Chapter
4
Sensory
evaluation of food and beverages
Introduction
Sensory evaluation as defined by the
sensory evaluation division of institute of food technologist is a scientific
discipline used to evoke, measure, analyze and interpret reaction to those
characteristics of food materials as they are perceived by the sense of sight,
smell, taste, touch and hearing. Sensory evaluation is procedure that is used
quite often in food science and technology because such sensory characteristics
of food products as flavor (odor or taste color and texture) are closely
involved with consumer appreciation and acceptance. It is no more an art that
can be done only by few experts. It has become a science, which can be taught
in a very systematic way.
Objectives
Sensory test are conducted to
a. Select
qualified judges and study human perception of food attributes
b. Correlate
sensory measurement with chemical and physical measurement
c. To
study the processing effect and ingredient substitution
d. To
evaluate quality
e. To
determine consumer reaction
Each of these above mentioned
objectives requires different tests to valid the results. Before one attempts
to run a sensort test he should define his problem and outlines of his
objectives so that appropriate sensory test can be applied. However, the most
common defect in our research laboratory is the use of one test regardless of
the objective. The next result is people working in this lab get a wrong idea
such tests frequently used is much superior and will neglect the importance of
other tests.
The first stage in designing a
sensory study is the planning. The proper planning requires a complete and
concise treatment of both the project objective and test objective for the
test. The selection of a test method depends primarily on the defined objective
of the test. Time is often wasted in carrying out inappropriate test.
Types of sensory tests
1. Discriminatory
or difference tests: Different tests are only used to determine whether a
detectable difference exists between two or more treatment without indication
of preference. These methods are usually used in quality control in research
and development. the most common difference tests are paired comparison test,
due trio test, triangle tests and other as a dual standard test, multiple
standard test, A and A’ which are also discriminatory test but not commonly
used.
2. Quantitative
difference tests: These tests requires panelist to rate specified
characteristics of the product according to established standards. Quality
scoring and ranking are commonly used in quantitative test. Hedonic rating test
is based on a scale of nine points.
3. Descriptive
tests: It analytically describes sensory characteristics of the product. It
requires the scoring out of many separable qualitative dimensions, which
explain the proper behavior towards the product. The test includes flavor
profile, texture profile, and quantitative descriptive analysis.
4. Effective
tests: It determines preferential degree of liking or disliking between the
products. Two alternatives are acceptance and preference.
Factors considered during testing
a. Design
or development: experiment error is possible in all experimental work. Errors
and bias during testing can be minimized through the use of technique such as
that of randomization. Replication also increases the precision of the
experiment. Randomization does two things.
It
prevents an overlooked effect from becoming identified with an experimental
factor and it ensure that any small overlooked effect is impartially
distributed among the comparision used to judge the methods.
b. Sample
and their preparation: When estimating the quantity of sample, required for a
series of tests, it is better to have more than required amount. In fact it is
practicable to double our original estimate unless we are working with rare and
expensive products. The quantity of the sample required is independent upon the
test method employed and the number of evaluation periods. It is advisable to
obtain sufficient amount of standard or controlled sample to be used through a
serried of tests extending over a period of time. Test materials should be
homogenous as possible. It is necessary to determine the most appropriate
method of preparation of sample to ensure that the judges will receive
identical samples. The samples can be diced, chopped, blended to get
representative samples. Samples coming from several cans should be mixed well
before portioning them to the judges. Law should be observed in such a way that
drying out of samples will be evaluated for juiciness. Serving containers
should also be identical and odor free. Colorless containers are advisable to
use to prevent bias in the evaluation of the samples. Disposable containers are
most ideal but might be too expensive particularly in food laboratories in
developing countries.
c. Condition
of judge: Judges are not advised to eat, smell or chew gum for at least one
hour prior to sensory testing. The best time for evaluation is between 10 to 11
AM or 3-4 PM, although there is no strict rule in this time schedule. Verbal
communication among the judge may result in inaccurate evaluation. Furthermore,
one judge might influence the decision of the other. Thus the use of
individually separated booths is recommended during evaluation. Rinse water
should be served with many products although rinsing between samples has to be
left open for each panel member. Panel member without too good memory can’t
sense in between otherwise they may forget the taste, flavor of previous
sample, other panel members might be so sensitive to test product that they
would suffer without rinsing. For these judges, rinsing is necessary and a good
memory helps them to remember taste and flavor of previous sample. Duplicate
samples of standard or control is usually served first as conditional samples.
It increases the judges’ ability to disetiminate between samples. Result of the
evaluation of the conditioned samples is not included in the statistical
analysis. Furthermore, the judges should not be aware of the inclusion of the
conditioned sample.
d. Requirement
of panel: The number of assessors in the panel should be uneven. The minimum
number is three. Several factors should be taken into consideration for optimum
performance of assessor. The following should be avoided just before assessing.
1. Heavy
meal, use of alcohol, smoking, highly flavored or spiced foods and so on
2. Excessive
number of samples and any other factors which would impair the ability to
assess.
General procedure for setting a test
1. D
2. F
3. G
4. G
5. H
6. E
7. D
8. determination
of stastical significance of tools.
Objective
analysis (Physical and Chemical)
1.
Moisture content
It
is useful index particularly in the case of vegetables for determining
tenderness at the time of maturity. In the case of sweet corn, a moisture
content of about 80% is too watery 75%, gives a product suitable for being
grades as fancy or grade A. White corns having a moisture content of less than
65% is so starchy that it is the standard level. Moisture content can be
determined by drying the prepared sample in a vacuum oven at 600C
for 6 hours or longer until there is no further weight loss. Rapid methods of
determination of moisture are based on distillation using immiscible solvents
for about 30 minutes.
2.
Insoluble solids
It
is a measure of texture rather than an index of maturity. From the prepared
samples, the soluble solids are leached out and the residue is dried in oven
that provides the measurement of insoluble solids.
3.
Alcohol insoluble solids
It
has been successfully applied for determining the quality of canned corn and
peas. By this procedure, salt, sugar and alcohol soluble solids are extracted
so that the residual dried material contains mostly the highly polymerized
carbohydrates such as starch, hemicellulose, cellulose, pectin and crude fiber
and alcohol insoluble protein. Low alcohol insoluble solid content indicates
less maturity and better suitability for purpose of canning. The alcohol
insoluble solid test has been shown to be more accurate for canned peas and
tenderness test for fresh peas.
4.
Fiber content
Vegetables
like French beans, fresh green beans, waxed beans becomes more fibrous with maturity.
The AOAC method of determining the fiber content involves the digestion of the
sample with 2% NaOH solution and subsequent treatment of the residue with 2%
HCl. The acid digested sample is strained, washed, dried and weighed. Waxed
beans containing more than 0.15% fiber are considered to be sub-standard.
5.
Sugar acid ratio
It
is important criterion from a stand point of taste appeal and more so in the
case of juice. For quality control point of view, sugar to acid ratio is the
ratio of sugar value as determined by a refractometer (in grams) to the acid
content as determined by titration. The ratio is kept 40:1 for apple product
and 10:1 for orange juice. Sugar t acid ratio cannot, however, be applied to
tomatoes as the acidity varies from season to season and from different growing
areas. pH control is more important than acidity to enable the tomato product
to be processed as a fruit.
6.
Brine flotation
This
method has been made use for tenderness,
maturity for the purpose of grading of peas used for canning.
Shelled peas are floated in brine the number of floaters and sinkers are
recorded. The method is rapid simple and provides not only a measure of average
quality but also uniformity. In addition to peas, the method has been applied
for maturity grading of lima beans and chestnuts.
7.
Soluble solids content
It
indicates the maturity of the sample. In fruits higher soluble solid content
indicates increased ripeness as well as sweetness of the sample while
vegetables with higher soluble solid content indicates less maturity. From the
quality control point of view, soluble solid content is usually a value
obtained by the use of Abbe’s refractometer with the assumption that the
soluble solids consists entirely of sucrose. For determining tomato solids in
different tomato products, the revised national canners association table
should be referred. Brix hydrometer may also be made use in the determination
of total soluble solid.
8. Acidity
It
is a measure of sourness and is important from flavor standpoint and wholesomeness
of the processed product. The titrable acidity indicates the sourness while pH
is more important from the processing point of view.
Hidden
factors
Nutritional
factors: Nutrients are food components those nourish our body and can be
classified as essential and non essential. Essential nutrients are more complex
compound such as vitamins, proteins and minerals that are not produced by the
body or are produced in small amount insufficient to meet cellular needs. Thus
these should be provided in the diet. Non essential nutrients are those used by
the body in its chemical laboratory and can be manufactured from other
compounds or nutrients, e.g. fats and carbohydrates whose main function is to
produce energy, are necessary for the chemical reaction in our body. The
distribution and quality of these nutrients vary in plant and animal tissues.
These are also known to be of different sensitivity to external factors such as
temperature light and air to which the food is subjected in course of
processing defeating the original value of food, i.e. to nourish. Unfortunately
food processing is an important step in making the available food supply to
meet the demands of a given population. It is not advisable to stop food
processing to maintain the nutritional value of food because in doing so, there
will be severe famine. In this regard the food technologist and the
nutritionist work together to treat a product i.e. nutritional and at the same
time of prolonged shelf life in order to meet the demands of the entire population
throughout the year and not only during peak season. At present, there is
growing eagerness among consumer regarding the nutritional information value of
available food. Some kinds of nutritional information in minimum standards that
specific products should meet are necessary. This is to allow consumer to know
whether characteristics or components of food items are comparable to the
specific product they claim to represent.
Standard
of identity
It
defines what a food product must consist of to be legally labeled and sold by
its common and usual name. These help in determining whether adulteration or
mislabeling of food has been practiced and given the consumer protection
against deception and assurance of the basic nutritional value of food. A number
of products have an established standard of identity. Among these are bakery
and cereal products, meat products canned fruits and vegetables, margarine,
cheese and its products, milk and cream, frozen desserts, macaroni and noodles
and tomato products. If these products do not meet the required standard of
identity, these are usually labeled imitation.
Measurement
of nutritional value or nutritional quality frequently can be assessed by
chemical or instrumental analysis for vitamins and other nutrients. In many
cases, however, these are not sufficient and animal feeding tests or equivalent
biological tests must be used. Animal feeding tests are particularly common in
evaluating new protein sources. In this case, the increasing variables or
protein level, amino acid components, digestibility and absorption of amino
acids all contribute to the determined biological value.
A
food additives are defined as a substance or mixture of substances other than a
base foodstuff that is present in afood as a result of any aspect of production
processing storage or packaging.
According
to FAO/WHO expert committee, food additive is defined as a non-nutritice
substance added intentionally to a food, generally in small quantities to
improve its appearance, flavor, texture or storage properties.
Over
3000 different chemical sompounds are used as food additives. They are
categorized into different groups as shown below;
|
1. Antioxidant
|
8. pH
controlling agents
|
|
2. Chelating
agent
|
9. Preservatives
|
|
3. Coloring
agents
|
10. Stabilizers
and thickners
|
|
4. Curing
agents
|
11. Clarifying
agents
|
|
5. Emulsifying
agents
|
12. Firming
agents
|
|
6. Flavors
and flavor enhancing agents
|
13. Freezing
agents
|
|
7. Artificial
sweeteners
|
14. solvents
|
Food
additives may be either intentional or unintentional.
1. Preservatives
Preservatives can generally be
defines as chemicals inhibiting or retarding the group of bacteria or any other
microbial flora. Substances which have an antioxidant function, may also serve
as preservatives. National legislation relating to preservative is extremely
valid by in general it is necessary to carry out quantitative test in order to
ensure that not permitted preservatives are absent and quantitative analysis to
ensure that permitted preservatives do not exceed any legal limit there may be.
In addition to the chemical preservatives it should not be forgotten that salts
especially common salt itself and acids such as vinegar, sodium diacetate and
fruit acids all have a preservative action. One of the most common
preservatives used for canned or bottled food is benzoic acid usually as its
potassium or calcium salt. Benzoic acid retards the growth of mold and yeast
and work best in food products having an acid pH of 2.5-4. Its effectiveness
decreases automatically when the pH rises above 5. Group of effective benzoic
acid derivatives are compounds commonly referred to as parabens. There are CH3,
C2H3, 2C3H3 and parahydroxy
benzoate. Their main usefulness is that they are effective over a wide range of
pH than benzoic acid and are quite stable. Sorbic acid is often used in dairy
products such as cheese to inhibit mold growth as that they are effective over
a wide range of benzoic acid and it doesn’t affect the lactobacillus present.
Like benzoic acid, it is added as salts of sodium, potassium or calcium. Another
widely used preservative is SO2, which is added in food primary as
the sulfite, bisulfate or metabisulfite of sodium, postassium or calcium. It’s
primarily a preservative but has antioxidant property as well and is often used
to prevent browning. Similarly, nitrate and nitrite are added in meat products
and boric acid is added in fish.
Classification of preservatives
Class I: Common salt, sugar,
dextrose. wood, smoke, spices, vinegar, acetic acid, honey, hops, alcohol
Class II: Benzoic acid including
their salts, sulfurous acid including their salts, nitrates and nitrites, Na-,
K- propionate, sorbic acid including their salts.
2.
Antioxidants
Antioxidants mean those substances
which when added to food retard or prevent oxidative deterioration of foods and
do not include sugars, cereal, oils, flours, herbs and spices
