So how do you feel about enzymes in food…more specifically enzymes and bread?
When you think about the science behind bread making…some questions you should ask yourself how fermentation occurs? is the sugar for fermentation part of flour? how do you get sugar from yeast? where does the flavor come from… the ethanol evolved during fermentation?
Understanding the incredible actions of enzymes and its involvement in dough making can help answer these questions and maybe make you ask a few more.
So what happens when you make bread….first thing you want to concern yourself with is the ‘rising of the dough’
This occurs via the action of fermentation which produces a gas CO2 which allows the dough to expand or rise. The longer the dough is left alone, in optimum conditions…the higher the concentration of CO2 evolved and the greater the expansion.
So what, when, where, how and why does fermentation happen in bread making?
When ‘proofed’ yeast is added to flour, sugar and salt
Where…in the dough which is hopefully in a bowl or the kitchen counter?
How? well here’s where it gets interesting…. Fermentation is a metabolic process in which an organism converts a carbohydrate, such as starch or a sugar, into an alcohol or an acid. Yeast ferments to obtain energy by converting sugar into alcohol; pyruvate (from glucose) is broken into ethanol and carbon dioxide. The net chemical equation for the production of ethanol from glucose is:
C6H12O6 (glucose) → 2 C2H5OH (ethanol) + 2 CO2 (carbon dioxide)
So how does that tie in with bread and enzymes for that matter? Well the first thing to note is that although flour contains just about 1 to 2% sugar…we can’t forget that the primary component of flour is starch. Starch which is a protein that can be broken down into sugars…glucose sugars to be specific. The breakdown of the starch is a result of the work of …u guessed it…enzymes.
AN ENZYME IS A GLOBULAR PROTEIN THAT CATALYZES A BIOLOGICAL REACTION. Enzymes speeds up reactions by reducing the activation energy needed for a reaction to occur.
Side Note: Most important biological reactions take millions of years to occur without enzymes. Enzymes are extremely important molecules as it allows the existence of life.
The activation energy is the energy barrier of a reaction. It is the energy that reactants must be given, in excess of the energy they normally possess, in order to start forming products. A catalyst affects the rate of a reaction by affecting the activation energy. Enzymes are catalysts because they reduce the activation energy which results in more successful collisions and a faster rate of reaction.
In bread making the enzymes catalyzes three major reactions; starch to maltose; complex sugars to simple sugars; and breaking protein chains.
ENZYMES ARE SPECIFIC
EACH ENZYME HAS A SPECIFIC JOB TO DO AND IT ONLY INTERACTS WITH MOLECULES FOR WHICH IT WAS DESIGNED TO INTERACT WITH. THEY REACT WITH THE SUBSTRATE TO FORM AN ENZYME SUBSTRATE COMPLEX WHICH RESULTS IN THE FORMATION OF THE PRODUCT AND AN UNCHANGED ENZYME MOLECULE. THE ENZYME IS NOT CONSUMED OR CHANGED WITHIN THE REACTION THEREBY ALLOWING CONTINUOUS CATALYSIS.
To understand the specificity of enzymes, you have to understand the ‘Fischer’s lock and key hypothesis’.
The basis of the lock and key hypothesis;
Just like each lock is specific to a certain key and can only be opened by that key…. An enzyme would only bind with a certain substrate. The enzyme acts as the lock and the substrate acts as the key. The substrate binds to the enzyme via its active site, which has a shape similar to that of the substrate. The bond formed between the active site and the substrate is weak, i.e. hydrophobic bonds, and alters the substrate to allow a favorable reaction. When the reaction occurs, the enzyme releases the products and moves on.
The first enzyme to take action in bread dough is amylase. Amylase reacts with starch (either amylose or amylopectin), and breaks the chain between adjacent sugar rings. There are two kinds of amylase: α-amylase randomly breaks the chain into smaller pieces while β-amylase breaks maltose units off the end of the chain.
Flour is made up of wheat kernels which contains amylase. Wheat kernels contain amylase because they need to break starch down into sugar to use for energy when the kernels germinate.
Amylase is a large molecule with hundreds of amino acids and is activated when water is added to the flour. Many different groups contribute to the bonding between the amylase and the starch substrate.
Because of amylase, some of the starch in bread dough is broken into maltose, a double-ring sugar composed of two glucose molecules; but fermentation reactions require single glucose rings. Simple sugars like glucose also provide flavor to the bread and participate in browning reactions that occur at the crust during baking.
This is where the yeast used in bread-making comes into play as yeast contains the enzyme maltase, which breaks maltose into glucose. Yeast absorbs a maltose molecule and the maltase binds to the maltose and breaks it into two glucose molecules.
Yeast cells also contain invertase, another enzyme that can break sucrose. This enzyme works on the small percentage of sucrose found in the flour. These two enzymes are responsible for producing much of the glucose needed by the yeast for fermentation.
The other major enzyme at work in bread dough is protease. Protease acts on protein chains, breaking the peptide bonds between amino acids. There are hundreds of proteases, but only a few are found in bread dough, where they chop the gluten into pieces. Proteases occur naturally in flour, yeast cells, and malt.
Gluten is a combination of proteins that forms a large network during dough formation. This network holds the gas in during dough proofing and baking. The strength of this gluten network is therefore extremely important for the quality of all bread raised using yeast. This is why only a little bit of protease is required, as it would soften the dough making it more workable and too much protease activity would break up the gluten, destroying the network that forms during kneading. If the dough is allowed to rest, proteases have time to work before kneading, making the dough easier to knead.
In addition to affecting the consistency of the dough, proteases affect its flavor. Proteases result in single amino acids when they break the last peptide bond of the protein chain. These amino acids can participate in the flavor and browning reactions that occur at the crust during baking.
So these magnificent enzymes help to make amazing things in the kitchen like:
this focaccia and ciabatta bread;
The crust for this pizza;
and the ‘carrier’ for these sandwiches
Without enzymes, bread-making would not be possible. Then again, neither would we.
Happy eatings to all 😀