FOOD ENGINEERING

Lesson 9. MEASUREMENT OF FOOD TEXTURE

Module 1. Rheology of foods

Lesson 9

MEASUREMENT OF FOOD TEXTURE

9.1 Introduction

Texture is one of the major criteria which consumers use to judge the quality and freshness of many foods. When a food produces a physical sensation in the mouth (hard, soft, crisp, moist, dry), the consumer has a basis for determining the food's quality (fresh, stale, tender, ripe). The crispiness of a potato chip, the crunchiness of a pickle, the freshness of bread, cookies and crackers, the firmness of jam and preserve, the spreadability of butter, margarine and cheese and creaminess of puddings are just a few examples of texture and mouthfeel characteristics that make food appealing and satisfying to consumers.

In formulations of new foods, or modification of the existing products while maintaining the desirable sensory characteristics sensory evaluation plays a pivotal role. For instance arriving of minimum sensory standards in nutrient fortified foods for domestic as well as for export purposes, and the development of substitutes for consumers on special diets such as low-calorie, low-sodium, low-cholesterol or lactose-free foods. Sensory evaluation techniques have been used to assess the progress of the product development in the food industry. Many consumers purchase a product on the bases of the sensory experience which it delivers. Food technologist in general, and sensory analyst in particular, recognize the need to focus attention on measuring the perception of these characteristics. In similar manner, the textural measuring devices are helpful in evaluating the product quality.

9.2 Texture Terms Used in Sensory Texture Profiling

A major challenge facing food developers is how to accurately and objectively measure texture and mouthfeel. To develop new product or to modify existing product to have better sensory and rheological attributes developer should understand different texture terms used in sensory texture profiling. The different texture terms used in sensory texture profiling are listed below:

(i) Adhesiveness: Force required to remove the material that adhere to a specific surface (e.g. lips, palate, teeth).

(ii) Hardness: Force required to deform the product to given distance, i.e. force to compress between molars, bite through with incisors, compress between tongue and palate.

(iii) Cohesiveness: Degree to which the sample deforms before rupturing when biting with molars.

(iv) Springiness: Degree to which the product returns to its original size/shape after partial compression (without failure) between the tongue and palate or teeth.

(v) Fracturability: Force with which the sample crumbles, crakes or shatters. Fracturability encompasses crumbliness, crispiness, crunchiness and brittleness.

(vi) Chewiness: Number of chews (at 1 chew/sec) needed to masticate the sample to a consistency suitable for swallowing.

(vii) Guminess: Energy required to disintegrate a semi-solid food to a state ready for swallowing.

(viii) Bounce: The resilience rate at which the sample returns to the original shape after partial compression.

(ix) Coarseness: Degree to which the mass feels coarse during product mastication.

(x) Denseness: Compactness of cross section of the sample after biting completely through with the molars.

(xi) Dryness: Degree to which the sample feels dry in the mouth.

(xii) Graininess: Degree to which a sample contains small grainy particles.

(xiii) Heaviness: Weight of product perceived when first placed on tongue.

(xiv) Moisture absorption: Amount of saliva absorbed by product.

(xv) Mouth release: Amount of wetness/juiciness released from sample.

(xvi) Mouth coating: Type and degree of coating in the mouth after mastication (for example fat/oil).

(xvii) Roughness: degree of abrasiveness of product's surface perceived by the tongue.

(xviii) Slipperiness: Degree to which the product slides over the tongue.

(xix) Smoothness: Absence of any particles, lumps, bumps, etc. in the product.

(xx) Uniformity: Degree to which the sample is even throughout.

(xxi) Uniformity of chew: Degree to which the chewing characteristics of the product are even throughout mastication.

(xxii) Uniformity of bite: Evenness of force through bite.

(xxiii) Viscosity: Force required to draw a liquid from a spoon over the tongue.

Wetness: Amount of moisture perceived on product's surface.

Sensory texture profile is defined as the organoleptic analysis of the texture complex of a food in terms of its mechanical, geometrical, fat and moisture characteristics, the degree of each present, and the order in which they appear from first bite through complete mastication. The data on these parameters is generally collected using either interval or ratio scales.

9.3 Instruments for Measuring Texture Properties

There are diverse range of instruments for measuring texture properties of food products. The Instron universal testing machine is an instrument for measuring texture through tension and compression testing and it is a versatile instrument for applications in research, development of new products and quality control laboratories. It comprises of a standard load frame and drive unit, a load weighing system and a microprocessor based control system. A beam carrying a load cell (moving cross heads) is located between the base unit and the fixed crosshead at the top of the frame. The cross head moving in vertical direction at a selected speed is supported and driven by two lead screws. It contains a force sensing and recording system which measures the force during the test and transmits them to a strip chart recorder. The Instron can be programmed for automatic return, cycling and relaxation test etc. Fig. 9.1 shows response of Instron in the form of Instron curve, based on which major textural parameters are calculated, as follows:

(i) Hardness (Kg_f): The force necessary to attain a given deformation, i.e. the highest point of peak in the first bite curve (Fig.1).

Hardness = H₁ , Kg_f

(ii) Brittleness (Kg_f): Force with which the sample crumbles, crakes or shatters

Brittleness (or Fracturability) = H_2, Kg_f

(iii) Adhesiveness: It is the work necessary to overcome the attractive forces between the surfaces of the sample and the other materials with which sample comes in contact. It is negative force area for the first bite curve (Fig.1)

Adhesiveness = A₃

(iv) Cohesiveness: The extent to which a material can be deformed before it ruptures

Cohesiveness = A₂/A₁

A₁ = Area under the first bite curve before reversal of compression

A₂ = Area under the second bite curve before reversal of compression

(v) Springiness (mm): The height sample recovers between the first and second compression, on removal of the deformation force

Springiness = S, mm

(vi) Gumminess (Kg_f): It is the energy required to masticate a sample to a state ready for swallowing a product of hardness and cohesiveness

Gumminess = Hardness x Cohesiveness x 100

(vii) Chewiness (kg-mm): It is the energy required to masticate a sample to a state ready for swallowing. It is a product of hardness, cohesiveness and springiness

Chewiness = Hardness x Cohesiveness x Springiness