What Is GDU?
• GDU is Gelatin - Unit of Enzyme Viability
GDU is Gelatin - Digesting Units. It is a specific unit that measures the activity of pineapple protease. Simply put, the higher the value of GDU, the greater the ability of bromelain to break down gelatin, a protein substrate. For example, one GDU of bromelain is capable of digesting a certain amount of gelatin in a certain amount of time (e.g., one hour) under defined experimental conditions.
This unit is set so that the measure of enzyme activity can be standardised. This is because the activity of an enzyme plays a crucial role in its effectiveness in various applications. In industrial production and scientific research, the activity of an enzyme needs to be known precisely to use the enzyme preparation appropriately.
• Relationship between GDU and enzyme activity
There is a positive correlation between the activity of pure bulk bromelain powder and GDU values. When we say that a bromelain product has a higher GDU value, it means that it can break down proteins faster and more efficiently. In food processing, for example, during meat tenderisation, a bromelain enzyme with a high GDU value breaks down the myofibrillar proteins in the meat faster, resulting in more tender meat.
From the chemical kinetics point of view, enzyme activity (measured by GDU) determines the rate of enzyme-catalysed reaction. According to the Mie equation (v = Vmax [S]/(Km+[S]), where v is the rate of reaction, Vmax is the maximum rate of reaction, [S] is the concentration of the substrate, and Km is the Mie constant), the higher the enzyme activity (the higher the GDU value), the faster the rate of reaction will be, provided that there is sufficient substrate. It is like in a factory, the higher the efficiency (GDU) of the worker (enzyme), the faster the product (broken-down protein product) is produced.
Factors Affecting GDU
The GDU (Gelatin Digestion Unit) value of bromelain reflects the activity of the enzyme. It is influenced by a number of factors.
1. Temperature factor
• General effect of temperature on enzyme activity
Bromelain is like most enzymes. Its activity has a significant temperature dependence. Within a certain temperature range, the activity of the enzyme will gradually increase as the temperature rises. This is because an increase in temperature increases the thermal movement of molecules. This will make it easier for substrate molecules and enzyme molecules to collide with each other, thus speeding up the rate of the reaction. For example, at lower temperatures, such as 10 - 15°C, the activity of bromelain is lower. Its GDU value is also relatively small.
The optimum temperature for pure bulk bromelain powder is usually around 37 - 40°C. In this temperature range, the active centre of the enzyme molecule binds to the substrate most efficiently. It breaks down gelatin quickly and efficiently and the GDU value is at its highest. The catalytic reaction of the enzyme can proceed efficiently when the temperature is close to the human body temperature (37°C). This corresponds to the environment in which bromelain acts in living organisms.
• Effects of Excessive Temperature
When the temperature exceeds the optimum temperature range, the activity of the enzyme decreases dramatically. This is because high temperatures cause the denaturation of enzyme proteins. The spatial structure of enzyme proteins is critical to their activity. Excessive temperature destroys the secondary and tertiary structure of the enzyme molecule. This causes a conformational change in the active centre, which loses its ability to bind substrates and catalyse reactions. For example, when the temperature reaches 60 - 70 ℃, bromelain bulk powder will undergo severe denaturation and the GDU value almost to zero.
2. pH Factor
• General effect of pH on enzyme activity
The activity of bromelain is also strongly influenced by pH. Different pH environments will change the charge state of the enzyme molecule's active centre and the enzyme protein's conformation. Within a certain pH range, enzyme activity varies with pH. Generally speaking, bromelain shows better activity in the pH range of 6 - 8, with relatively high GDU values.
In this pH range, the dissociation of acidic and basic amino acid residues in the enzyme molecule is favourable for the formation of the correct enzyme-substrate complex with the substrate. For example, at around pH 7, the active centre of the enzyme molecule can interact optimally with the peptide bonds in the gelatine molecule, facilitating the hydrolysis reaction.
• Effects of high or low pH
Enzyme activity decreases gradually at pH values below 6 or above 8. Enzyme proteins can be denatured in too-acidic or too-alkaline environments. For example, in a highly acidic environment (pH < 4), basic amino acid residues in the enzyme molecule are overpronated, resulting in a conformational change in the enzyme protein, destruction of the active centre and a significant decrease in the GDU value. Similarly, in an overly alkaline environment (pH > 9), acidic amino acid residues will be overly dissociated, which will also cause the enzyme to lose its activity.
3. Substrate concentration factor
● The general effect of substrate concentration on enzyme activity
When the substrate concentration is low, with the increased substrate concentration, the opportunity for the enzyme to combine with the substrate increases. The reaction rate will be accelerated and the GDU value will be increased accordingly. For example, when the gelatin concentration is increased from 0.5% to 1%, pure bulk bromelain powder has more substrate to act, the efficiency of gelatin decomposition is increased, and the GDU value increases.
• Effect of high substrate concentration
When substrate concentration is too high, the growth trend of enzyme activity will gradually slow down. This is because the number of active centres of the enzyme is limited. When the substrate concentration reaches a certain level, all the active centres of the enzyme are occupied by the substrate molecules, and increasing the substrate concentration will not significantly increase the reaction rate, and the GDU value remains stable.
The significance of GDU in different fields
• Pharmaceuticals
In medicine, bromelain has anti-inflammatory and anti-swelling effects. Its GDU value is very crucial in determining the drug dosage. For example, when treating post-traumatic swelling or inflammation, the GDU value of bromelain is needed to accurately calculate how much of the enzyme should be given to the patient. This is the only way to achieve optimal therapeutic results while avoiding possible side effects due to excessive enzyme activity.
• Food industry
In the food industry, such as the meat tenderisation mentioned earlier. Different meat products and processes may require different GDU values of bromelain. If the GDU value is too low, the desired tenderising effect may not be achieved. If it is too high, it may break down proteins excessively, resulting in a loss of elasticity and poor flavour. In addition, pure bromelain powder is used in beer production to prevent cold clouding of beer. Bromelain at the right GDU value breaks down turbidity-causing proteins, improves the stability and clarity of the beer, and extends the shelf life of the beer.
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