Download 2.7 helpful bacteria

Unit 02 - Student book
9/25/03
12:59 PM
Page 48
TECH CONNECT 2.6 QUESTIONS
(Page 115)
Understanding Concepts
1. UHT milk can be transported and stored without refrigeration. Bacteria have been destroyed in processing, and the
unopened container has a shelf life of 9–12 months. No additives or preservatives have been added, and the nutritional
value is identical to fresh milk.
2. pasteurization: the process of heating milk to a specific temperature for a specific period of time in order to kill
microorganisms that could cause disease, spoilage, or undesired fermentation
homogenization: the process of making homogeneous or uniform in consistency; with milk, the emulsification of its
fat content
sterilization: the process of making milk free from live bacteria or other microorganisms
standardization: the process of comparing with a standard; an acknowledged measure of comparison for quantitative
or qualitative value
3. Aseptic packaging is free of pathogenic organisms. The contents will remain this way until the packaging is opened.
Aseptic packaging is a safe way of transporting and storing a perishable product.
Making Connections
4. Evaluation of UHT technology:
Advantages of UHT Technology
Disadvantage of UHT Technology
– provides a safe source of protein in tropical
areas where refrigeration is not available
– allows the consumption of milk in wilderness
situations where packing fresh milk is not feasible
– can be used in emergency or survival kits or shelters
– packaging is compact and easy to transport and store
– requires expensive equipment, skilled workers,
and expertise in production techniques
– product is more expensive than fresh milk
– packaging may not be biodegradable
– some problems with flavour have contributed
to slow consumer acceptance
– can result in the loss of vitamins and amino acids
5. Any group that wants to consume milk over a period of time without access to refrigeration would benefit from UHT
processing: Guide and Scout camps; wilderness tour groups; boaters and campers. Packets of UHT milk are useful in
emergency ration kits. The Canadian and American armies use this product.
6. One in four Canadian workers is employed, either directly or indirectly, in agriculture and food production. Careers in
the dairy area may involve processing and manufacturing, packaging and handling, distribution and retailing, market
research, product development, food quality management, or dairy farm management. Several colleges and universities
in Canada have co-op programs, internships, and work placements to provide hands-on experience in agriculture and food
science. Extensive information is available on an agriscience link from the Nelson Science Web site. More than
25 specific careers in the diary industry are listed, along with their National Occupation Classification (NOC) Codes. The
Human Resources Development Canada Web site at http://jobfeatures.ca/noc/browse-occupations-noc.shtml provides
details of each coded career.
2.7 HELPFUL BACTERIA
SECTION 2.7 QUESTIONS
(Page 117)
Understanding Concepts
1. E. coli bacteria act as recyclers in the human intestine, releasing digestive enzymes and breaking down organic matter.
E. coli may also be involved in probiotics. E. coli is a normal resident of the large intestine in healthy people. It is a
type of probiotic organism because it crowds out disease-causing bacteria. E. coli also makes vitamin K, which
humans need to be healthy.
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Unit 2 Student Book Solutions
NEL
Unit 02 - Student book
9/25/03
12:59 PM
Page 49
2. Key information in this section:
Pollution control
bioremediation uses
bacteria to consume toxins
in the environment
Recyclers
saprophytes release digestive
enzymes to decompose
organic matter
HELPFUL BACTERIA
Probiotics
some bacteria help maintain
health and may prevent
disease
Industry
bacteria make enzymes
which are used to produce
consumer products
Applying Inquiry Skills
3. As organisms metabolize, heat is released. If the temperature of compost relates directly to bacterial activity, the
bacteria were most active on Day 3.
Making Connections
4. When bacteria metabolize, enzymes are released. In nature, these enzymes promote decay of organic matter. In industry,
these enzymes are harvested to produce consumer products. Bacterial enzymes are essential in each situation.
5. Microorganisms have been used for centuries to produce food and wine. The many exotic cheeses we enjoy today
would not be available without controlled use of bacteria. The key word here is “control.” A live organism may be
unpredictable when even small changes are made during processing. Good safety and quality control procedures must
be in place in all industrial procedures.
Exploring
6. Industry uses bacteria to make many consumer products. Some examples additional to those listed in Table 1 (p. 117 of
the Student Text) are: Aspergillus niger (production of citric acid, which is used in soft drinks, candies, inks, engraving
materials, and a variety of pharmaceuticals such as anticoagulants and effervescent tablets like Alka-Seltzer);
Lactobacillus bulgaricus (makes lactic acid, which is used to preserve foods, finish fabrics, prepare hides for leather,
dissolve lacquers, and ferment a variety of foods); E. coli and Enterobacter aerogenes (produce lysine, used in production of breads, breakfast cereals, and other foods); Bacillus subtilis and Aspergillus oryzae (produce the enzyme
protease, used in liquid glues, laundry presoaks, meat tenderizers, drain openers, and spot removers); Ashbya gossypii,
Pseudomonas, Propionibacterium, and Streptomyces (used to produce vitamins B2 and B12).
A sample report on the commercial production of yogurt:
(a) Consumer product (photo of yogurt should be included here):
Yogurt is a dairy product produced by the controlled fermentation of milk. Two species of bacteria ferment the sugar
in milk (lactose) to acid (lactic acid). Production of acid causes the formation of the characteristic curd in yogurt. Acid
also restricts growth of bacteria that cause spoilage and food poisoning. For this reason, the storage capacity of yogurt
is about 10 days under refrigeration, compared to only a few days for fresh milk.
(b) Bacteria involved (diagrams of shapes should be given):
Streptococcus thermophilus and Lactobacillus lactis subspecies cremoris are the two types of bacteria used in yogurt
production. S. thermophilus is a Gram-positive, nonmotile, nonsporulating coccus (0.2 2.5 µm) found in chains. It
is a microaerophilic, aerobic organotroph. L. lactis is a Gram-positive, usually nonmotile, nonsporulating bacillus
(0.8 2 µm) found singly or in variable-sized clusters. It is an anaerobic organotroph that must obtain energy exclusively by substrate-level phosphorylation. Both bacteria are homofermentative—they produce lactic acid as the sole
product of fermentative metabolism. Yogurt quality is determined by the correct balance of the two bacteria. A master
culture is formed by growing a dried culture on pasteurized milk. Refrigerated portions can be used to inoculate the
milk, and the last portion can be re-inoculated into milk to form a new master culture. With good hygiene practices,
the process can continue for weeks; eventually undesirable bacteria will contaminate the culture and it must be
replaced. Spoilage by bacteria or moulds and maintenance of correct incubation temperature are two potential problems in making yogurt.
NEL
Section 2.7
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Unit 02 - Student book
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12:59 PM
Page 50
(c) Steps for the commercial production of stirred yogurt:
1. Heat milk to 85–95°C for 15–30 min.
2. Homogenize milk.
3. Cool milk to incubation temperature.
4. Add bacterial starter.
5. Incubate mixture at 40–46°C for 4–5 h (until the pH has fallen to around 4.3).
6. Stir thickened yogurt and cool to 5°C.
7. Add fruit, flavourings, colourants (if required).
8. Pack and transport yogurt, keeping it refrigerated.
(d) Variations: Yogurt can be either set or stirred. Stirred yogurt is fermented in bulk, stirred, then dispensed into pots. For
set yogurt, inoculated milk is poured into pots and fermented in place. Thoroughly cleaned fruit and blanched nuts
may be added as flavouring. In some countries, a layer of fruit syrup is placed on top of set yogurt. In other areas, a
thicker stirred yogurt is popular. This is made by adding dried skimmed milk to the original milk before pasteurizing.
Sometimes, other thickeners (starch or pectin) are used.
2.8 CASE STUDY: HARMFUL BACTERIA
CASE STUDY 2.8 QUESTIONS
(Page 119)
Understanding Concepts
1. Symptoms of E. coli O157:H7 poisoning include vomiting, cramps, bloody diarrhea, fever, and death in some cases.
2. Sources of E. coli O157:H7 contamination include ground beef, processed meats, sprouts, leafy green produce, unpasteurized milk and juice, and contact with cattle. Drinking inadequately chlorinated water or swimming in contaminated
lakes or pools is a potential source of exposure. The organism is easily transmitted from person to person.
3. Graphic organizer for Table 1 on page 119 of the Student Text:
Lactobacillus
souring of milk
Streptococcus
strep throat, scarlet fever,
pneumonia, food spoilage,
blood infections, eye infections
Staphylococcus
boils, food poisoning, skin
infections, pneumonia
Clostridium
botulism,
tetanus,
gangrene
Pseudomonas
food spoilage, gasoline spoilage,
blood infections, eye infections
Bacillus
destruction of
silkworms,
tuberculosis,
anthrax
Spirillum
syphilis
coliform bacteria
pollution of water sources, soft rot in
plants, gastroenteritis, dysentery
Applying Inquiry Skills
4. The graph shows that E. coli cases in Canada rose exponentially from 400 cases in 1985 to 2400 in 1989, fell to 1600
during 1990, rose to 1800 in 1991, dropped to 1000 in 1994, and rose to 1300 by the end of the test period. Awareness
of the problem likely led to better tracking and recording practices, early recognition of symptoms, and prompt
medical attention. Government legislation and practices involving water testing and treatment may have taken effect
since 1989. Weather may play a role, considering that bacteria multiply at optimum temperatures. Because the disease
is readily transferable, one case quickly turns into others, so it is unlikely that a flat line will appear on the tracking
graph, despite best attempts to eradicate this infection.
Making Connections
5. Government legislation on testing and treatment of municipal drinking water, proper chlorination of water, and maintenance of heath standards in public pools can prevent E. coli contamination. People must be vigilant: cook hamburger
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Unit 2 Student Book Solutions
NEL