Malcolm C. Bourne

Chapter 1 – Texture, Viscosity, and Food

Publisher Summary The four principal quality factors in food include its appearance, flavor, texture, and nutrition. Appearance, flavor, and texture are the “sensory acceptability factors” because they are perceived by the senses directly. Nutrition is a quality factor that is not perceived by the senses. The sensory acceptability factors of foods are extremely important because people obtain great enjoyment from eating their food. The importance of texture in the overall acceptability of foods varies widely, depending upon the type of food. Achieving the desired textural quality of food has important economic considerations. The importance of texture, relative to other quality factors of foods, may be affected by culture. The chapter describes the vocabulary of texture of food, as it is very important, especially in sensory testing and consumer verbalizations of quality. It is also reported that time of day exerted a strong influence on textural awareness and flavor. The chapter also presents the difference between texture and viscosity.

Physics and Texture

This chapter discusses the branches of physics that are relevant to texture, mainly rheology and physical properties of materials. Rheology is the study of the deformation and flow of matter. Its principles can be applied to any kind of material ranging from mobile fluids, to plastics, from to foods and beverages. . There is a large number of practicing rheologists, and it is not surprising to find that the field of rheology is well developed and thriving. Most of the rheological concepts and instruments were developed for nonfood products and the food rheologist; while borrowing freely from conventional rheological theory and some of the properties of both solids and liquids, and measuring and specifying their properties is sometimes difficult. Rheology is divided into two parts: deformation usually applies to materials that are predominantly solid-like in nature and flow usually applies to materials that are predominantly fluid-like in nature. The most important elements in both deformation and flow are the fundamental quantities of distance, time, and mass.

Chapter 4 – Principles of Objective Texture Measurement

Publisher Summary The chapter describes various types of tests for measuring food textures. A wide variety of methods are available to measure the textural and rheological properties of food. It becomes necessary to attempt to classify them into groups in order to understand the system. There is such a wide range in types of foods and the types of textural and rheological properties they exhibit, and such a wide variety of methods used to measure these properties, that it becomes necessary to classify them into groups to understand the system. Several classification systems have been propounded. It is possible to classify texture measurements according to the commodity that is being tested; for example, tests that are used for cereals, meat, fish, poultry, vegetables, fruit, dairy products, fats, confectionery, beverages, legumes, emulsions, suspensions and oilseeds, and miscellaneous foods. The classification of texture measurements on the basis of commodity or the type of textural properties is useful but what is probably a better type of classification is based on the type of test that is used, because many tests are applicable to more than one type of food.

Calibration of Rheological Techniques Used for Foods

Abstract It is essential that rheological instruments be calibrated in fundamental units based on functions of mass, length, and time; for example, shear rate, shear stress and the geometrical dimensions of those parts of the instrument that are in contact with the food. This calibration is sufficient for engineering design purposes such as designing pumps, pipelines and heat transfer equipment. However, although essential, this calibration is not sufficient if the measurements are intended to predict sensory correlation of textural properties and mouthfeel of foods. The rheological techniques must also be calibrated against people because people use different rheological techniques for different foods. If an inappropriate rheological technique is used for a given food or inappropriate test conditions are used, there will be a disappointingly low correlation between sensory evaluation of texture and the instrument reading no matter how well the instrument is physically calibrated and operated.

Textural Changes in Ripening Peaches

Abstract Clingstone and freestone peaches of varying degrees of ripeness were subjected to a puncture test, a modified G. F. Texture Profile, and a set of rectangular punches that enable a compression coefficient (Kc), and a shear coefficient (Ks), to be evaluated. Adhesiveness and viscosity were absent in the G. F. Texture Profile. Cohesiveness was constant for clingstone peaches although the two areas whose ratio is the cohesiveness parameter decreased at the same rate as the puncture test. The other textural properties: fracturability, hardness, elasticity, chewiness, Kc, and Ks decreased at about the same rate as the puncture test. Correlation coefficients between these textural parameters and the puncture test were all significant. This leads to the conclusion that almost any kind of textural property can be used successfully as an index of textural quality of fresh freestone or clingstone peaches because the various textural parameters change in the same direction and at approximately the same rate as the fruit rlpens. The results also indicate that compression (Kc), is the major contributor to the puncture reading and that shear is a minor contributor.

Texture, Viscosity, and Food

This chapter discusses texture, viscosity, and food. The four principal quality factors in foods are appearance, flavor, texture, and nutrition. The importance of texture in the overall acceptability of foods varies widely, depending upon the type of food. Texture of foods has the following characteristics: (1) it is a group of physical properties that derive from the structure of the food; (2) it belongs under the mechanical or rheological subheading of physical properties; (3) it consists of a group of properties, not a single property, (4) texture is sensed by the feeling of touch, usually in the mouth, but other parts of the body may be involved; (5) it is not related to the chemical senses of taste or odor; and (6) objective measurement is by means of functions of mass, distance, and time only. Viscosity is defined as the internal friction of a fluid or its tendency to resist flow. Both gases and liquids have viscosity. At first sight, the distinction between texture and viscosity seems simple— texture applies to solid foods and viscosity applies to fluid foods. Unfortunately, the distinction between solids and liquids is so blurred that it is impossible to clearly demarcate between texture and viscosity. While rock candy can definitely be considered as a solid and milk a liquid, there are many solid foods that exhibit some of the properties of liquids and many liquid foods that exhibit some of the properties of solids.

CHAPTER 1 – Texture, Viscosity, and Food

Publisher Summary This chapter discusses texture, viscosity, and food. The four principal quality factors in foods are appearance, flavor, texture, and nutrition. The importance of texture in the overall acceptability of foods varies widely, depending upon the type of food. Texture of foods has the following characteristics: (1) it is a group of physical properties that derive from the structure of the food; (2) it belongs under the mechanical or rheological subheading of physical properties; (3) it consists of a group of properties, not a single property, (4) texture is sensed by the feeling of touch, usually in the mouth, but other parts of the body may be involved; (5) it is not related to the chemical senses of taste or odor; and (6) objective measurement is by means of functions of mass, distance, and time only. Viscosity is defined as the internal friction of a fluid or its tendency to resist flow. Both gases and liquids have viscosity. At first sight, the distinction between texture and viscosity seems simple— texture applies to solid foods and viscosity applies to fluid foods. Unfortunately, the distinction between solids and liquids is so blurred that it is impossible to clearly demarcate between texture and viscosity. While rock candy can definitely be considered as a solid and milk a liquid, there are many solid foods that exhibit some of the properties of liquids and many liquid foods that exhibit some of the properties of solids.

CHAPTER 3 – Principles of Objective Texture Measurement

Publisher Summary This chapter discusses the principles of objective texture measurement. There is such a wide range in types of foods and the types of textural and rheological properties that they exhibit, and such a wide variety of methods used to measure these properties, that it becomes necessary to attempt to classify them into groups to understand the system. It is possible to classify texture measurements according to the commodity that is being tested, for example, tests that are used for cereals, meat, fish, poultry, vegetables, fruit, dairy products, fats, confectionery, beverages, legumes and oilseeds, and miscellaneous foods. The classification of texture measurements on the basis of commodity or the type of textural properties is useful but what is probably a better type of classification is based on the type of test that is used, because many tests are applicable to more than one type of food. When food is placed in the mouth, the structure is destroyed by the act of mastication until it is ready to be swallowed. The basic process of mastication occurs regardless of what kind of food is in the mouth. Therefore, it seems logical to concentrate on the type of test rather than the nature of the food. The chapter discusses the types of tests for measuring food texture.

Effect of Storage Time, Relative Humidity and Temperature on the Cookability of Whole Red Kidney Beans and on the Cell Wall Components of the Cotyledons

Abstract Red kidney beans were stored for eight months under three storage conditions: 1) 0°C; 2) 30°C - 80070 RH; 3) 40°C - 80070 RH. Hardness of cooked whole beans from treatments 2 and 3 increased during storage. Application of the detergent system for analysis of cell wall components to whole ground cotyledons showed significant increases in cell wall content, cell wall nitrogen and hemicellulose for cotyledons of treatment 3. These increases were highly correlated with hardness of cooked beans. Acid detergent residue, lignin and cellulose contents of cotyledons did not change in any of the treatments. The synthesis of nitrogen containing compounds in cell walls during adverse storage may be a contributing factor in the development of hardness by hindering dissolution of the middle lamella during cooking.

Correlation Between Physical Measurements and Sensory Assessments of Texture and Viscosity

This chapter is designed to discuss the correlation between physical measurements and sensory assessments of texture and viscosity. There are several reasons for measuring physical properties of foods: engineering process design, determination of structure, and texture. Sometimes these measurements are employed to establish a quality grade used to set a price for the product. The quality of correlation between sensory and objective measurements of texture is of paramount importance. To be of value, instrument readings need to have a high level of predictability of sensory assessments of textural quality. The human assessment of texture has to be the standard against which instrument readings are calibrated. Texture is a sensory attribute, perceived by the senses of touch, sight, and hearing. Thus, the only direct method of measuring texture is by means of one or more senses. Nonsensory techniques can never be more accurate than sensory methods. The accuracy of the former can only be judged by their ability to predict the sensory quality being studied. Consumers have a rich vocabulary of words relating to quality.. Scientists have the task of translating these descriptors into scientific principles, which can be measured by instruments. The number of instruments being used to measure food texture or viscosity is much smaller than the number of human beings measuring texture.