8/6/2019 FST 104 Mid2-W08A

1/6

1

FST 104 Winter 2008 Name______________________________Midterm #2 (March 5, 2008) Student ID #________________________

PLEASE RECORD YOUR TEST VERSION LETTER (shown on page 5 of the exam) and the correctanswers to questions 1-28 on a blue Scantron form UCD 2000 using a #2 pencil. (If you did notbring the Scantron form, circle the letter of the correct answer directly on the exam pages. Wewill grade your exam by hand and assess a penalty of ten points.) Please write your answers for

questions 29-32 directly on the exam in the space provided.

MICROBIAL CHARACTERISTICS. For questions 1-4, chose the correct letter of the group ofmicroorganisms from the list given immediate below. A letter may be used more than once. [3points each]

A. MoldsB. Lactic Acid BacteriaC. Endospore-forming BacteriaD. Enteric Family & RelativesE. Pseudomonas & Relatives

1. Members of this group can spoil food handled under unsanitary conditions.

2. Almost all members of this group possess peroxidase and superoxide dismutase butnone possess catalase.

3. Some members of this group produce cellulases.

4. Members of this group are normal flora of all plants and animals and are commonlyfound in large numbers on their exterior surfaces, even in the absence of handling.

MULTIPLE CHOICE [3 points each]

5. Which of the following would usually be considered a thermophile?A Campylobacter jejuniB Pseudomonas fluorescensC Bacillus coagulansD Staphylococcus aureusE Clostridium botulinum

6. Lowering the redox potential in food would be most effective in preventing growth forwhich of the following microbes?

A Lactic acid bacteriaB Desulfotomaculum nigrificansC Listeria monocytogenes

D E. coli O157:H7E All molds

7. Which of the following is a false statement regarding Intermediate Moisture Foods (IMF):

A IMF foods have an aw in the range of 0.60 to 0.85B No pathogen or spoilage organism can grow in IMFC IMF can be made by blending traditional ingredients such as chocolate or honeyD Use of humectants such as glycerol or sorbitol in IMF bind water without giving the sensation of drynessE No other treatment to IMF is needed to prevent the growth of dangerous anaerobes such as C. botulinum

8/6/2019 FST 104 Mid2-W08A

2/6

2

8. Which of the following is a false statement about food spoilage?

A Food spoilage occurs when microbes are present at a certain level, even if they havent grownB Food spoilage occurs not just because microbes are present but because they have grownC The initial level of contamination is an important contributor to the time it takes for spoilage to appearD Food that is "too clean" might allow pathogen growth before the food is rejected on sensory groundsE In the United States microbial growth causes more spoilage than does infestation by rodents and insects.

9. A company decides to add 0.12 g of sorbic acid per 100 grams of a soft drink with a pH =5. Which group would not usually be inhibited by this amount of sorbic acid?

A YeastsB MoldsC EnterobacteriaceaeD Spore-forming bacteriaE All of the above groups would be inhibited

10. Given the mixture of microbes commonly found in raw ground beef, which of the listedgroups would be the most likely spoilage agent for this raw ground beef, refrigerated at 7C in an O2-permeable wrapper?

composition = 0.4% soluble sugars, 15% protein, 20% fat pH = 6.5aw = 0.98 redox = +200 mV

A Pseudomonas & relativesB Enteric Family & relativesC Endospore-forming bacteriaD Lactic acid bacteriaE Molds

11. Assume that the ground beef in question 10 indeed becomes spoiled. If it is made intopatties, properly cooked to an internal temperature of 71 C (165 F) and then consumedimmediately, which of the following is likely to be a food safety threat?

A Listeria monocytogenesB E. coli O157:H7C Clostridium botulinumD Pseudomonas fluorescensE None of the listed organisms is likely to be a food safety threat under the conditions described

12. Given the mixture of microbes commonly found on fruit, which of the listed groupswould be the most likely spoilage agent for fresh apple juice that has turned alcoholic andfizzy (with gas bubbles) after several days in a sealed container at 15 C?

composition = 2% soluble sugars, 0.5% protein, 0.2% fat pH = 2.9aw = 0.98 redox = -200 mV

A Enteric Family & relativesB Endospore-forming bacteriaC Lactic acid bacteriaD YeastsE Molds

13. Which oxygen protective enzymes does E. coli possess?

A Has both catalase and superoxide dismutaseB Has both peroxidase and superoxide dismutaseC Has catalase but no superoxide dismutase

D Has peroxidase and uses Mn++ in non-enzymatic reactions to remove the superoxide radicalE Has no apparent oxygen protective enzymes

8/6/2019 FST 104 Mid2-W08A

3/6

3

14. Which of the following is a true statement?

A Pasteurization is almost always a treatment for 30 minutes at 146 FB Pasteurization is a process designed to destroy the most heat-resistant spoilage organism in all foodsC Commercial sterilization is a process designed to destroy all the microbes in a given foodD Commercial sterilization is a process designed to destroy the most heat-resistant enzyme in the foodE Commercial sterilization is actually a pasteurization with the C. botulinum endospore as the target

15. Pectinolytic spoilage organism that can cause "soft rot" of vegetables but not acidic fruit.

A Aspergillus flavusB Pseudomonas fragiC Erwinia speciesD Listeria monocytogenesE Bacillus stearothermophilus

16. What is the widest redox range over which facultative anaerobes can grow?

A Between -400 and -50 mVB Between -250 and +50 mVC Between +100 and +400 mVD Between -400 and +400 mV

E Above 400 mV

17. Attached is plot of data for growth of a microorganism. Based on this data, what is thegrowth rate of this microorganism? [3 points]

A 1.0 hB 1.2 h

C 0.22 h-1

D 0.58 h-1

E 0.69 h-1

18. Ground chicken in an O2-permeable wrapper became spoiled after 72 hours at 10 C.Assuming that 10 C is above Tmin and that 30 C is below Topt, how long would it havetaken the chicken to exhibit the same level of spoilage at 30 C? (Assume Q10 = 2).

A 9 hoursB 18 hoursC 36 hoursD 144 hoursE 288 hours

19. Which of the following would increase the pH of food (make it more basic)?

A Growth of E. coli on sugars in the absence of O2

B Growth of Aspergillus flavus on organic acids in the presence of O2C Growth of Pseudomonas fluorescens on protein in the absence of O2 but in the presence of NO3D A and BE B and C

8/6/2019 FST 104 Mid2-W08A

4/6

4

20. For a bacterium with only an aerobic mode of energy metabolism, which of the followingtreatments would stop bacterial growth and increase survival?

A Exposure to ozoneB Exposure to temperature above the maximum for growthC Exposure to temperature below the minimum for growthD Exposure to pH below the minimum for growthE C and D

21. If your goal was to inhibit the growth of Clostridium botulinum in a canned ham, whichof the following would be the most effective treatment?

A Ensure that the redox of the canned ham was lowered to -200 mVB Treat the canned ham with SO2 (sulfur dioxide a sulfiting agent)

C Treat the canned ham with chlorineD Treat the canned ham with NatamycinE Treat the canned ham with NO3 (nitrate)

22. One conclusion for the experiment we discussed in class (heat-treated Staphylococcusaureus) was that injured microorganisms in food:

A may not grow on selective media unless allowed time to recover

B may not grow on non-selective media unless allowed time to recoverC are not a major concern because they are effectively deadD will cause bacterial counts on selective media to be falsely highE actually survive better above Tmax than uninjured organisms

23. Bacteria can protect themselves from the damage caused by H2O2 with:

A catalaseB peroxidaseC superoxide dismutaseD Either A or BE Either B or C

24. pH below which a food is considered acidic for the purposes of determining the heattreatment necessary in canning.

A 1.5B 3.0C 3.7D 4.5E 5.5

25. With regard to the type of energy generating metabolism, what is the food sciencedefinition of an aerobe that we gave in class?

A Performs aerobic respiration; may also perform anaerobic respirationB Performs only anaerobic respirationC Performs aerobic respiration and fermentationD Performs only fermentationE None of the above are correct

8/6/2019 FST 104 Mid2-W08A

5/6

5

26. Which of the following does not contribute to the ability of a microbe (or particle) towithstand high temperatures?

A A higher proportion of unsaturated lipids in the cell membrane of a bacteriumB A higher proportion of saturated lipids in the cell membrane of a bacteriumC The most heat sensitive enzyme required under the given conditions of growthD The degree of protection of cell lipids by structures outside of the membraneE The absence of an envelope in naked viruses

27. Modified atmosphere packaging helps to preserve food by:

A Inhibiting the growth of dangerous anaerobes present in the foodB Killing the spoilage aerobes present in the foodC Increasing the poising capacity of the food to withstand changes in pH caused by microbial growthD Lowering the redox potential of the foodE Raising the redox potential of the food

28. Which of the following is a false statement?

A The concern with using NO3 or NO2 (nitrate or nitrite) as food preservatives is the formation ofnitrosamines, a suspected carcinogen, upon cooking the foodB Use of NO3 or NO2 can promote a color in cured meats that is often pleasing to consumersC Bacteria can acquire antibiotic resistance from other bacteria by plasmid transferD Antibiotics used in animal feed can promote animal growth and prevent disease, but at the risk ofselecting for antibiotic-resistant bacteria and causing an allergic response in some peopleE All are true statements

Name______________________________Student ID #________________________

For questions 29 and 30, fill in the blank with both the genus and species of the correctorganism. Here pathogen refers to ability to cause food-borne human illness [2 points each].

29. _____________________ This bacterial pathogen is the last to stop growing as aw is

decreased from 0.99 to 0.5.

30. ___________________ __ This bacterial pathogen is the last to stop growing as temper-ature is decreased from +30 C to -20 C (2 possible answers).

Here is a formula from your syllabus that is used to solve some heat-treatment problems:

DT2 = DT1 x 10([T1-T2]/Z)

31. Given below are hypothetical survival data obtained for a new species of Salmonellaheated at 70C. Determine the D value using the semi log paper.

Time held (minutes) Number of Survivors

2 8.0 x 105

4 1.3 x 105

6 2.8 x 104

8 4.0 x 103

8/6/2019 FST 104 Mid2-W08A

6/6

6

32. You have discovered a new pathogen in milk. Given the following D values obtainedfrom your new pathogen, determine the Z value using the semi-log graph paper. Indicate Zvalue in correct units :

Temperature D-value

50C 50

60C 1470C 3.580C 0.9

33. The legal pasteurization for milk is 30 minutes at 63 C. If you know that you will neverneed more than 5 logs of your hypothetical new pathogen, is the current legal pasteurizationsufficient for safety?

Test Version: A