5 Dry-Milling Processes and Quality of Dry-Milled Products
C. Procedure (Sedimentation Test Method 56-60) This method was previously described in AACC
5.3.5 Q uality of g roats
The aim of the oat-milling procedure is to obtain the maxi-mum yield of stabilized groats free of hulls. The groats rich in both soluble and insoluble dietary fiber should have an adequate stability throughout storage. Groats are further processed into regular and instant flaked oats or milled into meals or flours for the production of bakery products.
The most relevant tests for oats are cooking properties, color, protein, dietary fiber, total starch, and fat stability or rancidity.
5.3.6 Qualityof DecorticateD sorghuM anD refineD MealsanD flours
The aim of the sorghum-milling procedure is to obtain the maximum yield of decorticated kernels free of pericarp and germ. The pearled kernels can be transformed into grits, meals, or flours for the production of many traditional foods.
Thus, the decorticated kernels or refined dry-milling frac-tions are low in fiber and preferably contain less than 1% oil.
The extent of pericarp removal is usually evaluated with the May–Gruenwald dyeing technique (Scheuring and Rooney 1979) previously detailed in procedure in Section 5.3.2.1. The most common quality control procedures to evaluate the qual-ity of refined sorghum fractions are color, particle size distri-bution, ash, fat, total starch, and amylose/amylopectin ratio.
5.3.7 research suggestions
1. Compare the chemical properties, color, and dam-aged starch of white and yellow refined maize grits.
2. Compare the cooking properties, elongation factor, and amylose content of a short waxy rice, a long regular rice, and a long parboiled rice.
3. Compare Pelshenke, sedimentation, and gluten con-tent values of two contrasting wheat flours (i.e., soft and hard wheat) and then relate these simple test parameters with farinograph and alveograph data.
4. For a given sample of refined wheat flour, determine and compare gluten assayed by the hand-wash pro-cedure and the automatic Glutomatic.
5. Compare color, ash, damaged starch, and rheologi-cal dough properties of straight grade and patented flours obtained from the same wheat.
6. Evaluate the effects of the addition of potassium bro-mate and ascorbates (20 ppm and 100 ppm, respec-tively) or sodium bisulfite (20 ppm) to refined wheat flour. How do these additions affect the dough rheo-logical properties evaluated with the farinograph, extensigraph, and alveograph.
7. Evaluate the effects of soft wheat flour chlorina-tion on the dough rheological properties evaluated with the farinograph, extensigraph, alveograph, and mixolab.
8. Compare extensograph parameters obtained after analyzing the same sample with the Brabender exten-so graph and the Kieffer dough and gluten extensibil-ity rig of the TAXT2 texture analyzer.
9. Obtain mixolab curves and the flour profiler graph (mixing, absorption, gluten, viscosity, amylase, and retrogradation) of hard, soft, and all-purpose flours with different falling number values.
10. Compare the chemical properties, color, particle size distribution, gelatinized starch, and suscepti-bility to rancidity of oat flour obtained after milling with and without steaming.
11. Compare the chemical properties, color, particle size distribution, and damaged starch of refined sor-ghum meals obtained after 20% decortication and milling of hard white and soft red sorghums.
5.3.8 research Questions
1. Define the following terms widely used in quality control of dry-milling operations:
a. Slick test b. Pelshenke test
156 Cereal Grains: Laboratory Reference and Procedures Manual
k. Dough development time l. Mixolab profiler graph
2. What are the main color meters used by millers?
Describe the principles of at least three different color meters?
3. During maize dry-milling, an array of refined frac-tions are obtained, what are their particle sizes and main uses? Which of the refined dry-milled prod-ucts is the most expensive? Why?
4. What kind of considerations, in terms of raw mate-rials and changes in the corn dry-milling process, would you make to optimize yields of flaking grits (U.S. no. 6)? What is the typical chemical composi-tion of flaking grits?
5. Compare the chemical composition and typical extraction rate of brewing maize and rice grits.
Which grits are preferred for the production of light-colored beers? What is the typical particle size and fat content of these brewing grits?
6. What is the assay or factor most related to the cook-ing characteristics of rice? List three other methods related to rice cooking?
7. What is the principle and use of the May–Gruenwald test?
8. What is parboiling? Why is parboiling still widely practiced? Why is parboiled rice considered to have more nutritional attributes compared with regular rice?
9. Compare the properties and cooking characteristics of a regular white vs. a parboiled white rice.
10. Why is the alkaline water absorption test widely used for cookie flours made with alkaline solution?
11. What are the principles of the Pelshenke and sedi-mentation tests?
12. What kind of compounds are removed during the hand or machine gluten washing process? What is the typical chemical composition of vital gluten?
13. Draw the typical farinograph curve and name the four major parameters that are obtained after ana-lyzing the curve.
14. Draw the typical extensogram curve and name the three major parameters that are obtained after ana-lyzing the curve.
15. Draw and compare typical mixograph curves for soft and hard wheat flours and name the three major parameters that are obtained after analyzing the curve.
16. What are the differences and similarities between the farinograph and mixograph?
17. Draw the typical alveogram curve and name the three major parameters that are obtained after ana-lyzing the curve.
18. What are the reasons for why saline solutions are used to produce doughs for the alveograph and extensograph tests?
19. What would happen to the farinograph, mixograph, and alveograph parameters if the test flour is supple-mented with 20 ppm of sodium bisulfite?
20. What is the main advantage of the mixolab compared with other rheological instruments? Investigate how a flour profiler graph is obtained after obtaining the various mixolab parameters.
21. List at least three quality control measurements closely related to the quality of refined oatmeal.
22. List at least three quality control measurements closely related to the quality of decorticated sorghum.
23. What is the general effect of the different dry-milling processes on the nutraceutical properties of cereals?
Which important phytochemicals or nutraceutical compounds are partially lost during milling?
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