Investigation of the Background of Greening of Fatty Goose Liver (Foie Gras) during Prolonged Frozen Storage under Vacuum

Abstract

During vacuum-packaged frozen storage of fatty goose liver (“foie gras”), a yet unknown, but fully reversible (package opening and thawing), greening was found at a Hungarian processing plant. Laboratory analysis revealed hydrogen sulfide (H2S) and remnant blood in 35 livers. Microbial spoilage was under the limit of detection for H2S-producing strains. In liver homogenates and in thawing exudates, sulfhemoglobin was found and confirmed (acid-alkali reactions), with spectrophotometric analysis. Slaughtered geese are chilled to 2C (24 h) in a non-eviscerated condition to maintain liver shape. With logistic regression, the H2S (most probably from the intestinal tract) was of primary importance in the green color development. In an experimental group (n = 10) dissected after 2 h of body chilling, H2S was absent in the liver. Results indicate that intestinal tract-originated H2S is diffusing the fattened goose liver, leading to a color defect of a delicatesse, without consumer health risks. Practical Applications Hungary leads the world's “foie gras” production, and a rarely occurring production-technology-associated green color defect negatively affects product perception. Fattened, slaughtered geese are chilled to 2C for 24 h in a non-eviscerated form to keep liver intact during dissection. Based on the industrial observations and analytical results, foie gras contains sulfhemoglobin, a non-toxic, green pigment, which is sensitive towards oxidative stimuli. The color defect occurs only in frozen-stored and vacuum-packaged livers. After excluding microbiological spoilage and proving the presence of sulfhemoglobin, we suggest the application of an oxidative packaging technology, e.g., modified atmosphere. Further conditions possibly precluding the formation of sulfhemoglobin may be fresh, warm dissection (immediately after slaughter) or the improvement of the efficacy of bleeding during slaughter. Though the green pigment has no consumer health risk, its full elimination would positively affect the quality of a high-value delicatesse.