Topic: Causes of food spoilage

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 the causes of food spoiling and the natural ways of storing and preserving it.

Key competences

• communication in foreign languages;

• digital competence;

• learning to learn.

Criteria for success
The student will learn:

• to name the causes of food spoilage;

• to name and discuss the natural methods of food preservation.

Methods/techniques

• activating

  • discussion.

• expository

  • talk.

• 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.

3. Health and safety - before starting experiments, the teacher acquaints students with the characteristics of the substances that will be used in the lesson. He indicates the need to be careful when working with them.

Realization

1. The teacher, introducing students to the subject of classes, mentions the deterioration of food and the ways of its storage and preservation. He explains that various micro‑organisms are responsible for the processes of spoilage. Unpleasant smell from the waste basket, bad smell of butter or sausage are the results of the presence of bacteria. Food, such as bread and fruit, loses suitability for consumption also under the influence of fungi (molds). For centuries people have been trying to give food as long as possible, bring out its taste and diversify the meals eaten. The so‑called food additives, including to protect food against the loss of nutrients and increase its attractiveness.

2. The teacher refers students to the abstract, textbook and the internet, asking them to get acquainted with the causes of spoiling the food. After a while he starts a discussion in which the participants of the classes present the collected messages.

3. In the summary of the discussion, the teacher asks the students to search for a film on the Internet entitled „Spoiling food - the action of microorganisms”.

4. The teacher explains the rational storage of food. He initiates the discussion by asking questions about natural ways of storing food; what should be done to keep the freshness characteristics and the ability to consume or process as long as possible; What conditions prevail in specially equipped rooms or separate buildings, or warehouses, etc. In summary, the teacher asks for clarification of food preservation processes and examples of products that can be pasteurized, thermally sterilized, blanched, cooled, frozen, dried, smoked, pickled, salt.

5. At the end of the lesson, the teacher asks students to do interactive exercises - individual work.

Summary

1. The teacher chooses one student by random method and asks him or her to explain in own words the meaning of a given word or concept learned during the lesson.

2. The teacher briefly presents the most important issues discussed in class. He answers the additional questions of the proteges and explains all their doubts.

Homework

1. Develop a lap book containing issues learned during the lesson and bring your work to the next class.

The following terms and recordings will be used during this lesson

Terms

Texts and recordings

Causes of food spoilage

Food (meat, fish, fruit, vegetables) quickly loses its taste qualities, turns sour rancid, rots and therefore becomes unfit for consumption. The spoilage occurs under the influence of physicochemical or biological factors. The physicochemical factors include: light, air, water, temperature while the biological factors include – bacteria and fungi.

The chemical changes in food ingredients are of high toxicological significance. Apples, potatoes and mushrooms turn brown quickly when peeled. This is the result of a process that occurs in the presence of oxygen with the participation of enzymes present in their cells and catalyzing this process. The action of the enzymes may be inhibited by boiling or adding an antioxidant, e.g. citric acid.

Another reason for food loss is the molding caused by mold fungi. In the past, bread did not go mold, but it became stale – it dried up and hardened, because it lost water. Today bakeries use chemical additives that prevent bread from drying and prolong its freshness, but such bread becomes an excellent culture medium for molds. Preservatives that prevent the growth of mold in bread are often sorbic acid and sorbates E 200 – 203.

Rancidification of fats occurs due to the action of oxygen, light and moisture. It consists in the formation of free butyric acid (butanoic), and is accompanied by the emission of an unpleasant odor. To prevent fats from going rancid, they should be stored in cool and dry conditions, away from sunlight.

The reason for milk souring are changes caused by the growth of microorganisms that convert milk sugars into lactic acid. The milk’s shelf‑life is prolonged by subjecting it to a high‑temperature treatment process, so‑called pasteurization UHT. For a few seconds milk is heated to a temperature exceeding 100°C, and then it is cooled down similarly quickly. At this temperature microorganisms die and the product does not lose its nutritional value.

• Food preserving substances have been used for thousands of years.

• The spoilage occurs under the influence of physicochemical or biological factors. The physicochemical factors include: light, air, water, temperature while the biological factors include – bacteria and fungi.

• Preservatives are substances that prolong food shelf‑life.