Starch, an essential part of our food, provides us and many other species with essential energy. It is a type of complex carbohydrate that is widely distributed in plants and serves as the main source of energy storage. Amylose and amylopectin are the two principal polysaccharides that make up starch. Although there are certain similarities between these two, they also have unique qualities that set them apart. This makes them fascinating objects of study.
Starch is classified as a polysaccharide, which is a type of carbohydrate consisting of multiple sugar molecules linked together. In the case of starch, these sugar molecules are primarily glucose units. The individual glucose units in starch are connected by glycosidic bonds, which are chemical bonds formed between the carbon atoms of adjacent glucose molecules. These bonds create long chains known as polysaccharides, mainly amylose and amylopectin.
Starch demonstrates distinctive chemical characteristics like retrogradation and gelatinization. Starch granules get gelatinized when heated in the presence of water, which causes the granules to expand and absorb water. The structured structure of starch gets disrupted during this process, which causes a viscous gel to form. However, retrogradation is the process whereby the gelatinized starch goes through a rearrangement upon chilling, resulting in the creation of insoluble amylose and amylopectin complexes. Retrogradation is the process that causes items made from starch to stiff or stale over time.
You might also like: What Is Xanthan Gum And Its Substitutes?
Gelatinization and retrogradation are both processes that can be controlled by understanding the molecular structures and properties of starch, as well as its major components, amylose and amylopectin. The way they interact during cooking, baking, and using other food processing methods has a big impact on the qualities of the finished product, from sensory attributes to stability.
Let’s see the difference between amylose and amylopectin.
AMYLOSE VS AMYLOPECTIN
As already mentioned, amylopectin and amylose are two major components of starch. Amylopectin, a branching polysaccharide, accounts for the majority of starch. It has a linear chain of glucose molecules connected by α-1,4-glycosidic linkages, comparable to amylose. However, amylopectin contains more α-1,6-glycosidic linkages, which provide branching points. These branches appear at regular intervals, resulting in a heavily branching structure that looks like a tree. Amylopectin’s branch points enhance its molecular weight, making it bigger and more complex than amylose. The molecular weight of amylopectin is 300 times more than that of amylose.
Amylose is a polysaccharide composed of glucose units that are interconnected solely by α-1,4-glycosidic linkages, forming a linear structure. In contrast to amylopectin, amylose’s linear arrangement enables close packing and organization, leading to a more condensed molecule. The spatial orientation of glucose units within amylose tends to adopt a helical configuration, adding to its distinctive molecular shape.
The ratio of amylopectin to amylose in starch varies between sources and has a significant impact on its characteristics. Starches with a greater amylopectin content have more branching and, as a result, are more soluble and digestible. The branching form of amylopectin gives a wider surface area, allowing enzymes to easily reach the glucose molecules for digestion. Starches with a higher amylose content, on the other hand, have a more rigid and resistant structure, resulting in longer digestion and a more progressive release of glucose.
The ratio of amylose to amylopectin determines the characteristics and functions of native starches from diverse sources. Waxy maize has a nearly 100% amylopectin ratio; potato, tapioca, and rice starches also have a high amylopectin percentage when compared to wheat and dent corn starches. The trace amounts of phosphate, protein, and lipids also influence the properties of starch.
Let’s discuss further.
Solubility and Digestibility
The solubility of amylose is typically higher than that of amylopectin due to their contrasting molecular properties. Amylose has a more compact and orderly structure with fewer branches, enabling improved interaction between water molecules and the individual amylose chains. As a result, amylose exhibits greater solubility. The linear configuration of amylose facilitates the easy entry and hydration of water molecules, leading to the formation of a colloidal dispersion.
In contrast, amylopectin’s highly branched structure limits the interaction between water molecules and the starch chains. The numerous branching points and side chains in amylopectin hinder the water’s ability to effectively solvate and separate the individual chains. As a result, amylopectin exhibits lower solubility in water compared to amylose.
And in terms of digestibility, amylopectin is more digestible than amylose. The ratio of amylose and amylopectin is one factor that affects starch digestibility. Amylose’s linear structure makes it more resistant to enzymatic digestion by amylase, the enzyme responsible for starch breakdown. This resistance is caused by the limited accessibility of the α-1,4-glycosidic linkages in amylose’s tightly packed helical shape. But in the case of amylopectin, the presence of α-1,6-glycosidic bonds at branch points allows amylase enzymes to easily cleave the -1,4-glycosidic bonds. Because of this accessibility, amylopectin is broken down and digested more quickly, resulting in the rapid release of glucose during digestion.
Functional properties of amylose and amylopectin
Understanding the distinct characteristics of amylose and amylopectin is essential for harnessing their functionalities and leveraging them in product development and formulation.
Amylose can produce gel at concentrations above 0.9 to 1.0%, even at room temperature. This is because of its linear structure, wherein the amylose molecules. Because of its linear structure, amylose molecules can associate and form a network, resulting in the creation of firm and stable gels. These amylose gels exhibit remarkable thermal stability, remaining intact even at high temperatures of up to 248°F (120°C). This characteristic is especially essential in confectionery applications, where gels provide texture, shape, and stability to goods such as gummy candies and fruit snacks.
In contrast, amylopectin typically does not contribute significantly to gel formation. As the amylopectin content increases, the resulting starch paste becomes more viscous, albeit without the formation of a gel structure. A higher concentration of amylose promotes the formation of a stronger gel, as amylose molecules readily associate and establish chemical linkages. Only at concentrations above 10% and temperatures below 41°F (5°C) does amylopectin have the potential to form gels. However, the gelation process is slow, and the resulting gels are thermoreversible. So they melt when exposed to temperatures between 104°F (40°C) to 140°F (60°C), similar to starch gels.
In some processes where the starch must exhibit stability throughout the product’s expected shelf life, starch may be modified. Specific modified starch varieties enhance the stability of products during various processes. An example of such modified starch is the “waxy” corn variety. This is a starch that has minimal or no amylose content and a higher concentration of amylopectin. So it does not readily form networks or meshes. As a result, it imparts improved resistance to congealing and separation when cooled. Thus, it is suitable for sauces and gels. Additionally, waxy starches prevent liquid leakage or the formation of watery residue when products are defrosted, addressing a common issue associated with high-amylose starches.
Both amylose and amylopectin have the ability to modify the viscosity of foods. They improve the mouthfeel and texture of sauces, gravies, soups, and desserts. But amylopectin’s branching structure improves water-binding capability, resulting in greater stability and texture in a variety of food formulations.
References
M. Gibson (2018). Food Science and the Culinary Arts. Academic Press.
P. Cheung, B. Mehta (2015). Handbook of Food Chemistry. Springer.
J. deMan, J. Finley, W. Jeffrey Hurst, C. Y. Lee (2018). Principles of Food Chemistry (4th edition). Springer.
. Provost, K. Colabroy, B. Kelly, M. Wallert (2016). The Science of Cooking: Understanding the Biology and Chemistry Behind Food and Cooking. John Wiley & Sons, Inc.
S. Damodaran, K. Parkin (2017). Fennema’s Food Chemistry (5th edition). CRC Press.
N. A. Michael Eskin, F. Shahidi (2013). Biochemistry of Foods (3rd edition). Academic Press.
V. Vaclavik, E. Christian (2014). Essentials of Food Science (4th edition). Springer.
