UNIT 10 - BROWNING

INTRODUCTION

Browning is the process of food turning brown due to the chemical reactions that take place within. The process of food browning is one of the most important reactions that take place in food chemistry and represents an interesting research topic regarding health, nutrition, and food technology.
Though there are many different ways food chemically changes over time, browning in particular falls into main 2 categories,
1.    Enzymatic and
2.    Non-enzymatic processes.
The browning process of foods may yield desirable or undesirable results, depending on the type of food.

Enzymatic Browning

• Enzymatic browning is one of the most important reactions that takes place in most fruits and vegetables as well as in seafood.
• These processes affect the taste, color, and value of such foods. 
• Generally, it is a chemical reaction involving polyphenol oxidase, catechol oxidase, and other enzymes that create melanin's and benzoquinone from natural phenols. 
• Enzymatic browning (also called oxidation of foods) requires exposure to oxygen. 
• It begins with the oxidation of Phenols by Polyphenol oxidase into Quinones.

Examples:
Developing color and flavor in Coffee, Cocoa beans, and tea.
Developing color and flavor in dried fruit such as figs and raisins.

Non-enzymatic browning

• It is a process that also produces the brown pigmentation in foods, but without the activity of enzymes. 
• The two main forms of non-enzymatic browning are caramelization and the Maillard reaction. 
• Examples non-enzymatic browning:
• Fresh fruit and vegetables, including apples, potatoes, and black spots on peels bananas and avocados.
• Polyphenols oxidases is the major reaction in the formation of Melanosis in crustaceans such as shrimp. 

Caramelisation

• Caramelisation is the oxidation of sugar, a process used extensively in cooking for the resulting nutty flavor and brown color.
•  Caramelization is a type of non-enzymatic browning reaction. 
• As the process occurs, volatile chemicals are released producing the characteristic caramel flavor. 
• The reaction involves the removal of water (as steam) and the break down of the sugar. 
• The caramelization reaction depends on the type of sugar. Sucrose and glucose caramelize around 160 degree C (320 degree F) and fructose caramelizes at 110 degree C (230 degree F).
• The highest rate of the color development is caused by fructose as caramelization of fructose starts at 110 degree C. Baked goods made from honey or fructose syrup will therefore give a darker color.

Maillard reaction

• The Maillard reaction, creates flavor and changes the color of food. 
• Maillard reactions generally only begin to occur above 285°F (140°C). 
• Until the Maillard reaction occurs meat will have less flavor.
• The Maillard reaction is a chemical reaction between an amino acid and a reducing sugar, usually requiring the addition of heat.
•  Like caramelization, it is a form of non-enzymatic browning. 
• The Maillard reaction occurs between reducing sugars and principally free amino acids and peptides (usually from proteins) when heated.
•  The reaction is also known as the browning reaction.
• Browning by the Maillard reaction occurs more quickly in alkaline than in acid conditions and also at intermediate water activities. The reaction is also time/temperature related. 
• Thus baking at low temperatures slowly gives the same colour results as baking at high temperatures quickly provided that the atmosphere around the product does not become too dry.
• The Maillard reaction is most important for the production of brown hues on the surface of baked biscuits. The inclusion in biscuit dough of glucose or invert syrups is to ensure that the Maillard reaction occurs as required. If there is excessive Maillard reaction it may be difficult to dry the biscuit without too much colour formation. Sometimes proteins are added as milk powders. Milk contributes lactose which is a reducing sugar. The Maillard reaction contributes flavours to baked products.
• It reduces the nutritional value of food.

Prevention of Enzymatic Browning

Enzymatic browning is the second largest cause of quality loss in fruits and vegetables.
Chemical, physical (blanching, freezing), controlled atmosphere and coating methods, can be used to prevent enzymatic browning .

1. Treatment with antioxidant agents

 Antioxidants can prevent the initiation of browning by reacting with oxygen.

2. Treatment with agents of firmness 

Calcium salts are the best known; they are used in the strengthening of cell walls. The cell walls are more stable to different treatments.

3. Treatment with acidifying agents 

PPO is sensitive to pH variations. The fruit is a naturally acidic environment, additional acidification may reduce the PPO activity or inactivate it below pH 3.

4. Blanching 

Blanching food is a heat treatment. Blanching treatments are presented according to the heat medium used: blanching in boiling water and/or in steam; blanching by using microwave was also developed the last years. The blanching time varies depending on the technique used, the type of product, size or maturity status.
This process inactivates the enzymatic systems responsible for sensory and vitaminic alterations . In addition, the colours of plants are heightened, for better presentation.

5. Freezing 

Freezing is a technique often used to stop browning reactions in fruit. Indeed, freezing causes a decrease in available water for enzymatic reactions.

6. Conservation in modified atmosphere 

Oxygen is essential for the oxidation reaction and PPO activity, a solution to control enzymatic browning reactions would be to change the oxygen content of the storage atmosphere. The studies dealt with modified atmosphere packaging, by modifying the composition of atmosphere, showed that the enzymatic systems are delayed without altering product quality

7. Coating 

The coating agents are usually used to extend the shelf-life of fruits during their storage. It consists on the application of a layer of any edible material on the surface of fruit. Actions of these agents deal with the decrease of moisture and aroma losses, the delaying of colour changes and gas transfer, and the improvement of the general appearance of the product through storage.

UNIT 9 - FLAVOURS

FLAVOUR

Definition

Flavour is the sensory impression of food or other substance, and is determined primarily by the chemical senses of taste and smell.
The Flavor of the food, as such, can be altered with natural or artificial flavorings.
Flavor is defined as the combined effect of taste and aroma of food.
The flavor and aroma of food usually declines when it is handled processed or stored, like in coffee, milk, and cooked meats.
However in certain exceptions the flavor of food is enhanced on processing like cheese is ripened, wine is aged, or meat is aged.

Classification of Flavours

Description of food flavours

TEA

• Tea is the second most widely consumed beverage around the world after water . 
• The popularity of tea as a global beverage rests on its pleasant flavor, mildly stimulating effects, and nutritional properties, which people find appealing and attractive. 
• According to the manufacturing process, tea can be divided into at least three basic types: non-fermented green tea, fully fermented black tea, and semi-fermented oolong tea .
• The flavor of tea can be divided into two categories: aroma, which consists mainly of volatile compounds; and taste, which consists mainly of non-volatile compounds. 
• The volatile aromas are important criterion in the evaluation of tea quality.
• The liquid that results from brewing tea is called the liquor.

Flavour and Aroma of Tea

• The sense of smell and taste are intricately linked together. 
• Tea is filled with natural antioxidants, also known as polyphenols. 
• These provide the health benefits in tea and also a good portion of the taste.
• Polyphenols bind with our saliva and create a dry sensation on the tongue and sides of the mouth.
• They also provide the brisk, tannic (acid) bite that is associated with tea.
•  Also important to note: astringency is a physical sensation, whereas bitterness is a flavor - the two can easily be confused, but they are different. 

COFFEE

• Coffee owes its characteristic flavor to caffeine although by itself caffeine without its aroma has a faint bitter taste. 
• Coffee also contains alkaloids, volatile aromatic products and substances belonging to the phenolic series. 
• It stimulates the central Nervous System. 
• The composition of coffee is – 15.30%-nitrogenous substances 11.40%-fatty matter 70.2%-caffeine.

WINE

• The biggest contributor to flavor is yeast. 
• It is the fermentation process that truly gives a wine its flavors. 
• In order for a yeast to live it has to eat and what it likes to eat most is sugar. In the process, the sugar is digested and ends up as two things—carbon dioxide and ethyl alcohol. Once all the sugar is gone, the yeast stop growing and eventually die. 

MEAT

• Most of meat's flavor develops when it is cooked. The amount of fat in meat influences its flavor, as does a process called the Maillard reaction. Flavor can also be added to meat through brining and marinating.
• The Maillard reaction occurs when the denatured proteins on the surface of the meat recombine with the sugars present. The combination creates the "meaty" flavor and changes the color. 
• The Maillard reaction occurs most readily at around 300° F to 500° F. When meat is cooked, the outside reaches a higher temperature than the inside, triggering the Maillard reaction and creating the strongest flavors on the surface. 
• The molecules of the amino acids and sugars combine to form new aromas and flavors. The Maillard reaction is also responsible for the brown colour of cooked foods.
• It normally occurs at very high temperatures, but if there is a high concentration of sugars and amino acids, then it will occur at lower temperatures. 

FISH

• Fish gets its flavor from the natural oils present in the fish all over its body.
• The higher the fat content, the more powerful the taste, as evidenced in appropriately named species like King Salmon. 
• Colder water increases this fat content and therefore the level of deliciousness. 

SPICES

• Spices give aroma, color, flavor, and sometimes even texture to food.
• Each spice, chile, or herb has specific, unique chemical compounds that create these sensual qualities. 
• When talking about spices, a true spice aficionado simply cannot be limited to just four or five. 
• For these people, there are many more equally identifiable flavor characteristics- cooling (mint, fennel), earthy (cumin, saffron), floral(lemon grass, coriander), fruity(star anise, tamarind), herbaceous(oregano, rosemary), hot(mustard, chilli), nutty(fenugreek seeds, sesame seeds), piney(bay leaf, thyme), pungent(garlic, ginger), spicy(nutmeg, curry leaves) and woody(cinnamon, cloves).
• Spices usually do not have a single flavor profile. 
• For example, the popular spice cumin falls into a few of the flavor profiles as it is both earthy and spicy. Thyme is bitter, floral, herbaceous, and piney.

UNIT 8 - COLLOIDS

INTRODUCTION

A colloid is a material composed of tiny particles of one substance that are dispersed, but not dissolved, in another substance.
The mixture of the two substances is called a colloidal dispersion or a colloidal system.
All prepared food dishes are examples of a mixture known as a colloid.

There are many types of colloidal systems depending on the state of the two substances mixed together.
Gels, sols, foams (e.g. egg white foam) and emulsions (e.g. butter) are all types of colloids.
The substance which is dispersed is known as the disperse phase and is suspended in the continuous phase.
Egg white foam is an example of this. Air bubbles (disperse phase) are trapped in the egg white (continuous phase) resulting in a foam.

Functions of colloidal systems in food products

Most colloids are stable, but the two phases may separate over a period of time because of an increase in temperature or by physical force.
They may also become unstable when frozen or heated, especially if they contain an emulsion of fat and water.

Sols and gels

Sols and gels are both liquid loving (lyophilic) colloids.
A sol is a liquid colloid or mixture in which solid particles are dispersed in a liquid phase.
The disperse phase is attracted to molecules of the continuous phase.
Sometimes the mixture needs to be heated and stirred.
When this solution cools, the sol changes into a gel, which resembles a solid rather than a liquid.
Both protein and starch can be used in the formation of a sol or gel.

When a jelly is made, gelatine is dispersed into a liquid and heated to form a sol.
As the sol cools, protein molecules unwind forming a network that traps water and forms a gel.
 If cornflour is mixed with water and heated, the starch granules absorb water until they rupture, the starch then disperses in the water and the mixture becomes more viscous and forms a gel on cooling.

Other types of gel 

Other types of gel are formed with pectin and agar.
Pectin, a form of carbohydrate found in fruits, is used in the production of jam to help it set.
 However, for it to gel there must be at least 50% sugar and conditions should be acidic.
Agar is a polysaccharide extracted from seaweed which is capable of forming gels.
If a gel is allowed to stand for a time, it starts to ‘weep’.
This loss of liquid is known as syneresis.

Emulsions  

When water and oil are shaken together, they form an emulsion. This emulsion is unstable. If left to stand, the oil will form a separate layer on top of the water, e.g. traditional French dressing. The two liquids are immiscible (they will not mix together). A stable emulsion is formed when two immiscible liquids are held stable by a third substance, called an emulsifying agent.
An emulsion may be oil-in-water (o/w) in which case small oil droplets are dispersed through water, e.g. milk, or water-in-oil (w/o) in which case small water droplets are dispersed through oil, e.g. butter.

Foams

Foams are composed of small bubbles of gas (usually air) dispersed in a liquid, e.g. egg white foam.
 As liquid egg white is whisked, air bubbles are incorporated.
The mechanical action causes albumen proteins to unfold and form a network, trapping the air.
 If egg white is heated, protein coagulates and moisture is driven off. This forms a solid foam, e.g. a meringue.
 Ice cream, bread and cake are other examples of solid foams.

Properties of Colloidal Solutions

Following are the important physical properties of colloidal solutions:

1. Heterogeneity: Colloidal solutions are heterogeneous in nature. These consist of two phases-dispersed phase and dispersion medium. 

2. Visibility of dispersed particles: Although colloidal solutions are heterogeneous in nature, yet the dispersed particles present in them are not visible to the naked eye and they appear homogeneous. This is because colloidal particles are too small to be visible to the naked eye. 

3. Filterability: Due to very small size, the colloidal particles pass through an ordinary filter paper. However, they can be retained by animal membranes, cellophane membrane and ultrafilters. 

4. Stability: Lyophilic sols in general and lyophobic sols in the absence of substantial concentrations of electrolytes are quite stable and the dispersed particles present in them do not settle down even on keeping. However, on standing for a long time, a few colloidal particles of comparatively larger size may get sedimented slowly. 

5. Colour: The colour of a colloidal solution depends upon the size of colloidal particles present in it. Larger particles absorb the light of longer wavelength and therefore transmit light of shorter wavelength. 

UNIT 7 - EMULSION

EMULSIONS

Theory of emulsification

An emulsion is a system containing two liquid phases, one of which is dispersed as globules in the other.
That liquid which is broken up into globules is termed the dispersed phase, whilst the liquid surrounding the globules is known as the continuous phase or dispersing medium.
The two liquids, which must be immiscible or nearly so, are frequently referred to as the internal and external phases respectively.

Types of emulsions

There are two basic types of emulsions: oil-in-water (O/W) and water-in-oil (W/O). These emulsions are exactly what they sound like, as pictured below.

How to make an emulsion

Mechanical Force - To make an emulsion you first need to apply a mechanical force to break down the dispersed phase into small droplets that become suspended in the continuous phase. For this you can use a whisk, blender or other lab equipments.

Emulsifier - The next problem to solve is to make the emulsion stable. The higher the force you applied when making the emulsion, the smaller the droplets and the more stable the emulsion is. However, no matter how small the droplets are, the ingredients will eventually separate without the presence of an emulsifier that keeps the molecules with different polarity from repelling each other.

Thickener - Finally, adding a thickener to the continuous phase can make the emulsion even more stable as this makes it more difficult for the dispersed droplets to move and combine.
How to make an emulsion
Any mixture of oil and water can be transformed into an emulsion, even without emulsifiers. However, without emulsifiers, the mixture will also quickly separate back into its immiscible (not mixable) parts. You can try a simple experiment with oil and water. Quickly whisk together oil and water, and it will eventually turn into an cloudy mixture. You'll notice plenty of bubbles, however, and those bubbles will quickly grow larger until the water and oil are completely separate.

Properties of an emulsion

Viscosity
When you mix oil and water, the resulting emulsion usually has a higher viscosity than each of the ingredients before the emulsification process. This effect is produced by the interaction of the molecules in the emulsion. For example, mayonnaise is more viscous than the oil and lemon juice it is made of. Most emulsions are shear-thinning fluids which means that the viscosity decreases if you start stirring them strongly.

Color
The transparency and color of the emulsion depend on the size of the droplets of the dispersed ingredient. The smaller they are, the whiter the color of the emulsion. This is due to the way the droplet size affects the light reflection.

Common culinary emulsions

Following are a few of the more common culinary emulsions, both traditional and modernist.

Vinaigrette Emulsion

Vinaigrettes are traditional oil-in-water emulsions made with oil, vinegar, other flavorings, and mustard. The emulsifying ingredient is mustard. Specifically, the network of naturally-occurring mucilage in mustard emulsifies the oil and water. In addition to mustard, a common ingredient in vinaigrettes is honey. While honey is not an emulsifier, its thick consistency helps to stabilize the mixture.

Dairy Emulsion

All dairy products that is, anything made with milk, contains milk proteins that act as emulsifiers and help milk fats stay suspended in water. Milk and cream are O/W emulsions while butter is a W/O emulsion. In addition, any recipe that calls for cream, milk, or butter will benefit from the natural emulsifying properties of these dairy proteins.

Egg Emulsion

Both parts of the egg contain important emulsifiers. The proteins in egg white act as emulsifiers and thickeners. Egg whites or egg white powder can be used to create soft foams . You can also use them to create meringues or add fluffiness to recipes.
Egg yolks contain two important things not found in egg whites: fat and lecithin. Lecithin is a powerful emulsifier. A small addition of lecithin to a vinaigrette or sauce containing oil will help the liquids stay mixed for a longer time. Many modernist chefs use lecithin derived from soy beans instead of egg lecithin because it is cheaper to produce and because recipes using soy lecithin have the added benefit of being completely vegan.
Fat can support emulsions, but can also interfere with them. Fat is what gives vinaigrettes their body, but even a little fat in an egg white foam can cause the foam to destabilize. That's because foams combine nonpolar air with polar liquids. Fat takes the place of air in some cases and makes the foam weaker.

Cheese Emulsion

While cheese is technically a dairy product, it is worth mentioning separately here due to it unique properties. Most cheeses are solids at room temperature, but many become creamy emulsions when heated. But if you've ever accidentally overheated a brie in the oven or tried making your own cheese sauce in the microwave, you know that some cheeses will split into unattractive masses of oil and cheese matter. The problem lies in emulsifiers. Once again, it is the milk proteins in cheese that act as emulsifiers. The particular ratio of fats to other ingredients in cheese determine how it will behave when melted.

Emulsion stabilizers and emulsifiers

Traditional emulsifiers such as dairy and eggs continue to be widely used in modernist cuisine. Where modernist technique innovation comes in is with the addition of emulsion stabilizers and modern surfactant emulsifiers.

Emulsion Stabilizers

Modernist thickeners and gelling ingredients can make emulsions more stable. Besides giving emulsions more texture, thickeners also help to slow down the rate at which emulsions separate. As the liquid is more viscous, the suspended droplets can't move around so easily to eventually combine in a specific area. This is important for everything from a sauce, which needs to stay emulsified for as long as it would take a dinner to eat it, to ice cream, which needs to stay emulsified to prevent the growth or ice crystals.
Agar, carrageenan,  sodium alginate , gellan,  xanthan gum , gelatin, guar gum, can all be used as emulsion stabilizers.

Emulsion techniques

The appearance, texture, and stability of an emulsion depend both on its ingredients and on how you prepare it. There are several tools you can use to make an emulsion but the higher the force, the smaller the droplets in the emulsion and the more stable it will be.

Handheld whisk

Using a handheld whisk will produce the weakest emulsions but it may be more than enough if you prepare it right before serving. Some emulsions, such as mayonnaise, can be mixed by hand and will stay stable in the refrigerator for days, even weeks. But one problem with mayonnaise is that it can curdle or invert. That is, the ratio of oil added to eggs and other ingredients can cause clumps of butter-like water-in-oil emulsion bits to form. This makes the finished product less than ideal.

Immersion blender

Use an immersion blender for small quantities or when you need to make the emulsion while heating. To combat the previously mentioned problem when making mayonnaise, try using an immersion blender.

Blender

If you're making larger batches of emulsion, nothing beats a powerful blender. Use traditional blender for larger quantities or for more difficult emulsions that need more power. Commercial blenders have more power than household blenders and produce better emulsions with smaller droplets.
The quality of a blender-made emulsion depends on two factors: shear stress and carafe shape. Shear has to do with the speed at which the blender's blades turn through a liquid. The faster the shear, the smaller the particles in an emulsion. The smaller the particles, the creamier the result, until the particles are so small that your tongue can no longer distinguish them, resulting in a milk-like texture. In addition to shear, the size and shape of a blender's carafe determine the blade's ability to fully interact with all of the carafe's contents. If only a small portion of an emulsion benefits from maximum shear, the end result will still be poor.

Rotor-stator homogenizer

Not a traditional kitchen tool and expensive, rotor-stator homogenizers are used to make fine emulsions. It generates much higher shear forces than a regular blender thanks to the two blades that move very close to each other to produce fine emulsions. One of the blades is stationary and the other one rotates. (shown in left picture)

Ultrasonic homogenizer

Another expensive lab tool usually used to make an existing emulsion even finer through mechanical vibrations that create microscopic bubbles.

High-pressure homogenizer

The ultimate lab tool to make the finest emulsions ever works by applying pressure to the liquid.

Emulsion tips

In addition to picking the right emulsifier for the desired application and using the right tool as described above, there are a few other things to consider when making an emulsion.

Viscosity

An emulsion can be made more stable by increasing the viscosity (thickening) of the continuous phase in the emulsion as this makes it more difficult for the dispersed droplets to move and combine. Remember that in an O/W emulsion the continuous phase is the water and in an W/O emulsion the continuous phase is the oil. So adding a thickener to the continuous phase can help you make the emulsion more stable.  This is a widely used technique and that's why you'll frequently see the use of thickeners and emulsifiers combined to make effective stable emulsions.

Density

Mixing oil and water is not only hard because of the polar differences but also because of the difference in density. The oil molecules are lighter than the water molecules but if you make the oil heavier, the emulsion will be more stable. This is not usually necessary in most culinary applications.
Speed of incorporating ingredients
When making an emulsion, it is usually better to disperse the emulsifier first in the continuous phase and then slowly incorporate the dispersed phase while you are mixing with the selected tool.

Role of emulsifying agents in food emulsions

The use of food emulsifier began with adding monoglyceride and lecithin to margarine. Originally, these substances were only known as emulsifiers. However, as studies progressed, more functions were found and they began to be used in various fields, such as bread, ice cream and cake. Nowadays, emulsifiers are applied to Japanese foods like tofu and minced fish products. Why do bread and tofu need emulsifiers? Generally speaking, an emulsifier is well known for its emulsifying effects, however, actually it has various functions and followings are just some examples: Modifies oil crystal and prevents water spattering in cooking;Destroys emulsion to stabilize foam and to make smooth texture in ice cream, and keeps its shape; Reacts with proteins to make a smooth easy-rising dough in bread;Acts on starch to make bread soft.
Emulsifiers have various effects on the production process of food and improve its quality. They are used in various types of food. Functions of emulsifiers are listed below.


Emulsifiers have various effects on the production process of food and improve its quality. They are used in various types of food. Functions of emulsifiers are listed below.
Bread and sweet rolls sold at super-markets and convenience stores are usually mass-produced. Mass production and mass distribution require time and speed from start to finish. Emulsifiers are used to maintain the softness as long as possible and to make bread dough suitable for machine production.
Emulsifiers are not only used for emulsification, but also for dough modification, that is, dough gets tolerable against mechanical force by modulating the proteins in wheat flour.


Emulsifiers make a rigid complex with starch to protect starch granules and improve the quality of starchy foods.

Noodles

Effects of emulsifiers on macaroni, spaghetti of low water content, fresh noodles containing high water content and dried instant noodles are different, however, the basic effects on starch are similar.
For macaroni and spaghetti, emulsifiers provide elasticity and smooth uniform surface which prevents sticking after boiling.
In fresh noodles, emulsifiers make easy-to-handle dough and increase the water absorption rate by 1-2%. The surface of noodles becomes smooth, uniform, and less sticky, which improve and streamline the production process.

In instant noodles, emulsifiers improve absorption and decrease cooking time.

Cakes are classified on the basis of the compounding ratio of fat to flour as shown in the following table.

Oils and Fats Content Ranging
0-10% Sponge Cake
10-50% Butter Sponge Cake
30-100% Butter Cake
Sponge cake is made by utilizing the foaming ability of eggs.
Butter sponge cake is made by further additions of butter and margarine.
On the other hand butter cake is produced from a batter foamed after the addition of large amount of butter or margarine.

Sponge and butter sponge cake are basically made from sugar batter method. Sugar is added to whole eggs after foaming and combined with flour.
The use of emulsifier makes it possible to produce an all in one-mixture method, in which all materials are mixed at the same time and foamed.

ICE CREAM
Concerning the manufacturing process of ice cream, a liquid form mixture of raw materials is prepared and homogenized by a high pressure homogenizer. After short period of high-temperature sterilization, the homogenate is stabilized by letting it stand sit for several hours at a temperature below 5℃.
Soft cream is produced by foaming in a freezer at -2 to -9°C, and pouring into a small container followed by rapid freezing.
Oils and fats, ones of the major components of ice cream, form fat balls by emulsification, and their surfaces are covered with emulsifiers and are coated with milk-like protein like casein. By combining with an emulsifier, the fat balls become fine and stable.

Unit 6 - EVALUATION OF FOOD

Introduction

Quality is a desired attribute for any food product.
Consumer choose food on the basis of its quality and their individual likes and dislikes.
When consumer makes a selection they basically look for food that is attractive in terms of colour, flavour, texture, the nutritional quality and shelf  life.
Keeping quality and cost factor are other criteria which may affect their selection .
Today’s consumers are discerning, demanding and more knowledgeable about food.
Therefore knowing consumer’s preferences of the sensory characteristics of food and beverage products is vital to food manufacturers as well as caterers.
Without appropriate evaluation, there is high risk of market failure.

Objectives of Food Evaluation

The major objectives of evaluation of food are:
(1) To develop new products – the food industry depends on evaluation in developing new products and maintaining quality in existing products.
(2) To observe consumer reactions – how the consumer reacts to particular food dictates the quality of the product.
(3) To identify changes in menus to make food acceptable – catering supervisors in institutional food service depend on evaluation to identify changes in menus to make food acceptable.
(4) To collect information of food acceptability –the studies on plate waste provide valuable information regarding food acceptability.
(5) To assist in determining the shelf life of a product.
(6) To understand how the product competes in the market.
(7) To determine whether or not consumers can detect differences between products due to recipe modification.

QUALITY can be evaluated by
(1)sensory methods i.e. by sensory organs like eyes, nose
and mouth
(2)objective methods i.e. by use of instruments.

Sensory Evaluation of Food

When quality of food is assessed by means of human sensory organs the evaluation is said to be SENSORY OR SUBJECTIVE OR ORGANOLEPTIC EVALUATION.
 The method of judging of food is done by a panel of judges.
The evaluation deals with measuring, analyzing, and interpreting the qualities of food as they are perceived by the senses of sight, taste, touch, etc.
By the senses of sight the size shape and colour of the food and other characteristics like transparency, opaqueness, turbidity, dullness or gloss can be perceived.
Other sensory organs i.e. nose and mouth are utilized to obtain information on flavor.
Flavour of a substance is due to the combined senses of taste and a composition sensation known as mouth feel.

The various attributes to be judged are:
APPEARANCE: - The surface characteristics of food product contribute to the appearance
          Example: surface of a chocolate is smooth.

COLOUR – Colour provides variety to the diet and used as an index of quality for a number of foods
          Example: Ripeness of fruits and the strength of tea and coffee.

FLAVOUR – Flavor has 3 components odour, taste, and mouth feel. Mouth feel consists of texture, consistency and temperature of food.
The texture of the food can be smooth or velvety as that of an ice cream or can be coarse as that of corn flakes.

Classification of Methods of Evaluation

Sensory Evaluation

Sensory evaluation is the evaluation of the sensory properties of food (appearance, flavour, texture)
• It can be carried out by the following steps:
Look at the food and describe the overall appearance
Smell the food and describe its aroma
Cut the food and feel its texture
Chew the food and describe the taste and mouthfeel

Sensory properties of food are
Appearance
Involves the sense of sight
Can be described in terms of colour, size, shape, consistency and crumb
• Example: golden brown, small, round, smooth

Texture
• Involves the senses of sight and touch
• Mouthfeel is the sensation when we bite and chew food
•Different cooking methods produce different textures  Example: soft, chewy, crispy, sticky, grainy, coarse etc.

Flavour
• Flavour is produced by a combination of taste and aroma
• Taste – The taste buds on our tongue enable us to detect the different tastes of food – Example: sweet, spicy, bland, buttery, nutty
• Aroma – Involves the sense of smell – Detected by the nose – Example: fragrant, burnt, floral, fishy, fruity

Conducting Sensory Evaluation

A panel of judges is selected. They should be unbiased for tasting.
Physical, psychological and environmental conditions should be maintained as these affect one’s judgement.
The sampling has to be done homogenously.

Preference Test

Judging should be done in individual booths.
This assures independent judgement and communication between panel members should be allowed except for consultation with the panel leader on any point of doubt.
The best time of day for sensory testing is morning 10.00 am to 12 noon and 3 to 5 pm.
The size of the panel is usually 50 to 100 people to avoid any experimental error.
Judgement should be done quickly, but not hurriedly.
They are valuable in developing new foods and in evaluating quality.
These tests are designed to provide information on selected characteristics and to indicate preference or acceptability of products.

Acceptance Preference Test

In this method, a single sample or two samples may be tested.
It is used to find out whether a product will be used by consumers and this also shows their preference for the sample being tested.
If a new food is introduced, only one sample is offered to the panel, but if a food is modified then two samples are offered and their preference is seen.
The HEDONIC SCALE is most commonly used for evaluation.
In this scale ratings of preference or liking and disliking are measured.
It is generally used with untrained assessors.

HEDONIC SCALE
There is also a Facial Hedonic Scale consisting of 5 to 9 faces depicting varying degrees of pleasure and displeasure , it may be used with young children.

Fact Scale

FACT SCALE – food action rating scale

It is a more sensitive method made up of a nine point food action rating scale.
The codes used clearly indicate the action the panelist would take regarding the food i.e. how often the subject would like to eat the food.
FACT Scale

DIFFERNCE TESTING

These tests are designed to determine whether the difference in two or more food products can be detected.
The result of these tests are more precise and reproducible. Tests in this category are:
(1) Discrimination tests
(2) Descriptive tests
Discrimination tests

Paired comparison test 

Prepare two different samples of the food product you wish to test.
Compare one attribute, e.g. which one is smoother?
 Record the response from the tasters.

Duo-trio test

In this test, three samples are to be tested of which two are control samples and one is variable sample.

One of the control sample is presented first followed by the other two sample, and evaluator is requested to identify which of the two sample is different from the control.
The chances of guessing correctly are 50%.

Triangle Test

Prepare three food samples, two of which are the same.
Arrange the samples in a triangle.
Ask the tasters to decide which of the samples is the odd one out.
Record the responses from the tasters
Two Samples A and B can be presented in two combinations AAB and BBA and for replication in six different- AAB,ABA,BAA,BAB,ABB and BBA.

Dilution test

This test is used to measure the quality of an ingredient which has been substituted.
A standard sample is presented to the judges followed by other samples which may or may not contain the unknown at a definite level of dilution.
Example: use of dried egg powder with fresh eggs. If of good quality the product quality will be difficult to get detected, if poor quality the product will be detected at low concentration or high dilution.

Taste threshold test

This test determines the lowest concentration of a substance that can be detected.
It also indicates the lowest concentration of a substance required to be able to identify it.
The taste threshold of sweet, salty, sour, and bitter tastes can be detected.
Sweet - usually indicates energy rich nutrients.
Umami - the taste of amino acids (e.g. meat broth or aged cheese).
Salty – the taste of common salt.
Sour - typically the taste of acids.
Bitter - allows sensing of diverse natural toxins.
Ranking order

 DESCRIPTIVE TESTS

These tests describe the sensory attributes of food in exact words and the judge / evaluator is asked to select the exact word description from the score card which matches with the sample.
These tests are superior to preference tests which provide information about acceptability of a food sample and discrimination tests which detect deviations between samples.
Accurate descriptions of each characteristic of the sample to be evaluated by the judges is described over a range.
The score cards needs to be carefully designed for descriptive testing.
These are two types of descriptive tests.

 Profiling

In this, a panel of experts sit together and formulate a very detailed word description, generally of flavors which is used as a standard for evaluating further product.

Score cards

In this method food samples are individually evaluated by judges with the help of score cards which have a series of descriptive terms or levels of a characteristic.
Numerical values or scores are assigned to each descriptive term.
FOR EXAMPLE : The juiciness of meat which is a textural characteristic is evaluated on the basic of one of the following terms:

Extremely juicy     - 6
Moderately juicy   - 5
Slightly juicy          - 4
Slightly juicy          - 3
Moderately dry     - 2
Extremely dry        - 1

Score cards

While evaluating the food, the judge should think of the appropriate descriptive adjective and take a decision and not decide on the basis of the score.
It is preferable not to mention the numerical score on the score card which is given to the evaluator.
All score cards should have columns to fill the name of the judge and date of evaluation, and this should be filled in advance.

The following are the point to be kept in mind while preparing score cards.

• Select the different characteristics of a food product which need to be evaluated – example – appearance , colour , flavor , texture.
• Select appropriate descriptive terms pertaining to the characteristics chosen and arrange in sequence.
• Give numerical values to the descriptive terms.
• All products which are to be evaluated should be given a code. Codes could be symbols, colours or randomly selected three digit numbers.
• Score cards should be descriptive.

Score cards

Score cards

Environment for conducting sensory test

• Separate sensory booths should be provided so that judges do not interact with each other except when preparing profiles because judges work together to develop vocabulary needed to describe food samples.
• Controlled air and lighting so that food is correctly visible and booth is free from odours other than the sample . Temperature should be comfortable and non-smoking zone observed.
• Small sinks should be provided for spitting out samples or rinsing ones mouth

Sample preparation and presentation

• Samples should be of identical size.
• They should be in identical shape or from identical portions e.g.  edge of cake from one sample and centre slice from another sample should not be taken.
• It should be served at the customary temperature example. e.g.Soup should be served hot.
• Sample plates should be marked.
• Plates or containers used should be of identical size and colour.
• Necessary cutlery, glass of water should be provided at room temperature.
• Only a limited number of samples should be evaluated at a time to avoid fatigue and for efficient judging.

Members of the Panel

• The judge should neither be too hungry or too well fed.
• Smoking, chewing gum or nibbling snacks 20 minutes prior to the test should not be permitted.
• The judges should be healthy and not suffering from a cold as this will affect their sense of taste and smell.

PROXIMATE ANALYSIS

A method for the quantitative analysis of the different macronutrients in food is the proximate analysis
Proximate Analysis is a partitioning of compounds in a food into categories based on the chemical properties of the compounds. The categories are:
moisture
ash
crude protein
crude lipid
digestible carbohydrates &  crude fibre
Purpose of proximate analysis
Estimation and determination of how much of the major food components, which are Moisture, CHO,
Lipids, Proteins, Ash, Crude Fiber, exist in a given food.
It is important to remember that proximate analysis is not a nutrient analysis, rather it is a partitioning of both nutrients and non-nutrients into categories based on common chemical properties.
Purpose of proximate analysis
Moisture Analyses
Crude Fat Analyses
Crude Protein - (Non-protein nitrogen also included) most proteins contain 16% nitrogen. Therefore the general “protein factor” is 100/16=6.25. If we multiply the percent nitrogen by 6.25, we obtain crude protein.
Ash - residue after burning all organic material. Some minerals become volatile at high temperatures of burning and therefore can be lost. Also some minerals occur in the form of salts of organic acids like citrates which contain carbon and are lost.
CHO and Crude Fiber Total carbohydrate = 100 - [moisture + crude fat + crude protein + ash].
Crude fiber: residue left after alkaline and acid digestion of organic matter. If we subtract the total of 1-5 from 100, we get the digestible carbohydrates.

RHEOLOGICAL ASPECTS OF FOOD

It is the science of measuring forces, which are needed to deform food materials or to study the flow properties of liquid foods. It deals with the viscous behaviour of a system.
Solid food can be chopped up, ground, minced, sliced, torn apart or broken while it is being prepared or eaten, the texture is determined as crisp, tough, chewy, creamy, sticky, spongy etc.
Liquid foods are fluid or viscous. Viscosity is defined as the resistance of a liquid to flow. It is measured by an instrument called viscometer. This property of liquid is seen in batters, sauces and syrups.

REOLOGICAL PROPERTIES OF FOOD

ELASTICITY is the tendency of solid materials to return to their original shape after being deformed. Solid objects will deform when forces are applied on them. If the material is elastic, the object will return to its initial shape and size when these forces are removed. Elasticity is a characteristic of importance in baked products such as cake especially when they are fresh. Elastic deformation is reversible.

PLASTICITY- is the tendency of food items to be moulded into shape while soft, and then set into a rigid or slightly elastic form.

VISCOSITY is resistance of a liquid to flow. It is a measure of the resistance of a fluid to deformation under shear stress. It describes a fluid’s internal resistance to flow and maybe thought of as a measure of fluid friction. Thus water is thin having low viscosity while vegetable oil is thick having a high viscosity.