Lecture 18

Question 1

What are the characteristics of psychotrophic bacteria? What do they do to cause spoilage in milk?

Answer 1

• Grow at less than 7 degrees celsius
• aerobic and gram -
• spoil raw and pasteurized milk
• produce lipolytic and proteolytic enzymes which break down fats and proteins leading flavor defects and proteins

Question 2

Whats and example of a psychotrophic species of bacteria which produce spores in milk and can survive pasteurization? What are some of it’s characteristics?

Answer 2

B. Cereus. It produces spores post pastuerization, yellow buttons at the bottom of the container. Bacillus Cereus forms lots of spores in milk which convert vegatitive cells after pastuerization and release proteases which break down proteins leading sweet curdling and lipases which break down fat leading to bits of cream damage.

Question 3

How long can pasteurized milk stay on the shelf?

Answer 3

12-20 days

Question 4

What is the process that spoilage microbes undergoe to spoil milk?

Answer 4

Spoilage microbes use up glucose in milk and then begin to oxidize lactose to produce lactobionic acid, ketones and alchohol causing bad milk flavor.

Question 5

How does psuedomana and other pyschotrophic bacteria work to spoil milk?

Answer 5

They produce proteases and lipases during their late exponential and stationary phases of growth, at a population greater than 6logCFU/ml to do so.

Question 6

Describe 2 main types of proteins found milk and describe their characteristics

Answer 6

1) casien: Proteins in the form of michelles or in fat globules is readily broken down by proteases and lipases.
2) Whey: Protein can not be broken down by proteases

Question 7

What are fats in milk in the form of? What are their main forms?

Answer 7

They are in the form of triglycerides and their main forms are palmitic acid, stearic acid, oleic acid, myrisitic acid.

Question 8

How do lipases produce bad smells?

Answer 8

They break down fats to produce low molecular weight short chain fatty acids which produce bad smells

Question 9

Spoilage that milk undergoes?

Answer 9

1) Lactic acid: combine with small amounts of saturated fatty acids to produce sour taste and bad smell
2) Clostridium and coliform species: Produce gases
3) Certains species of bacteria which produce and release polysaccharides: cause ropey slime layer to develop on milk

Question 10

What are pencillium and geotrichium? What products are they accepted by consumers in?

Answer 10

They fungi or multicellular mold which can produce a variety of consumer acceptable cheeses but spoil milk.

Question 11

What are fruits and vegetables defined as?

Answer 11

Fruits: The seed bearing organs of plants
Vegetables: All othe edible portions of plants beside the seed bearing organs

Question 12

How does the microbiota of soil impact plant health.

Answer 12

It influences what microbes make up the plant micrbiota and whether the plant will get infected and die.

Question 13

How do polyphenols impact the body and what foods are they found in?

Answer 13

Polyphenols decrease the risk for chronic disease, contain ability to fight microbes and viruses, change the types of microbes in the human gut microbiota, defend against environmental stresses, and fight microbes.

Question 14

What is the purpose of washing vegetables with chlorine water? How do you prevent the growth of clostridium botilinunum in vegetables?

Answer 14

• Chlorine kills bacteria in the water to prevent it from getting onto the vegetables when they are washed.
• Vegetables must be subjected to a high temperature and pressure in an effort to kill C. botulinum spores.

Question 15

How are fruits different from vegetables? What kinds of microbes grow on fruits?

Answer 15

Fruits are more acidic and they contain a lower aw to fight against spoilage microbes. Osmolphillic yeast and xerotolerant mold grow on fruits

Question 16

The two types of spoilage are active and passive spoilage

Answer 16

Active spoilage is a result of direct pathogen invasion of microbes

Passive spoilage is the result of opportunistic microbes breaking into plant wounds and cuts

Mechanisms:
insects, environmental stress can cause breakages
people can damage plants by not properly picking or handling them
Plant pathogenic molds produce degrative enzymes such as pectinases and cellulases which cause breakages in plants allowing microbes to enter reach internal cells and extract nutrients

Question 17

Climatric vs. nonclimatric

Answer 17

Climatric states: Fruits and vegetables that contibue to ripen post harvest and are more perishable to spoilage or senesence caused by degradable enzymes which damage cellular structures making fruits and vegetables more susceptible to microbial spoilage.

Nonclimatric state: Fruits and vegetables that stop ripening post harvest and not as prone to spoilage.

Question 18

What is Food spoilage?

Answer 18

It is the microbial, chemical and enzymatic activity which leads to damage of food or make food unappealing to a consumer. Microbes produce metabolites that cause racid odors, changes in color and texture, bad tastes, and slime and work by breaking down a food.

Question 19

Do all foods spoil at diff time lengths/rates? Why or why not?

Answer 19

No because different levels of microbes inhabit different foods.

Question 20

Which contain more bacteria? Shellfish or fish

Answer 20

shellfish because they are filter feeders.

Question 21

How are off odors triggered? How much bacteria is required?

Answer 21

They are triggered through the production of gas phase microbial compounds which include ketones, aldehydes, and alchols. 10^8CFU/ml

Question 22

What are the reactions involved in producing off colors? How much bacteria is required

Answer 22

• hydrogen sulfide (H2S) + heme in myoglobin=Sulphomyoglobin (green pigment)
• hydrogen peroxide(H2O2) + heme in myoglobin=several green pigments.

-10^7CFU/ml is required

Question 23

How many CFU/cm^2 is required to make polysaccharides secrete a ropy slime layer

Answer 23

10^8CFU/cm^2

Question 24

Low aw favors what microbes?

Answer 24

yeasts and molds

Question 25

What are the mechanisms that lead to food spoilage

Answer 25

1) o2 reacts with unsaturated fatty acids to produce aldheydes and ketones which cause bad smells and tastes due to oxidative rancidity
2) bacterial proteases and lipases release enzymes which break down fats and proteins leading to bad smells and tastes
3) Preslaughter Stress:
- Stressed out animals deplete their glycogen supply so not a lot of lactic acid bacteria grow and this causes meat to become more basic or exceed a pH of 5.6 leading to dark, firm and dry meat.
- If animals are slaughtered right after vigorous excercise, lactic acid bacteria builds up in their muscles causing a meat to develop at a pH less than 5.6 making the meat undergoe a soft pale color and texture which turns off consumers

Question 26

What are the factors needed to control bacterial growth in fleshy food products?

Answer 26

-Rinses and sprays eliminate physical and microbial contaminants
-Temperature: Most important. Must regrigerate food product to slow down spoilage
-Modifed atmosphere packaging
-Increases lag and stationary phase time of bacteria
-O2 sometimes used to maintain myoglobin but levels need to be balanced to prevent spoilage
-Irradiation of .2kg-.8kg can inactivate 90% of vegatative cells and 3.5 kg or more can inactivate 90% of clostridium spores
Unattractive in eyes of consumer
-High Pressure Processing
-greater than 400MPa for 3-15min will lead to a greater than 5 log reduction in microbes
-