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Chapter 15

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University of Guelph
Food Science
FOOD 2010
Massimo Marcone

FOOD*2010 (DE) W12 - Principles of Food Science Chapter 15 15.1 Sensory evaluation - is the assessment of all the qualities of a food item as perceived by the human senses (food colour, texture, flavour, aftertaste, aroma, tactile response, and even auditory response (pop, crackle)). * is a scientific method used to obtain and analyze Sensory evaluation or sensory science is a quantitative science in which numerical data are collected to establish specific relationships between product characteristics and human perception. The main applications of sensory evaluation in the food industry are in quality assurance and product development. 15.2 Two types of senses are involved in sensory perception: chemical (taste and odour) and physical (sight, sound, and touch). Character notes are the sensory attributes of a food that define its appearance, flavour, texture, and aroma. Taste may be defined as the sensation derived from food as interpreted though the tongue-to-brain sensory system. The four primary taste sensations of sweet, salty, sour, bitter, as well as a fifth one, umami (meaning delicious along with meaty and savoury suggestions) all trigger brain response. Tastants: molecules that possess the primary sensory characteristics of sweet, bitter, salt, and sour as sensed by the tongue. Taste buds are actually epithelial receptor cells organized into clusters of 50-150, which are embedded into structures all papillae. Newborns have 8000-10,000 taste receptors, adults 4000-6000 and 2000-3000 later in life. People are either supertasters (greatest number of fungiform papillae), medium tasters, or nontasters of PROP (6-n-propylthiourcacil). Taste transduction: mechanism f cell-to-cell communication through pores in cell membranes (ion channels) that function as “gates” between the tongue and the central nervous system (CNS) Depolarization: accumulation of a positive charge in the cell, marking the membrane potential less negative than normal, and more positive. Accompanying depolarization is neuronal signalling the release of neurotransmitters to the brain. Odour plays a major role in terms of the enjoyment of food. Olfaction strictly refers to the perception of odours by the never cells in the nasal area. Airborne odorants are sensed by the olfactory epithelium, which is the outer layer of receptor located on the food on the nasal cavity. Food flavour is an overall impression of combining taste, odour, mouth feel factors (coolness, heat and texture), and trigeminal perception. Retro-inhalation: refers to the passage of flavour stimuli from the mouh through the pharynx up to the nose. 15.3 Sensorytexture has to do with the structure and compostition of food, and it involves food molecules, their perception, and measurement (shapes, sizes, thickness, and hardness). EX. The visual appearance of mashed potatoes prepares one for the texture that is anticipated. Mechanical sensory characteristics are generally due to attractive forces between the molecules in a food and the opposing force of disintegration (chewiness, viscosity, hardness, cohesiveness (degree by which a food will deform between teeth before it breaks), and adhesiveness of food (sticky, tacky, gooey)). Sensory viscosity is related to the force required to draw a fluid from a spoon across the tongue at a steady rate. Ranges from thick to thin viscous (ketchup, honey, and water). Geometrical characterisitics of food also implies sensory texture – the size of food particle, as well as shape and orientation (chalky, gritty, grainy and coarse). Sensory overload: excessive sensory stimulation, saturating the sensory system. Food possess colour based upon wavelengths of reflected and absorbed visual light (range from 350-800 nanometres (NM), which communicate to the brain so we can see the colours of food). Colour can be used as an indicator of the economic value of the products (ripeness etc.). Hunter tristimulus: in food colour analysis, the three values of L (lightness), a (red to green colour dimension), and b (yellow to blue colour dimension), as represented by a three-dimensional colour solid. 15.4 Sensory study involves quantifying a response to a stimulus. 1. The stimulus interacts with the sense organ (tongue, nose, and eye) and is converted into nerve signals that travel to the brain. 2. The brain interprets the incoming signals and organizes them into perceptions. 3. A response is elicited from the subject based upon these perceptions Sensations correspond to objective functioning, while perceptions are subjective. Many features of food quality related to flavour, texture, colour, and odour are measurable by objective procedures (testing procedures using analytical equipment). Intensity has to do with the product stimulus, while sensitivity has to do with panellist ability to sense. Intensity is the degree to which a character note is present, as determined by its product concentration and perception by a person. Time-intensity measurement: measurement of sensory attributes evaluated over a period of time following an initial exposure. Threshold for sensitivity refers to distinct points of transitipn for sensory judgements corresponding to cencentraions of stimuli. Detection threshold is the point at which a person initially responds to a stimulus, the dividing line between the lack of sensation to sensation. Recognition threshold is the point at which the identity of a stimulus is made. Difference threshold refers to the minimum amount of stimulus change that results in a change of sensation. Terminal threshold is the amount of stimulus above which increase in intensity cannot be detected without the use of reference standards. 15.5 To carry out effective and meaningful sensory research, the main guiding principal is that the objective of the specific project determines the sensory technique and test chosen by specialists. Other principals include: 1. Trained panellists should not be used to obtain acceptability judgements 2. Consumer panels should not be used to obtain accurate descriptive information 3. Samples should be labelled with random 3-digit codes to minimize bias. Affective tests attempt to quantify the degree of liking or disliking of one product over another, and include preference, hedonic, and consumer acceptance tests. Ranking is a form of preference testing that uses more than two samples. Rating is a term meaning the assigning of number by panellists to characterize products in various response categories based on specific sensory attributes, and is a type of acceptance test. Discrimination (or difference) tests simplify attempt to answer whether any differene at all exists between two types of products. Triangle test: simple discrimination or
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