Flour functional characteristics and their relationship to end-product quality
Component of Quality
* Flour quality factors can be divided into two basic groups:
* Those that are inherent in the wheat
* Those that might be altered during the process of converting the wheat into flour
Composition and Functionality of Wheat Flour Components
* Protein
* Carbohydrates
* Lipids
* Mineral content
* Vitamins
* Enzymes
Protein
. Endosperm protein possesses distinctive property of forming gluten when wetted and mixed with water.
. Gluten is the skeleton or framework of wheat flour dough, and is responsible for gas retention, that makes the production of light, leavened products
Flour Proteins
. Non-gluten, 15% (Non-dough forming) - albumins(60%)
- globulins (40%), peptides, amino acids
- flour enzymes
- Soluble, foaming proteins
- Coagulable proteins
. Gluten, 85%
a) Gliadin (low mol. wt.)
= extensible
= low elasticity
b) Glutenin (high mol. wt)
= low extensibility
= elastic
= complexes with lipid
Carbohydrates
. Starch is the principal carbohydrate of wheat and flour.
. It is present as granules sizes (small spherical granules and lenticular particles) Carbohydrates
. Starch is not usually considered a major factor influencing flour baking quality.
. But the physical condition of the granules may influence mixing time, dough handling characteristics, and response to amylolyctic enzymes.
Lipids
. Located mainly in the germ
. Consists of fatty oils (glycerides of oleic and linoleic acids), phosphatides (lecithin and sitosterol)
. Lipids may affect baking in many ways:
- Modify gluten structure at the mixing stage.
- Act as lubricants
- Improve gas retention by sealing gas cells.
- Prevent interaction between starch granules during gelatinization.
- Give some structural support to the gluten.
- Retard water transport from protein to starch
- Retard starch gelatinization
- Act as an anti-staling agent
Mineral Content
. The inorganic substance(mineral content) of wheat are concentrated in the bran and aleurone cells.
. Ash content is regarded as an indicator of the extraction (milling side)
. Ash content can have a direct effect on the baking properties of flour and is an indicator of extraction rate, therefore indirectly to color, bran specks and other characteristics which may be more difficult to specify than ash content.
Vitamins
. Wheat (like other cereals) contains appreciable amounts of vitamins of B group.
. Thiamine, riboflavin, niacin, panthothenic acid and pyridoxine are present in significant amount.
. But wheat is almost completely lacking in Vit. C unless the grain has sprouted. Vit D is also absent.
. Nearly all vitamins are much more concentrated in the bran and germ then in the endosperm.
Enzymes
. Modern methods of producing bread and other yeast-raised baked goods require the fermentation process to proceed at a uniform rate.
. Therefore the yeast must be supplied with fermentable sugar - to be converted to CO2, alcohols and aldehydes which are associated with flavor, with the help of enzymes
Wheat flour contains:
- B-amylase
- A-amylase
- Proteases
- Lipoxygenase
- Catalase
Chemical Test of Flour
* Most frequent chemical determination applied to flour are:
. pH
. Moisture
. Ash
. Protein
Moisture
. Moisture test is valuable not only because it gives a measure of the amount of "active substance" (flour solids) present in the ingredient, but it has also predictive value for storage stability.
. Flour with high moisture content can undergo microbiological deterioration.
Ash content
It is the material remaining after a sample of flour has been heated in a muffle furnace for a specified time and a specified temperature.
Protein content
. Determined using Kjeldhal method or NIR
. The value is a measure of a total organic nitrogen in the flour.
NIR Instrument
Kjeldhal Method Physical Tests
These includes:
. Farinograph
. Extensograph
. Amylograph
. Farinograph
It has a bowl in which two mixing arms operate. The resistance of the dough to the agitator arms is recorded on a chart as a function of time.
Factors measured on the curve include:
. Absorption (% of added water required to get a consistent dough)
. Dough Devt. Time (time required for maximum development)
. Stability
. Mechanical Tolerance Index
- Farinograph
- Farinograph curve
- Amylograph
. Measures the viscosity changes of starch suspension which are being heated at a
controlled rate.
. The data are related to the performance of wheat flours in certain application where
starch gelatinization is a factor.
Amylograph Instrument
Extensograph
. Measures the resistance to stretching of a cylinder of flour-water dough.
. Doughs may be measured at various intervals after mixing to show changes in
extensibility with time.
. Extensograph measurements most often of value to the bakery:
- Resistance to extension
- Extensibility
. Microbiology
- The microbial population is lower in flour than in parent wheat because much of the
microbial population of wheat is on the outer surfaces.
- Microbial population in wheat is related to growth, harvest, transport and storage
conditions.