SUMMARYThe formation of volatile bases and volatile acids during heat processing of albacore tuna loin sections was studied, using a closed system swept with nitrogen gas. The cell containing the tuna was heated gradually to 100°C, and the volatile acids and bases were trapped in standardized solutions. During the first 80 min of heating, at precooking temperatures, volatile acid evolved exceeded by threefold the slight amounts of volatile base (less than 0.5 mcq per 1000 g). Later during the heating cycle equal amounts of volatile acids and bases were formed.The ratio of sulfur to iron responded directly to the initial vacuum present in canned tuna. At high vacuum the ratio was 0.575. Sulfur was absent from the black deposits when the cans were sealed without evacuation, even when high levels of cystine were added. In commercially packed shrimp the sulfur to iron ratio was 0.322, which is consistent with a deposit of mixed oxides of iron, combined with ferrous sulfide. Addition of acetic acid (a volatile acid) at 10 mMper can suppressed the formation of black deposits at all closing vacuums in a model system containing added cysteine, while the addition of ammonium hydroxide (volatile base) or no addition resulted in the formation of black deposits at 26 inches Hg of closing vacuum
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