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when hemagglutination is used for determining milk protein in liver sausages (50).

Another immunological method used for food analysis is the quantitative precipitin technique. An insoluble complex forms when soluble food antigens react with specific antibodies in solution. The precipitate is further analyzed by protein assay (30). Methods based on the turbidimetric or nephelometric analysis of suspended antigen-antibody complexes have become more popular (51-55). These methods are also automated for clinical use (31).

A large number of immunodiffusion assays have been developed for analysis of nonmeat proteins. A detailed list of references is provided in Table 1. It should be noted that although these methods have found widespread use for soy analysis there are a number of disadvantages encountered (77). (1) The diffusion in gel method is slow and is only suitable for limited numbers of samples. (2) Low recoveries of protein antigens are common because mild sample extraction conditions are used to decrease loss of protein antigenicity (3) None of the antisera developed are able to recognize all of the soy protein derivatives. In addition, due to the low aqueous solubility and low molecular charge of gluten proteins, rocket immunoelectrophoretic methods have not found wide application in gluten detection. One qualitative method has been described (78). The classical methods based on antigen diffusion in gels are designed for optimal use with water-soluble proteins. Gluten and related cereal storage proteins are insoluble in aqueous buffers. Acidic buffer conditions have been used to analyze gluten extracts by double immunodiffusion (79) and 3 M urea containing gels have been used for gluten analysis by immunoelectrophoresis (80). Isotopic and nonisotopic ias have been described for nonmeat protein additives (Table 2).

An immunofluorescent method was described for detecting soy protein in meats. It was labor intensive with respect to sample preparation drying and fixing (81). The first RIA and EIA for soy protein determination were elucidated in the early 1980s (82,83). Another RIA was developed that detected native and formaldehyde-treated soy protein (83). There have been a number of EIAs developed for soy detection (Table 2). For example, a two-step antigen competition immunoassay was developed (83). The same investigators then analyzed a set of model beef burgers that contained known quantities of particular soy isolate (86). The effectiveness of the method has been tested in two collaborative studies (116,117). When compared to

Table 2. Isotopic and Nonisotopic Immunoassays for Detection of Nonmeat Proteins

Assay

Sample

Ref.

Fluoroimmunoassay

Soy in cooked meats

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