Waching daily Nov 26 2017

We all had that problem, the problem where you were just cutting your apples

for you afternoon snack and just when you went and get a glass of water and

when you come back to it you realize the Apple has turned brown. This is what we

called enzymatic browning. Fruits and vegetables such as apples and carrots

can be oxidized when it is left out and exposed to the air for a while leaving a

brown and dark pigment appearance to it and the longer it is the darker they

become and this happens because apples and carrots contain two enzymes called

polyphenol oxidase PPO and peroxidase POD. The common solution that everyone

knows to this problem is by salting them applying lemon juice or boiling them

Salt which binds with water can lower down the water activity of the solution

and lemon juice changes the pH value of the solution and the entire oxygen

compounds to reduce the reaction leading to inhibiting the enzyme activity.

However that would usually result in a change of the sensorial qualities and

its nutritional values which is undesirable.

Therefore in this study we seek to discover and investigate on the enzyme inhibiting effects of glucose,

fructose, sucrose as well as Maillard products on polyphenol oxidase PPO as

well as peroxidase POD but before we go through the process and results, let

us explain the components and what will be involved in this experiment.

Enzymatic browning is an oxidation reaction which is not reversible. It occurs in some of the fruits&vegetables causing

negative effects on colour, taste, flavor and nutritional value. However, it can be prevented

by adding some reducing agent to avoid the enzyme to react on the surface of

fruits and vegetables Apple is rich in PPO, polyphenol oxidase

causing it to turn brown so easily the reaction is the consequence of Phenolic

compounds' oxidation by PPO which triggers the generation of dark pigments

The active side of PPO contains Copper ions which can change between Cu+ and Cu2+. This mechanism let the enzyme pumps in a lot of Oxygen within a short period of time

to the polyphenol increasing the rate of Browning Effect! The enzyme Peroxidase allows Biological

processes to occur. It's an enzyme that oxidizes that is break down ester into two

alcohols Glucose is a monosaccharide that

provides energy when broken down. It is a polyhydroxy aldehydes with the formula

C6H12O6. Although very less amount can be found in glucose solution, the glucose

in open chain form potentially act as reducing agent to prevent enzymatic

browning. In this experiment, glucose solution are investigated on the effect

to inactivate Enzymatic Browning. Fructose has the same molecular formula

as glucose but the way atoms connect is slightly different. It's sweeter than

sucrose and it is a reducing sugar.

Sucrose is a table sugar we commonly use in kitchen. It is a disaccharide which

combines one glucose molecule and one fructose molecule. High concentration of

sucrose solution is used as preservative and in this experiment we'll figure out

its effect on preventing enzymatic browning.

Maillard reaction also known as non-enzymatic browning which is a chemical reaction

between an amino acid and a reducing sugar which require the addition of heat.

The reactive carbonyl group of sugar interacts with nucleophilic amino

group of the amino acid resulting poorly in characterized odor and flavor molecules

In this video, we will show you some sugar reducing agents and the effects

on preventing Enzymatic Browning! And now, I'm going to describe how the experiment runs. First, carrot and apple are being peeled and cut into 1cm square

cubes then they are blended together and the juice is filtered out with 4 layers of

cheesecloth. The juice is added with PPO and POD which I don't really know

where they come from. Then, take samples out of it.

After that, different concentrations of glucose, fructose, sucrose, and Maillard products are added

in the sample. However, 1 sample is remained pure as the control group. In the result, the control group is known as 100% relative activity which means if the result

is more than 100%. The enzymes are being activated and if the enzymes are inhibited, the result will

be lower than 100%. Easy to understand right? According to our results the effects of

glucose, fructose and sucrose on PPO is shown in this figure. An inhibiting

effect on PPO activity was achieved only at high concentrations of sugar

The result of sucrose stops at 1.1 mol but glucose and fructose stop

at around 2 mol. Might be due to the solutions being too saturated. The

hypotheses that we predict is that water molecules that are not binded with other

substances are free molecules which is available for chemical reactions and the

higher number of free water molecules there are, the higher water activity it

is. This provides a suitable environment for enzymes to work. So the activity of

PPO rises. However, the addition of sugar molecules will bind to free water molecules

due to the polarity of sugar molecules. Thus, the environment is in low water activity causing

the enzyme to be slightly inhibited. As for POD, an activation was observed at very

low concentrations of glucose and sucrose

the activity remained constant with increasing sugar molarity. Fructose on

the contrary showed a slight inhibiting effect. Consequently fructose was shown to be

the most effective sugar in inhibiting both enzymes. Maillard products is very effective in

inhibiting both PPO and POD. The longer time the glucose or glycine is

heated, the more effective it is. It must also be pointed out that PPO and POD

activities in the presence of Maillard reaction products cause a lag phase

which increased with increasing volume of the added solutions. In both cases

after the addition of relatively high volumes of strongly heated glucose or glycine

solutions, no activity was observed for at least 15 minutes. The Maillard

products appear to have an important role in preventing enzymatic browning ;the

strong anti browning action could be related to their antioxidant properties

but other mechanisms may be involved. In fact, Maillard reaction products have shown

two different effects on PPO and POD and inhibition of the enzyme activity

and the appearance of an initial lag phase. The presence of a lag phase may be

because of the reducing properties of some Maillard products which reduces the

early enzymatic oxidation products preventing the formation of colored

compounds. The enzymatic reaction probably starts when all the reducing

compounds that are present in the Maillard mixture are consumed. The chelating

properties of some Maillard products could also cause a decrease of enzyme activity

by reaction with Cu and Fe ions contained in PPO and POD respectively.