Starch, a paramount storage product in plants, stands as a cornerstone in human nutrition as one of the most vital carbohydrate sources. Beyond its nutritional significance, starches wield a profound influence on the textural properties of food products, making them indispensable in various food manufacturing processes.
Diverse Applications of Starch in Food Manufacturing
The versatility of starch unfolds in its multifaceted applications, serving as gelling agents for puddings, thickeners in sauces and desserts, integral components in baking products, and extending its reach into the non-food sector, particularly the paper manufacturing industry.
Starch manifests in the form of granules, their size and shape varying based on the plant of origin. These granules can take on spherical, oval, polygonal, or lenticular shapes, with diameters ranging from 2 to 175 µm. The intriguing aspect lies in the assembly of these granules, whether single, assembled in compounds, or seemingly assembled, revealing its complexity.
Compound Starch Granules: A Hidden Complexity
In compound starch granules, the true nature of individual granules becomes visible only after a swelling step. These granules, ranging from a few to several thousand in number, introduce an additional layer of intricacy. Notably, certain plants, such as wheat, rye, and barley, boast two distinct types of starch granules, each with its unique characteristics.
Starches exhibit properties influenced by granule size, shape, composition, and crystallinity, dictated by their botanical origin. Trace elements like fat, nitrogen, and phosphorus, despite their minute concentrations, contribute to the overall properties of starch granules. Water content in starches varies, impacting their characteristics, with some starches containing up to 20% water.
Decoding the Chemical Structure of Starch
Starch, primarily composed of α-D-glucose molecules, constitutes a blend of two glucanases—amylose and amylopectin. The typical ratio averages 23 ± 3% amylose to 74-77% amylopectin. Amylose, a predominantly linear molecule, forms helical inclusion complexes and tends to associate with itself. On the other hand, amylopectin, with a molecular weight of 108, emerges as one of the largest molecules in nature. Its highly branched structure, featuring α-1,6-links, imparts a unique two-dimensional, discoidal character.
Insights into Amylopectin Structure
Amylopectin showcases a cluster-like structure with A-, B-, and C-chains, each playing a distinctive role. The radial arrangement of the amylopectin molecule within the starch granule leads to a tangential alignment of crystals, forming ellipsoid structures known as blocklets. These structures contribute to the overall crystalline and semicrystalline nature of starch granules.
Unraveling Starch Crystallinity
While starch is partially crystalline, up to 30% of a starch granule consists of crystallites, and its birefringent character is evidenced by the typical dark Maltese crosses in light microscopic examinations. Starches exhibit three main X-ray diffraction patterns—A, B, and C—each associated with specific crystallinity types. The intricate interplay of factors like hydration and heat-moisture treatment can alter the X-ray diffraction pattern, leading to variations in starch crystallinity.
Starch Biosynthesis: A Cellular Symphony
Starch biosynthesis unfolds within plastids, self-replicating organelles divided into amyloplasts and chloroplasts. Amyloplasts, dedicated to starch storage, witness the growth of starch granules through radial deposition, emanating from the hilum as the growing point.
The synthesis involves a complex series of enzymatic reactions, with starch synthases and branching enzymes playing pivotal roles. The journey begins with carbon transport in the form of sucrose, metabolized into ADP-glucose, the key building block for starch synthesis.
The Bounty of Raw Materials for Starch Production
Major sources for starch production in the industry include maize, potato, tapioca, and wheat. Each raw material contributes unique characteristics to the resulting starch. Wheat starch, for instance, comprises two fractions—A-starch and B-starch—each with its distinctive granule size.
Potato tubers, a rich source of starch, undergo wet milling to produce starch with comparatively large granules. Tapioca starch, derived from the roots of Manihot utilissima, demands swift processing to prevent spoilage.
In conclusion, the journey of starch, from its varied plant origins to its intricate granule structures and crucial role in food manufacturing, showcases the nuanced interplay of chemistry, biology, and technology. As research advances, unlocking the full potential of starch promises not only a deeper understanding of its complexities but also innovative applications across diverse industries.
Some properties of wheat, potato, and tapioca starches are listed in table 2.1.
| Type of starch | Wheat | Potato | Tapioca |
| Granule size [µm] | < 45 | < 100 | < 35 |
| Diameter [µm] | 2-38 | 15-100 | 5-35 |
| Average diameter [µm] | 8 | 27 | 15 |
| Number of granules per g [x106] | 2600 | 60 | 500 |
| Number of starch molecules per granule[x1012] | 5 | 50 | 4 |
| Specific surface area [m²/ kg] | 500 | 100 | 200 |
| Amylose content [%] | 26-31 | 21-23 | 17 |
| Amylopectin content [%] | 72 | 79 | 83 |
| Gelatinization temperature [°C] | 53-65 | 58-66 | 52-64 |
| Water content [%] | 13 | 19 | 13 |
| Protein [%] | 0.30 | 0.06 | 0.10 |
| Fat [%] | 0.80 | 0.05 | 0.10 |
| Ash [%] | 0.20 | 0.40 | 0.20 |
| Phosphorous [%] | 0.06 | 0.80 | 0.01 |