Colorimetric analysis of protein sulfhydryl groups in milk: applications and processing effects.
Methods for protein sulfhydryl (SH) group analysis in food systems have been largely overlooked. Nevertheless, changes in SH group concentration affect both physical and nutritional characteristics of high protein foods and ingredients. Food scientists and technologists require improved understanding of protein SH chemistry in order to design processes that minimize loss of thiol groups. This article surveys colorimetric methods for food protein SH group analysis with applications to fluid milk and dried milk powder. Most colorimetric assays (chloromeribenzoate, pyridine disulfide, Nitrobenzo-2-oxa-1,3-diazole, papain reactivation assay, etc.) were found to be inferior to the Ellman method based on the use of 5,5'dithio (bis-2 nitro benzoic acid). Techniques for SH group analysis in fluid milk and dried milk powder are described, along with typical results, their interpretations, and current research related to processing effects and the role of milk SH content on a wider range of technological issues, such as development of cooked flavors, fouling and cleaning of plate heat exchanges, protein-protein interactions, and the storage stability. Finally, a number of areas requiring further research are presented.
Owusu-Apenten
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Department of Food Science, Borland Laboratory, Pennsylvania State University, University Park, Pennsylvania 16802, USA. rko10@psu.edu
D000818:Animals; D002364:Caseins / Q000032:analysis; D003124:Colorimetry / Q000379:methods; D004228:Dithionitrobenzoic Acid; D006801:Humans; D007782:Lactoglobulins / Q000032:analysis; D008894:Milk Proteins / Q000032:analysis* / Q000737:chemistry; D010084:Oxidation-Reduction; D011208:Powders; D013438:Sulfhydryl Compounds / Q000032:analysis* / Q000737:chemistry; D000067816:Whey Proteins; D015014:Yogurt
D002364:Caseins; D007782:Lactoglobulins; D008894:Milk Proteins; D011208:Powders; D013438:Sulfhydryl Compounds; D000067816:Whey Proteins; D004228:Dithionitrobenzoic Acid