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Observations on the Application of the Nitroprusside Test to Heated Milk

1949; Elsevier BV; Volume: 32; Issue: 5 Linguagem: Inglês

10.3168/jds.s0022-0302(49)92058-5

1529-9066

Stuart Patton, D.V. Josephson,

Food Allergy and Anaphylaxis Research

Tbe nitroprusside test has proven to be a satisfactory technic for studying the presence and behavior of reduced sulfur in various mediums and under widely varying conditions.One of its classic uses is for the qualitative determination of sulfur in organic compounds in conjunction with the sodium fusion reaction (13).Other important applications include its use in studying protein denaturation (1) and in the detection of sulfhydryl compounds (11).Many sulfur compounds are notorious for their intense and often disagreeable odor.The findings of many workers in the field of dairy research have demonstrated that sulfur compounds are implicated in flavor changes resulting from the heating of milk and dairy products.It is the consensus that consumer acceptance of milk products, the processing of which requires high heat treatment, could be improved greatly if the associated flavor problems could be overcome.The nitroprusside test should be a very useful research tool in the investigation and possible solution of these problems. REVIEW OF LITERATUREIn 1911 Arnold (2) observed that denatured egg protein gives a color reaction with sodium nitroprusside.Anson (1) since has demonstrated that potassium nitroprusside may be used to measure quantitatively the sulfhydryl groups of denatured egg albumin.Shinohara and Kilpatrick (12) suggest that before hydrogen sulfide is liberated from cystine as a result of heating, the cystine is converted to cysteine, the reduced form.Such a theory is helpful in explaining the mechanism by which sulfhydryl compounds are liberated in heat-denatured proteins, since proteins behaving in such a fashion invariably contain comparatively large quantities of cystine.Jackson (5) was the first to focus interest on the possible use of the nitroprusside test in connection with milk.He found that raw milk does not give a positive nitroprusside test, but that tests become positive if the milk first is treated with sodium cyanide, a strong reducing agent.He proposed that this phenomenon is traceable to the cystine in the protein complex of milk.Jackson et al. (6) reported that sterilization of cream produced "volatile sulfur" which could be detected by the nitroprusside test if heating was carried to 120 ° C. for 30 minutes.Gould and Sommer (4) could find no correlation between the intensity of the nitroprusside reaction and the temperature at which cooked flavor and sulfide liberation occur in milk.However, they did find some correlation between these factors when sodium cyanide was added to the milk