Texture in Food

Solid Foods

David Kilcast, David Kilcast

• Éditeur: Woodhead Publishing
• Année: 2004
• ISBN:
  9781855738362
• Sujet: Technologie et ingénierie
• Sous-sujet: Sciences de l'alimentation

Texture is one of the most important attributes used by consumers to assess food quality. With its distinguished editor and international team of contributors, this authoritative book summarises the wealth of recent research on what influences texture in solid foods and how it can be controlled to maximise product quality.The first part of the book reviews research on understanding how consumers experience texture when they eat, and how they perceive and describe key textural qualities such as crispness. Part two considers the instrumental techniques used for analysing texture. It includes chapters on force/deformation and sound input techniques, near infrared spectroscopy (NIR), nuclear magnetic resonance (NMR) and magnetic resonance imaging (MRI). The final part examines how the texture of particular foods may be better understood and improved. A number of chapters review ways of controlling the texture of fruits and vegetables, including the role of plant structure and compounds, the handling of raw materials and technologies such as freezing and vacuum infusion. A final group of chapters discuss the texture of cereal foods, including bread, rice, pasta and fried food.Texture in food Volume 2: Solid foods is a standard reference for the food industry. It is accompanied by a companion volume on the texture of semi-solid foods.

• Reviews developments in measuring the texture of solid foods
• Examines the influences on texture and ways of maintaining textural properties
• Written by an expert team of authors

Part I

Consumers, texture and food quality

1

Measuring consumer perceptions of texture: an overview

D. Kilcast Leatherhead Food International, UK

1.1 Introduction: texture and food quality

In prosperous societies, we have available an enormous and ever-increasing range of foods, and manufacturers find themselves in an intensely competitive situation. In less well-developed societies, hunger will be the constant driving force, and our diet will be determined by availability of any food that satisfies our basic nutritional needs. It is increasingly clear that if we are to understand what drives consumers’ choice of food, no single factor can be considered in isolation from others. For some years, psychology researchers have been developing models to understand consumer behaviour (e.g. Shepherd and Sparks, 1994). Although there are many possible circumstances under which non-sensory factors such as price and nutritional image can have dominant effects, the sensory characteristics of foods are central to their continued purchase.

The importance of a holistic approach is also becoming more clear when the components of sensory perception are considered. During the sequences of actions that constitute food consumption, we perceive a whole range of different characteristics relating to the appearance, flavour and texture of the food. Numerous tools are available for investigating the sensory properties of foods, and the information required must be carefully defined if appropriate tools are to be selected. Systematic development of new products will inevitably depend on the use of different tools at different stages of the development cycle.

1.1.1 The human senses

It is generally accepted that human beings have five senses in operation, namely sight, smell, taste, touch and hearing, although warmth, cold, movement and pain may also be considered as senses of importance in a food context (Fig. 1.1). Foods are complex mixtures of chemical compounds, arranged into structural units. The perception of the sensory characteristics of foods results from the stimulation of all our senses to some extent by the physicochemical properties of the foods. The sensory characteristics of food are generally grouped into three categories, namely appearance, flavour and texture. These categories are, however, not independent of one another. For example, colour, which is obviously an important appearance characteristic, can be shown to have an influence on flavour perception; consumers will assign higher scores for flavour intensity to darker foods than to lighter foods. The interaction between appearance and flavour is referred to as ‘visual flavour’. Similarly, textural characteristics such as viscosity can influence the perception of flavour, and some flavour characteristics, e.g. acidity, can affect textural characteristics. One means of defining flavour, texture and appearance is by taking into account the fact that each can be attributed to the stimulation of one or possibly two of the senses. On this basis the International Standards Organisation (ISO, 1992) has proposed working definitions for flavour, texture and appearance, as given below.

Fig. 1.1 Schematic diagram of the human senses and their operation in the perception of food quality.

• Appearance: sensory characteristics of foods perceived largely by way of the visual sense. Input from other senses, especially smell, may contribute.

• Flavour: the combination of taste and odour. Pain, heat, cold, tactile and visual sensations may also contribute.

• Texture: sensory characteristics perceived largely by way of the senses of movement and touch. Input from other senses, especially vision and taste, may sometimes contribute.

The above definitions give little information on how the senses are used in the perception of quality attributes. Appearance is sometimes, mistakenly, equated only with colour, and yet many other visual aspects of form, shape, translucency, etc., may influence our use of the visual senses. Taste (gustation) is strictly defined as the response by the tongue to soluble, involatile materials. These have classically been defined as four primary basic taste sensations: salt, sweet, sour and bitter, although umami, the sensation associated with monosodium glutamate, is now widely recognised as a basic taste. This list is frequently extended further to include sensations such as metallic and astringency. The taste receptors are organised groups of cells, known as taste buds, located within specialised structures called papillae. These are located mainly on the tip, sides and rear upper surface of the tongue. Taste stimuli are characterised by the relatively narrow range between the weakest and the strongest stimulants (ca 10⁴), and are strongly influenced by factors such as temperature and pH (Meilgaard et al., 1999).

The odour response is much more complex, and odours are detected as volatiles entering the nasal passage, either directly via the nose or indirectly through the retronasal path via the mouth. The odorants are sensed by the olfactory epithelium, which is located in the roof of the nasal cavity. Some 150–200 odour qualities have been recognised, and there is a very wide range (ca 10¹²) between the weakest and the strongest stimulants (Meilgaard et al., 1999). The odour receptors are easily saturated, and specific anosmia (blindness to specific odours) is common. It is thought that the wide range of possible odour responses contributes to variety in flavour perception. Both taste and odour stimuli can be detected only if they are released effectively from the food matrix during the course of mastication.

The chemical sense corresponds to a pain response through stimulation of the trigeminal nerve. This is produced by chemical irritants such as ginger and capsaicin (from chilli), both of which give a heat response, and chemicals such as menthol and sorbitol, which give a cooling response. With the exception of capsaicin, these stimulants are characterised by high thresholds. The combined effect of the taste, odour and chemical responses gives rise to the sensation generally perceived as flavour, although these terms are often used loosely.

Texture is perceived by the sense of touch, and comprises two components: somesthesis, a tactile, surface response from skin, and kinesthesis (or proprioception), which is a deep response from muscles and tendons. For many foods, visual stimuli will generate an expectation of textural properties. The touch stimuli themselves can arise from tactile manipulation of the food with the hands and fingers, either directly or through the intermediary of utensils such as a knife or spoon. Oral contact with food can occur through the lips, tongue, palate and teeth, all of which provide textural information.

1.1.2 Texture and food enjoyment

Most studies which have investigated the importance of different sensory modalities on consumer acceptability conclude that flavour is the most important modality, followed by texture and then appearance (e.g. Moskowitz and Krieger, 1995). Such conclusions do not reflect the enormous efforts that the food industry devotes to designing appealing textural characteristics, and to maintaining those characteristics to long-term production. Research with consumers in the USA carried out by Szczesniak and Kahn (1971) showed that awareness of texture lies at a subconscious level, and that textural properties are taken for granted. If the expectations of texture are violated, however, awareness of textural defects is accentuated, and texture becomes a focal point for criticism and rejection of the food. Expectations are being increasingly recognised as important factors in food choice by consumers (e.g. Vickers, 1991; Cardello, 1994).

1.1.3 The interactive role of texture

In addition to its direct contribution to consumer acceptance, texture has a vitally important secondary effect, through modulation of flavour release. If flavour components are to be pe...