4.3 x108 cfu/g after 3 days of ripening in M2 treatment, while the lowest count was 2.6 ×108 cfu/g in the same treatment after 56 days of ripening, no yeast was found in the treatments that had dead yeast cells, all treatments under study were decreased in the total count of coliform bacteria, Staphylococcus aureus and psychrotrophic bacteria after 14 days as they were within the standard specifications of these groups of microorganisms, Then reached to zero in the late time of ripening. M2 showed the best results of sensory evaluation in taste, flavor, textures, color and bitterness after 56 days of ripening.