Food Analysis Methods Questions and Answers

Answer: A

The first analysis is acid-insoluble ash content.

Acid-insoluble ash is the residue left after ashing the sample and boiling the ash in dilute hydrochloric acid. It is mostly silica, so it measures the sand, soil and dust that contaminate spice and herb powders. That is the direct measure of physical cleanliness, and spice standards set a limit on it.

Pesticide residues and mycotoxins are chemical safety tests, done after cleanliness is established and needing more elaborate methods. Volatile oil content measures quality, the strength of flavour and aroma, not whether the powder is clean.

Answer: D

The soup provides 118 kcal.

Use the energy factors for each nutrient: 4 kcal per gram of carbohydrate, 4 kcal per gram of protein and 9 kcal per gram of fat. Water supplies no energy.

\[ \begin{aligned} \text{carbohydrate} &= 20 \times 4 = 80 \\ \text{protein} &= 5 \times 4 = 20 \\ \text{fat} &= 2 \times 9 = 18 \\ \text{total} &= 80 + 20 + 18 = 118\ \text{kcal} \end{aligned} \]

80 kcal counts only the carbohydrate. 108 kcal comes from counting fat at 4 kcal a gram instead of 9, and 110 kcal is a near miss with no nutritional basis.

Answer: D

Fat is detected with the ethanol emulsion test.

The sample is shaken with ethanol, in which fats dissolve, and the liquid is then poured into water. If fat is present it comes out of solution as fine droplets, giving a cloudy white emulsion.

The other tests detect other nutrients. The iodine test turns blue-black with starch. Benedict's test gives a brick-red precipitate with reducing sugars. The biuret test turns violet with proteins.

Answer: A

The description is that of column chromatography.

Chromatography is classified partly by the shape of the stationary bed. In column chromatography the stationary phase is held in a narrow tube, the column, and the mobile phase is forced through it under pressure (or allowed to flow by gravity). The definition in the question is the standard definition of this form.

In planar chromatography, such as paper and thin-layer chromatography, the stationary phase is a flat layer, not a tube. Liquid and gas chromatography are named after the state of the mobile phase, and each can be run in a column, so neither name describes the tube arrangement the question is asking about.