Introduction to Food Science | Properties of Food

What is Food?

Food is any substance ingested in order to provide an organism with nutritional help. Food typically originates from plants, animals or fungi, and contains important nutrients. A food product consisting essentially of protein, carbohydrates, fat, and other nutrients used to maintain growth and vital processes and to provide energy in the body of an organism. The body’s absorption and use of food is essential to nutrition and is aided by digestion.

Colloid System of Food

A colloid system is a type of mixture in which one component is continuously distributed over the next. When one component is spread through another, colloid systems are typically formed, but do not combine to form a solution. Therefore, many kinds of colloidal systems rely on the nature of the two parts that are mixed together.

Two different phases occur in a colloidal system: a dispersed phase (or internal phase) and a continuous phase (or dispersion medium). In the continuous phase, the component that is dispersed is known as the dispersed phase and is suspended. Based on the states of matter constituting the two stages, colloidal systems in food can be divided into different categories. The sols, gels, emulsion, and foam are food colloids. For instance, a simple colloid system is egg white foam. In the egg white (continuous phase), air bubbles (disperse phase) are created, resulting in a foam.

Food colloids give many different food items structure, texture, and mouth-feel; for example, jam, ice cream, mayonnaise, etc. Food colloid comprises hydrocolloid that provides food products with thickening, gelling, emulsifying, and stabilizing properties.

Food hydrocolloids are hydrophilic biopolymers of high molecular weight that are used to alter microstructure, texture, flavor, and shelf-life as functional constituents in food processing. The term ‘hydrocolloid’ includes all the different polysaccharides extracted from plants, seaweeds, and microbial sources, as well as modified biopolymers produced from starch or cellulose by chemical or enzymatic treatment. In the preparation of emulsions and in the regulation of emulsion shelf life, one of the main functional roles of food hydrocolloids. Most hydrocolloids can serve as oil-in-water emulsion stabilisers (stabilizing additives), but only a handful of them can act as emulsifiers (emulsifying agents). The second feature includes significant surface activity at the oil-water interface, and thus the ability to facilitate the production and stabilization of fine droplets during and after emulsification.

Stability of colloidal systems

The majority of colloids are stable, but due to an increase in temperature or by physical force, the two phases can separate during a period of time. In addition, after freezing or heating, they can become unstable, especially if they contain an emulsion of fat and water.

Sols and Gels

A sol can be described as a colloidal dispersion in which the dispersed phase is a solid and the continuous phase is a liquid. Some examples are gravy stirred custard and other thick sauces. Gelatin is dispersed into a liquid when jelly is made, and heated to create a sol. Protein molecules unwind as the solution cooks, forming a network that collects water and forms a gel.

If corn flour is combined with water and heated, water is absorbed by the starch granules until they are raptured, then the starch granule disperses in the water and after cooling the mixture becomes more viscous and forms a gel. Pectin and agar are used to shape additional forms of gel. In the production of jam, pectin, a type of carbohydrate found in fruit, is used to help it set. Agar is a seaweed-extracted polysaccharide capable of forming gels. If a gel is permitted to stand for a while, it begins to “weep.” This liquid loss is referred to as syneresis. To achieve the required viscosity of the sols at a certain temperature, the correct ratio of the ingredients is necessary.

As a result of a temperature drop, Sols may be converted into gels. The pectin molecules are a major phase in pectin gels and the liquid is the dispersed phase, while the pectin molecules are a minor phase in pectin sol, and the liquid is a major phase. Sols can be created as an initial step in the development of a gel. Traditional cases that produce a sol before the preferred structure are jams and jellies produced using pectin.

Emulsions

Many natural and refined foods are either relatively or completely emulsified or have been developed with milk, cream, butter, margarine, fruit drinks, soups, batters, mayonnaise, cream liqueurs, sauces, desserts, salad cream, ice cream, and coffee whitener in an emulsified form at some stage.

Emulsion products exhibit a wide variety of different physicochemical and organoleptic characteristics in appearance, aroma, texture, taste, and shelf-life. The selection of appropriate raw materials (e.g., water, oil, emulsifiers, thickeners, minerals, acids, bases, vitamins, flavors, colorants, etc.) and processing situations influence the processing of an emulsion-based food product with specific quality characteristics (e.g., mixing, homogenization, pasteurization, sterilization, etc.).

Two immiscible phases (typically oil or water) constitute an emulsion, with one of the liquids dispersed into the other as fine sphere-shaped droplets. An oil-in-water or O/W emulsion is called a system containing oil droplets dispersed in an aqueous phase (e.g., mayonnaise, milk, cream, soups, and sauces). A device containing water droplets dispersed in an oil phase is called an emulsion of water-in-oil or W/O. (e.g., margarine, butter, and spreads).

Multiple (or double) emulsions are multipart liquid dispersion systems, also known as emulsion emulsions, where droplets of one dispersed liquid (water-in-oil or oil-in-water) are dispersed more widely into another liquid (water or oil, respectively), producing W/O/W or O/W/O. In the multiple emulsion, the innermost dispersed droplets (hereinafter called inner droplets or just droplets, while the droplets of the multiple emulsion are labeled, for simplicity, drops) are disconnected by a film of another phase from the external liquid phase.

Although multiple emulsions are an evolving technology, the industry only has a few industrial products based on multiple emulsions. A safety mechanism for the controlled release of active compounds is the principal application of multiple emulsions. In the food industry, W/O/W emulsions, including oxidation, light and enzymes, are able to increase the solubility of particular active materials, solubilize oil-insoluble ingredients, and function as safe liquid reservoirs for molecules sensitive to external environmental reactivity, and act as trapping reservoirs for flavor and odor cover.

Foams

Foams consist of tiny gas (often air) bubbles dispersed in a liquid, egg white foam, for example. Air bubbles are included, as liquid egg white is whipped. The mechanical activity contributes to the unfolding of albumen proteins to create a network, trapping the air. Protein coagulates when egg white is cooked, and moisture is driven off. This produces strong foam, a meringue, for instance. Other examples of strong foams include ice cream, bread, and cake.

Free, Bound and Entrapped Water

In all living organisms, and also in almost all foods, water is present unless steps have been taken to eliminate it. Most natural foods, unless they are dehydrated, contain water up to 70% of their weight or greater, and fruits and vegetables contain water up to 95% or greater. Water that can be easily extracted by squeezing or cutting or pressing from food is known as free water, while water that cannot be easily extracted is known as bound water.

Usually, bound water is defined in terms of how it is measured; different measurement methods have different values for bound water in a specific food. Many food constituents can bind or hold onto molecules of water, so that they cannot be easily extracted and do not function like liquid water. Some features of bound water include:

• It is not free to act as a solvent for salts and sugars.
• It can be frozen only at very low temperatures (below freezing point of water).
• It exhibits essentially no vapor pressure.
• Its density is greater than that of free water.

There is more structural bonding than liquid or free water in bound water; it is also unable to act as a solvent. The molecules do not escape as vapor because the vapor pressure is negligible; the molecules in bound water are more tightly packed than in the liquid state, because the density is greater. The water present in cacti or pine tree needles is an example of bound water; water cannot be squeezed or pressed out; intense desert heat or a winter freeze does not impact bound water adversely and the vegetation stays alive. Food retains bound water even upon dehydration.

Molecules such as starches, pectins, and proteins bind to water molecules to polar groups or ionic sites. The water nearest to these molecules is retained most strongly; the following layers of water are held less tightly and less orderly, until the free water structure eventually prevails.

Water can also be trapped in foods such as gels of pectin, fruit, vegetables, and so on. Entrapped water is immobilized in capillaries or cells but flows freely when released during cutting or damage. Entrapped water has free-water properties and no bound-water properties.

In part, the presence of water determines the freshness of any substance. When free water is gradually lost by dehydration, food products look more wilted.

P^H Value

A food’s pH value is a direct function of the ions of free hydrogen present in that food. These hydrogen ions are released by acids found in foods, giving their distinct sour taste to acid foods. Thus, as a measure of free acidity, pH can be described. PH is defined more specifically as the negative log of the concentration of hydrogen ions.

It is commonly considered that the pH spectrum ranges from zero to 14. As pure water has a pH value of exactly 7, a pH value of 7 is neutral. Values below 7 are known to be acidic, while those above 7 are considered to be basic or alkaline. A few foods may be basic, such as egg whites, sweet corn, and some baked goods. Naturally, most foods are acidic with a pH value of less than 7.0. Nevertheless, the pH value of a specific food can have a drastic impact on the form of processing required to preserve it safely.

Osmosis

The word osmosis describes the passage of a liquid from a less concentrated solution to a more concentrated one through a semi-permeable membrane. Osmosis is also used to preserve fruits and meats, but the mechanism for both is very distinct. In the case of fruit, osmosis is used to dehydrate it, while osmosis draws salt into it when processing meat, thus preventing the intrusion of bacteria.

The majority of fruits have around 75% water, which makes them highly susceptible to spoilage. It must be dehydrated to preserve fruit, which, as in the case of the salt in the meat, provides bacteria with a less than hospitable setting. People have tried a number of methods for drying fruit over the years, but most of these appear to shrink and harden the fruit. The explanation for this is that most drying methods are relatively fast and extreme, such as heat from the Sun; osmosis, on the other hand, is slower, more mild and similar to nature’s actions.

In fact, osmotic dehydration techniques result in fruit that can be processed by other methods for longer than fruit dehydrated. In essence, this makes it possible to offer a larger range of fruits to customers during the year. Also, though holding out microorganisms, the fruit itself appears to preserve some of its taste and nutritional qualities.

Since only about 50 percent of the water in most ripe fruits can be extracted by osmosis alone, the dehydration process often requires a secondary method. The fruit is blanched first, or put momentarily in scalding water to avoid enzymatic action. Next, by dipping it in, or spreading it with, a specially made variety of syrup whose sugar draws water from the fruit, it is subject to osmotic dehydration. Air drying or vacuum drying finishes the process after this. The resulting product is ready to eat; under most climatic conditions, it can be stored on a shelf; and can even be powdered to make confectionery products.

Osmotic Pressure

The pressure that needs to be applied to a solution to avoid the inward flow of water through a semi-permeable membrane is osmotic pressure. It is also known as the minimum required osmosis nullification pressure. The osmotic pressure phenomenon emerges from the propensity of a pure solvent to pass through a semi-permeable membrane and through a solution that contains a solution that is impermeable to the membrane. In biology, this mechanism is of essential importance since the membrane of the cell is selective for many of the solutes present in living organisms.

Osmosis allows water to flow from an area of low solute concentration to an area of high solute concentration, until the ratio of solute to water in the two areas is equal. Normally, the solute often diffuses towards equilibrium; however, all cells are surrounded by a lipid bilayer cell membrane that allows water to flow in and out of the cell, but under certain circumstances limits the flow of solute. As a consequence, water floods into the membrane when a cell is put in a hypotonic solution, increasing its volume. Eventually, the cell’s membrane is extended so that it presses against the cell’s rigid wall. Water flows into the cell in an isotonic solution at the same rate that it flows out. Water actually flows out of the cell into the surrounding solution when a cell is put in a hypertonic solution, causing the cells to diminish and lose their turgidity. Two of the most common substances used to create hypertonic environment for microorganisms and prevent them from increasing are salt and sugar. In food preservation, they are commonly applied.

The main ingredient used in meat preservationt is table salt, also known as sodium chloride. Water removal and salt addition to meat create a solute-rich environment in which osmotic pressure draws water from microorganisms, thereby delaying their growth. Doing this requires a salt concentration of nearly 20%.

Sugar is used for the preservation of fruit, either in fruit syrup such as apples, pears, peaches, apricots, plums or in a crystallized form where the preserved content is cooked to the point of crystallization in sugar and the resulting product is then kept dry. The aim of sugaring is to establish an atmosphere hostile to microbial life and prevent food spoilage. Sugar has also been used for non-food preservation from time to time. The growth of molds and fungi, however, is not suppressed as effectively as bacteria growth.

Boiling Point

Boiling is the cooking of food by immersion in water heated to near its boiling point (212 ° F [100 ° C] at sea level; water boils at lower temperatures at higher altitudes, with a decrease in boiling temperature of around one degree Celsius per 1,000 feet [300 meters]). Water-soluble compounds increase the boiling point of the water, such as sugar and salt). For cooking meats and vegetables, boiling is usually used. Depending on individual preferences and regional or conventional dictums, the degree of cooking varies.

For methods of cooking with hot water, a variety of particular terms apply. In water heated to about 185 °F (85 °C), scalding is carried out, typically in a double boiler that conducts water heat contained in a larger pan to a smaller pan containing food, thereby preventing contact between food and water. For breads and custards, this technique is widely used to prepare milk. Water begins to circulate visibly and to shiver at just above the scalding temperature; food, particularly eggs and fish, may be poached at this stage.

The surface of the water breaks into small bubbles at the simmering point, variously defined, but usually reaching the boiling temperature; simmering is typically used to cook soups, stews, and pot roasts in a covered or open pan. To remove the outer skin, boiling water is poured over vegetables, fruits, or nutmeats while blanching. Parblanching consists of immersing the food in cold water and then slowly bringing it to a boil or simmer.

Melting Point

Fats, when heated, melt. As fats are triglyceride mixtures, they do not have a separate melting point, but they melt over a range of temperatures. The temperature is known as the slip point when melting occurs. At temperatures of 30 °/ 40 ° C, most fats melt. The melting point for oil is below normal air temperature – the more double bonds, the lower the temperature of the air. These melting point differences represent differences in the degree of unsaturation of the constituent fatty acids and the number of carbon atoms. Typically, triglycerides originating from animal sources are solids, while those of plant origin are usually oils.

Freezing Point

The temperature at which the first ice crystal appears and the liquid at that temperature is in equilibrium with the solid is known as the freezing point. This temperature would equate to 0 °C (273 °K) if the freezing point of pure water is considered. However, because of the presence of both free and bound water, the mechanism becomes more complicated when food systems are frozen. Except at very low temperatures, Bound Water does not freeze. Soluble solids contain unfreezable water, causing a drop in the freezing point of water below 0 °C. The concentration of soluble solids increases in the unfrozen water during the freezing process, resulting in a difference in the freezing point. The temperature at which the first ice crystal forms is, thus, generally known to be the initial freezing temperature.

Freezing is one of the oldest and most commonly used food preservation techniques, which helps more than any other process to preserve flavor, texture, and nutritional value in foods. The freezing process is a combination of the beneficial effects of low temperatures in which microorganisms are unable to expand, chemical reactions are decreased and metabolic cellular reactions are delayed.