Yeast

YEAST-IMPORTANCE-VARIOUS YEAST

1. PRINCIPLES OF FOOD SCIENCE AND NUTRITION TOPIC:YEAST NAME:D.NIHARIKA CLASS:NAG-A UID:111718012012

2. DEFINITION: A microscopic fungi consisting of single oval cells that reproduce by budding and are capable of converting sugar into alcohol and carbohydrate yeast formentations are involved in the manifacture of foods such as bread,bear,wines,vinegar & surface ripened cheese & yeasts are grown for enzymes & for food.

3. MORPHOLOGY OF YEAST They are single celled fungi Size:generally larger than most bacteria(1 to 5 um)wide and (5 to 30 um)in length Size and shape varies among species Yeast cell lacks flagella and other organ of locomotion Cell wall:composed of thin chitinous cell wall The protoplasm is surrounded by cell membrane which contain all the usual cell organelles like ribosomes,mitochondria,ER,nucleus etc. Vacuole is single,large and centrally located

4. REPRODUCTION IN YEAST CELLS Yeast generally reproduce by asexual method such as budding or fission Yeast lack sex organs( anthridium & oogonium ) Sexual reproduction in yeast is highly variable

5. BUDDING: It occures during abundant supply of nutrition Parent nuclieus divides and moves towards daughter cell Enzymatic activities increases Septum formation and bud seperates into individual cell

6. SEXUAL REPRODUCTION: Sexual reproduction is highly variable in yeast Three different pattern of life cycle found in different genes Haplodiplobiontic life cycle Haplobiontic life cycle Diplobiontic life cycle

7. CULTURAL CHARACTERS YEAST Not Non – filamentous unicellular fungi ; cultures resemble bacteria when grown on the surface f lab media ,but are 5-10 times larger then bacteria ; spherical (or) cylindrical Yeast do not or do have aerial hyphae /supporting sporangia

8. Budding Fission One of two ways yeast reproduce asexually an out growth from the parent cell pinches off ,producing a daugter cell One of two ways yeasts reproduce asexually , the parent cell elongates ,its nucleus divides,and it splits evenly into two daugter cells

9. Ascospore Ascus Four haploid nuclei (sexual spores);produced during yeast sexual reproduction Houses ascospores ;when this structure ruptures , the ascospores are released and conjugate ,starting the sexual reproduction cycle again

10. Lactophenol cotton blue Chitin The dye that permit to visualization of the fungi under optic microscope ,it adheres to the “chitin” of the fungi walls of hyphae A carbohydrate that composes the cell wall of fungi

11. PHYSIOLOGICAL CHARACTERISTICS yeasts are commonly grown best with a plentiful supply of available moisture But some yeasts grow in the presence of greater concentration of solutes than most bacteria In general sugars are the best source of energy for yeasts,although oxidative yeasts Eg:the film yeasts,oxidise organic acids etc

12. Physiological characteristics of yeast

13. Conjugation of small daughter cells

14. Producer after isogamic conjugation

15. Heterogamic conjugation

16. Ascospores in yeast

17. Fission in yeast

18. Arthrospores in yeat

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20. Pichia yeast These pichia species are encouraged to grow on jerez and arbois wine,to which they are supposed to impart distinct flavors and esters They can tolerate high High levels of alcohol And oxidise alcoholic beverages

21. Osmophilic yeasts Grow well in an environment of high osmotic pressure i.e.high concentrations of sugars, salts,or other solutes, causing spoilage of dry fruits,concentrated fruit juice,honey and high sugar solutions

22. Salt tolerant yeast These yeasts grow in curing brinds ,salted meat and fish,soy sauce,misco paste and tamari sauce

23. Conjugation in ascospores

24. Yeast and their importance

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