In continuation with last diacussion on Flour Miling now would like to discuss about chemical analysis of Wheat Flour. Here is a brief of the same:
MOISTURE (AACC method 44-19.01)
1. A small sample of flour or ground wheat (2 to 3 grams) is weighed and placed in a moisture dish.
2. The sample is heated at 130 degrees Celsius in an air oven for 1 hour.
3. The sample is cooled to room temperature and the residue is weighed.
• Moisture content is determined by heating a flour or ground wheat sample in an air oven and comparing the weight of the sample before and after heating.
• The amount of weight loss is the moisture content.
• Moisture content results are expressed as a percentage.
Determining moisture content is an essential first step in analyzing wheat or flour quality since this data is used for other tests. Flour millers adjust the moisture in wheat to a standard level before milling. Moisture content of 14 percent is commonly used as a conversion factor for other tests in which the results are affected by moisture content. Moisture is also an indicator of grain storability. Wheat or flour with high moisture content (greater than 14.5 percent) attracts mold, bacteria, and insects, all of which cause deterioration during storage. Wheat or flour with low moisture content is more stable during storage. Moisture content can be an indicator of profitability in milling. Flour is sold by weight, grain is bought by weight, and water is added to reach the standard moisture level before milling. The more water added, the more weight and profitability gained from the wheat. Wheat with too low moisture, however, may require special equipment or processes before milling to reach the standard moisture level. Other methods of determining moisture content are used in the industry.
PFA limit- 14% max.
ASH CONTENT (AACC Method 08-01.01)
1. A sample of flour or ground wheat (3 to 5 grams) is weighed and placed in an ash cup.
2. The sample is heated at 585 degrees Celsius in an ash oven until its weight is stable (usually overnight).
3. The residue is cooled to room temperature and then weighed.
ACID INSOLUBLE ASH
1. Ash obtained above is boiled with 25 ml HCl (1:2.5) for 5 minutes in water bath, covering the dish with watch glass.
2. It is then filtered through ashless fliter paper No. 40.
3. The residue is washed with water until free of acid.
4. It is then ignited at 6000C for 20 min.
5. It is then cooled and weighed.
• Ash content is determined by high temperature incineration in an electric muffle furnace.
• When a sample is incinerated in an ash oven, the high temperature drives out the moisture and burns away all the organic materials (starch, protein, and oil), leaving only the ash. The residue (ash) is composed of the noncombustible, inorganic minerals that are concentrated in the bran layer.
• Ash content results for wheat or flour ash are expressed as a percentage of the initial sample weight. Wheat or flour ash is usually expressed on a common moisture basis of 14 percent.
The ash content in wheat and flour has significance for milling. Millers need to know the overall mineral content of the wheat to achieve desired or specified ash levels in flour. Since ash is primarily concentrated in the bran, ash content in flour is an indication of the yield that can be expected during milling. Ash content also indicates milling performance by indirectly revealing the amount of bran contamination in flour. Ash in flour can affect color, imparting a darker color to finished products. Some specialty products requiring particularly white flour call for low ash content while other products, such as whole wheat flour, have a high ash content. Acid insoluble ash indicates silica contamination.
Ash- Max 1%
AIA- Max 0.10%
GLUTEN (AACC method 38-10.01)
1. 25 gram flour is kneaded with about 15 ml water to make a dough ball.
2. The dough ball is allowed to immersed in water for one hour to ensure hydration.
3. After this the starch is washed out by kneading gently in a gentle stream of water over a fine sieve of silk till the washed liquid is clear.
4. The cohesive gluten obtained is pressed as dry as possible & then weighed.
5. The wet gluten so obtained is then dried at 1000 C for 24 hr. and weighed again to get the value for dry gluten.
Gluten in a sample can be estimated by washing the dough free of starch, sugars, water soluble proteins, and other minor components. The wet cohesive mass obtained is wet gluten while the dried product obtained from it is called dry gluten
It helps to understand the gluten content in flour and thereby selection of flour as per the product to be manufactured.
FALLING NUMBER (AACC Method 56-81.03)
1. A 7-gram sample of ground wheat or flour is weighed and combined with 25 milliliter of distilled water in a glass falling number tube with a stirrer and shaken to form a slurry. When grinding a wheat sample to perform a falling number test, it should be at least 300 grams to assure a representative sample
2. As the slurry is heated in a boiling water bath at 100 degrees Celsius and stirred constantly, the starch gelatinizes and forms a thick paste.
3. The time it takes the stirrer to drop through the paste is recorded as the falling number value.
• The falling number instrument analyzes viscosity by measuring the resistance of a flour-and water paste to a falling stirrer.
• Falling number results are recorded as an index of enzyme activity in a wheat or flour sample and the results are expressed in time as seconds.
• A high falling number (for example, above 300 seconds) indicates minimal enzyme activity and sound quality wheat or flour.
• A low falling number (for example, below 250 seconds) indicates substantial enzyme activity and sprout damaged wheat or flour.
The level of enzyme activity measured by the falling number test affects product quality. Yeast in bread dough, for example, requires sugars to develop properly and therefore needs some level of enzyme activity in the dough. Too much enzyme activity, however, means that too much sugar and too little starch are present. Since starch provides the supporting structure of bread, too much activity results in sticky dough during processing and poor texture in the finished product. If the falling number is too high, enzymes can be added to the flour in various ways to compensate. If the falling number is too low, enzymes cannot be removed from the flour or wheat, which results in a serious problem that makes the flour unusable.
ALCOHOLIC ACIDITY % as H2SO4 :
1. About 8-10g sample is weighed in & flask & freshly prepared 50ml of 90% neutralized ethylalcohol is poured in sample & allowed to stand overnight with occasional shaking.
2. The alcoholic extract is filtered through Whatman Filter paper no. 1 in a conical flask
3. Initial 10 ml extract is rejected and balance quantity is rejected.
4. 10 ml of extract is then titrated against 0.05 N Sodium hydroxide solution using phenolphthalein as indicator.
It is expressed as H2SO4
The Acidity due to the presence of acidic Organic materials in the flour- expressed as H2SO4. Higher alcoholic acidity is an indication of higher acidity of the germ oil in the flour though there is no direct relationship or equivalence between the two.
GERM OIL CONTENT AND ACIDITY :
1. The flask with the extracted germ oil is treated with 50 ml of benzene-alcohol-phenolphthalein mixture.
2. Contents are mixed thoroughly & then titrated against 0.05 N Sodium hydroxide.
3. End point is the appearance of pale permanent pink colour.
During wheat milling, irrespective of the care taken by millers, a small amount of Germ is bound to be mixed with the endosperm. Germ, with its high content of fat is prone to deterioration. While the higher content of germ oil in flour is an indication of poor milling/higher extraction rate. Higher acidity of the germ oil is an indication of the age & storage of wheat/flour. The acidity of extracted fat in biscuits is greatly influenced by the germ oil content & acidity in the flour.
SEDIMENTATION VALUE (AACC method 56-60.01)
1. A small sample of flour or ground wheat (3.2 grams) is weighed and placed in 100-milliliter glass-stoppered graduated cylinder.
2. Water (50 milliliter) is added to the cylinder and mixed for 5 minutes.
3. Lactic acid solution is added to the cylinder and mixed for 5 minutes.
4. The cylinder is removed from the mixer and kept in upright position for 5 minutes.
5. The sedimentation volume is recorded.
• The sedimentation test is conducted by holding the ground wheat or flour sample in an acid solution.
• During the sedimentation test gluten proteins of ground wheat or flour swells and precipitate as a sediment.
• Sedimentation values can be in the range of 20 or less for low-protein wheat with weak gluten to as high as 70 or more for high-protein wheat with strong gluten.
• The sedimentation test provides information on the protein quantity and the quality of ground wheat and flour samples. Positive correlations were observed between sedimentation volume and gluten strength or loaf volume attributes. The sedimentation test is used as a screening tool in wheat breeding as well as in milling applications.
Would like to have your inputs/comments on the same.