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Appendix 4

Examples of procedures for the preparation of analytical samples

Root vegetables

Food sample collection procedure: Replicate purchases of approximately 1 kg each were made in the towns that were major distribution centres in a country. The places of purchase in the town were randomly chosen by volume of sales from the various types of outlet (supermarket, greengrocer, farmgate stall, etc.)

Laboratory procedure:

1. Opposing quarters of each purchase diced quickly in a domestic food processor and mixed quickly in a bowl with a plastic spatula

  1. 2 20 g taken into metaphosphoric acid for immediate vitamin C analysis
  2. 2 5 g taken into hot 80% v/v ethanol for sugars, starch and dietary fibre analysis
  3. 2 10/20 g (larger portion if food is very low in folate) taken into 1 percent w/v buffered ascorbate for folate analysis
  4. large portions taken for ashing for inorganic constituents, analysed over a period of weeks
  5. analytical samples freeze-dried and stored for amino acid analyses
  6. remaining material mixed, diced, frozen, stored at –20 C and analysed for remaining B vitamins within two weeks

2. Remaining quarters sliced, homogenized and blended thoroughly together

  1. 2 10 g taken for overnight moisture analysis.
  2. remainder frozen, stored at –20 C, and analysed for total nitrogen, phosphorus, chloride, sulphur, fat and carotenoids

 Meat

Example: Twenty meat cuts purchased, two from each of ten regions; purchases distributed between butchers and supermarkets in the ratio 7:3, evenly distributed throughout the regions. One cut from each region remained to be analysed raw; one from each region to be analysed grilled.

Raw

Each cut weighed and measured, including width of superficial fat, then dissected into edible (fat and muscle) and inedible (bone and gristle) portions, weighed separately.

1. The ten muscle samples were chopped coarsely and mixed thoroughly together in a bowl

(a) 100 g removed, deep-frozen and crushed; crushed sample shaken to mix it further

(i) 2 20 g taken for ashing and analyses of inorganic constituents

(ii) remainder stored at –20C in heat-sealed polythene bag with minimum headspace for check analyses

(b) remaining fresh mix minced and mixed thoroughly

(i) 2 10 g taken for moisture analysis

(ii) 2 50 g heated with alcoholic KOH solution and frozen for retinol analysis

(iii) 2 50 g taken immediately for thiamin analysis

(iv) analytical samples stabilized with an antioxidant and stored at –30C for fatty acid analysis

(v) analytical samples deep-frozen for other B vitamin analyses (performed within two weeks), fat, total nitrogen, other minerals, vitamins D and E

(vi) cholesterol and other sterols stored at –30C in sealed container under nitrogen

2. The ten fat samples were treated similarly.

Cooked

Cuts were weighed before and after grilling, then treated in the same way as raw cuts, with lean and fat being analysed separately (Paul and Southgate, 1977). 


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