Bài giảng - Food microbiology

Food Microbiology• Microorganisms are involved in producing many foods and beverages • Fermentation produces desirable characteristics of various foods • Microbial metabolism has other

© 2012 Pearson Education Inc.

Lecture prepared by Mindy Miller-Kittrell

North Carolina State University

Microorganisms in Industry

Food Microbiology

• Microorganisms are involved in producing many foods and beverages

• Fermentation produces desirable

characteristics of various foods

• Microbial metabolism has other functions

– Acts as a preservative – Destroys many pathogenic microbes and toxins – Can add nutritional value in form of vitamins or other nutrients

• Microbes are used in food production

• Microbes can help control food spoilage

Food Microbiology

• The Roles of Microorganisms in Food

Production

– Fermentation

occurs as a result of microbial growth

– Spoilage is unwanted change to a food due to various reasons

– Consistently perform specific fermentations

– Many common products result from fermentation of vegetables, meats, and dairy products

Industrial Microbiology

• The Roles of Microbes in Industrial

Fermentations

– Primary metabolites

Figure 25.1 The cheese-making process

Pasteurization kills unwanted microorganisms

Addition of starter bacterial culture

Coagulation of milk proteins (curd formation)

Disposal of liquid whey as waste product

Production of unprocessed cheeses

Cutting

of curds

Production of processed cheeses through pressing, addition of secondary microbial cultures, and aging (ripening)

Typical starter bacteria include Lactococcus lactis subsp

lactis or cremoris, Streptococcus salivarius subsp

thermophilus, Lactobacillus delbruckii subsp bulgaricus, and Lactobacillus helveticus.

Adjunct cultures are used to provide or enhance the

characteristic flavors and textures of cheese Common

adjunct cultures added during manufacture include

Lactobacillus casei and Lactobacillus plantarum for flavor in

Cheddar cheese, or the use of Propionibsacterium

freudenreichii for eye formation in Swiss

Yeasts and molds are used in some cheeses to provide the

characteristic colors and flavors E.g Penicillium roqueforti

in blue cheeses

Blue cheese Cheddar cheese

Swiss cheese

applications of alcohol fermentation

fermentation

Figure 25.2 The wine-making process

Preparation of must by stemming and crushing of grapes (or other fruit)

Addition of starter culture

of yeast and bacteria

Fermentation

of must (crushed fruit) or of juice alone into wine

The species of yeast that is used to ferment grape juice into

wine is Saccharomyces cerevisiae

The most problematic bacterium for wine production is of the

genus Acetobecter This organism has the potential to

convert wine into vinegar overnight Fortunately,

Acetobecter is sensitive to free sulfur dioxide

In wine aging process: the acidity decreases, clarification

takes place, and components of wine form compounds to

enhance flavor and aroma

Figure 25.3 The beer-brewing process

Barley is moistened and germinated, producing enzymes that convert starch into sugars Barley is then dried

to halt germination, and crushed to produce malt.

Mashing malt and adjuncts with warm water allows enzymatic activity

to generate more sugars Solids are removed to produce wort. Mashing kettle

Addition of hops for flavoring

Cooking of wort halts enzymatic activity, extracts flavor from hops, and kills the microorganisms present.

Removal

of hops

Addition of yeast culture

Wort ferments into beer.

Aging, filtering

or pasteurization, and bottling finish the process.

How to Make Hard Cider

http://www.motherearthnews.com/real- zmaz07onzgoe.aspx

food/fermenting/how-to-make-hard-cider-Nata de Coco

of Acetobacter xylinum, A pasteurianus and A

hansenii in coconut water medium enriched with

carbon and nitrogen

compiled into a thousand chain sugars or

cellulose fibers Of the millions of biomass grown

in the coconut water, will produce millions of

pieces of cellulose threads that eventually

appear solid white to transparent, called nata.

Nata de coco

Gram-negative, rod-shaped, strictly aerobic, acidophilic

bacteria able to oxidize ethanol to acetic acid,

and acetate and lactate to carbon dioxide and

water

Food Microbiology

• The Causes of Food Spoilage

– Food spoilage results from intrinsic or extrinsic factors

itself

handling of food

Table 25.2 Factors Affecting Food Spoilage

Food Microbiology

• The Causes of Food Spoilage

– Classifying foods in terms of potential for spoilage

Food Microbiology

• The Causes of Food Spoilage

– The prevention of food spoilage

Figure 25.4 Industrial canning

Food Microbiology

• The Causes of Food Spoilage

– The prevention of food spoilage

– Salt and sugar remove water from the food – Garlic contains allicin, which inhibits enzyme function – Benzoic acid interferes with enzymatic function

– Certain spices and herbs interfere with the functions of membranes of microorganisms

– Chemical preservatives can be purposely added to foods

Food Microbiology

• The Causes of Food Spoilage

– The prevention of food spoilage

– High temperatures desirable to prevent food spoilage

– Proteins and enzymes become denatured

– Low temperatures are desirable for food storage

– Cold slows metabolism and retards microbial growth

– Found in certain dairy products

– Symptoms include nausea, vomiting, diarrhea,

fever, fatigue, and muscle cramps

http://www.theguardian.com/world/2013/aug/05/fonterra-baby-formula-milk-bacteria