Unit

Food Science

Problem Area

Handling and Storing Plant Products

Lesson

Testing for Food Additives

Student Learning Objectives

 1. Describe food preservation and its benefits.

 2. Describe the methods used in controlling food contamination.

 3. Explain why food additives are important to food preservation.

 4. Explain a variety of food additives and their purposes.

Terms

          air-blast freezing antioxidants blanching chemical drying commercial sterilization conduction convection drying fermentation flavor enhancer           food additives food preservation food spoilage freeze drying freezing irradiation liquid freezing mechanical drying pasteurization pickling

Terms cont.

       plate freezing radiation refrigeration senescence sequestrants sterilization texture enhancer

What is food preservation? How does food preservation benefit consumers?

 All foods eventually undergo spoilage; some spoil much faster than others. Foods can undergo natural deterioration or can become contaminated by microorganisms causing spoilage to occur at a much faster rate. 

Senescence

is considered to be a terminal, irreversible deteriorative change in living organisms, leading to cellular and tissue breakdown and eventually death. Senescence is the period following ripening, during which growth ceases and aging processes replace ripening processes.

 A.

Food preservation

is the treatment of food to keep it from spoiling. It also aids in retaining nutrients and improving taste.

 B.

Food spoilage

is the condition in which food becomes unsafe to eat. Food spoilage can be caused by the invasion of bacteria, fungi, mold, and other foreign materials.

 1. Bacteria are one-celled microscopic plants. They are the most difficult of all microbes to control in the prevention of food spoilage. Microorganisms use the food as a food source.

 2. Food may be exposed to other foreign materials. These materials are not intended to be part of the food. Their introduction leads to spoilage. Examples of foreign materials that cause food spoilage are rodents, insects, and chemicals.

 C. Food preservation helps foods retain their nutritional value. As foods deteriorate, they lose the nutrients that they naturally contain. Fruit juices that are not refrigerated typically lose their nutrients. The loss of nutrients is known as nutrient depletion.

 D. Food preservation aids in helping foods retain their taste. Palatability means that an item has an agreeable taste. Various processes are used to improve food palatability. Care must be taken to not decrease a food’s nutritional value when increasing its palatability. For example, sugar is added to foods to improve its palatability. How-ever, if too much sugar is added, the nutritional value of the food is decreased.

What are the methods used in food science to control contamination?

 Environmental controls that are commonly used in storage of perishable plant products are:  A. Heat —Most bacteria, molds, and yeasts grow best at temperatures of 16 –38ºC. For sterility, a temperature of 121º C must be maintained for at least 15 minutes. Heat is the most effective means of preserving a food product. It is commonly used in canning foods.

 1. In food processing, heat energy is transferred in one of three ways to aid in preservation:  a.

Conduction

is a method of heating in which energy moves from one particle to another through direct contact. Conduction may be compared to a chain reaction. As each particle of food is heated, it passes energy on to other particles it is touching. Examples of foods that are preserved through conduction heating include canned tuna or ham.

 b.

Convection

is a method of heating that involves the movement of a heated air or liquid through the food being heated. This is the same type of heat used in a kitchen oven. In convection heating, the movement of the heated air or fluid around the food causes it to be heated. Examples of foods that are preserved through convection heating are canned soups.

 c.

Radiation

is a form of conduction in which heat energy is transferred through the electromagnetic spectrum. The electromagnetic spectrum is a linear arrangement of all known forms of energy. In radiation, energy from the infrared and ultraviolet range of the spectrum are used to heat the food. An example is the infrared radiation lamps used in restaurant buffets to keep food warm.

 2. Heat preservation is the most complete means of food preservation. When food is heated, it is altered. The extent to which a food is altered depends on the amount and duration of heat it is subjected to.

 a.

Sterilization

is the complete destruction of all microorganisms. Sterilized foods will last a very long time. Because they have undergone a high level of heat treatment, sterilized foods go through significant alterations.

 b.

Commercial sterilization

is the complete destruction of all microorganisms except some spores. Commercially sterilized foods will eventually become unsuitable to eat. They will not cause sickness. Instead, they become unpalatable.

 c.

Pasteurization

is a heat treatment that destroys all pathogenic microorganisms, but not organisms that cause spoilage. A pathogenic organism inflicts illness in humans.

 d.

Blanching

is a heat treatment used with vegetables where their temperature is raised to between 180 ° and 190° and followed by rapid cooling. This process does not destroy microorganisms. It does inactivate enzymes that might alter the taste or color of the vegetable.

 B. Cold —When water in foods is completely frozen, there is not multiplication of microorganisms. At a temperature of below 10º C, growth is slowed and becomes even slower as the cold increases. Cooler temperatures slow senescence. Refrigeration and freezing are not as effective as heating in preserving foods. Heating destroys all microorganisms. Cold treatments only slow the metabolisms of the microorganisms.

 1.

Refrigeration

is the storage of foods at a temperature below room temperature, but above freezing. It is used as a transitional environment. A transitional environment means that the food product will ultimately be heated or consumed. It will not stay refrigerated forever.

 2.

Freezing

is the storage of food products at temperatures where water contained in the products becomes ice. When a food is frozen, it is the water in the food that freezes. The three main methods of freezing used in commercial food preservation are:  a.

Plate freezing

uses the surface of metal plates to sandwich the food product to be frozen. As the food and plates contact each other, fluid that circulates in the plate removes heat and freezes the product.

 b.

Air-blast freezing

uses high speed air and cold temperatures to freeze the product. Air is the freezing medium in this method.

 c.

Liquid freezing

involves spraying fluid refrigerants such as liquid nitrogen on individual food products as they move down a conveyor belt. This method is commonly used on meat patties.

 C. Drying —Preservation by drying succeeds because decay-causing organisms usually do not grow at moisture contents below 10-15%. Microorganisms need water for growth and survival.

 1.

Drying

involves removing the moisture from a food product. When moisture is removed, most of the substances that lead to spoilage are also removed. Food is dried in one of three ways:  a.

Mechanical drying

uses a machine to remove the moisture in the food product.

 b.

Freeze drying

involves freezing the food product then placing it in a chamber where all air and moisture are removed.

 c.

Chemical drying

uses a chemical substance to remove moisture from the food. Salt is the most common chemical used in chemical drying.

 D. Acid —Because of their value as preservatives, and in some instances their effect as flavor enhancers, certain organic acids, including acetic and ascorbic acid, are used to preserve plant products. Microorganisms can only survive at a specific range of pH values. By increasing the acidity of the food, the environment becomes unfavorable for microbial growth.

 E. Oxygen and carbon dioxide —Respiration is directly affected by oxygen and carbon dioxide levels. Since respiration is an oxidation process, a reduction in the amount of oxygen reduces the respiration rate. High concentrations of carbon dioxide may inhibit or prevent respiration and may inhibit the ethylene production that stimulates ripening.

 F. Humidity —In general, low humidity favors desiccation and wilting. Also, high humidity favors the development of decay, especially if the temperature is too high.

 G. Fermentation and pickling —The action of certain bacteria and yeasts in decomposing carbohydrates is known as

fermentation

.

 1. After decomposition by different organisms, the end products include carbon dioxide and water (complete oxidation), acids (partial oxidation), alcohols (alcoholic fermentation), lactic acid (lactic acid fermentation), and others. These act as preservatives by retarding enzymatic deterioration, and they impart flavors that are regarded as desirable.

 2. When the fermentation process is combined with salting, it is called

pickling

. Pickling may be accomplished without the direct use of microorganisms by placing food in organic acids (vinegar or citric acid).

 3. Citric, lactic, maltic, and tartaric are also added to foods. All of these acids occur naturally in plant juices.

 4. Fermentation can take place under either of two conditions: aerobic fermentation takes place with air present and anaerobic fermentation takes place without the presence of air.

 H. Sugar and salt —Sugar is metabolized by microorganisms, but dissolved molecules of sugar reduce the activity of water and inhibit the growth of microorganisms just like dissolved salt. Salt is an efficient preservative because it reduces water activity. When bacteria, yeasts, or molds are placed in a heavy salt brine, water in the cells moves out (diffuses) through the cell membranes and into the concentrated brine solution (osmosis). Salt can also raise the boiling point or lower the freezing point of water.

 I. Air —With this process, a partial or total vacuum can be created to prevent aerobic microorganisms from growing. The storage and handling of fresh fruit and vegetable commodities must slow the reactions that tend to break down the product. These degradation reactions are essentially those resulting from respiration, whereby the carbohydrates synthesized during photosynthesis are broken down to carbon dioxide and water. Procedures that slow or stop the rate of respiration frequently also slow or stop the rate of deterioration. Respiration of stored crops can be reduced by limiting the amount of oxygen.

   J.

Irradiation

is the exposure of food to gamma rays generated by a radioactive material.

 1. Gamma Rays have no charge. They are used to destroy enzymes or microorganisms in the food product.

 2. Food that has been irradiated does not mean that it is radioactive.

K. Controlling Air Movement —molds, yeasts, and bacteria travel through the air. If the movement of air is controlled, the chances for contamination are minimized. This is one reason why large food processing machines are covered with lids.

L. Segregation —every component in food preparation is a source of contamination. When foods are processed, each step is separated so that the contaminant does not travel from one step to the other. Segregation is routine in food processing plants. Most people are not as careful at home. The same cutting board may be used to cut different foods without being washed.

Why are food additives important to food preservation?

 It is almost impossible to eat food that does not contain preservatives of some kind. Unless you cook all of your meals from scratch and raise your own food, preservatives are being consumed.

 A. Additives are used to keep food from spoiling.

Food additives

are non-nutritive substances that are added to foods in small quantities to improve flavor, texture, appearance, or shelf life. Substances which are not intentionally added to foods are called food contaminants.

 B. Food additives are chemicals added to a food product to increase its length of usefulness. The chemicals used are not dangerous. Instead, they prolong the useful life of the food by slowing the natural deterioration process.

 C. Food additives can be used for a variety of reasons.

 1. Improve the quality of the food.

 2. Reduce the amount of waste.

 3. Maintain or improve the nutritional value of the food.

 4. Improve the shelf life.

 5. Increase consumer acceptance.

 6. Increase the availability of foods.

 7. Make food preparation easier.

 D. Food additives are not the sole solution to food preservation. Additives are used in combination with physical and non-chemical methods of preservation.

 E. Companies are responsible for meeting the guidelines set forth by the US Food and Drug Administration. Other countries have similar agencies and requirements. Food additives must meet several strict requirements before they are allowed in foodstuffs.

 1. It must be safe for humans to consume. Extensive testing must be completed and validated by the FDA.

 2. The additive must work as indicated in the specified conditions.

 3. The nutritional value of foods may be not reduced by the additive.

 4. Customers must not be deceived by the additive and it must not be used to mask unfavorable ingredients.

 5. A specific method for determining the presence and amount of must be available.

 6. The additive may not be used instead of good manufacturing practices.

What are some food additives and how do they help to preserve foods?

 Food additives fall into a variety of substance categories. The following table outlines the substance categories:  A. Food Additives Substance Categories

 B. The following are examples of food additives:  1. Monosodium glutamate (MSG) is derived from seaweed. It has very little taste, but can be used quite effectively as a

flavor enhancer

. Additives that have either no flavor or little flavor, but can improve the flavor of a food are called flavor enhancers.

 2. Natural or synthetic substances that are used to boost a flavor or regain a flavor that was lost during processing are called flavoring agents. Oils, oleoresins, and extracts are examples of flavoring agents.

 3. Polyols are an example of a

texture enhancer

. Texture enhancers not only improve the texture of a food, but they also improve water retention. Glycerine, mannitol, propylene glycol, and sorbitol are examples of polyols. These are found in diet drinks, gum, candy, and ice cream.

 4. Many foods contain a variety of metals which are naturally present.

Sequestrants

are additives that combine with these metals helping to inactivate the metal. Sequestrants prevent the metal ions from oxidizing with fatty acids resulting in off-flavors. Malic acid, tartaric acid and citric acid are examples of sequestrants. They are also antioxidants. They can prevent oxidative rancidity from occurring.

 5. When salt is placed in water, it dissociates into sodium and chlorine ions. It can thus increase the boiling point or reduce the freezing point of water. Osmosis can occur as equilibrium is trying to be reaching. This creates a lower amount of water present for microbes to use.

 6. Mold growth can be inhibited by sodium or calcium propionate. The shelf life of bakery products is increased, but the flavor is not affected.

 7. Sorbic acid hinders mold and yeast growth in cheese and fruit drinks.

 8. Sodium benzoate and benzoic acid are used in candied products.

 9. Processed meat products can contain butylated hydroxyl toluene (BHT) or butylated hydroxyl anisole (BHA). These

antioxidants

help to prevent oxidation of the animal fat.

 10. The application of sulfur dioxide allows the fruit or vegetable to dry faster and destroys the enzymes which are responsible for browning.

Review/Summary

 What is food preservation? How does food preservation benefit consumers?

 What are the methods used in food science to control contamination?

 Why are food additives important to food preservation?

 What are some food additives and how do they help to preserve foods?