Some Sorghum Milling Techniques versus Flour Quality

Tabat a Sudanese sorghum cultivar was collected from local Khartoum market season 2009; three samples were cleaned and prepared for milling. A commercial decorticator was used to decorticate 10% from Sample A and 5% from Sample B, Sample C was whole grain. The three samples were milled on commercial stone mill and a laboratory disc mill. The mills were set to produce the finest and coarsest possible flours. Milled stocks were analyzed to examine some milling quality parameters: moisture and protein losses, color, ash content and granularity. Fine sorghum semolina was evaluated as wheat flour improver ingredient carrier. When sorghum and wheat fine semolina were compared as wheat flour improver carrier no significant differences were observed on farinograph results. It can be concluded that with suitable mill adjustment and suitable sifting media stone and disc mills can produce wide range of sorghum products: flour fine semolina and coarse semolina for diverse uses, when a decorticated or partially decorticated sorghum is used.

Tabat a Sudanese sorghum cultivar was collected from local Khartoum market season 2009; three samples were cleaned and prepared for milling.A commercial decorticator was used to decorticate 10% from Sample A and 5% from Sample B, Sample C was whole grain.The three samples were milled on commercial stone mill and a laboratory disc mill.The mills were set to produce the finest and coarsest possible flours.Milled stocks were analyzed to examine some milling quality parameters: moisture and protein losses, color, ash content and granularity.Fine sorghum semolina was evaluated as wheat flour improver ingredient carrier.When sorghum and wheat fine semolina were compared as wheat flour improver carrier no significant differences were observed on farinograph results.It can be concluded that with suitable mill adjustment and suitable sifting media stone and disc mills can produce wide range of sorghum products: flour fine semolina and coarse semolina for diverse uses, when a decorticated or partially decorticated sorghum is used.
Most of This sorghum is milled on stone mills; decorticated or whole depending on consumer preference, since most of the stone mills are operated as customer mills.In the capital and big towns most of the sorghum is decorticated.Little sorghum is milled on commercial mills.Very little sorghum is milled using traditional pestle and mortar for decortication and saddle stones for milling.
Many trials of sorghum milling techniques have been examined: roller milling after conditioning with the same technique of wheat milling, or decortication then milling on rollers mill (Merwet et al. 2005),(Iva 2011).Decortication used for rice and parley also been used for sorghum it is reported to produce meals that contains 25% less fat, 10% less crude fiber and 15% less ash than manual hand pounding, and that the meal has three months shelf life, (Gomez 1993), (Pertin 1977), (Bassey and Schmidt 1989).(Beshata et al. 2006)reported that the most common and widely used type of commercial milling plants in Africa are hammer and stone mills, with capacities of 100-1800 kg/hr and 25-1200 kg /hr respectively.Decortication and hammer milling is the common industrial milling in South Africa.However the main techniques of milling sorghum into flour :either to decorticate or use as whole meal milled on hammer or stone mill or on roller mill in the same or alike technique used for wheat milling.The common application in the Sudan is decorticating and then milling on stone mills.Stone is unlike hammer and roller milling where milled stocks have a controlled granule size.Stone milling fineness depends on the miller experience and stones corrugation or flutes condition.The decortication of sorghum grains reported to decrease moisture, ash, fat, crude protein, iron and phosphorous content (Abdelghafor et al. 2013).

Milling quality differs according to technique
used.According to (Wingfield1983), the milling quality is measured by: flour yield, freedom of the flour from impurities, as well as flexibility of a mill to produce wide range of products, adaptability of the mill to handle different types of grains and ability of the mill to minimize protein loss from grain to flour (protein recovery).Reviewing the sorghum milling literature we did not find much studies focusing on sorghum semolina.The quality of pasta is highly related to the quality of raw material and also depends on the milling process.In addition to satisfactory agronomic characteristics, the good milling quality is required from sorghum grains in order to provide acceptable industrial flour for the pasta industry (Miche et al.1977).A lower extraction rate may significantly improve the pasta appearance.Milling fractions of less than 1% ash content and 1% lipid content are preferred for pasta and may be obtained by preliminary dehulling with a sorghum mill (Perten 1977).However the semolina produced in this study was compared to general purpose wheat semolina from local market of Khartoum for comparing color.Unlike wheat, sorghum flour does not contain gluten.This makes it a suitable alternative food for people with wheat gluten allergies.It is not modified genetically and can be used for products that are labeled as non-genetically engineered products.The objectives of this Study were to 1-compare between milling quality of sorghum milled by different techniques 2-to produce fine and coarse semolina and to evaluate their quality and yield 3-to study the effect of fine sorghum semolina on wheat flour quality particularly farinograph and color when the sorghum semolina is used as improver filler.

MATERIALS AND METHODS Grain
Tabat a Sudanese sorghum white cultivar was collected from local Khartoum market season 2009.With 8.4 moisture, 10.4 % protein content, 27g TKW.

Cleaning and decortications
The grain was manually cleaned from impurities by winnowing and stones were picked out.A commercial abrasive decorticator (Type 65 NS-33, 1400 rpm) was used to extract 10% (Sample A), 5% (sample B) and ( sample C)was the whole grain.

Milling
The three samples were milled on commercial stone mill (locally made in Sudan, Omdurman, industrial area workshops) and on Buhler disc mill type Bühler-Miag MLI-204 grinder Bühler AG,(Gupfenstrasse 5 9240 Uzwil Switzerland).The mills were set to produce the finest and the coarsest possible flours.Flour samples were collected mixed thoroughly, sealed into plastic bags and kept at 4°C for analysis.

Moisture, Protein and Ash content
Perten NIR flour analyzer type 8600/01 calibrated for sorghum was used to determine moisture, protein and ash content of grain and flours.The milling moisture loss was calculated by subtracting the moisture content of the produced flour from the moisture content of the milled grain.Protein recovery was calculated by the following equation: Protein recovery % =

Granulation Test
A laboratory sifter (Antriebstechhick type KM10/80-4EVB5S) equipped with sieves of 1000, 700, 530, 355, 280 and 200 microns were used for granulation test.The sample size was 70 gm; the sifting time was 7 minutes, the overtails were weighed.Accumulative overs and throughs were calculated as performed by (Abdelrahim2002).

Color test
"Pekar Flour Color Test was used to evaluate flour and semolina.A simple way for comparing the color of a flour sample with a standard sample.Also called the ""slick"" test, it involves placing a small sample of the test flour on a paddle or other flat surface so that one edge forms a straight line next to a similarly placed sample of a standard flour.Both samples are then slicked with an edge to form a smooth surface that exhibits a distinct line of demarcation between the two flours so that any difference in their color becomes evident.

(Baking Business 2014) Farinograph
Brabender farinograph method was carried out according to AACC 2000.To compare between wheat base flour improved by standard improver (the ingredients carrier is wheat fine semolina) and the same base flour improved by improver whose ingredient carrier is sorghum semolina.

RESULTS AND DISCUSSION Fine Stone Milling Flour moisture and moisture milling losses
With reference to Table1, the flour moisture content and milling moisture losses were found to be 4.44, 4.32, 4.01% and 3.47, 3.72, 4.14% for samples A, B and C respectively.The moisture content of flour milled on fine stone milling setting is very low with high milling loss; this can be attributed to the high temperature of milling chamber generated by shear and abrasive force (80°C when tested).Thermal processing is reported to be the most extensively used method in food preservation to destroy microorganisms, and minimize the undesirable changes in lipids, thereby extending shelf-life (Salih et al. 2013), (Kadlag et al. 1995).

Protein and protein recovery
The protein recovered was found to be 94, 96, and 99% for samples A, B and C respectively.This finding is comparable to the results obtained by (Desikachar 1982) who reported the protein recovery of 10 and 5% decorticated sorghum as 95 and 96.77%.
The 1% losses in whole grain protein may be due to excessive milling resulting in protein heat degradation.

Ash content and color
Ash content of samples A, B and C flours were estimated at 1.55, 1.69, and 1.83% respectively the late is not far from (Abdualrahman and Ali 2012) who reported the ash content of Tabat whole grain as 1.78.Referring to Table 2, it is obvious that the ash content of all samples fine milled on stone mill are higher than the original grain ash content.The increase in ash may be due to stone traces made by abrasive and sheer force of excessive milling, (Badi et al. 1990); however this finding is in agreement with (Desikachar 1982) who reported that the milling on stone mill can increase the ash by 1.5 -2%.Howe ever according to the researchers experience and Pekar test the flour produced is acceptable and with the range of flour color that is available in local Khartoum market.The color test of the flours produced form fine stone milling showed darker color than that produced on coarse stone milling, fine and coarse disc milling.The intensity of milling may affect the color in form of stone fragments traced with flour.

Granularity and size distribution
The granularity test showed that sample A produced the finest flour (97% passed through 280 micron).Sample B was coarser than sample A (95.5 % passed through 280 microns); whereas sample C was found to be the coarsest 84% passed through 280 microns.Fig. 1 and Table 3 show the flour granularity of the fine stone milling.These results indicate that the milling of decorticated or partial decorticated sorghum could produce flour with a very good fineness.These results are far better than (Eggum et al. 1982)    The overtails stocks of non decorticated sorghum were observed to be mainly bran or branny offals; traces of attached endosperm were also seen overtailing some sieve covers namely 355 microns.
The incidence rates of oral cancer are 3.7% for men and 2.6% for women in the Sudan (GLOBOCAN, 2008) .Several lifestyle risk factors for the development of oral cancer are familiar, including tobacco products, alcohol, infections, dietary factors, chemical irritants and frank carcinogens.Prevalence of oral cancer is 3.2% in Sudan and the disease is mainly attributed to N-nitrosamine rich oral snuff consumption (GLOBOCAN, 2008).There are mainly 4 smokeless tobacco products: loose leaf or chewing tobacco, snuff, plug tobacco and twist or roll tobacco (IARC, 1985Cullen et al. 1986).The oral use of snuff in North America and Western Europe is causally associated with an increased risk for cancer of the oral cavity and pharynx, and other pre-neoplastic changes such as leukoplakia (IARC, 1985Cullen et al. 1986).In Sudan, oral snuff, known locally as Toombak, is home-made from finely ground leaves of Nicotianarustica, a tobacco species with a particularly high content of nicotine and minor alkaloids.

Fine Disc Milling Flour moisture and moisture milling losses
The fine milling on Buhler laboratory disc mill showed less moisture milling losses than that of the commercial stone mill.The milling losses of samples A, B and C were found to be 0.30, 0.46and 0.60 % respectively, Table 1.

Protein and protein recovery
The protein recovery was generally better than that of the fine stone milled flours; samples A, B, and C protein recovery was 95, 97, and 100% respectively.

Ash content and color
It was observed that sample A has the best color, sample B has less dark color and sample C has darker color (in both flour and semolina).Ash content showed no change between grain and stock milled (Table 2).The ash content values obtained are in comparable to the findings of (Abdualrahman and Ali 2012) who reported the ash content of Tabat flour as 1.78%, while the ash content of samples A, and B was closed to values reported by (STPO 2014).

Granularity, size distribution and farinograph test results
Table 4 and Fig. 2 show the granularity of fine flour milled on Buhler laboratory disc mill.Granularity test showed that the fine disc milled flours were coarser than that of the stone milled flours through the three samples.Samples A, B, and C granulation were 70.16, 65.98, and 56.12% through 280 microns respectively.Fine semolina was produced at 33.7, 38.08 and 51.4% from samples A, B, and C respectively.Semolina and flour extracted from samples A, and B was comparable to that extracted by (Viraktamath et al. 1971) who recovered 33.5% fine semolina 33.75% flour.This semolina was tested as wheat flour improver filler, the sorghum flour and semolina is known to be gritty, so this characteristic will facilitate the mixing and the ingredients will not stick on.Illustrated on Table 5, no significant differences were detected when we compared the results of farigraph test for flour improved with wheat and sorghum as filling material of 0.7%.

Coarse Milling Stone Flour moisture And Protein and protein recovery
The coarse stone milling produced flour with less moisture losses, which were found to be 0.52, 0.73, and 1.09 in samples A, B, and C respectively.While the protein recovery exhibited no change between milled grain and produced stocks; this finding is strengthening that excessive milling may reduce protein recovery.

Ash content and color
Flour produced through 280 microns was 27.77, 20.06 and 18.22% from Samples A, B, and respectively.Coarse semolina showed only slight differences in color between samples A and B; but there was noticeable difference when we compared samples A and C. Ash content of coarse semolina from samples A, B, and C is shown in Table 2.The ash results showed no differences between grain and milled flour except sample B ash is slightly greater.

Granularity and size distribution
Tables 6 and Fig. 3 exhibit the granularity of the coarse stone milling.Two types of semolina were produced; coarse semolina over 710 micron samples A, B and C extracted 61.14, 71.68, and 76.82 respectively.Coarse semolina produced from samples and B has acceptable color, sample C semolina was less dark.The fine semolina extracted through 710 and over 280 microns was found to be 15.61, 12.3 and 6.82% from samples A, B and C respectively.

Coarse Disc Milling Flour moisture and protein and protein recovery
Samples of coarse stocks milled on Buhler disc mill did not show any change in moisture losses nor protein content.

Color and ash content
There was no change in ash content between grain and milled flour.

Granularity and size distribution
Table 7 and Fig. 4 demonstrate the granularity of the coarse stocks milled on the disc mill.Two types of semolina were extracted; the coarse semolina was 75.62, 81.22, and 85.96 % from samples A, B, and C respectively.Fine Semolina extracted through 710 and over 280 was 10.49, 8.08, and 6.72 % from samples A, B, and C respectively flour produced was 18.6, 10.3, and 7.25%.Among the three samples the granules size and color sample A quality was the best, sample B has less quality and sample C has the least quality.

Table 1 :
Flour moisture content and milling moisture losses.

Table 2 :
Ash content

Table 3 :
Accumulative overs and throughs of fine stone milling

Table 4 :
Accumulative overs and throughs of fine disc milling

Table 6 :
Accumulative overs and throughs of coarse stone milling