Laboratory‎ > ‎Analysis of Flour

Theory: 

Wheat quality and methods in wheat quality determination is important. Determination of the quality of bakery products which have significant position in the food industry and nutrition is necessary from the point of product features and economic view. However, the choosing appropriate raw material according to that appropriate quality of wheat/flour/semolina is very important to produce products such as bread, biscuit etc. Beside that methods and analysis which are used to determine the quality must be applied exactly and results must be well evaluated by the aid of good qualified technical person and equipment. Nowadays the importance of technical person, equipment and methods for determination of quality is accepted by the consumers and producers.

Wheat is important than other grain. Because;

1-It is raised in large area due to fit different climate and earth condition.

2-high yield and easy agriculture

3-easy storage and high nutrition value

4-when wheat flour is contact with water, protein particles in flour form gluten (wet germ).No grain’s protein except wheat form wet germ.

Wheat Kernel

Wheat kernel contains some layers, germ, endosperm, aleuron layer, bran, outer kernel layer. The germ and bran are removed from the kernel when white flour is milled, even though they contain nearly all the fiber and B vitamins; they are removed because they also negate the elastic properties of the gluten, which is so vital to the texture and crumb of the bread.

The percentage of total product in any desired fraction of flour is called extraction. In other words, straight grade flour that is %72 of the total product is % 72 extraction flour. The composition of flour with various percent extractions is given

Approximately composition of flour

Component

Flour

(72%)

Flour

(80%)

Whole meal

(95-100)

Wheat

Germ

Wheat

Bran

Moisture (%)

13-15

13-14.5

13-14

9-12

14

Protein (%)

8-13

8-14

10-15

25-30

12-16

Fat (%)

0.9-1.4

1-1.6

1.5-2.5

8.5-11

3-4

Carbohydrate (%)

65-70

64-70

60-68

39-45

Fibre(%)

0.1-0.3

0.2-0.4

1.8-2.5

2-2.5

9-12

Ash (%)

0.3-0.5

0.6-0.9

1.2-2.0

4.0-4.5

4-6

 

Wheat that is between the bread and pastry types are used for cracker, doughnut, and all purpose flour. There are physical and chemical test of flour. These:

Physical Tests: including test weight, kernel hardness, gluten washing, density, internal infestation evaluation, thousand kernel weight, pearling index, granulation and particle size.

Chemical Tests: Moisture, ash, and protein tests are the most widely used on wheat. The kjeldahl protein test normally is made on al hard wheat. To report protein content on uniform moisture basis, the moisture lost is necessary. Miller and Johnson (1954) state that moisture is related to quality of wheat and flour in at least three ways:(1)flour yield varies inversely with moisture content (2)composition percentage are inversely related to percentages of moisture  present; and(3)deterioration of grain during storage may depend on the moisture relationships in the wheat kernel.

The ash test is significant as a way to determine flour grade. Since the ash content of bran is about 20 times that of endosperm; the ash test indicates how thoroughly bran and germ were separated from the kernel endosperm. There is considerable variation in the amount of mineral matter in wheat, depending on the class of wheat and the area it was grown; therefore, the ash test is often applied to wheat as well as to flour.

Color tests, such as the Pekar or the slick test, also are used to judge milling results or flour grade, and recently photo electric methods such as the Agtron for assessing flour color have come into use. Many attempts have been made to appraise wheat quality on the basis of the amino acid composition of wheat gluten. Determining the amino acid composition of wheat is no longer a tedious and expensive procedure, but pence 1950 failed to show essential differences in the amino acid content of 17 flours milled from different varieties and types of wheat.

Starch damage is a subject of recent concern to wheat processors and to the baker. The extent of starch damage alters flour characteristics and end use.

The amylase activity of wheat and flour are measured by the Falling Number test, Blish-Sandstedt method, and the amylograph. The description of those tests and other mentioned can be found in Cereal Laboratory methods (1962) and wheat and wheat technology.

Variental Differences in Gluten Quality: Many techniques have been developed to separate gluten from the other constituents of wheat flour. The washing-out process can be done by hand or mechanically. A quantitative test consist merely of weighing the gluten either wet or after being dried, but estimating gluten quality is a more difficult matter.

The measurement of gluten quality has been based on four general principles, namely; expansion by heat, recovery from compression, and gluten extension and gluten relaxation of gluten.

Although there is agreement that many properties of dough are due to the gluten component of flour, most cereal chemist in the United States prefer to study the properties of dough rather than to separate gluten and thus attempt to appraise quality. Regardless of the methods used, differences in gluten properties between classes and varieties of wheat are obvious

The production of flour affects quality of making bread. Therefore, before production of flour, suitable wheat must be selected firstly and analyzed in laboratory. Hence, produced flour is both high in quality and suitable for quality.

The flour production is made three different type of wheat;

  • Triticum durum: for macaroni

  • Triticum aestivum: for bread

  • Triticum compactum: for biscuit

 Some criterions very important for flour;

  • amount of protein and quality

  • amount of normal starch and damaging starch

  • moisture content

  • amount of aflatoxin

  • amount of alfa amilaze

Procedure: 

                Analysis of Flour

The routine analysis of  flour may include the determination of moisture, ash, added chalk,SO2,oil,protein,acidity,iron,thiamine and nicotinic acid, an examination for improves and bleaching agents and a microscopic examination.

Industrially, certain other types of analysis are of some importance, etc., examination of the gluten, physical tests on the dough produced from the flour, determination of the particle size, maltose, color and grade figures.

Determination of Ash in Wheat Flour

Materials: Bunsen burner, porcelain cruse, desicator, flour, oven, balance.

Procedure:  First of all 2gr of flour was weighed into well-dried porcelain, and then was heated onto a Bunsen burner until 350-400 oC then it was transferred into oven. After two hours ash was transferred to desicator. After cooling it was weighed. Finally total ash was calculated as a percentage of samples.

Determination of Crude Gluten in Flour

Materials: Beaker, flour, KI, balance.

Procedure: Firstly 25gr of flour was placed in beaker, added about 25ml water, and mixed into dough with a spatula. Then was kneaded the dough gently under water for 10-15min, so that soluble matter and starch were washed away. KI was used to control presence of starch. Then rolled dough into a ball was weighed the moist gluten and expressed as percentage of flour. Also was noted its color. Then it was dried at 100oC   to constant weigh and expressed repeat as a percentage of flour.

Acidity of Wheat Flour

Material: Conical flask, water bath, clear filtrate, phenolphthalein

Procedure: 18gr of flour was shaken with 200 ml of CO2-free water in a conical flask. Then it was placed in a water bath at 40 degree for 1hour with flask. And filtered then titrated with 0.05 M NaOH solution by using phenolphthalein as an indicator. Finally the acidity of the water extract was calculated as KH2PO4 or lactic acid.

Moisture Content of Wheat Flour

Materials: Pre-dried dish, desicator, oven, balance

Procedure: 5 g of sample was weighed and placed into dish. But it was noticed that we should spread the sample as thinly as possible over the base of the dish. Then was put dish in oven maintained at 105oC, and dried for 2hour.And was removed to cool in desicator and weighed. We must not forget to continue until a constant weight has been reached. Finally; the moisture content from the weight loss of the sample was calculated.

Results:

Group No

Ash

Moisture Content

Acidity

Soy Flour

Gluten %

Name of Sample

Wet

Dry

A-9

1,0535

11,108

0,196

+

15,57

5,715

Opened Flour

A-10

0,81

15,20

0,2712

+

10,6

3,74

Bread Type Flour

A-11

3,69

10.072

0,578

+

41,5

18,64

Bran Mixed Flour

A-12

6,512

7,74

0,260

+

0

0

Corn Flour

A-13

5,758

7,325

1,02

+

95,075

46,918

Soy Flour

A-14

 

9,68

0,277

+

31,5

30,82

Pınar

A-15

0,925

9,46

0,333

+

28,67

11,97

Home Flour

A-16

0,9

12,4

0,236

+

15,9

Tat Semolina

Discussion: 

In this experiment we made moisture, ash, gluten and acidity analysis of different types of flours. We should compair our samples with each other,and then TS 4500.

But we should understand and learn limition of quality standards and Why is important for human health. For instance;the moisture content of flour is a important point for us.We observed moisture contents between 7.325 (Soy Flour) and 15,20 (Bread Type Flour) Our samples, except “bread type flour” are suitable for moisture content according to TS 4500 because it should not be over limit %14.5.

The reason of moisture content can be many such as klimate,wetand temperature of warehouse or rain harvest.More wet amount cause a problem during milling.

One other way of quality determination is ash of sample.Obtained resuls by at the end of experiment changes between 0.81 and 6,512.The percentage amount of Bran is higher with compair to normal flour.Because inorganic matter diffuse quickly into Bran,then they diffuse inside wheat particles.So,inorganic matter exist in low amount at center of wheat particles.Ash contents of  bran mixed, corn and soy flours are too high according to TS 4500 because maximum value is 2,0 for “under semolina flour”.

Also a important quality analysis is gluten amount determination of flour and bran.If gluten amount of flour is high sufficient,this is very well.Because this effect swelling of bread during fermentation of yeast in it.At the end of reactions CO2 gases is produced during fermentation.In this event,gluten service to hold to coming out CO2 gases.Dry gluten results of samples, except bread type flour are suitable,according TS 4500 it should not be under 9%.Our results are higher than this values.

References: TÜRK GIDA KODEKSİ BUĞDAY UNU TEBLİĞİ (Tebliğ No: 99/1)

TS 4500

    Food Quality Control Laboratory Manual;

                        Hüseyin BOZKURT and Fahrettin GÖĞÜŞ

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