**Pretest one "+" per correct organism, and one per correct use

GOOD GUYS - SMALL PACKAGES

List as many beneficial microorganisms as possible and explain what makes them a good guy. If you can't remember specific examples of organisms, go ahead and describe situations where microorganisms are used for beneficial purposes.

GOOD GUYS - SMALL PACKAGES

Goal: to acquaint and inform students about beneficial microorganisms

Day 1 : Pretest (I use teams and rewards)

yogurt activity

assign pairs to look up food producing microorganisms

Day 2 : pair-share with documentation of finding

assign pairs to look up microorganisms in agriculture

pair-share with documentation

Day 3 : yogurt party

notes and discussion pharmaceuticals and vaccines

natures recyclers- sewage treatment/decomposers

Day 4 : water treatment plant tour

Day 5 : Discuss/Review

Post test

**Post test

BENEFICIAL MICROORGANISMS TEST

*Name and explain how microorganisms are useful in each situation.

Food Production (3 examples)

Agriculture (2 examples)

Medicine (3 examples)

Recycling/Decomposing (2 examples)

Yogurt Production

BSAA-ANSC 305-3 11

Technical Supplement

1. How is yogurt produced? Yogurt is a cultured dairy product that has a gel-like, custard consistency. L. bulgaricus and S. thermophilus are used as starter cultures. The fermentive action of these bacteria is responsible for the texture and flavor of yogurt. The resulting lactic acid destabilizes the milk protein structure (casein micelle). Increased acidity causes the milk to coagulate and form a gel structure. During fermentation, enzymes convert lactose into lactic acid. Lactic acid is the end product of lactic fermentation. Yogurt is produced by adding powdered milk to whole milk and scalding but not boiling the mix. Cool the mix and add a starter yogurt culture. An incubation period is needed in order to get the mix to coagulate. Finally, the mixture, now yogurt, is refrigerated.

2. What role do bacteria play in yogurt production? Lactic acid bacteria produce polysaccharides that increase viscosity (resistance of a fluid to flow) and water retention. Yogurt has a high moisture content of 85%. When yogurt reaches the desired acidity (pH of 4.25 - 4.5), bacterial fermentation is stopped by cooling the yogurt. Cooled yogurt should have between 0.9% - 1.2% lactic acid.

3. Why does yogurt have a sour taste? During fermentation, enzymes released by the bacteria convert lactose into lactic acid. Lactic acid is the main product of lactic fermentation. Since acids have a sour taste, yogurt is a sour tasting dairy product. Fermentation is an example of anaerobic respiration. Some yogurt contains live bacteria and others have been fermented but pasteurized after fermentation.

4. What process is responsible for the gel-like texture of yogurt? Milk proteins have the unique ability to curdle. Curdling is caused by proteolytic enzymes, heat, lactic acid, and other means. Each milk gel consists of a protein matrix, which is modified by lactic acid to produce a smooth yogurt product. Heating milk causes the casein micelles to interconnect to form a gel matrix. Heat also destroys undesirable microorganisms. Lactic acid bacteria produce polysaccharides that decrease the flowability of the yogurt. Frozen yogurt is made by mixing yogurt with ice milk. Frozen yogurt is usually less acidic than fresh yogurt and has lower levels of viable bacteria, thus less sour tasting.

References

Ed Osborne, Biological Science Applications in Agriculture, Interstate Publishers, Inc., Danville, Illinois, 1994.

Elmer L. Cooper, Agriscience Fundamentals and Applications, Delmar Publishers, 1990.

Ray V. Herren and Roy L. Donahue, The Agriculture Dictionarv, Delmar Publishers, 1991.

Prepared by Mike Walsh, Steve Heilman, Larry Plapp, anc' Dave Wilson for AGED 400E.

| Time required for lesson: 2-3 days |

Yogurt Production

Agricultural Applications and Practices

Yogurt is the fastest growing product in the dairy industry. Some food products, like yogurt, are developed by intentionally inoculating a base product (milk) with microorganisms (bacteria).

Although the principles of food fermentation are well understood in laboratory settings, the scaling-up of these processes to commercial production is complicated. Microbiology, biochemistry, genetic engineering of anaerobic bacteria, and general food engineering processes all play an important role in the development of cultured milk products. The therapeutic value of yogurt and other cultured milk products is still being debated. Some believe that the balance of microflora in the intestines is positively affected by eating fermented food products.

Interest Approach

Bring to class several samples of fresh yogurt types. Have students taste the yogurt samples and attempt to describe the taste of yogurt. Also ask students to compare yogurt and milk on the basis of texture and taste. Challenge students to describe the yogurt making process.

Science Connections—Questions for Investigation

1. How is yogurt produced?

2. What role do bacteria play in yogurt production?

3. Why does yogurt have a sour taste?

4. What process is responsible for the gel-like texture of yogurt?

Purpose of Lab and Student Performance Objectives

The purpose of this lab is to explore the process of yogurt production and to recognize the role of bacteria in making yogurt and similar dairy products. Upon completion of this lab, students should be able to:

1. describe the scientific processes involved in yogurt production;

2. attribute changes in milk characteristics to correct biochemical processes;

3. explain the conditions necessary for anaerobic respiration; and,

Ideas for Additional Experiments -

1. Compare the rate of reaction and final product for whole versus skim milk.

2. Examine the effects of incubation temperature on final product quality and characteristics.

Underlying Science Concepts and Principles

A. Biological Concepts

anaerobic respiration

bacteria

enzyme

fermentation

viscosity

B. Key Terms

1. aerobic respiration—the total oxidative degradation of glucose.

2. anaerobic bacteria—any bacteria that can survive in the partial or complete absence of air.

3. anaerobic respiration—takes place in the absence of oxygen and consists essentially of the early stages of aerobic respiration. Glucose is converted to a variety of end products, such as lactic acid.

4. end product—the final compound or substance resulting from a chemical reaction.

5. enzyme—a protein with catalytic activity which is restricted to a limited set of reactions. Specificity of enzymes is designated by the suffix -ase.

6. fermentation—a slow decomposition process of organic substances induced by microorganisms or by enzymes.

7. food fermentation—the study of microbial activity, usually anaerobic, on suitable substrates under controlled or uncontrolled conditions. Resulting food and beverage products are characteristically more stable, palatable, and nutritious than the raw substrate.

8. lactic acid—the end product of anaerobic metabolism of glucose.

structure consisting of a protein matrix and other components. This gel matrix has the ability to immobilize the liquid phase of milk. By modifying this ability, it is possible to manufacture stable milk products with a high water content (e.g., yogurt).

10. Milk to be used in yogurt production is usually heated to increase the total solids content in order to make a firm product. Heating causes the micelles to interconnect in chains to form the gel matrix.

11. Ropy (slime-producing) lactic acid bacteria produce polysaccharides that are released into the yogurt where they increase viscosity and improve water retention. Yogurt has a high moisture content of 82 - 86%.

12. Lactic acid provides the tart flavor of yogurt, as well as the formation of a gel structure. The major flavor components in yogurt are carbonyl compounds; among these acetaldehyde is most important and gives yogurt its green apple or nutty flavor.

13. The fat content of yogurt varies from O to 3.5%; most yogurt is low fat and contains 1 or 1.5% fat.

14. Milk SNF (solids-not-fat) content varies from 9 to 16%. SNF can be increased by adding milk powder, and by other means. Increased SNF levels are needed to increase protein content, which helps to increase product viscosity to desired levels.

15. Cooling of the yogurt after incubation (fermentation) stops bacterial fermentation.

16. Frozen yogurt is manufactured by mixing varied amounts of fermented yogurt with ice milk containing sweeteners, stabilizers, etc.

Yogurt Production

Agricultural Applications and Practices

Yogurt is the fastest growing product in the dairy industry. Some food products, like yogurt, are developed by intentionally inoculating a base product (milk) with microorganisms (bacteriaj.

Although the principles of food fermentation are well understood in laboratory settings, the scaling-up of these processes to commercial production is complicated. Microbiology, biochemistry, genetic engineering of anaerobic bacteria, and general food engineering processes all play an important role in the development of cultured milk products. The therapeutic value of yogurt and other cultured milk products is still being debated. Some believe that the balance of microflora in the intestines is positively affected by eating fermented food products.

Science Connections—Questions for Investigation

1. How is yogurt produced?

2. What role do bacteria play in yogurt production?

3. Why does yogurt have a sour taste?

4. What process is responsible for the gel-like texture of yogurt?

Research Problem

How is yogurt produced?