http://meetings.aps.org/Meeting/MAR17/Session/S38.2

Sensory evaluation of food and beverages

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

How to use datedif function of excel?

Datedif function in excel is used to calculate the difference in date and expressed either in years or months or both. If you want to find the age of man born on say 9/20/1998 and the current date or date of survey is 6/15/2014. To find out his age in year and month in excel using datedif function,call for the following function =DATEDIF(A1,B1,"y")&"."&DATEDIF(A1,B1,"ym") if you want to express the age in year and month both. In the example below, 15.8 means the man is 15 years and 8 months old. similarly if you want to express the age only in month then call for the following function in excel =datedif(a1,b1,"m") In the example below, 188 means the man is 188 months old. Additionally if you just want to round up with the age expressed in years call for the following function in excel =datedif(a1,b1,"y") In the example below, the numeric value in e1 indicate the age of the man and this figure is rounded only for the number of years.

Hope this will help you to solve your problem related to age calculation in excel. Thank you

NMR spectroscopy

 NMR

Nuclear magnetic resonance spectroscopy (NMR) is basically another form of absorption spectroscopy. Under appropriate condition in a magnetic field a sample can absorb electromagnetic radiation in the radiofrequency region, as frequencies being governed by the characteristic sample. Absorption is a function of certain nuclei in the molecule. A plot of the frequencies of the avsorption peaks versus peak intensities constitutes an NMR spectrum. NMR is a powerful tool for the investigation of molecular structure.

A hydrogen nucleus may have a clockwise (+1/2) or anticlockwise (-1/2) spin and the nuclear magnetic moment μ in the two cases are in the opposite direction. In an applied magnetic field, all protons have their magnetic moment either aligned with the field or opposed. The two spin state of hydrogen atom +1/2 is at lower energy since it aligned with the applied magnetic field while the spin state -1/2 is of higher energy state since it opposes the applied magnetic field.

Reasons for taking tetramethylsilane (TMS) as a reference compound
1. TMS has 12 equivalent protons and gives an intense single signal.
2. The electronegativity of silicon is very low as compared to carbon as a result of this the shielding of equivalent proton in TMS is more than that of almost all organic compound.
3. TMS is chemically inert and has a very low boiling point (300K) so that it can easily be evaporated after the spectrum has been recorded.
4. TMS is not soluble in aqueous solution.
Please click NMR below for full version of this note and download as .pdf 
NMR 

Electrophoresis

Electrophoresis

Introduction

Electrophoresis is the motion of dispersed particles relative to a fluid under the influence of a spatially uniform electric field. It is a technique that describes the migration of charge particles under the influence of an electrical field. This technique is mainly applied for the analysis of macromolecules like amino acids, peptides, proteins and nucleic acid since these possess ionisable groups. 

The sample material must be dissolved or suspended in buffer for electrophoresis to take place and the supporting medium must also be saturated with the buffer in order to conduct the current. If the buffer used is at a pH above that of the isoelectric point of the molecule, the sample will be negatively charged and under the influence of the electric field it will migrate toward the anode and if buffer used is at pH below the isoelectric point of the molecule it will be positively charge and eventually migrate towards the cathode.  

Please click the link below for full version of this note and download as .pdf 

https://sites.google.com/site/gkrishnakharells/instrumental-technique-of-analysis

What is choke coil? Write its importance. 

Choke coil is a device used in ac to control; the current without significant loss of electrical energy in the form of heat.

It consists of large number of turns of thick insulated copper coil having small resistance to d.c. circuit. The coil has high inductance so it offers a large reactance X_L, in a.c. circuit. This control the alternating current so,Irms = Erms/XL

But the average power consumed in a pure inductance is zero. Thus choke coil is preferred to a resistance in an a.c. circuit to change the magnitude of current. 

D.C. Motor 

A motor is a machine for converting electrical energy into mechanical energy. It is based on the fact that a current carrying conductor experience a torque in a magnetic field. 

Construction 

A.C motor consists of an armature coil DCBA wound on a laminated iron core. It is placed in the magnetic field produced by current flowing through the field winding. The ends of the coil are connected to a split ring commulator which is in contact with brushes B1 and B2 to which a d.c. voltage is supplied.

working

Suppose a current from a battery flows round the armature coil in the direction DCBA. Assuming that the plane of coil is initially horizontal then, by fleming's left hand rule an upward force acts on DC and an equal downward force will act upon D.C. These force form a couple which rotates the coil in clockwise direction. but the couple become 0 when the coil is vertical, but owing to its monentum , the coil can pass the vertical position. the two half of split ring now make contact with the other two brushes as a result of which, the direction of current in the coil is reversed. hence the part of the coil moving upward in earlier condition will move down in this latter condition and viceversa and consequently the coil continues to move in same direction. each time the current pass the vertical position, the current in the coil reverses and thus the coil rotates continuously. the mechanical energy for driving the coil is obtained from the electrical energy supplied by battery. 

the motion of single coil is jerky so in order to obtain uniform motion, the single coil should be replaced by a number of evenly spaced coils, which are connected to a commulator having corresponding number of segments.

Hazards due to radio isotopes
Use of radioisotopes require careful consideration of their human toxicity. An individual handling radioisotope must not only think about its overdose but also should be conscious about its potential threats in the day to come because its effect may be prevalent over a decade. The hazard due to radioisotope can be summarized into following points. 
1. Genetic distortion: Write about mutation and take the example of Hirosima and Nagasaki
2. Cancer: Write about carcinoma formation
3. Blindness:
Properties of Ultraviolet rays and its application:
Properties
1. They don't carry any charged particle
2. It is electromagnetic wave so that it can never be deflected by electric or magnetic field. 
3. Due to high frequency compared to visible light, it has high energy. 
4. It shows florescence effect. 
5. It can effect the photographic plate
6. Its velocity is 3 x 10⁸m/s
Application 
1. Visible light is produced in CFL lamp due to striking of UV in the fluorescent powder coated inside CFL lamp. 
2. This light is used used in UV-Visible spectroscopy. 
3. In lab for analytical purpose
4. As disinfectant: to destroy microorganism 
5. Vitamin D is synthesized in human body in the presence of U.V light.