aeration of cereal dough by yeast

Aeration of cereal dough by yeast November 21 2009

B.K.K.K.Jinadasa (GS/M.Sc./FOOD /3608/08)

Aeration of cereal dough by yeast

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Aeration of cereal dough by yeast Introduction The purpose of adding yeast to dough is to produce carbon dioxide that is necessary to obtain a light texture of the crumb. At the same time yeast consumes sucrose, glucose, fructose and maltose. Gas production by yeast is dependent on yeast concentration, available nutrients and salt concentration. In addition to these nutrients such as ammonium chloride and calcium sulphate also increase the rate of gas production. Yeast assists in bringing about ripening or mellowing of the gluten of the dough. Gluten is the water insoluble protein, which forms by interaction of glutenin and gliadin. This interaction takes place during kneading of the dough. Constituents like lipids, enzymes, none starchy polysaccharides etc. in the flour too contribute to the final character of the dough and the derived product. Objective of the practical is to study the effect of dough ingredients, flour type and temperature on gas production and gas retention during dough formation. Enzymes involved in bread making:

ENZYMES SOURCES FUNCTION Alpha Amylase. Flour, malt. Converts damaged starched to

dextrin. Beta Amylase. Flour, malt, fungal

enzyme. Converts dextrin to maltose.

Protease. Flour malt, yeast extracts. Conditions gluten. Maltase. Yeast Converts maltose to glucose.

Invertase. Yeast. Converts sucrose to glucose & fructose.

Zymase Yeast Converts inverted sugar to alcohol & CO2, flavour.

Lipase. Yeast. Converts fats to fatty acids.


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1.1. Effect of yeast concentration on gas production 1.1.1. Materials Measuring cylinders Graduated pipettes Mixing bowls Spoons Conical flasks Stoppers for conical flasks Rubber tubes Weighing scale Wheat flour Malt Sodium chloride 20% Bakery yeast 20% 1.1.2. Method Three doughs were prepared using following formula with varying yeast concentration. A B C Flour 50g 50g 50g Malt 0.25g 0.25g 0.25g 20% salt solution 5ml 5ml 5ml Yeast 5ml 10ml 15ml Water 22ml 17ml 12ml

Three dough pieces were mixed in separate containers using spoons and finished kneading with fingers incorporating all lose particles. After mixing three dough pieces each one was placed in 500 ml conical flask connected to 500 ml measuring cylinders inverted in a container of water to measure the gas production. Amount of gas produced in three dough pieces were recorded after every 15 minutes until the rate of gas production is established. 1.1.3. Results Time (min) Volume (mL)

A B C 15 0 40 60 30 23 95 120 45 50 160 207 60 88 208 262 75 112 255 310 90 143 280 350 105 165 305 390 120 198 365 390 135 220 400 392 150 250 415 405


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Figure 1

1.1.4. Discussion Yeast strains, e.g. those belonging to the genus Saccharomyces, are used worldwide in the production of ethanol and leavening of bread. The yeast cell is equipped with highly efficient machinery for the rapid fermentative conversion of fermentable sugars that are available in the dough, e.g. maltose, glucose and sucrose, into equimolecular amounts of CO 2 and ethanol. For many years, one of the major goals in yeast research has been the improvement of the CO 2 production rate of baker's yeast, which is commercially available as active dry 92-94%, instant dry 94-97%, compressed 26-33%, or cream yeast 15-21% dry matter. The rate and volume of gas production is increased with the increase of the yeast concentration. This is because when the concentration of yeast cells increases the rate of fermentation increases and therefore gas production is high at the sample containing high yeast concentration.


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1.2. Effect of temperature on gas production 1.2.1. Materials Measuring cylinders Graduated pipettes Mixing bowls Spoons Conical flasks Stoppers for conical flasks Rubber tubes Weighing scale Water bath Wheat flour Malt Sodium chloride 20% Bakery yeast 20% 1.2.2. Method The same formula, which used for the B dough was weighed again in order to check the effect of temperature on gas production. Prepared dough was placed in 500 mL conical flask connected to 500mL measuring cylinder inverted in a container of water which was at 40°C. Amount of gas produced was recorded after every 15 minutes as above experiment. 1.2.3. Results Time (min) Volume (mL) 15 45 30 128 45 190 60 255 75 305 90 373 105 405 120 435 135 460 150 478

1.2.4. Discussion By looking at the graph (figure 1) it can be seen that the rate of gas production is high in the dough, which was kept at 40°C. The reason for this is the dough, which kept at 40°C is having a higher rate of fermentation than the dough which was kept at room temperature. Enzymes of yeast cells reach to an optimum temperature for their reactions with the increase in temperature. Therefore the rate of fermentation increases. But if the temperature rises more than the optimum level enzymatic reactions seize due to denaturation of the enzymes.

1.2.5. Conclusion Gas production is more when the dough is kept at 40°C than the room temperature.


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1.3. Effect of malt extract on gas production 1.3.1. Materials Measuring cylinders Graduated pipettes Mixing bowls Spoons Conical flasks Stoppers for conical flasks Rubber tubes Weighing scale Wheat flour Malt Sodium chloride 20% Bakery yeast 20% Corn flour

1.3.1. Method Same experiment was repeated using B formula using corn flour instead of malt extract. Apparatus were kept in room temperature. Amount of gas produced was recorded after every 15 minutes.

1.3.2. Results Time (min) Volume (mL) 15 45 30 115 45 185 60 243 75 255 90 260 105 260 120 260 135 260 150 260

1.3.3. Discussion From the above graph it can be seen that the rate of gas production is high in the dough with malt added than the dough with corn added. The main reason for this is that the malt has enzymes, which can break starch molecules. Therefore when malt is added to the dough starch compounds will break into simple sugar molecules. This increases the availability of substrates for yeast to act on. Therefore the gas production is more in the malt added dough than the corn added dough. 1.3.4. Conclusion Gas production is high in the dough, which malt was added instead of corn flour.


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1.4. Effect of salt concentration on gas production

1.4.1. Materials Measuring cylinders Mixing bowls Spoons Conical flasks Stoppers for conical flasks Rubber tubes Weighing scale Flour Malt Salt 1.4.2. Method In order to check the effect of salt concentration on gas production again three doughs were prepared as follows with varying concentrations of salt. a b c Flour 50g 50g 50g Malt 0.25g 0.25g 0.25g 20% salt solution 0ml 5ml 10ml 20% yeast solution 10ml 10ml 10ml

Gas production was recorded after every 15 minutes as above experiments.

1.4.3. Results Time (min) Volume (mL) a b c 0 0 0 0 15 130 75 33 30 245 170 95 45 333 260 143 60 397 325 195 75 425 358 255 90 450 430 302 105 468 435 335 120 475 470 358 135 492 485 385 150 500 488 405 165 515 500 414


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1.4.4. Discussion Salt added to bread dough affects the rheologicle properties of dough and the biological activities of yeast, salt strengthen gluten properties of dough and inhibits protease activity, and controls yeast metabolism. According to the graph gas formation has decrease with high salt concentration. This is because salt has a tightening effect on yeast cells which reduces the gas production. 1.4.5. Conclusion Gas formation of the dough decreases with the increase in salt concentration.


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1.5. Gas retention Effect of protein content and flour type on gas retention

1.5.1. Materials Measuring cylinders Mixing bowls Spoons Weighing scale Perforated plungers Wheat flour Gluten added wheat flour Rice flour Malt Salt Yeast suspension Water

1.5.2. Method Three doughs were prepared using wheat flour, 5% gluten added wheat flour and rice flour using following formulations. D1 D2 D3 Wheat flour 50g - - Gluten added wheat flour - 50g - Rice flour - - 50g Malt 0.25g 0.25g 0.25g 20% salt solution 5mL 5mL 5mL 20% yeast suspension 15mL 15mL 15mL Water 12mL 12mL 12mL Each dough was placed in measuring cylinder and covered with paraffin oil. Then perforated plungers were placed on all three doughs to keep them immersed in oil. Apparatus were kept at room temperature and oil level was measured after every 15 minutes. Oil level indicates the gas retention of the dough with time. 1.5.3. Results Time (min) Volume (mL) D1 D2 D3 0 300 300 300 15 350 325 300 30 360 337 300 45 372 342 300 60 380 345 300 75 384 345 300 90 386 345 300


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105 388 347 300 120 390 347 300 135 392 347 300

1.5.4. Discussion According to the graph gas retention is highest in the gluten added wheat flour dough. Gas retention depends on the amount of gluten formed in the dough and on the strength of the gluten. For the c2 dough wheat flour which used has added gluten. Therefore it contains a more amount of gluten than the normal wheat flour and hence c2 dough showed a high gas retention. Rice flour has a very little amount of gluten and it’s very weak. Therefore the gas retention in the dough containing rice flour has the least amount of gas retention. 1.5.5. Conclusion Gas retention capacity increases with the amount of gluten protein present in the dough.


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1.6. Effect of additives on gas retention 1.6.1. Materials Measuring cylinders Mixing bowls Spoons Weighing scale Wheat flour Malt Salt Yeast suspension Water Potassium bromate Sodium metabisulphite 1.6.1. Method Two doughs were prepared using B formulation. In addition to ingredients which used before 0.05 g of potassium bromate was added to one dough mixture and 0.05g of sodium metabisulphite was added to the other dough mixture. Two doughs were placed in measuring cylinders and covered with paraffin oil and oil level was measured which relates to the gas retention. 1.6.2. Results Time (min) Volume (mL)

Potassium bromide Sodium metabisulphite 0 300 300 15 370 375 30 373 410 45 380 413 60 390 413 75 395 413 90 400 413 105 400 413 120 400 413 135 400 413

1.6.3. Discussion Potassium bromate has been used in the baking industry since the early part of this century. It is applied either as flour additive in the flour milling process or as bakery ingredient in the bake shop. It has been very effective in improving volume of bread products and improving bread grain. Potassium bromate is unique in that its application has a wider spectrum than any of the known oxidants used in baking. This uniqueness is due to the late-acting characteristic of potassium bromate. This has been very helpful to the baker because it helps strengthen the gluten at the time when the dough is at its weakest point - between late proofing and early oven. According to the graph, gas retention capacity is increased in the dough with sodium meta bisulphite. Sodium metabisulphite has the capacity to break disulphide bonds and produce more elastic network.


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Potassium bromide reduces the elasticity of the dough and reduces the gas retention capacity. 1.6.4. Conclusion The dough which contained sodium metabisulphite retains gas more than the dough which contained potassium bromide.


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1.7. References: Emily Buehler; Bread science; the chemistry and craft of making bread Cecylia J. Marek and W. Bushuk; Study of gas production and retention in dough with a modifier Brabender oven rise recorder Kiyohiko Toyoda and Ikko Ihara; Evaluation of effect of salt on the bread dough fermentation analysis of dough expansion and gas retention capacity by electrical impedance spectroscopy

aeration of cereal dough by yeast

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