Yeast and Molds Lactic Fermentation

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Yeast and molds Lactic Fermentation

YeastYeast-lactic fermentationFermented milk products which are made from certain strains of lactic acid bacteria and yeasts are called yeast-lactic fermentation yeast E.g :1.Kefir 2.Related products like Koumiss and Acidophilus yeast milk These products are also known as alcoholic milk beverages


YeastYeast-lactic fermented products are originated in central Asia between caucasus mountains and Mongolia. These are very popular in many countries liky former USSR, Poland, Hungary, Bulgaria and some Scandinavian countries. The popularity of the alcoholic milk beverages help their consumption and promote these products as good for health.


Kefir is a fermented milk drink that originated with Shepherds of the north caucasus region Kefir is white or yellowish fermented milk having balanced yeasty aroma with acidic flavour but have pleasant and refreshing charactersc It have elastic consistency Lactic acid, volatile acids, diacetyl, CO2 and diacetyl, ethanol are main compounds influencing the sensory properties of kefir.

Kefir grains

Appearance and chemical composition Size range # 0.3-2.0cm or more in diameter 0.3The kefir grains are irregular, folded or uneven surface resembling cauliflower florets in shape and colour White or slightly yellowish in colour and a characterstic smell These grains have specific biological function

Microflora of Kefir grains

Complex microflora Lactic acid bacteria, Yeast, Acetic acid bacteria bacteria, and Moulds According to Polish standards LactobacilliLactobacilli- 80% YeastsYeasts-12% LactococciLactococci-8%

Lactic acid bacteria

Main LAB microflora Lactococcus spp mainly L.lactis subsp lactis Lactobacillius spp Streptococcus thermophilus Leuconostoc spp Lb. delbrueckii subsp bulgaricus, Lb. helveticus, Lb. bulgaricus, helveticus, casei subspp pseudoplantarum, Lb.brevis are also pseudoplantarum, found.


Kluyeromyces marxianus var. lactis Saccharomyces cerevisiae Candida inconspicua Candida maris Kluyeromyces spp are permanently present on grains and responsible for yeasty aroma in the products


Acetobacter aceti and Acetobacter rasens MouldMould- Geotrichum candidum Lactococcus spp is located on the surface of the kefir grain while lactobacilli and yeasts are present in the deepers layer of the grain.

Different microflora in kefir and kefir grainsOrganisum Lactococci and Leuconostoc spp. Yeasts Lactobacilli In kefir 80% 1010-15% 55-10% In grains 5-25% 510-15% 1060-80% 60-


The mechanisms responsible for the production of flavor compounds are results of metabolism Yeast metabolism in kefir is not well established Lipolysis of fat in milk results in formation of free fatty acid which is precursors of flavour compounds in kefir Methylketones, alcohols, lactones and esters


Protein hydrolysis Yeasts also degrade casein to small peptides and free amino acids and latter these are converted to alcohols aldehydes, volatile acids, ester and aldehydes, SulphurSulphur-containing compounds

Production of exopolysaccharides

Microflora held togther in a matrix of protein and polysaccharide EPS produce by LAB contribute to texture of grain and fermentate EPS produce by LAB is known as Kefiran Kefiran material posses anti cancer activity EPS produce by LAB can affect rheological properties of products like improve the texture and mouth feel


Also exhibit biological properties such as Immunostimulatory Antimutagenic Antitumour AntiAnti-ulcer activities Act as a prebiotic compound


Traditionally kefir was produced in animal skin bags in which fresh milk seeded with kefir grains, as the products consumed, fresh milk was added. Current methods 1.Traditional method based on the use of kefir grains 2.Industrial process using DVI or DVS kefir culture

Chemical composition

Based on FAO/WHO Protein contents not less than 2.7g/100g Fat level not more than 10g /100g Titratable acidity not less than 0.6mL /100mL Bacterial count in 1g not specified Yeast count not less than 10 cfu/ g cfu/

Metabolic pathway of YeastLactose CitrateCO2 CO2, Acetate

D-Lactate CO2 ACAC-TPP Co2 L-Lactate Acetaldehyde -AcetolactateCO2 CO2





Nutritional value

According to Halle et al., Kefir contain (g 100g) 3.03.0-3.4 protein 1.5 fat 2.02.0-3.5 lactose Vitamins in kefir made using grains and milk from different spp of mammals increased by 20% likelikeThiamine(B1)only in ewes milk kefir Pyridoxine (B6) in ewes milk+ goats milk Folic acid in all kefir except mares milk Increase in biosynthesis of riboflavin(B2) and ascorbic acid when oxygen is injected into medium during fermentation

Therapeutic properties

Antibacterial activity Used in the treatment of tuberculosis, cancer, gastrointestinal tract disorders and a variety of diseases


First mentioned in the 5th century as drink of god In 7th century koumiss became an everyday drink of the Mongolian tribes Traditional it is produced by mares milk In Mongolia by camel milk In Europe and North America from full and skimmed milk


Lactobacilli( Lb.delbrueckii subsp bulgaricus and Lb. acidophilus) acidophilus) lactose fermented yeasts (Saccharomyces (Saccharomyces spp, spp, candida koumiss NonNon-lactose fermenting yeast S.cartilaginosus NonNon-carbohydrate fermenting yeasts (Mycoderma) (Mycoderma)


Traditional mare milking starts early in the morning and takes place every 2 hrs, means six times milking in a day In the evening, fresh milk is added in the already fermented milk in a wooden pots to provide ongoing fermentation Traditional milk was fermented in horse-hide horsebags known as chochuur or tursuks or burduks.


At present, wooden containers are used, which is also contain previous season microflora When fresh milk is added to fermentate, mixture is fermentate, stirred vigorously for 1hr using special implement to introduce air which cause good growth conditions for yeasts The amounts of yeasts determines the alochol in the products More alcohol is produces, better the quality of Koumiss

Industrialised process

The protein content of mares milk is very low compared to cows milk so that fermentate does not coagulate Cow milk is used for the production of koumiss due to the limited availability of mares milk Protein and lactose contents of mares milk are different from cows milk

Manufacture of KumissFresh mares milk or Cow milk Heating (90-920C) Cooling (26-280C) Inoculation with 30% starter (1 part L.bulgaricus at 370C for 7 hr+ 2 parts Torula spp. at 300C for 15 hr) Acidity 1.4% in mares milk Incubation (280C till acidity 0.7-0.8%) Agitation every 1-2 hr Cooling (200C) Packaging Storage (4-50C for 24 hr)


According to Tamime and Marshall to modify cows milk composition for the manufacture of koumiss include following Addition of 2.5g sucrose 100g to skimmed milk Blending different powders9 whole milk, skimmed milk, cheese whey)

Nutritional properties

Apart from nitrogenous compound in koumiss including free essential amino acids Starter culture microflora exhibits bacteriocidal and bacteriostatic properties against many pathogens such as E.coli, bacillus cereus and mycobacterium spp Some of the yeast spp present in koumiss also exhibit an antibiotic activity against S.aureus, b.cereus

Miscellaneous products

AcidophilusAcidophilus-yeast milk Calpis Korean alcoholic fermented prodcts Bulgaros Awasi Togwa Skyr

MoldMold-lactic fermentationApart from mold-ripened cheeses, there are moldfew dairy products that deliberately include mold in the microflora, microflora, such as Viili


Viili is a cream layer with white mold growing on the surface that give productv velvety apperance viili is mildly sour, aromatic in taste, and stretchy, and it can be cut easily with a spoon The flavor of Viili is similar to other types of buttermilk product, but with a slightly musty aroma that is attributed by G. candidum The mold layer on the surface of the product may be advantageous in preventing the growth of spoilage microorganisms

Types and starter culture

Three types of Viili 1. Low-fat viili Low2.Whole2.Whole-fat villi 3.Cream viili

Starter cutureLactobacillus lactis subsp lactis Leuconotoc mesenteroides subsp cremoris and a mold Geotrichum candidum


Viili is made from non-fortified and fat nonstandardised milk Milk is not homogenize or aerated But heat-treated at 950C for 5 mins heatThen cooled at 200C and inoculated by 3-6ml 100ml 100ml of starter culture Inoculated milk is packaged, placed on trays, palletised and transferred to a ripening tunnel


The containers are incubated 200 C for 18-24hrs at pH 18below 4.6 Because the milk base was not homogenized, the fat and mold spores rise to the surface during the incubation period. The mold grows on the surface of the milk to give rise to the velvet-like appearance of the product Natural Viili consists of two layers (i.e., the coagulated milk and a cream layer plus the mold growth)


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