Soy protein is the vegetable protein that is most frequently used in meat products. Accordingly, detection and determination procedures have mainly been focused on soy proteins. Cereal proteins received far less attention analytically, let alone the less conventional vegetable proteins. Every method published has only a limited applicability, determined by both the type of soy preparation concerned and the heat processing of the sample. The methods may be divided into five categories. 1. Chemical methods are based on analysis of tracer substances accompanying the soy proteins by nature. Their specificity is rather low; other vegetable proteins may contain the same substances. Soy flour, concentrates and texturates respond quantitatively, and sometimes even qualitatively, different. The methods are almost useless for isolated soy proteins. 2. Microscopic methods may allow rapid detection of soy products except isolates. They may be used for quantitation purposes. However, representative results will only be secured at the expense of time and labor. 3. Electrophoresis methods rely on the recognizability of soy protein bands in the pherogram pattern. Field of application and specificity are satisfactory. Efficient media enable complete solubilization of soy protein from meat products, if not severely heat‐processed. 4. Immunochemical methods, although very sensitive and specific, are only suitable for detection purposes, provided the sample temperature did not exceed 100 C during processing. This holds, of course, only true if the soy produced used is not excessively heated during preparation. 5. Methods based on amino acid composition or sequence are based on computer matching of the amino acid pattern of the meat product sample with those of varying mixtures of all proteins that could be contained in the sample.
A method was developed for the selective extraction of fat from ruptured fat cells in cornminuted sausage batters. It was found that over a wide range of chopping temperatures (4-28°C) the level of extractable fat in an unheated meat batter is significantly correlated (P < 0.001) with the percentage of fat separation after heating to 80°C or 120°C. The results indicate that the integrity of the fat cells in a sausage batter rather than the availability of released fat for emulsification determines the heat stability of the batter.
The results are reported of a collaborative study in which five meat products containing different known levels of one of five different commercial soya ingredients, together with a blind duplicate and a blank, were analysed for soya protein by 26 laboratories in 10 European countries. Two techniques were tested: the sodium dodecylsulphate-polyacrylamide gel electrophoresis (SDS-PAGE). method of Armstrong et al. (J. Food Technol. 1982, 17, 327-337) and the enzyme-linked immunosorbent assay (ELISA) method of Hitchcock et al. (J. Sci. Food Agric. 1981, 32, 157-165). It was concluded that both methods give zero blanks and similar interlaboratory variances; SDS-PAGE gives more repeatable intralaboratory data, while ELISA gives more accurate determinations. The results reflect significant progress to an interim stage of methodology development; both methods are useful, but require further refinements to make them generally acceptable for control purposes.
An improved procedure for the determination of protein-bound nitrite (PBN) in meat products, based on Mirna's method, is described. The results obtained with this modification are significantly higher, and have a lower variation coefficient, than those provided by the old procedure. This is demonstrated by comparison of the analytical results.
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