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.)
1. Opposing quarters of each purchase diced quickly in a domestic food processor and mixed quickly in a bowl with a plastic spatula
2. Remaining quarters sliced, homogenized and blended thoroughly together
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.
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 –20°C 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 –30°C 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 –30°C in sealed container under nitrogen
2. The ten fat samples were treated similarly.
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).