Does flour have a soul?
Let’s look at the Flour! Every day we come across with a wide variety of food, both from animal and vegetable origin. We handle it, look at it, sometimes cook it, and eat it....
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Every day we come across with a wide variety of food, both from animal and vegetable origin. We handle it, look at it, sometimes cook it, and eat it. Often we have wondered what its appearance would be under a simple magnifying glass or at much greater magnification, for example employing an optical microscope or a scanning electron microscope.
In this short article, we will see how flour, a product of plant origin, appears and is used every day.
First, what is flour? When we use this term without introducing any further specification we mean wheat flour obtained from the grinding of wheat grains. In reality, behind this term, there are various types of flour, the result of grinding different kinds of wheat grains: durum wheat, soft wheat, spelt, etc. On the other hand, we specify which flour we intend to talk about when it comes to the product of rice, chestnuts, potatoes (potato starch), corn grinding (Fig. 1) .
There are many types of flour obtained from different plants all around the world. Some of these are particularly successful in the food sector and widely marketed. Others are relegated to traditional uses in the cuisine of more or less defined geographical areas.
Parts of the plants, which are particularly rich in starch, are grounded to obtain the flour. Starch is the energy reserve par excellence of vegetables and is made up of long molecules that are formed by polymerization of glucose, the sugar synthesized with the photosynthetic process starting from water and carbon dioxide, thanks to the energy supplied by sunlight. Plants store starch in the seeds to provide for the first energy needs of the new young plants when these have not yet properly developed the green parts where photosynthesis takes place. They also store it where photosynthesis is not possible because there is no light, such as in the central part of the stems or in the underground portion of their body.
At the cellular level, the starch of plants is formed inside special organelles that take the name of amyloplasts (also called leucoplasts, if we want to emphasize the fact that they are white and not green like chloroplasts) (Fig. 2).
Starch is progressively stored around a hilum, which can be either point-like, or linear, or branched, forming the starch granule that will grow to reach dimensions that can vary also within the same plant. Furthermore, the shape the starch grain acquires can be different, from spherical to ellipsoidal, ovoid or polyhedral. There are starch granules that are formed starting from a single point called hilium (simple granule) and granules that are formed starting from an even large number of distinct hila (compound granules). The original structure of the starch granules modifies during the cooking process. The compound granules tend to disintegrate and give origin to types of flour that are easier and faster to digest. In fact, due to the granules disintegration, the surface attackable by digestive enzymes is considerably increased. An example is rice flour that people use in the diet of young children and that, as known, causes a rapid glycemic increase in those who eat rice, greater than the increase observed in those who have eat pasta made from wheat flour, which is composed of simple granules. The size and shape of the granules, together with the morphology of the hilum, are important characteristics for identifying the plants from which the flour derives.
If we observe the flour under an optical microscope, the difference among the starch granules of the different types of flour becomes evident. We can see that wheat flour (Fig. 3) is composed of simple granules, lenticular in shape and with a central point-like, linear, or Y-shaped hilium, and a large number of very small spheroidal granules.
Potato flour (Fig. 4) is composed of ovoid granules or irregular yet still rounded granules, of variable dimensions, which can be even substantial. The hilum is point-like and eccentric. The granules have marked concentric streaks that are not – or hardly – noticeable in other varieties of flour.
Rice flour (Fig. 5) is formed by small angular grains with a central hilum united in very compact compound granules.
All the flour granules, if not altered during cooking and not damaged during the grinding, have a particular feature when observed in polarized light (Fig. 3, 4, 5): the whole granule appears luminous and crossed by two dark lines that meet at the level of the hilum to form a more or less regular cross.
With the scanning electron microscope, the starch granules (Fig. 6) appear rather smooth and with rounded profiles.
Man produces flour since the Paleolithic, using spontaneous plants found in the environment.
The oldest flour we know dates back more than 30,000 years.
MARTA MARIOTTI LIPPI
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