Name: ______

FDSC 400: Exam 1

Answer all questions. There are only 50 min available for this exam so make an effort to work quickly and answer all questions.

Question / 1 / 2 / 3 / 4 / 5 / 6 / 7 / 8 / 9 / 10 / 11 / 12 / 13 / 14
Points available / 14 / 2 / 18 / 6 / 10 / 4 / 4 / 8 / 4 / 6 / 6 / 2 / 4 / 12
Points gained
  1. Milk is usually thermally processed to kill bacteria. Unfortunately the vitamin thiamin naturally present in the milk is also readily thermally inactivated and heating means a nutritional loss. The options are to either (i) process for a long time at a lower temperature or (ii) heat to very high temperatures for a shorter time. The different heating times at each temperature have been calculated to give similar degrees of sterility (elimination of bacteria) to the milk but knowing the activation energy for thiamin destruction is 30 JK-1mol-1 and the activation energy for spore destruction is 60 JK-1mol-1 explain which process is preferred and, using your knowledge of the Arhennius equation, why.

(14 points)

  1. The number of bacteria in a food doubles every 10 mins. What is the order of the growth “reaction”?

(2 points)

  1. Briefly define/explain the meaning of the following terms and provide a food example of each

(2 points for each definition, 1 for each example)

Definition / Example
Oil-in-water emulsion
Colloid
Supersaturation
A plasticizer
A foam
Nucleation
  1. Cotton candy is made by melting sucrose then spinning the liquid through narrow nozzles into thin strings. What state is the sucrose in cotton candy? How and why does it change when left in a moist environment for even a relatively short period of time?

(6 points)

  1. Moisture diffuses from raisins to the wheat flakes in a breakfast cereal.
  • What is the driving force for the diffusion?
  • The solutions proposed to this problem are either to add glycerol to the raisins or coat them with a layer of oil. Why would each method work?

(10points)

  1. True or false: Crystals are amorphous solids.

(4 points)

  1. Sketch water molecules packed around a sodium ion

(4 points)

  1. Assuming a first order reaction, sketch on the following axes the degradation kinetics of chlorophyll in pea puree at a high and a low temperature. What are the units for a first order rate constant?

(8 points)

  1. Chemical assays show the carboxylic acid on hypothetic acid is completely protonated at pH 2. Based on that single measurement, what can you deduce about the pK of hypothetic acid?

(4 points)

  1. Sketch a diagram to illustrate the difference between flocculation and coalescence of emulsion droplets

(6 points)

  1. To keep potato chips crisp you want to store them at as low an aw as possible – why might you not want to store too low?

(6 points)

  1. Assuming no creaming, which would be more viscous - an emulsion containing 15% by volume milkfat in 1 m droplets or a foam containing 15% by volume air in 1 mm bubbles?

(2 points)

  1. Why do bubbles rise to the surface of Guinness slower than they rise to the surface of a light beer? (The beers are of very similar viscosity).

(4 points)

  1. You are seeking to develop a lab protocol run an accelerated shelf life test on a nutritional bar for refugee populations. It seems the limiting factor is the amount of folic acid in your sample. Your technician proposes a protocol

“We will take the bars, grind them up and put them in Petri dishes in the lab. We will store some at 100°C, some at 150°C and some at 200°C. Every few weeks we will take a sample and measure the vitamin content by standard methods. From that data we can calculate the rate constant of the reaction at each temperature. Plotting rate constant as a function of temperature we can fit a straight line to the data and extrapolate to calculate the rate at 0°C and thence the shelf life.”

There are at least three significant errors in this protocol. Explain what they are and why they will lead to misleading results.

(2 for each reason, 2 for explaining why each is a problem)

  1. Problem 1
  1. Problem 2
  1. Problem 3