Department of microbiology microbial food technology group a diploma in quality assurance in microbiology diploma



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Picture gallery


Idli and Vada served with sambar and two type of chutneys (green and red) on banana leaf.



The South Indian staple breakfast item of idli, sambar, and vada served on a banana leaf. Note the stainless steel plates and cups; characteristic of south Indian dining tables.



Tatte Idli: variations from Karnataka





Sambar idli: Idli soaked in sambar. Chutney is the best companion for this dish.



MTR idli: Famous Mavalli Tiffin Room idli served with pure ghee and sambar. Pure ghee is poured on steaming idli and relished with chutney or sambar.

Button Idli. This usually contains fourteen idli and is therefore called "fourteen idli". However this name came from Floating idli (small idlies floating on sambar, rasam or butter milk)




Sanna(s), a Goan variant of idli.






12.Write a brief account on bread making.

BREAD

Bread is one of the fermented food products, the fermentation being brought about mainly by yeast.



Methods of bread production:-

The bread is made by a number of procedures. But the most common methods utilized are,



  1. Sponge dough

  2. Straight dough

  3. Continuous mix

  4. Liquid ferment.

Sponge dough:-

This is the predominant bread making method using by the baking industry.

Sponge comprises of about 65% of about total flour + a portion of total dough water + yeast & yeast food, its first mixed. This mixing period is brief. The sponge is then discharged into a trough where it will undergo a fermentation period of 4-5 hrs from starting temperature of about 25 0 C to a final rise by 6 0C. Due to exothermic reactions brought about by yeast activity. Sponge volume will increase due to CO2 production.

At the end of sponge fermentation, the sponge is transferred into a dough mixture. The balance of the flour, water remaining ingredients are added into the mixture and allow mixing. First at low speed & at higher speed until the dough is completely mixed. At this point dough has been transformed from a sticky wet appearing nature into smooth cohesive dough characterized by glossy sheen, upon addition of water & input of energy wheat protein & lipids form gluten. The dough due to the unique nature of gluten able to retain the gas & is thereby leavened.

The mixed dough is placed in troughs & allows resting for 20-30 minutes.

Dividing the dough is the next stage. The dough is cut into pieces of desired weight by a machine & conveyed on a belt to a rounder where the rough appearing pieces are removed such that the pieces are held for a rest period of 8-12minutes to compensate for the loss of gas.

The dough pieces are conveyed to moulding machines, which transform the round dough pieces into cylinders. Automatic moulders feed the dough cylinders into bread pans.

Pans-containing dough pieces are placed in fermentation unit called proof-boxes, for last fermentation period prior to baking. They are held at 35-43 0C at a relative humidity of 80-95% for 60minutes. The proof lobes are placed in oven for baking. Gas within the dough expands. Steam & alcohol vapors also contribute to this expansion. Enzymes are active until the bread reaches 75 0C. At this temperature starch gelatinizes & dough structure is set. When the bread surface temperature reaches the 130-140 0C sugars & soluble proteins react chemically to produce an attractive crust colors. The center of the leaf doesn’t exceed 100 0c.

Remaining stages in bread making process includes cooling of the baked bread, slicing, wrapping & distribution to stores.

Function of yeast in bread making:-

Major function of yeast in bread making includes:



  1. Leavening

  2. Flavor development

  3. Dough maturing

  1. Leavening:-

Dough is usually leavened by bread yeast which ferment the sugars in the dough & produce Co2 &

alcohol. There is little or no growth during the first 2hrs, after the yeast is added to dough, but some growth in 2-4hrs & then there is a decline in growth in 4-6hrs. Fermentation by the yeast begins as soon as the dough mixed & continuous until the temperature of oven inactivates the yeast enzyme.

During fermentation conditioning of the dough takes place when the flour proteins (gluten) mature i.e., it becomes elastic & springy & are therefore capable of retaining maximal amount of CO2 produced by the yeast. The conditioning results from action on the gluten by: -


  • Proteolytic enzymes in the flour from the yeast & Malt.

  • Reduction in pH by the acids added & formed.

Dough conditioners called yeast foods are added which include ammonium salts to stimulate the yeast &

various salts.

Example:- Kbro3,Cao,KIO 3 to improve dough characteristics.

Adding increases the rate of gas production by the yeast,



  • More yeast.

  • Sugar or amylase bearing malt

  • Yeast food.

The main objective of the baking during leavening is to have enough gas produced & to have dough

that will hold the gas at the right time.

Heterofermentative lactic acid bacteria & saccharolytic anaerobes can accomplish leavening. Leavening by chemicals is accomplished by using baking powder or by C02 gas, which may be incorporated directly, or ammonium bicarbonate may be used.


  1. Flavor development:-

Fresh bread has a pleasing & appealing flavor. Bread flavor is derived from 2 main sources.

  • Yeast fermentation:-

The characteristics flavor yeast raised bread arises from yeast fermentation & subsequent reaction of

fermentation products with other dough compounds during baking. During baking some of these flavor compounds escape & other react with amino acids & other compounds of the dough to yield characteristic flavor of bread. Fermentation byproduct formed during yeast fermentation is organic esters, acids, alcohol, carboxyl compounds. Some of the organic compounds formed during fermentation may arise from bacterial action.

Lactic acid bacteria found in dough are associated with yeast. In addition to Saccharomyces cerevisiae other yeast may be responsible for characteristic flavor of certain breads.

Breakdown products of flavor proteins play an important role in flavor & color development. Yeast proteolytic enzyme modify peptones & polypeptides for growth, a portion of these product react with sugars to impart desirable flavor upon baking.



Crust Browning:-

The extent of crust browning is influenced by previous activities of in the Saccharomyces cerevisiae dough. A part of bread flavor is formed in the crust during baking & then diffuses into crumb where it becomes observed.



Compounds produced during Fermentation & Baking:-

Organic acids Aldehydes/Ketones Alchol Carbonyl compounds

Butyric Acetaldehyde Ethanol Furfural

Succinic HCHO n-propanol Glyoxal

Propionic Acetone Isobutanol Methional

Isobutyric Diacetyl Amyl alcohol Hydroxy methyl furfural

Isovaleric Acetoin Isoamyl alcohol

Palmitic

Acetic

Lactic

Formic

Caproic

Valeric

Lauric

Myristic

3. Dough Maturing:-

The changes caused by yeast in the dough are called dough maturing or ripening. A properly matured



dough exhibits optimum rheological properties [optimum dough balance of extensibility & Elasticity] such that it may be machined well & will lead to bread with desirable volume & crumb characteristics, some of the reactions leading to dough maturing are as follows.

  • Alcohol & Co2 are derived from yeast fermentation. Alcohol is water miscible & since appreciable amounts are formed. It influences the colloidal nature of the flour proteins & alters the interfacial tension within the dough. Some of the CO2 dissolves in aqueous phase & form carbonic acid, which lowers the pH of the system. CO2 also distends the dough work into the dough system.

  • Ammonia from ammonium sulphate & ammonium chloride added to the dough, as yeast foods are assimilatory S. cerevisiae causing a liberation of H2SO4 & HCl. These acids along with carbonic aid lower the pH, Which in turn influences

  • Gluten hydration & Swelling

  • The reaction rate of enzyme in the dough

  • Oxidation-reduction reactions &

  • Various chemical reactions.
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