National Postgraduate Entrance Examination — Food Science and Engineering

China · Ministry of Education (national papers) and admitting universities (specialist papers) · pg · unverified source

11practice questions written to this syllabus
3subjects

Format

Unverified. National papers in politics and a foreign language, plus university-set specialist papers that for food science commonly cover food chemistry, food microbiology or food engineering principles.

Over the years

Unverified: only the official postgraduate admission portal home page was confirmed. Specialist papers differ by university.

Official source: https://yz.chsi.com.cn/

Subjects this exam draws on

Mathematics for Food Science & Engineering1 questionsGeneral Microbiology8 questionsPrinciples of Food Science & Food Preservation2 questions

Five practice questions, worked

Original questions written to this exam's published syllabus and pattern. Not past papers.

1. In principal component analysis of NIR spectra, the eigenvalues of the covariance matrix are 6.0, 3.0, 0.6 and 0.4. What fraction of total variance do the first two components explain?

  1. 60%
  2. 95%
  3. 75%
  4. 90%
Answer and working

D. 90%

Total variance is the sum of the eigenvalues (the trace): 6.0 + 3.0 + 0.6 + 0.4 = 10.0. The first two explain (6.0 + 3.0)/10 = 90%. 60% counts only the first component; 75% divides 9 by 12; 95% adds the third component.

Mathematics for Food Science & Engineering · Eigenvalues, eigenvectors and the Cayley-Hamilton theorem

2. Using the relation d = 0.61 λ / NA, what is the resolution limit for green light of 550 nm with an objective of numerical aperture 1.25?

  1. 268 nm
  2. 220 nm
  3. 440 nm
  4. 721 nm
Answer and working

A. 268 nm

d = 0.61 × 550 ÷ 1.25 = 268.4 nm. 220 nm uses the Abbe form λ/(2NA), not the formula stated; 440 nm is λ ÷ NA without the 0.61 factor; 721 nm divides by 0.61 instead of multiplying.

General Microbiology · Microscopy: light, phase-contrast, fluorescence and electron

3. What is hysteresis in moisture sorption?

  1. Water activity always equals moisture content divided by one hundred
  2. The isotherm moves to higher aw when temperature rises, at the same moisture content, in all foods
  3. The monolayer value equals the moisture at an aw of exactly 0.5 for every food
  4. Adsorption and desorption isotherms differ, so moisture at a given aw depends on direction
Answer and working

D. Adsorption and desorption isotherms differ, so moisture at a given aw depends on direction

At the same aw a food usually holds more water on desorption than on adsorption. Temperature effects on isotherms are a separate phenomenon.

Principles of Food Science & Food Preservation · Water activity and its relation to spoilage

4. D at 121 °C is 0.2 min and D at 111 °C is 2 min. The z-value is:

  1. 5 °C
  2. 1.8 °C
  3. 10 °C
  4. 20 °C
Answer and working

C. 10 °C

z = (121 − 111) ÷ log(2/0.2) = 10 ÷ 1 = 10 °C. 1.8 subtracts the D values.

General Microbiology · Control of microorganisms: physical and chemical agents and death kinetics

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