Mixolab: A New Approach to Rheology

By Arnaud Dubat

Publishing high-quality food production applications handbooks is a hallmark of AACCI PRESS and Mixolab: A New Approach to Rheology is no exception. Increasing consumer demand for quality foods with superior nutritional value makes innovative tools like the Mixolab of increasing interest to food developers and producers. Operators, breeders, millers, researchers, product developers, formulators, and bakers will find answers to their questions, along with guidelines for maximizing the use of the Mixolab for a wide range of applications. Gaining a better understanding of the instrument's capabilities will assist in discovery of novel uses by both research and production professionals.

Key Features:

• Technical description of the Mixolab and comparison with existing devices
• Coverage of durum wheat, rice, corn, buckwheat, and other cereals
• Specific focus on gluten, starch, ingredients, and enzymes
• Influence of sugar, fats, and salt on dough rheology
• International comparisons of HACCP experiences
• Table of uses for specific carbohydrates
• Descriptions of improved laboratory techniques
• Wheat testing for breeders

An Essential Reference For:

• Additive manufacturers
• Bakers
• Breeders
• Enzyme manufacturers
• Millers
• Quality control laboratories
• Research laboratories
• Research and development centers
• Storage elevators
• Students
• Universities
• Yeast producers

• Language: English
• Publisher: Elsevier Science
• Release date: Apr 27, 2016
• ISBN: 9780128104309

Arnaud Dubat

CHOPIN Technologies, Paris, France

Book preview

China

Preface

As with many industries, the cereal industry faces the challenges of a rapidly changing world. Final products are evolving, especially in response to food globalization. Wherever they are, consumers tend to enjoy new types of cereal products and at the same time look for healthier food. These demands have led the wheat/flour/bread industry to develop new strategies in order to offer the market innovative, healthy, and affordable cereal products. It is remarkable that, although the principles have not changed for centuries, the manner of producing bread or other cereal products has changed significantly in these last decades.

The demand for quality control has also experienced the same evolution. The use of new processes, new ingredients, and enzymes has demanded new or improved quality-control tools. These devices are being used either in the research and development area to create new products or in the quality-control lab to make sure that the raw material or the final product meets the user’s requirements.

The Mixolab is one of these innovative tools, and AACC International has commissioned this handbook to allow present and future users to gain the maximum information about how it works.

This handbook was conceived in order to answer the questions of many users. For operators, it describes the history and principle of the Mixolab, details the operating procedures and maintenance, and lists the external factors that can affect the Mixolab’s performance. It also provides a thorough comparison with existing equipment and facilitates a complete understanding of experimental protocols and results. Breeders will find information on how to use the Mixolab in wheat breeding. Millers will learn how to avoid bug-infested wheat. Researchers and formulation chemists will find much information concerning the main flour components such as starch and gluten but will also be able to understand the interactions with ingredients such as hydrocolloids, fibers, and enzymes. From a baker’s perspective, the book gives examples of the influence of different dough components such as salt, sugar, and fat. A chapter discusses gluten-free cereals, including rice, corn, and buckwheat, and examples are also given for waxy wheat, barley, and triticale. Durum wheat and rice analyses each have a specific chapter.

It would never have been possible to prepare this handbook without the support of many scientists and Mixolab experts worldwide. We would like to greatly thank our colleagues Neng Chen, C. Collar, Binwu Duan, M. G. d’Egidio, S. R. Frazer, A. Frier, S. Geoffroy, C. Hall III, Peisong Hu, K. Kahraman; H. Koksel, J. Le Brun, O. Lebrun, A. Marti, S. Moscaritolo, M. A. Pagani, R. J. Peña, G. Posadas-Romano, S. Simsek, G. Sinnaeve, M. C. Tulbek, Lihong Xie, and Zhiwei Zhu, for their contributions and for their patience.

This handbook does not pretend to be exhaustive, but we hope it will inspire readers by showcasing the potential of the Mixolab, and offering a good basis for future product development.

A. Dubat, C.M. Rosell and E. Gallagher

Part I

Device Presentation

Outline

Chapter 1: The Mixolab

Chapter 2: Factors Affecting Mixolab Performance

Chapter 3: Relationship Between the Mixolab and Other Devices

CHAPTER 1

The Mixolab

A. Dubat,     CHOPIN Technologies, Laboratoire d’Applications, Villeneuve la Garenne, France

1 PRESENTATION

1.1 History

The Mixolab is a modern device developed for the quality control of cereals. The instrument measures dough and flour quality by exposing a sample to predetermined heating and cooling cycles while placing the sample under a strain field. Data are collected as a set of stress-strain plots analyzed via an algorithm for multigraph data structure analysis. The method and analysis of the results from the measurement are based on the same principles used by the Pétrinex dough-testing equipment.

This measurement was initially envisioned in the early 1900s by van Stock, a Rotterdam miller (German patent 293078, dated 22/7/1914). Victor-Lambert Buys developed dough-processing machinery and rheology instrumentation during the 1940s and 1950s, culminating in the Pétrinex (French patents 918303A, 923252A, 923253A, 937227A, 987206A, 987207A, 1119928A, 1148944A, 1260716A). In the 1970s, Duranel (1970) and Bussiere et al (1972), among others, concluded that the Pétrinex was suitable as a quality control instrument based on the good repeatability of the results from its measurements. In 2000, the Multigraphe was created (Sinnaeve 2000). The instrument was then improved and redesigned by CHOPIN Technologies, and the final version was introduced in 2004 as the Mixolab (Dubat 2004b).

The Mixolab offers enhanced functionality over existing devices because of the geometry of the mixing blades and mixing bowl and the variable speed and temperature-testing options. It is possible to incorporate temperature cycles, warming the dough to 90°C (194°F) and subsequently cooling the sample. The user can, in a single test, determine the water-absorption capacity, mixing stability, gelatinization peak and temperature, amylase activity, and starch retrogradation. Wide measurement potentialities are therefore possible on various cereals (M. C. Tulbek, personal communication; Manthey et al 2007; Piguel et al 2007; Tulbek and Hall 2007), breads (e.g., the French baguette, by determination of flours according to their final use; Boizeau et al 2007), noodles (L. Cato, personal communication; L. Cato and M. C. Gianibelli, personal communication), and cakes (Koksel et al 2007). The Mixolab can also be used for ingredient assessment (Bollain and Collar 2005, Collar et al 2007) and for investigating the effects of additives, such as hydrocolloids (Rosell et al 2007) and proteins (Bonet et al 2006). Furthermore, the Mixolab is capable of analyzing ground whole grains in addition to flours, so it can be used for whole-cereal processing (Sinnaeve 2000, Lenartz et al 2006). The instrument has also proved its utility in the analysis of other cereals, such as durum wheat (Moscaritolo et al 2008).

1.2 Device Description

The Mixolab is shown in Figure 1.1. The mixer bowl (Fig. 1.2) is designed for a 50-g sample size. The sample can be in the form of flour or ground cereal. To facilitate cleaning, the mixer bowl can be fully dismantled with ease (Fig. 1.3).

Fig. 1.1 The Mixolab.

Fig. 1.2 The Mixolab mixer bowl.

Fig. 1.3 The Mixolab mixer bowl dismantled.

Heating resistances warm up the device to 90°C (194°F), and the cooling is controlled through water flow (i.e., open with tap water or closed with a water chiller). The mixer bowl temperature (and thus the dough temperature) is constantly recorded (using a patented system) to ensure thorough analysis of the quality of the tested sample.

The operation of the Mixolab is extremely simple. The user chooses an existing protocol (from among the protocols included with the Mixolab software or those created by a user of that particular system) and follows the instructions on the screen. The desired absorption and sample moisture are programmatically defined by the user, which in turn defines the quantity of flour needed for the test. The water injection nozzle is then placed above the mixer, and as mixing starts, the Mixolab automatically delivers the necessary quantity of water.

The Mixolab relies on the principle of conservation of mass. In the standard Mixolab procedure, the default value of dough weight is set to 75 g, but it can be set to 30–110 g, depending on the tested product and the user needs. The default value for mixing speed is 80 rpm, but it can be set to 30–250 rpm. Temperature and heating/cooling rates are similarly modular, thereby yielding endless possibilities for adapting the Mixolab protocol to any end user’s needs. The instrumental settings are shown in Table 1.1.

TABLE 1.1

Instrumental Settings Defined in Mixolab Software

With the operating software provided, the instrument comprises three parts, which are described in the following sections:

• the Mixolab Standard (for research or research and development purposes),

• the Mixolab Profiler (based on the Mixolab Standard, for quality control needs), and

• the Mixolab Simulator (to simulate Farinograph-equivalent results).

2 THE MIXOLAB STANDARD

In the two years following the launch of the Mixolab, the quality of its data collection (repeatability, reproducibility, and integrity) and the variability among instruments and trained users were carefully validated through a collaborative study led by the International Association for Cereal Science and Technology (ICC). The tests were performed in 13 laboratories by trained users from various countries with two different sample matrixes: flour and whole wheat. The results of that ring test (Table 1.2) led to development of the new ICC Standard 173. Results included method performance for torque and dough temperature measurement.

TABLE 1.2

Mixolab Ring Test Performance

aSr = Repeatability standard deviation.

bSR = Reproducibility standard deviation.

cCVr = Repeatability variation coefficient.

dCVR = Reproducibility standard variation coefficient.

The Mixolab showed excellent repeatability and reproducibility, with most parameters showing a standard deviation lower than 5%. The same methodology was approved by AACC International in 2010 as Method 54-60.01 (AACC International, no date) and is also accepted by the Association Française de Normalisation, the French national organization for standardization. The device and the method were widely described by various authors (Dubat 2004a, Rosell et al 2007). The dough consistency was measured as torque (Nm) of the dough during mixing at constant speed, and the dough was subjected to a series of temperature cycles (30 to 90 to 50°C; 86 to 194 to 122°F). An example of a typical Mixolab curve is shown in Figure 1.4 (i.e., the heavy curve).

Fig. 1.4 A typical Mixolab curve (heavy line). T = temperature.

Water is added to reach the first maximum consistency of 1.1 Nm. This provides information on the water-absorption potential. As the test continues, it provides information about dough rheology during mixing (phase 1), the strengthening of gluten (phase 2), the starch gelatinization (phase 3), the amylase activity (phase 4), and the starch retrogradation (phase 5). The Mixolab serves as a complete tool for analyzing dough behavior, which depends on composition, ingredient quality, and interactions. In fact, it reflects the complexity of the dough system, and this complexity is important to consider when analyzing each part of the Mixolab curve (Fig. 1.5).

Fig. 1.5 Main changes that occur during the Mixolab test.

2.1 Water Sorption

Water sorption is the first element used to assess flour quality. In baking terminology, the water sorption corresponds to the quantity of water required (in liters) for 100 kg of flour to reach the desired dough consistency. In industrial processes, the dough behavior must be consistent, for end-product quality assurance and to avoid production stops. It is of the utmost importance to know the optimum flour hydration and to understand the meaning of this value. The water sorption is influenced by five main parameters: 1) the flour moisture content, 2) the quality and the content of proteins, 3) the native starch, 4) the damaged starch, and 5) the fiber content (pentosans).

The drier the flour, the greater the amount of water that must be added; also, a wheat protein can absorb slightly more water than its own weight. An empirical method states that the absorption capacity increases 1% (w/w) for each 1% of additional protein (Sluimer 2005). Some studies have also determined that the quality of the gluten, in addition to the quantity, impacts the water-absorption capacity (Cauvain and Young 1998). The undamaged (native) starch of the flours absorbs only 40% of its weight of water (Sluimer 2005). However, the native starch strongly influences the absorption process. Indeed, approximately 60–70% of the flour is starch, which offers a large contact interface. Therefore, the native starch holds more than 20% of the water (surface absorption), as shown in Table 1.3. Because of the high pressure imparted by the cylinders during rotation, the starch granule is essentially damaged. This damage leads to an increase of the water-sorption capacity of the granules up to three times their weight. The fiber content (pentosans and arabinoxylans) also affects water sorption, with the fibers absorbing up to 10 times their weight of water (Hamer and Hoseney 1998, Sluimer 2005).

TABLE 1.3

Water Absorption Breakdown Between Various Flour Componentsa

aAdapted from Stauffer (2007).

Hydration impacts many parameters, but most importantly, it affects the mechanical properties, the dough yield (economical aspect), and the end-product quality (Hamer and Hoseney 1998). It has also been proven that high hydration decreases the protein and starch interactions (Hamer and Hoseney 1998).

Most of the time, increasing water absorption leads to more complete gelatinization, better oven rising, softer crumb, and lower retrogradation. These are the reasons that water-sorption capacity is so critical for breadmaking (Sluimer 2005).

2.2 The Mixing Stage

Under quiescent conditions at room temperature and typical atmospheric pressure, the mixing of flour and water is limited to surface absorption. The structural changes at the molecular level that are necessary to form dough can be realized only under the presence of shear introduced through a mixing stage. In addition to dough homogenization, a major objective of the mixing process is to yield extensible dough (Sluimer 1998).The mixing process also develops the gluten, so this stage is also called gluten development.

Gliadin and glutenin are the major constituents of gluten. Gliadins are low-molecular-weight protein molecules that confer extensibility to dough. Glutenins are high-molecular-weight protein molecules that strengthen the dough (Sluimer 2005). The mixing process increases the interaction of enzymes and substrate while incorporating air bubbles, which will become the alveols in the crumb. A dough that exhibits high resistance to mixing allows for a high level of air incorporation.

At the beginning of the dough-mixing process, the proteins hydrate and begin to expand. The increase in protein interactions leads to development of a viscoelastic gluten network. During this stage, the protein thiol groups play an essential role by creating disulfide bridges between and among the chains (Sluimer 2005). During the mixing process, these interactions are transient, breaking and reforming (Feillet 2000). The disulfide bridges are critical for the formation of structure during breadmaking. During baking, more disulfide bridges are created because of the thermal processing; this bonding sets a permanent protein network matrix (Hamer and Hoseney 1998).

These links bring a certain viscosity to the dough. The dough behavior is the result of the viscosity, elasticity, plasticity, stickiness, and relaxing, and it changes during mixing. At the beginning of the mixing process, the dough is not cohesive and breaks easily. Gradually, as the gluten develops, the dough becomes more cohesive and stronger. During mixing, the dough’s resistance to mixing develops until it reaches a peak value, after which the protein network breaks and this resistance decreases (Sluimer