Cereal Grains

Laboratory Reference and Procedures Manual

Sergio O. Serna-Saldivar

• Publisher: CRC Press
• Year: 2012
• Topic: Technology & Engineering
• eBook ISBN:
  9781439855669
• Subtopic: Nutrition, Dietics & Bariatrics
• Index: Technology & Engineering

Emphasizing the essential principles underlying the preparation of cereal-based products and demonstrating the roles of ingredients, Cereal Grains: Laboratory Reference and Procedures Manual is a practical laboratory manual complementing the author's text, Cereal Grains: Properties, Processing, and Nutritional Attributes. Organized so that readers

1	Physical and Morphological Properties of Cereal Grains

1.1 INTRODUCTION

Cereals are one-seeded fruits of the Gramineae family designed to store nutrients critically important for the perpetuation of the species. Kernels are protected by physical barriers and chemical compounds against external biotic agents. Nevertheless, the different genus, species, and types differ in their grains’ physical, chemical, and morphological characteristics. These features are also affected by the environment, especially during maturation in the field, and by storage conditions. The main criteria used to select grains for specific uses are related to their physical properties because they affect chemical composition, functionality, and end use.

Therefore, the determination of the physical properties, grade, and class plays an important and critical role in the market value of any given lot of grain. Grain classification and grading assures that a particular lot of grain meets preestablished quality parameters. Federal governments usually have impartial regulatory agencies in charge of assigning grain quality. Furthermore, the standardization of grain quality allows better and fairer marketing between sellers and buyers and also allows processors to blend lots of grains with similar grade or quality (Kiser 1991). The value of any given lot of grain depends on both grade and class. Grade is an indication of quality and grain health condition whereas class is related to the potential use or functionality of the grain (color, gluten type, hardness, etc.). The classification systems are aimed toward the facilitation of impartial commercialization of grains, providing information related to grain quality for storage and further processing, and providing information that can be further related to yields of products and by-products (milling yields, end-product quality, etc.).

All cereal plants produce protected or covered fruits. The kernel, which is botanically termed a caryopsis, is a monocotyledon. The caryopsis consists of a pericarp (fruit coat) and a true seed. The seed consists of a germ and endosperm covered by a seed coat or testa and a single or multilayered aleurone. Some cereal grains, such as oats, rice, and barley, tightly retain the glumes after harvesting and consequently are considered as husked grains. The rest of the cereals are commonly known as naked caryopses because they generally lose the ventral and dorsal glumes known as lemma and palea, respectively, during harvesting.

To understand the important changes that cereals undergo during processing, it is essential to comprehend the macrostructure and microstructure, physiology, and the composition of each anatomical part of the caryopsis. Among each type of cereal, important variations exist in endosperm hardness due to the different proportions of vitreous and floury endosperm types, pericarp color and thickness, type of starch, and kernel size.

1.2 DETERMINATION OF PHYSICAL PROPERTIES OF CEREAL GRAINS

1.2.1 TEST WEIGHT

The bushel, test or volumetric weight is the most critical criteria to determine grade and class. The test simply consists of first sampling the grain which is then placed in a container with a proven volume. The grain is weighed and the test weight or apparent density is calculated. Test weights are generally expressed in pounds per bushel (2150.42 in.³) or in kilograms per hectoliter (100 L). The conversion factors of pounds per Winchester bushel (2150.42 in.³) and pounds per imperial bushel (2219.36 in.³) to kilograms per hectoliter are 1.297 and 1.247, respectively. The bushel weight is closely related to the true grain density and therefore is affected by grain condition, grain texture, and even grain protein content. This test is very useful because insects, molds, and sprouted or heat-damaged kernels have a lower test weight when compared with healthy or sound counterparts. On the other hand, vitreous or corneous grains with a slightly higher protein content are usually denser. Lots of grains with higher moisture contents usually have a lower test weight because water has a density of 1 g/cm³, whereas starch has a density of 1.6 g/cm³. Insect-perforated kernels have a lower apparent density because the air in the perforations has a density of only 0.1 g/cm³. Both grade and class are affected by test weight. The most common way to measure test weight is by the Winchester bushel meter provided with different cups with a known volume.

1.2.1.1 Test Weight Procedure

Grain test weights are usually measured according to Method 55-10 (American Association of Cereal Chemists; AACC 2000).

A. Samples, Ingredients, and Reagents

• Different lots of grains

B. Materials and Equipment

• Digital scale

• Boerner divider

• Ruler

• Seed clipper or Carter dockage test meter

• Winchester bushel meter apparatus

• Strike-off stick

C. Procedure

1. Obtain a representative grain sample, preferably by using the Boerner divider.

2. Fill the hopper or the Cox funnel of the Winchester bushel meter with enough grain to fill the cup. Make sure the hopper gate is closed and to place a pan to collect excess grain.

3. Move the hopper so its gate is aligned right in the center of the cup.

4. Open the gate and allow the grain to flow and overfill the cup (Figure 1.1).

5. Carefully remove excess grain from the cup with the aid of a strike-off stick moved vertically over the cup’s rim. Excess grain should be removed with a zigzag motion.

6. Weigh the grains in the cup with an accuracy of 0.1 g.

7. Calculate test weight or apparent density by dividing the weight/volume. Express test weight in pounds per bushel (lb/bu) and kilograms per hectoliter (kg/hL). To convert test weight from kilograms per hectoliter to pounds per bushel, multiply the number by 0.6674. One bushel is equal to 0.303 hL.

1.2.2 TRUE DENSITY

True grain density, generally expressed in grams per cubic centimeter, is commonly determined by measuring the weight of a given volume that is displaced by a known weight of test material. True density can be determined by ethanol displacement or by air, nitrogen, or helium displacement using a pycnometer. Nitrogen is the most commonly used gas. Another popular way to determine density is by alcohol displacement. True density values are important because they are closely related to grain condition, endosperm texture, and milling yields. Dense grains are less prone to insect damage and have better handling properties (less susceptible to breakage) during storage, commercialization, and processing. For wheat, density values are strongly associated to class and functional use. The density of other grains, such as maize and sorghum, is also important for dry and wet millers. For dry-milling, the industry selects grains with higher density because they usually yield more and better quality products. The wet-milling industry typically uses less dense or softer kernels because these kernels require shorter steeping requirements and commonly yield more starch.

FIGURE 1.1 Determination of test weight. (a) Winchester bushel meter; (b) removal of excess grain; (c) determination of sample weight.

1.2.2.1 Determination of True Density with the Pycnometer

A. Samples, Ingredients, and Reagents

• Different lots of grains

B. Materials and Equipment

• Scale

• Multipycnometer (model MUP-1)

• Boerner divider

• Nitrogen gas

C. Procedure

1. Turn the multipycnometer power on 10 to 15 minutes before testing.

2. Obtain a representative grain sample, preferably by using the Boerner divider. Make sure the sample is free of foreign material, broken kernels, and other types of kernels. If necessary, clean the grain with a clipper, air aspiration system, or a Carter dockage tester.

3. Weigh an 80-g sample to an accuracy of 0.01 g and place it in the pycnometer cup (Figure 1.2). Place cup with grain in the sample cell.

4. With the selector valve at the cell position, open the “gas out” toggle valve and wait for a stable reading near zero.

5. Close the gas out valve and set the meter to zero.

6. Open the “gas in” toggle valve to pressurize the cell to 15 psi to 17 psi. Stop the gas flow by closing the gas in valve.

7. Record the pressure reading as P1 after stabilization and then turn the selector valve to cell position and record the pressure as P2.

8. Release pressure by opening the gas out toggle valve.

9. Calculate the volume of gas using the following equation: volume (cm³) = Vc – Vr × [(P1/ P2) – 1], where Vc = large sample cell volume = 149.67, Vr = large reference volume = 71.60. Calculate the true density by dividing grain weight/volume. Express true density in grams per cubic centimeter (Figure 1.2).

FIGURE 1.2 Pycnometer used to determine grain density.

1.2.2.2 Determination of Density with Alcohol Displacement

Density was calculated using the method of Rooney (2007).

A. Samples, Ingredients, and Reagents

• Different lots of grains

• Anhydrous ethanol

• Distilled water

B. Materials and Equipment

• Digital scale

• Air-aspiration system

• Graduated cylinders (100 mL)

• Boerner divider

• Carter dockage tester

C. Procedure

1. Prepare an 80% ethanol solution by mixing 20 mL of water and 80 mL of anhydrous ethanol.

2. Obtain a representative grain sample, preferably by using the Boerner divider. Make sure the sample is free of foreign material, broken kernels, and other types of kernels. If necessary, clean the grain with a clipper, air aspiration system, or a Carter dockage tester. The idea is to test only whole kernels.

3. Determine the weight of the empty graduated cylinder.

4. Fill the graduated cylinder to the 100 mL mark with the whole kernels. Tap the cylinder several times to settle the kernels and then add more kernels to bring the level back to the 100 mL mark.

5. Weigh the filled cylinder and subtract the empty weight to obtain the exact kernel weight.

6. Measure 100 mL of the 80% ethanol solution in the second graduated cylinder.

7. Pour the ethanol slowly into the cylinder containing the whole kernels. Fill this cylinder to the 80 mL ...

Table of contents

• Cover
• Title Page
• Copyright
• Dedication
• Contents
• Preface
• Acknowledgments
• Author
• List of Equivalences
• Chapter 1 Physical and Morphological Properties of Cereal Grains
• Chapter 2 Determination of Chemical and Nutritional Properties of Cereal Grains and Their Products
• Chapter 3 Determination of Color, Texture, and Sensory Properties of Cereal Grain Products
• Chapter 4 Storage of Cereal Grains and Detrimental Effects of Pests
• Chapter 5 Dry-Milling Processes and Quality of Dry-Milled Products
• Chapter 6 Wet-Milling Processes and Starch Properties and Characteristics
• Chapter 7 Production of Maize Tortillas and Quality of Lime-Cooked Products
• Chapter 8 Functionality Tests for Yeast and Chemical Leavening Agents
• Chapter 9 Production of Yeast-Leavened Bakery Products
• Chapter 10 Production of Chemical-Leavened Products: Crackers, Cookies, Cakes and Related Products, Donuts, and Wheat Flour Tortillas
• Chapter 11 Production of Pasta Products and Oriental Noodles
• Chapter 12 Production of Breakfast Cereals and Snack Foods
• Chapter 13 Production of Modified Starches, Syrups, and Sweeteners
• Chapter 14 Production of Malt, Beer, Distilled Spirits, and Fuel Ethanol
• Index