Food Texture What is It?
TEXTURE IS A QUALITY FACTOR • Nutrition: protein, carbohydrate, vitamins & minerals • Appearance: color, shape, size, etc (visual) • Flavor: taste(tongue), odor (nose) • Texture: tactile contact with some part of body and food
Physical properties derived from food structure • Mechanical or rheological science • Group of properties • Sensed by touch, usually in mouth • Not a chemical senses (taste/odor) • Objective measurement through M, L, T • Force MLT-2, work ML2T-2, flow L3T-1 • “Texture” usually applies to solids; “Viscosity” to liquids. Distinction sometimes difficult.
Texture is the composite of attributes which arise from the structural elements of foods and the manner in which it registers with the physiological senses (Philip Sherman, 1970)
Texture is the attribute of a substance resulting from a combination of physical properties and perceived by the senses of touch, sight, and hearing. Physical properties may include size, shape, number, nature, and conformation of constituent structural elements (Jowitt, 1974)
Texture is the human physiological-psychological perception of a number of rheological and other properties of foods and their interactions (McCarthy, 1987)
Texture comprises those properties of a foodstuff, apprehended by the eyes and by the and muscle senses in the mouth, including roughness, smoothness, graininess, etc. (Anonymous, 1964)
Food rheology: the study of the deformation and flow of raw materials, intermediate , and final products of the food industry • Psychophysics: relationship between measurable stimuli and corresponding human response • Psychorheology: deals with the sensory perception of rheological properties of foods
rheology Solids deform & spring back when pushed Liquids flow when pushed
DISCIPLINES RELATED TO FOOD TEXTURE • Food rheology • Other physical properties: wettability, phase changes, surface tension • Psychophysics, psychorheology/sensory science • Mastication/anatomy/physiology • Microscopy, x-ray diffraction, NMR
But rheology and mechanical properties are not texture • Empirical tests may do a better job of predicting texture as perceived by panelists
“The fact that fundamental rheological measurements may not correlate as well with sensory measurements of texture as do empirical tests may result from the incompleteness of the science of rheology to describe all the changes that are actually sensed in the mouth” Malcolm Bourne (1982)
TEXTURE: IMPORTANCE TO CONSUMERS • Critical: food in which texture is the dominant quality characteristic (meat, celery, chips) • Important: foods in which texture is significant but not dominant (fruit, bread, candy) • Minor: foods in which texture makes a negligible contribution (beverages, thin soups)
“If texture of a food is the way people have learned to expect it to be, and if it is psychologically and physiologically acceptable, then it will scarcely be noticed. If, however, the texture is not as expected... it becomes a focal point for criticism and rejection of the food. Care must be taken not to underestimate the importance of texture just because it is taken for granted when all is as it should be”. -Szczesniak and Kahn (1971)
Importance of Rheology • Rheology is the study of how materials flow or deform when subject to various forces • Rheological and mechanical properties are related to how we perceive food. Body, mouthfeel, chewiness, etc. related to how material deforms and flows • Rheological properties of food materials determine how they are processed (pump sizing, time in heating tube, extrudability)
Processing may be used to change food texture • flour grinding • fermentation of milk • freezing of ice cream • forming chicken pieces • Mechanical and rheological properties determine how food is handled • Sometimes changes are inadvertent and undesirable • Changes in frozen strawberries • Mushiness in overcooked products
Native foods: original structure of agricultural commodity determines texture. Is modified by drying, canning, size reduction, etc • Formulated foods: processed from a number of ingredients whose native structure is lost. More options for final texture. Jellies, sausage, sauces, candies, etc.
Types of Foods • Fluids: a substance that deforms continuously when acted on by a shearing force. • Elastic Solid: a material that deforms by a finite amount when a force is applied, but returns instantaneously to its original form when the force is removed • Semi-solids: solid foods that exhibit some properties of liquid (or vice versa)
Physical Versus Sensory Properties • Physical propertiesare measured by mechanical instruments, are quantitative, and reproducible • Sensory propertiesrelate to how people collect data about the outside world, and develop a perception about the world in their mind. Measured using human beings as the measuring instrument.
Sensory Property Color Brightness Pitch Loudness Aroma Hot/cold Physical Property Wavelength Intensity Frequency Volume Chemical composition Temperature
Sensory properties are difficult to quantify Humans are inherently non-linear instruments, with limited reproducibility • a sound with twice the air pressure will not be twice as loud • adding 3 times as much sugar to a drink will not cause it to be 3 times as sweet • materials with twice the “elastic modulus” may not be perceived as twice as “hard” or “springy”
Muller’s Description “Texture” often used to describe both physical and sensory properties. “Texture” is: • Rheology: branch of physics that describes physical/mechanical properties of food • Haptaesthesis: branch of psychology that deals with perception of the mechanical properties of materials
Young’s modulus Shear modulus Poisson’s ratio Viscosity Loss compliance Mouthfeel Hardness Chewiness Gumminess Adhesiveness TEXTURE Rheology Haptaesthesis
Texture: Do We Need It? • The identification of a food may rely a great deal on its texture characteristics. • However, while we are usually fairly conscious of flavor or appearance, texture may be evaluated at a more sub-conscious level
Other Tidbits • Relative importance of texture and words used to describe it vary with culture • Texture is readily discernible and an important food attribute • Texture awareness more subconscious than flavor. Awareness increases when textural expectations not met
Time of day exerts influence on texture awareness • Breakfast: prefer restricted range of textures that lubricate mouth, remove dryness • Evening: texture most appreciated and enjoyed • appetizers: non-demanding textures/stimulate saliva • main meal: wide variety, some chewy • dessert: require low energy for chewing • Children and teenagers rate texture as a more important attribute