BAKING REACTIONS IN BREAD MANUFACTURING

BAKING Process transforms an unpalatable dough into a light, readily digestible, porous flavourful product. Method of cooking food that uses prolonged dry heat, normally in an oven. Bread is the most common baked item Not a very simple process, it’s a complete science and most critical step in bread making. Natural structure of dough costituents altered irreversibly by a series of physical and chemical interactions.

Baking of bread Fermented , proofed piece of dough is transformed into bread after baking. The temperature of baking vary from 200 to 230c for 12 to 25 minutes depending upon the type and size of bread. Initially , dough increase its height and volume ,yeast still alive ,trapped gas expands due to higer temperature and formation of water vapor. Yeast cell die approx. 8 minutes after baking at temperature 220c,gluten denature, starch granules gelatinize and acqurire strong water holding capacity After baking bread crust is hard upon cooling soft because water moves from internally crumb to crust.

Precautions during baking If the loaf is large the temperature of the oven will have to be regulated so surface of loaf will not burn before baked. If the loaf is small the temperature will have to raised so the loaf will brown off before the crumb of loaf is overbaked. If the sugar content in loaf is higer than the temperature will have to be lowered vise versa

Complete bread processing

Reactions during baking Reactions occur during baking. Caramelization and Millard reactions. Starch gelatinization Protein denaturation Cell structure formation Components of dough produced polymer which contributes various flavor. 2nd is the thermal reaction of proteins or amine with carbohydrate. Gives flavor to the product

Maillard Reaction Is the thermal reaction of protein or amine with carbohydrate. End product of maillard reaction is being melanoidins. When proteins undergo a chemical reaction with reducing sugars upon applied heat. To produce desirable flavours, aroma, and crust colouring. Reducing sugar present in bread Maltose, Fructose, and Glucose.

CONTINUE…… Reducing sugars and amino acids react together in three distinct stages’ The initial stage is undetectably colourless crust and enables the sugars as well as the amino acids to condensate. intermediate stage , the sugars dehydrate and become fragments, at the meantime the amino acids begin to degrade as well. The final stage is where the most colour is produced and exhibited as golden brown on the crust of the baked item. Polymerization of Aldehyde-amine compounds and formation of heterocyclic nitrogen compounds occur in the last stage. Once each stage has passed, the Maillard reaction is complete and many aromatic and flavor compounds are produced yielding a high quality baked good that exhibits positive final product attributes such as crust color, crumb grain, volume, and mouth feel.

CONTINUE.. The Maillard reaction can occur at room temperature around 20-25 ℃ (68-77 ℉) in the presence of oxygen. When the temperature is over 30℃ (80 ℉), the reaction rate starts to increase. With every 10 ℃ (50 ℉) difference, the reaction rate would increase at least 3 times. Over the temperature of 80 ℃ (176 ℉), the reaction rate will be consistent and unaffected by temperature or oxygen level. in which a sugar aldehyde or ketone is converted to an unsaturated aldehyde or ketone: CH

Caramelisation Another thermal reactions in baking of breads.  Is the process by which colourless sweet substances, are transformed into compounds varying in colour from light yellow to dark brown and producing a mild and pleasant caramel flavor. All the compounds that form during caramelisation have not yet been identified. The end products of these reactions are mostly unsaturated complex polymers. Caramelisation needs higher temperatures to initiate the reaction. Also the flavour and aromatic compounds formed By this reaction totally different.

STARCH GELATINIZATION The starch granules begin to swell at a temperature of about 40°C. The viscoelastic properties of dough are replaced by fluidity when the temperature reaches the range of about 50 - 65°C. In the initial stage of gelatinisation, the starch granules absorb both free water and water held by the proteins of the dough. However a large proportion of the granules remain intact until the end of gelatinisation due to the fact that there is not enough water present to gelatinise all of the starch. The extent of starch gelatinisation is influenced by water availability, temperature and the duration of its action on the starch. In general there is a higher degree of starch gelatinisation between the crumb and the crust than in the centre of the bread due to longer exposure at higher temperatures.

PROTEIN DENATURATIONS Another reaction taking place during baking is the denaturation of the proteins. The gluten forming proteins binding approximately 31 % of the total water absorbed by the dough are present in the dough in a hydrated state. They contribute to the formation of the dough structure by providing the matrix in which small starch granules are embedded. The proteins begin to undergo thermal denaturation when the temperature of the crumb reaches about 60 tot 70°C. The denatured proteins start losing their water-binding ability and release the water from the protein to the starch which at that point is in the full process of gelatinisation. On the other hand, when the temperature of the dough rises above 75°C, the gluten films surrounding the individual gas vacuoles are denatured by heat and transformed into a semi-rigid structure by interaction with the swollen starch.