Some Observations on the Yellowing Phenomenon in Cooked Hams

Discolored parts in the cross section of yellowed cooked hams acquired from a factory emitted strong fluorescence under light at 336nm wavelength. There was no significant difference in analytical results for pH, moisture content, protein content or bacterial counts between the yellowed and normal parts from the yellowed cooked hams, normal cooked hams and those purchased on the market. Analyses of heme pigments showed that both the total heme content and the absorption spectrum of nitroso heme pigments were normal: the heme pigments developed a normal color. So far, several causes obscurely claimed to have relations with the occurrence of yellow discoloration are as follows: greening of cured meat, over or under curing, excessive pickle injection and PSE meat. However we found no clear relation between yellow discoloration and these causes at least in our present examination. A total of 173 cooked hams were produced experimentally by using 14 sorts of pickle which were prepared combining several protein materials such as whey protein powder with pH adjusted to 7.3 (symbol: WA), whey protein powder with a pH value of 6.9, whey protein isolates, sodium caseinate, soy proteins and egg whites with several sugar materials such as corn syrup solids (CS), glucose or sugar alcohol. The high occurrence rates of the color yellow and fluorescence were observed with the combination of WA and CS, especially when CS was solely used as the sugar material. This combination, which appears suited to the outbreak of the Maillard reaction, has been used at the factory when yellowing accidents take place. We presume that the Maillard reaction plays some role in the yellowing phenomenon.