See also: starch - rice starch - corn starch - wheat starch - potato starch
So is the Fecola
In common parlance, the term starch identifies the starch contained in potato tubers (Solanum tuberosum, Fam. Solanaceae). In reality, the name “starch” also belongs to the starch obtained from bananas, chestnuts, sago, maranta and cassava.
In the production process, the tubers are first washed and pulped, then left to macerate in water. The starch is then obtained by sieving the milky liquid that comes out of it, very rich in starch and other nutrients (soluble proteins and mineral salts), then separated by centrifugation.
From a chemical point of view, there are no significant differences between the various types of starch, except for the percentage of amylose / amylopectin and the morphology of the granules, which have a different structure and size depending on the plants from which they derive. If observed under the microscope, the starch is characterized by the presence of isolated granules, rather large (up to 150 μm), oval-shaped, similar to a pear or a shell, with eccentric hilum and marked streaks.
Amylose and Amylopectin
Like all starches, starch is made up of two different glucose polymers:
- Amylopectin (80%): branched molecule, more easily digestible, with a high glycemic index, responsible for gelatinization and the thickening and stabilizing properties of gels and emulsions;
- Amylose (20%): linear molecule with lower viscosity, responsible for the reorganization of starch after cooking (resistant starch, stale bread, etc.).
Compared to wheat starch, and even more so to corn starch, starch is richer in amylopectin (70% in corn, 75% in wheat), while the gelatinization temperature is around 60 - 65 ° C.
In 2005, the cultivation of a new waxy potato variety (Eliane) was started, containing a starch consisting practically only of amylopectin. Like waxy corn, this characteristic is rather sought after by the food industry, as it increases the thickening properties of the product. The addition of starches rich in amylopectin therefore allows you to save on the basic ingredient (yogurt, sauces, cheeses, creams, sausages, pastries, puddings, preserves, etc.) both for quality and quantity Unfortunately the result is a more palatable product, with some better organoleptic characteristics but deprived of some of its precious nutrients.
Influence of Temperature and Humidity
At room temperature, potato starch is insoluble in water and ethanol, but its solubility increases significantly due to the combined effect of water and heat. With heating, in fact, the starch particles undergo transformations that make them capable of absorbing water; this leads to a perturbation of the original crystalline structure, with a consequent increase in the viscosity of the system (gelatinization).
If the heating continues, the granules swell excessively, breaking, with leakage and partial solubilization of the starch material (amylose and amylopectin), and loss of viscosity. This phenomenon, following gelatinization, is called "pasting" and leads to the formation of what is commonly defined as a starch weld.
If the system is subsequently subjected to cooling, the starch molecules are reorganized into new crystalline structures (retrogradation), restoring structure and viscosity to the system (when this characteristic is negative for the product, it is necessary to choose starches that are poorer in amylose).
Unlike potato flour, starch contains only a high carbohydrate fraction (91%), while fats are present only in traces, with a rather modest amount of protein (about 1.4%). Consequently, starch it brings to the organism empty calories, conspicuous from the quantitative point of view but deprived of all those substances necessary in the diet (proteins, fats, minerals and vitamins).
Given the absence of gluten, potato starch can also be used as a diet for celiacs.
In the kitchen, potato starch finds its main use in the preparation of pastry products.