Sensory Evaluation Of Food PDF

SENSORY EVALUATION OF FOOD Sensory evaluation of food  Sensory Evaluation is defined as “A scientific discipline used to evoke, measure, analyze, and interpret those responses to products that are perceived by the senses of sight, smell, touch, taste, and hearing (Stone and Sidel 1993).”...

SENSORY EVALUATION OF FOOD Sensory evaluation of food  Sensory Evaluation is defined as “A scientific discipline used to evoke, measure, analyze, and interpret those responses to products that are perceived by the senses of sight, smell, touch, taste, and hearing (Stone and Sidel 1993).”  All of the senses are important when eating.  Sensory evaluation can be divided into two categories of testing ❑ Objective ❑ Subjective.  In objective testing, the sensory attributes of a product are evaluated by a selected or trained panel.  In subjective testing, the reactions of consumers to the sensory properties of products are measured.  The power of sensory evaluation is realized when these two elements are combined to reveal insights into the way in which sensory properties drive consumer acceptance and emotional benefits.  Linking sensory properties to physical, chemical, formulation and/or process variables then enables the product to be designed to deliver optimum or appropriate consumer benefits.  Four variables affect sensory evaluation: Food People Testing environment Test methods used  Themeasurements of sensory characteristics of foods should be taken carefully.  When done properly, sensory information can provide great insight into the world.  When measures are undertaken poorly they do more to mislead than to inform.  Carefulcontrols must be implemented and followed when conducting sensory analysis, including (1) Neutrality in the presentation of samples (2) Elimination of response bias (3) Use of methods that require panelists to demonstrate their ability rather than relying upon self-reports. Importance Of Sensory Evaluation  The role of sensory evaluation is to provide valid and reliable information to the research department, production and marketing in order for management to make sound business decisions about the perceived sensory properties of the product.  Costsaving may be realized by correlating sensory properties with instrumental, physical or chemical analysis.  Moreover, following points are equally important in sensory evaluation: 1. Man has well-developed like and dislikes for food products depending on their palatability. 2. Sensory evaluation will become paramount importance with increasing consumer awareness towards nutrition and quality. 3. Sensory evaluation assists in measuring the eating qualities of any food. 4. Optimal information can be obtained only through co- ordination of instrumental and sensory measurements. 5. Where no signal appears our senses may still perceive an odour or taste. 6. Senses give us a total impression of quality. Application in Food Industry  Companies can compare a competitor’s product.  Improve products by modifying or changing the ingredients.  Check that the specification is being met.  Monitor quality control by checking regular samples against specification.  Detect differences between products from different runs or batches.  Profile the characteristics of new products.  Describe specific characteristics of the product.  Demonstrate new products to marketing team.  Promote new or reformulated products to consumers. Advantages of sensory evaluation  Helps manufacturers, scientists, food technologists etc. to gain a clear perception of what ordinary consumers may experience.  Measures the overall impression of the product i.e. eating quality when consumed.  Sensory panel testing can be much more rapid than most non-sensory methods.  Uses more than one sense, making them more flexible instruments.  Can be very sensitive and good at detecting minute differences in product characteristics. Disadvantages  Sensory panelists can become fatigued with the entire process of testing and assessing descriptive data.  Assessors may be subject to biases e.g. from loss of interest or from distractions.  To ensure precision in the analysis and interpretation of the descriptive data and for statistical analysis, several assessors may be required, making it an expensive proposition.  The entire process of recruiting and training sensory panelists can be a time-consuming and costly process.  It may not be easy to replace assessors quickly, as the incoming assessor will have to be given intensive training to develop requisite expertise of the job.  Thesensory panel method can be more expensive than some non-sensory methods.  The panelists may not be good at quantifying perceptions.  Interpretation of results may get problematic and be open to dispute. Sensory perception Human sense Vision(Sight) The appearance of any object is determined by the sense of vision. Light waves reflected by an object enter the eye and fall on the retina. The retina contains receptor cells, known as rods and cones, which convert this light energy into neural impulses that travel via the optic nerve to the brain  Cones are responsive to different wavelengths of light relating to ‘colour’.  Rods respond positively to white light and relay information concerning the lightness of the colour.  The brain interprets these signals and we perceive the appearance (colour, shape, size, translucency, surface texture, etc.) of the object.  The characteristics of a food product that can be evaluated by sense of sight are:  style, neatness and cleanliness of package exterior, attractiveness of product finish, package closures, colour, consistency, body and texture and overall appearance. Colour  Colour and appearance aspects of products should not be overlooked because these features may render the product acceptable / unacceptable. The appearance is an attribute which a decision is taken to purchase or consume.  Color: A phenomenon that involves both physical and psychological components: ✓ Perception by the visual system of light of wavelengths 400 to 500 nm (blue), 500 to 600 nm (green and yellow), and 600 to 800 nm (red), commonly expressed in terms of the hue, value, and chroma of the Munsell color system. Deterioration of food is often accompanied by a color change. Size and Shape  Sizeand shape: Length, thickness, width, particle size, geometric shape (square, circular, etc.), distribution of pieces, e.g., of vegetables, pasta, prepared foods, etc.; size and shape are indications of quality of products. Shape Size Surface texture  Surface texture The dullness or shininess of a surface, the roughness, evenness; surface characteristics i.e wet, dry, soft, hard, crisp, tough are indicators of quality. Surface Texture Clarity  Clarity The haze or opacity of transparent liquids or solids, the presence or absence of particles of visible size are important indicators of quality. Gustation(Taste)  The sense of taste involves the perception of non-volatile substances which, when dissolved in water, oil or saliva, are detected by taste receptors in the taste buds located on the surface of the tongue and other areas of the mouth or throat.  The resulting sensations can be divided into five different taste qualities – salty, sweet, sour, bitter and umami.  Examples of compounds that elicit particular tastes are given as follows: Salty substances: sodium chloride, potassium chloride Sweet substances: sucrose, glucose, aspartame Sour substances: citric acid, phosphoric acid Bitter substances: quinine, caffeine Umami substance: monosodium glutamate What is umami?  Umami is a savoury taste, often known as the fifth taste.  It is a subtle taste and blends well with other tastes.  Most people do not recognize the taste unless attention is especially drawn towards it.  After eating Cheddar cheese or tomatoes, there may be a ‘savoury’ taste lingering - this is umami. Familiar foods with a umami taste  These are foods which all have an umami taste:  Tomatoes  Cured pork, e.g. ham, sausage, bacon  Cheddar cheese  Meat, e.g. beef  Yeast extract  Itis a myth that only certain areas of the tongue are sensitive to particular tastes.  In fact, different areas of the tongue can be responsive to all the taste qualities  However, some areas are more sensitive than others. Useful words to describe taste Sweet Cool Bitter Umami Warm Hot Tangy Sour Rich Salty Bland Rancid Acidic Strong Citrus Mild Savoury Spicy Tainted Weak Olfaction(Smell)  Volatile molecules are sensed by olfactory receptors on the millions of hair-like cilia that cover the nasal epithelium (located in the roof of the nasal cavity).  Consequently, for something to have an odour or aroma, volatile molecules must be transported in air to the nose.  Volatile molecules enter the nose orthonasally during breathing/sniffing, via the back of the throat during eating.  There are around 17,000 different volatile compounds.  A particular odour may be made up of several volatile compounds, but sometimes particular volatiles (character- impact compounds) can be associated with a particular smell, e.g. iso-amyl acetate (banana/pear) drops.  Individuals may perceive and/or describe single compounds differently, e.g. hexenol can be described as grass, green, unripe.  Similarly, an odour quality may be perceived and/or described in different compounds, e.g. minty is used to describe both menthol and carvone Touch (somesthesis, kinesthesis and chemesthesis)  Somesthesis: The skin, including the lips, tongue and surfaces of the oral cavity, contains many different tactile receptors that can detect sensations related to contact/touch, e.g. force, particle size and heat.  Kinesthesis: Nerve fibres in the muscles, tendons and joints sense tension and relaxation in the muscles, allowing the perception of attributes such as heaviness and hardness.  Chemesthesis: Some chemical substances can stimulate the trigeminal nerves situated in the skin, mouth and nose to give hot, burning, tingling, cooling or astringent sensations e.g. Piperine in pepper Capsaicin in chilli pepper Carbon dioxide in fizzy drinks Coolants in showers gel, warming compounds in muscle rubs Tannins in wine  When sensed in the oral cavity, they form part of what are collectively known as mouth-feel attributes. Texture perception is complex.  Attributes of food texture can be divided into three categories: (i) mechanical, e.g. hardness and chewiness; (ii) geometric, e.g. graininess and crumbliness and (iii) mouth-feel, e.g. oiliness and moistness.  These are generally described as being perceived during three phases: ❑ Initial phase (first bite), ❑ masticatory phase (chewing) ❑ residual phase (after swallowing). Audition(Hearing)  Sound is sensed by millions of tiny hair cells in the ear that are stimulated by the vibration of air from sound waves.  The noise created when touching or stroking objects, e.g. fabric, gives an indication of texture.  The noise emitted by food during eating contributes to the perceived texture of a food, e.g. crispness of potato chips and fizz of a carbonated drink.  When consumers eat food products, the sound waves produced can be conducted by the air and/ or bones in the jaw and skull.  The latter is known as intra-oral perception. Multimodal perception  Although distinct sensory organs exist for each of the different senses, it is important to note that information from each of the sensory organs is often integrated in the brain.  For example, the perception of flavour results from the interaction between taste, aroma, texture, appearance and sound.  Sound can also affect the perception of touch.  Similarly, texture perception is a combination of the visual, tactile and chemesthetic properties of the food or object under observation.  The sensory professional should, therefore, be aware of how changes in one sensory property can affect others. Think about eating a potato chip?  See Chip  Touch Greasy, or thick  Smell - Seasoning Or the oil it was fried or baked  Hear Crunch of the chip  Taste Saltiness (maybe you also experience some additional flavor) Importance of sensory evaluation  Compare similarities/differences in a range of dishes/products.  Evaluate a range of existing dishes/food products.  Analyse dishes/food samples for improvements.  Gauge responses to a dish/product, e.g. acceptable v unacceptable.  Explore specific characteristics of an ingredient or dish/food product  Check whether a final dish/food product meets its original specification  Provide objective and subjective feedback data to enable informed decisions to be made  Requirements of a sensory evaluation laboratory and sample presentation Requirements of a sensory evaluation laboratory and sample presentation  Samples ❑ Objective of a sensory test is to identify the effects of different product treatments. ❑ Ingredients used should be made known to the assessor before testing  Sample preparation ❑ The materials used for the preparation of samples should be of known origin and storage history ❑ Where several batches of a particular ingredient are required, the batches should be combined prior to use Equipment and utensils  The type of materials from which utensils and equipment are made.  Glass, glazed china or stainless steel are the most appropriate  Some laboratories may restrict the use of glass due to health and safety issues.  Wood should be avoided as it can be unhygienic and can absorb food materials which may be transferred to other samples.  Plastic is also capable of absorbing volatile compounds which could then be transferred to later samples.  Many standard plastic containers, bags and wraps are not suitable and so should be tested before use.  The use of equipment and utensils should be standardized across all samples.  Where this is not possible, e.g. different brands of food mixer, samples should be randomly allocated to the equipment Method  All samples should be prepared in exactly the same manner.  Procedures should be standardized through accurate use of balances, volumetrics, stopwatches, agitation rates, temperature probes or loggers, etc., where appropriate.  Similarly, the positioning of samples in ovens, refrigerators, incubators, etc., should be standardized.  If samples are to be stored prior to serving, then the impact of storage on the samples should be tested to ensure that sensory (and microbial) quality is not affected.  A preparation method should be chosen which is least likely to mask differences between product treatments. Sample presentation  Sample size and temperature ❑ Careful consideration should be given to sample size, although this may be constrained by the amount of product available. ❑ Prior testing with the panel can determine sample size where appropriate. ❑ For samples which consist of several components, the sample size should be sufficient to enable all components to be included. ❑ Clear instructions should also be given to the assessors concerning the sample size that they are to consume.  Serving temperature will be governed by the product and the test objectives.  It should be consistent across samples and within a narrow range specified at the beginning of the investigation.  The appropriate choice of container can also help maintain sample temperature, e.g. polystyrene cups, provided it does not affect the sensory properties of the product.  Water or sand baths, hotplates, vacuum flasks, ice, etc., can be employed to hold samples at the correct temperature provided that the holding time does not affect the sensory properties of the product. Some recommendations for sample temperature  Generally hot foods should be served between 600C and 660C, hot tea and coffee between 660C and 710C,  cold beverages between 50C and 90C  Many foods can be served at ambient temperature, e.g. snacks, jams and preserves, and cereals. Vessel  The vessel used for sample presentation will depend, to some extent, on sample size.  Whichever vessel is chosen, it should impart no additional sensory characteristic to the sample.  Glass is preferable, but not always feasible as it is more expensive, requires washing for reuse and can be a hazard.  Plastic and cardboard tend to be more popular but should be tested prior to use to ensure they do not affect the sensory properties of the product, e.g. avoid waxed board.  Identical vessels should be used for all products and the nature of the vessel should not bias the assessor.  Clear or plain white vessels are recommended unless the vessel is also being used to mask unwanted differences between products  e.g. dark opaque glasses are often used to mask differences in appearance between wines. Carrier  Some products, e.g. fat spreads, breakfast cereals, seasonings and flavourings, are not readily evaluated on their own and require an additional product to be presented as a carrier.  This is particularly the case in consumer tests in which presenting a product as it is normally consumed is especially important.  Careful consideration should be given to the choice of carrier as it can provide an additional source of variation in the data.  Furthermore, interactions between the product and the carrier (physicochemical and/or perceptual) may result in the evaluation of sensory sensations not uniquely related to the test product.  The sensory analyst should carry out preliminary investigations to ensure that the carrier does not distract assessor attention from the test product and does not influence its sensory character, either by adding to or by masking its sensory attributes.  Some typical carriers include unsalted crackers, white bread, rice, pasta, milk and bland white sauces.  The carrier, however, should always be congruent with the test product, e.g. bread is useful for spreads Coding  Coding samples removes a source of expectation error from the experiment.  Codes used for samples should be carefully recorded and random three-digit codes are preferred.  They can be randomly generated by computers and calculators or obtained using random number tables, although certain codes should be avoided  For example, codes such as ‘A’, ‘1’ or round numbers (e.g. 100, 250) can be associated with a higher score.  Different codes should be used for replicates to prevent assessors remembering samples.  All codes should be written in a consistent format and positioned similarly using the same odour-free pen or printed by computer on labels subsequently positioned on the presentation vessel. Palate cleanser  To avoid carry-over effects and adaptation to sensory stimuli, the use of a palate cleanser between samples is required.  Bottled mineral water at room temperature is successful in cleansing the palate for a wide range of products (the flavour of tap water tends to be too inconsistent).  However, some products can be more problematic.  Greasy foods tend to need something more astringent, e.g. pieces of apple can be useful between samples of chocolate.  Spicy foods tend to need a palate cleanser containing fat, so milk is a popular choice.  For astringent products like tea, melon is successful.  The sensory analyst should determine an appropriate palate cleanser prior to the investigation with input from the panel where appropriate.  The time given between samples can also be important for products with lingering effects. Number and order of samples  Balancing the order of sample presentation removes several sources of error  The number of samples to present will depend very much on the nature of the samples, the size of the sample, the objective and type of test, and the time available.  For visual assessments, tens of samples can be assessed in any one sitting, whereas for some spicy samples only one product per session may be possible. Reference samples  The purpose of the reference should be made clear to the assessor.  The same controlled procedures described earlier are required for the production of any reference samples, particularly when different batches need to be made.  Ifthe reference is at room temperature, it may be left in the booth for the duration of an experiment.  Some references, however, will need to be served at specific temperatures and hence renewed each time they are used.  The use of a reference sample should be standardised across assessors so as not to add a further source of variation to the experiment.  The reference may also be presented as a coded sample to evaluate the consistency of the assessors. Panel selection and training Assessors  The individuals who take part in product assessments are the most important asset in sensory evaluation.  It is essential that the most appropriate individuals are recruited, screened and selected to take part in sensory tests  They should be given the necessary training and tools to allow them to complete the test effectively  They should receive positive and constructive feedback on their performance and, above all, they must be treated with consideration and respect.  Untrained sensory panel - Consumers  Trained panel ❖ Individuals on a trained panel must exhibit suitable personality and attitude traits ❖ Be in good health ❖ Satisfy minimum criteria for sensory acuity (ability). Personality Generally, participants should:  be able to work as a team  have cosmopolitan preferences  be positive but not overbearing  be a good listener and communicator  be committed  be flexible. Health  Assessors must be in good general health  Any physiological or health restrictions must be documented, e.g. allergies, false teeth, as these may affect their participation in certain tests. Sensory acuity  Assessors should have at least normal sensory acuity with regard to  Detecting stimuli  Discriminating between stimuli  Recognizing and describing stimuli  In some circumstances, e.g. taint assessment, it may be desirable to select assessors with high sensitivity to certain stimuli. Good working practices for assessors Generally, the following good working practices should be observed by all assessors irrespective of training and test protocol.  Assessors should not smoke for at least 1 hour prior to the start of a food or fragranced product test as this affects their sensitivity to certain attributes and creates lingering odours that distract other assessors.  Assessors should not wear highly fragranced, personal care products or cosmetics, as this may interfere with the product assessment.  Assessors should not eat or drink for at least 1 hour prior to the start of a food or fragranced product test  Assessors should not talk during a test unless instructed to do so.  Assessors should observe good personal hygiene e.g. body odour may distract coworkers  Assessors should attend on time  Assessors should focus on the test and follow instructions. Training  The level of training required by each assessor is driven by the test method itself.  In some instances, no training beyond the instruction required to complete the test is necessary;  whereas, in other cases lengthy training on attributes and scales may take several weeks/sessions to complete.