Original questions written to this exam's published syllabus and pattern. Not past papers.
1. For the system Ax = b with three unknowns, rank(A) = 2 and rank([A | b]) = 2. What can be said about its solutions?
There is no solution, because the rank is less than three
There is a unique solution, because the two ranks are equal
There are exactly two solutions, one for each independent row
There are infinitely many solutions, with one free parameter
Answer and working
D. There are infinitely many solutions, with one free parameter
Equal ranks mean the system is consistent; the rank r = 2 is less than n = 3, so there are infinitely many solutions with n − r = 1 free parameter. Equal ranks give a unique solution only if the rank equals the number of unknowns. A linear system never has exactly two solutions.
Mathematics for Food Science & Engineering · Matrices, determinants, rank and systems of linear equations
2. The direct epifluorescent filter technique (DEFT) for raw milk counts:
Gas bubbles produced in Durham tubes after inoculating lactose broth
Electrons scattered by cells on a filter coated with gold in a vacuum
Fluorochrome-stained cells retained on a membrane
Colonies that grow on a membrane placed on agar for 48 hours at 30 °C
Answer and working
C. Fluorochrome-stained cells retained on a membrane
DEFT filters the sample, stains the cells on the membrane and counts them by epifluorescence within about an hour. Counting colonies after incubation is membrane filtration plating.
General Microbiology · Microscopy: light, phase-contrast, fluorescence and electron
3. Biscuits in a poorly sealed pack become soft. What type of deterioration is this?
Enzymatic: lipase action on the fat
Chemical: Maillard browning in storage
Physical: moisture gain from humid air
Microbial: growth of yeasts on the biscuit
Answer and working
C. Physical: moisture gain from humid air
Low-aw biscuits absorb water from humid air, losing crispness; this is a physical change controlled by packaging.
Principles of Food Science & Food Preservation · Causes of food deterioration: microbial, enzymatic, chemical, physical and pest
4. Which vitamin is most often used as an indicator of how severe a thermal or drying process has been?
Vitamin D, because its loss is proportional to the heat applied in any process
Vitamin C, because it is among the most labile to heat, oxygen and leaching
Niacin, because it is destroyed rapidly by light, heat and alkali in all foods
Vitamin B12, because it is the most heat-stable vitamin and so easiest to track
Answer and working
B. Vitamin C, because it is among the most labile to heat, oxygen and leaching
Ascorbic acid is easily destroyed and leached; if it is retained well, other nutrients usually are too. Niacin is one of the most stable vitamins.
Human Nutrition & Nutritional Quality of Processed Foods · Water-soluble vitamins: functions, sources and deficiency
5. Which of these organisms is a psychrotroph that can grow at refrigeration temperatures?
Clostridium perfringens
Listeria monocytogenes
Staphylococcus aureus
Campylobacter jejuni
Answer and working
B. Listeria monocytogenes
L. monocytogenes grows close to 0 °C. Campylobacter does not grow below about 30 °C, C. perfringens needs warm temperatures, and S. aureus does not grow at about 7 °C or below.