Topic: Methods of storing and preserving food

Target group

High school / technical school student

Core curriculum

New core curriculum:

High school and technical high school. Chemistry – basic level:

XXI. Chemistry around us. Pupil:

8) explains the reasons for food spoilage and proposes ways to prevent this process; presents the significance and consequences of using food additives, including preservatives.

High school and technical high school. Chemistry – extended level:

XXI. Chemistry around us. Pupil:

8) explains the reasons for food spoilage and proposes ways to prevent this process; presents the significance and consequences of using food additives, including preservatives.

Old core curriculum:

High school and technical high school. Chemistry – basic level:

XXI. Chemistry around us. Pupil:

7) explains the causes of food spoiling and proposes ways to prevent this process; presents the meaning and consequences of using food additives, including preservatives.

General aim of education

The student discusses ways of preserving food and lists preservatives added to it.

Key competences

• communication in foreign languages;

• digital competence;

• learning to learn.

Criteria for success
The student will learn:

• what are the ways of preserving food;

• recognize different types of preservatives.

Methods/techniques

• expository

  • talk.

• activating

  • discussion;

  • brainstorming.

• exposing

  • film.

• programmed

  • with computer;

  • with e‑textbook.

• practical

  • exercices concerned.

Forms of work

• individual activity;

• activity in pairs;

• activity in groups;

• collective activity.

Teaching aids

• e‑textbook;

• notebook and crayons/felt‑tip pens;

• interactive whiteboard, tablets/computers.

Lesson plan overview

Introduction

1. The teacher hands out Methodology Guide or green, yellow and red sheets of paper to the students to be used during the work based on a traffic light technique. He presents the aims of the lesson in the student's language on a multimedia presentation and discusses the criteria of success (aims of the lesson and success criteria can be send to students via e‑mail or posted on Facebook, so that students will be able to manage their portfolio).

2. The teacher together with the students determines the topic – based on the previously presented lesson aims – and then writes it on the interactive whiteboard/blackboard. Students write the topic in the notebook.

Realization

1. The teacher initiates an introductory interview. He asks students: „What do you know about the natural ways of preserving and storing food?”.

2. The students perform an interactive exercise. The teacher makes sure that the task has been correctly completed and gives feedback.

3. Students are divided into 4 groups. Each receives paper sheets and markers. They are to familiarize themselves with and develop content from various sources (abstract, textbook or internet) regarding the advisability of applying a given preservative to a specific food, taking into account the effect of the preservative and its advantages and disadvantages:
   group I - kitchen salt
   group II - benzoic acid and sorbic acid
   group III - vitamin C 
   group IV - sulfur dioxide.
   After the set time, the groups present their studies, and the other students evaluate their work (whether the information was useful, exhaustive, interesting, etc.).

4. The teacher recommends students to prepare an observation journal in abstract. He informs that they will watch the film „The influence of benzoic and sorbic acid on the process of spoiling the bread”. Before this happens, they are to formulate a research question and hypotheses and note them in the indicated place. After the screening, they set together observations, then conclusions, and write them down as well.

5. Students, working individually or in pairs, carry out interactive exercises to check and consolidate knowledge learned during the lesson. Selected people discuss the correct solutions for interactive exercises. The teacher completes or straightens the statements of the proteges.

Summary

1. Teacher asks: If there was going to be a test on the material we have covered today, what questions do you think would you have to answer? If the students do not manage to name all the most important questions, the teacher may complement their suggestions.

Homework

1. Make at home a note from the lesson using the sketchnoting method.

The following terms and recordings will be used during this lesson

Terms

Texts and recordings

Methods of storing and preserving food

When storing food, the aim is to ensure that it is protected against dangerous changes in quality resulting from biological and chemical processes and fit for consumption for a significant period of time. There are physical and chemical methods of food preservation. Physical methods include, among others, storage of food at low temperature or use of high temperatures – for example, cooking and pasteurizing, using hermetic packaging and ionizing radiation. Chemical methods of food preservation consist in adding chemical substances to food, e.g. benzoic acid, sorbic acid, sulfur dioxide, nitrate. Unfortunately, the physical and chemical changes that occur in foods as a result of these methods sometimes reduce the biological value of foods and can cause harmful effects.

The first natural agents that protected food against spoilage (preservatives) were salt and sugar, and later the preservative properties of vinegar and other acids, e.g. those produced by microorganisms during fermentation (cabbage, cucumbers), were discovered. These substances change the environment in which microorganisms live, preventing the growth of most of them. Currently, many natural and artificial preservatives are known.

Many substances added to food have undergone extensive studies in terms of their possible effects on the human body. The results of these studies contributed to the collection of detailed information on the properties of food additives. The most widely known list is the classification used in the EU. Substances added to foods have been marked with the E symbol (like Europe) and a number according to the international numeric system – INS (EN International Numbering System). The E numbers on packaging are the manufacturer's declaration that the substances added to food were used in the amount corresponding to the intended use and come from a list approved by the authorities of the European Community and that according to the current state of knowledge they are not harmful to health when used properly. With the list of E additives, a consumer of any nationality will know what is the actual chemical composition of the food product.

Food additives marked with E are the best studied group of compounds that make up its composition. The addition of preservatives increases the safety and quality of the product. Therefore, do not trust labels without E numbers, as it is not known what additives the manufacturer used. It can be assumed that in order to achieve the appropriate shelf‑life of the product, the manufacturer had to use some additives.

Preservation of meat by using rock salt is one of the oldest and the most popular methods of meat preservation, in addition to drying and smoking. In the 10% rock salt solution, the development of the majority of putrid bacteria is stopped. Rock salt has bacteriostatic effect, which means that it stops the growth of microorganisms, but does not kill them. The disadvantage of this preservation method is the loss of some vitamins and mineral salts. In addition, you have to take into account the loss of moisture and the penetration of sodium chloride into the meat.

Benzoic acid (E 210) and its salts have preservative properties in an acidic medium (pH 2.0 – 4.5). Their action consists mainly in inhibiting yeast development. They inhibit bacterial growth to a lesser extent. The efficacy of their action increases in the presence of sulfur dioxide, carbon dioxide and table salt. In the body, benzoic acid and its salts are rapidly absorbed and metabolized in the liver and then excreted in the urine. Clear symptoms of poisoning, such as vomiting and headaches, are observed only after very high doses, i.e. about 40 g of benzoic acid taken as a single dose. In people with allergy and asthma these substances may trigger allergic reactions.

Sorbic acid (E 200) is found in nature in rowan fruit, but as a food additive it is obtained synthetically. It has a preservative effect, inhibiting the growth of mold and yeast in acidic products with a pH of 3.0 – 6.0, where it works more effectively than benzoic acid. It inhibits the growth of many types of bacteria, with the exception of lactic acid bacteria. As a result, it is particularly useful in the production of fermented vegetables. Sorbic acid is used mainly for preserving vegetable sauces, fermented vegetables, jams, jellies and marmalades. It is one of the safest preservatives, because in the human body it undergoes a process typical for fatty acids, and the final products of its metabolism are usually carbon dioxide and water.

Vitamin C, or ascorbic acid (E 300), is a natural component of the diet and a substance that is an additive to food products. It has preservative and antioxidant properties. It is commonly found in many fruits and foods, e.g. citrus, apple, blackcurrant, tomato, pepper, potato, sauerkraut. It is one of the best known and indispensable ingredients of human food. It contributes to the proper function of connective tissue, participates in the processes of biological oxidation and improves the overall immunity of the body. Deficiency of this vitamin (avitaminosis) causes scorbutus (scurvy). The daily requirement of the body for ascorbic acid is approximately 100 mg.

Vitamin C is a colorless or yellowish solid, odorless, slightly acidic, soluble in water and alcohol. On an industrial scale, it is obtained from glucose. In solutions exposed to light and elevated temperature it decomposes (undergoes oxidation) to a biologically inactive chemical compound.

Sulfur dioxide is one of the oldest chemical preservatives. It was used already in ancient times. It is effective against bacteria and molds, but less so against the growth of yeasts. As a powerful antioxidant, it prevents so‑called food browning. Sulfur dioxide is mainly used for preserving wines, dried vegetables and fruits, and for disinfecting indoor areas and tanks. In products subjected to long‑term heat treatment, this compound causes loss of vitamins. It can cause allergy, therefore it should not be added to food intended for direct consumption.

• Preservatives are substances that prolong food shelf‑life.

• Common preservatives are, for example, table salt, ascorbic acid, benzoic acid, sorbic acid, acetic acid.

• Not only preservatives are used as food additives, but also substances that improve the color, consistency and taste of products are often used for this purpose.