Yoghurt fermentation

Food fermentation

1. Food fermentations - Part II – Yoghurt Dr. Dhanya KC Assistant Professor, Department of Microbiology St. Mary’s College, Thrissur-20, Kerala

2. Yoghurt A fermented milk product Either pasteurized or remain live Flavored with fruits Full fat yogurt - contain not less than 3.25% milk fat Low fat yogurt - contains not more than 2% milk fat Nonfat yogurt - contain less than 0.5% milk

3. The main ingredient – milk Whole milk for full fat yogurt Low fat milk for low fat yogurt Skim milk for nonfat yogurt Bacterial Culture Lactobacillus bulgaricus Streptococcus thermophilus Stabilizers - Improve the body and texture by Increasing firmness, preventing separation of whey, keeping fruit uniformly mixed Alginates, gelatins, gums, pectins , starch Sweeteners, Flavors or Fruit preparations

4. Bacterial cultures Lactobacillus bulgaricus and Streptococcus thermophilus Streptococcus thermophilus Acid from lactose in the milk pH drop to 4-5 from about 7.0 Causes milk coagulation Lactic acid - gives sour taste and limits growth of spoilage bacteria Lactobacillus bulgaricus O rganoleptic compounds, acetaldehyde Provide flavor Proteolytic enzymes and extracellular polymers from bacteria - protein-gel formation

5. Only 2 bacteria required to be present in yogurt Lactobacillus bulgaricus and Streptococcus thermophiles Other bacteria may be added - as probiotic cultures For improving lactose digestion For improving gastrointestinal function Stimulating the immune system Lactobacillus acidophilus Lactobacillus subsp. Casei Bifidobacteria

6. Steps in Yogurt Making Adjust Milk Composition & Blend Ingredients Pasteurize Milk Homogenize Cool Milk Inoculate with Starter Cultures Hold Cool Add Flavors & Fruit Package

7. 1 . Adjust Milk Composition & Blend Ingredients Add dry milk powder - achieve desired fat and solids content stabilizers are added 2 . Pasteurize Milk Pasteurize at 85°C for 30 minutes / 95°C for 10 minutes High heat - to denature whey proteins Form more stable gel P revents separation of water Reduces the number of spoilage organisms in milk

8. 3. Homogenize Mix all ingredients thoroughly Improve yogurt consistency 4. Cool Milk Milk is cooled to 42°C For ideal growth of starter culture 5. Inoculate with Starter Cultures L bulgaricus & S thermophilus are added 6. Hold Milk held at 42°C until pH 4.5 reached – take few hours Fermentation - formation of a soft gel and characteristic flavor

9. 7. Cool Yogurt cooled to 7°C, to stop fermentation 8. Add Fruit & Flavors At different steps depending on type of yogurt Set style yogurt F ruit added in the cup, Inoculated yogurt is poured Yogurt is fermented in the cup Swiss style yogurt Fruit blended with fermented cooled yogurt prior to packaging 9. Package Yogurt is packaged

10. References Industrial Microbiology: An Introduction, M J. Waites , N L. Morgan, J S. Rockey , G Higton Modern Industrial Microbiology and Biotechnology, Nduka Okafor, Science Publishers http:// www.milkfacts.info/Milk%20Processing/Yogurt%20Production.htm   Thank You…..