The formula of Stubbs & More for the calculation of ‘lean meat content’ of meat products on the basis of their nitrogen content is discussed, in particular the factors 3.40 for beef and 3.60 for pork. The mean nitrogen content of fat‐free beef and pork is calculated from publications by different authors, who have analysed English, Dutch, American and German meat. The factor 3.60 in the Stubbs & More formula for pork proves to be higher than most of the values derived from this literature survey. The relation between the Stubbs & More factors and district of growth, age of animal and fat content of the meat is discussed. The nitrogen, fat and moisture content of 19 samples of fresh Dutch pork and of 19 samples of salted Dutch pork have been determined. The mean Stubbs & More (SM) factor for fresh Dutch pork is found to be 3.40; this is different by about 6% from the factor of 3.60 now in use. The mean factor found for animals of 5 1/2–6 months of age is the same as that for animals of 7–8 months. A slight correlation between SM factor and fat content seems to exist. The Yorkshire stock shows a lower mean factor than the ‘Veredeld Land‐varken’ stock. The loss of moisture and protein during the period of salting is calculated.
KOTES 101 Notes THE DETECTION O F SERINE AND THREONINE BY THECOMPOWNUS, whose molecules contain adjacent hydroxy and amino groups, such as serine and threonine, are de-aminated to enediols by alkaline hypochlorite, and these enediols yield a violet colour with 1 :%dinitroktlzene. METHOT) REAGENTS-reagent grade 1 :&dinitrobenzene in copper-free distilled water.have its available chlorine content checked occasionally. "Milton" is a convenient form of the reagent. PROCEDURE-To 1 ml of a neutral solution containing at least 1 mg of the amino-acid, add 2 rnl of the dinitrobenzene reagent, 5 drops of 20 per cent. sodium hydroxide solution, and 3 to 6 drops of 1 per cent. hypochlorite solution. Mix well and maintain the solution at room temperature. In a positive test a violet colour develops slowly within 10 minutes. A control containing no hypochlorite should be tested at the same time, to detect interference from preformed enediols. 1 :Z-DINITROBENZENE -ENEDIOL REACTION 1 :2-L)initrobenaene sozzstion, approxiniately 0-02 per cent.-A saturated solution of analytical This solution keeps indefinitely. Sodium hy@chZorite solution, 1 per cent.-The solution must not be strongly alkaline, and should The proprietary product known as RESIJLTS DELICACY-In the absence of interfering solutes, the test will detect free serine or threonine at concentra-An excess of hypochlorite must be avoided in testing diluteSerine is more reactive with hypochlorite than threonine, and gives an enediol reaction within Under similar conditions, Sensitivity is diminished by excess of other amino-acids, amines, ammonium ions, or other This interference can be overcome by tions as low as about 1 in 5000.solutions, as it tends to bleach the violet pigment.30 minutes in 0.1 N sodium hydroxide solution at room temperature. threonine gives no appreciable colour.
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