Proteomic analysis of duck fatty liver during post-mortem storage related to the variability of fat loss during cooking of "foie gras"

Integrated multi-omic data reveal the potential molecular mechanisms of the nutrition and flavor in Liancheng white duck meat

The Liancheng white (LW) duck is one of the most valued Chinese indigenous poultry breeds. Its meat is rich in nutrients and has distinct flavors, but the molecular mechanisms behind them are unknown. To address this issue, we measured and compared multi-omic data (genome, transcriptome, and metabolome) of breast meat from LW ducks and the Mianyang Shelduck (MS) ducks. We found that the LW duck has distinct breed-specific genetic features, including numerous mutant genes with differential expressions associated with amino acid metabolism and transport activities. The metabolome driven by genetic materials was also seen to differ between the two breeds. For example, several amino acids that are beneficial for human health, such as L-Arginine, L-Ornithine, and L-lysine, were found in considerably higher concentrations in LW muscle than in MS duck muscle (p < 0.05). SLC7A6, a mutant gene, was substantially upregulated in the LW group (p < 0.05), which may lead to excessive L-arginine and L-ornithine accumulation in LW duck meat through transport regulation. Further, guanosine monophosphate (GMP), an umami-tasting molecule, was considerably higher in LW muscle (p < 0.05), while L-Aspartic acid was significantly abundant in MS duck meat (p < 0.05), showing that the LW duck has a different umami formation. Overall, this study contributed to our understanding of the molecular mechanisms driving the enriched nutrients and distinct umami of LW duck meat, which will provide a useful reference for duck breeding.

Application of Metabolomics to Identify Hepatic Biomarkers of Foie Gras Qualities in Duck

Foie gras is a traditional dish in France that contains 50 to 60% of lipids. The high-fat content of the liver improves the organoleptic qualities of foie gras and reduces its technological yield at cooking (TY). As the valorization of the liver as foie gras products is strongly influenced by the TY, classifying the foie gras in their potential technological quality before cooking them is the main challenge for producers. Therefore, the current study aimed to identify hepatic biomarkers of foie gras qualities like liver weight (LW) and TY. A group of 120 male mule ducks was reared and overfed for 6–12 days, and their livers were sampled and analyzed by proton nuclear magnetic resonance (¹H-NMR). Eighteen biomarkers of foie gras qualities were identified, nine for LW and TY, five specific to LW, and four specific to TY. All biomarkers were strongly negatively correlated to the liver weights and positively correlated to the technological yield, except for the lactate and the threonine, and also for the creatine that was negatively correlated to foie gras technological quality. As a result, in heavy livers, the liver metabolism was oriented through a reduction of carbohydrate and amino acid metabolisms, and the plasma membrane could be damaged, which may explain the low technological yield of these livers. The detected biomarkers have been strongly discussed with the metabolism of the liver in nonalcoholic steatohepatitis.

Detection of Frozen-Thawed Duck Fatty Liver by MALDI-TOF Mass Spectrometry: A Chemometrics Study

The marketing of poultry livers is only authorized as fresh, frozen, or deep-frozen. The higher consumer demand for these products for a short period of time may lead to the marketing of frozen–thawed poultry livers: this constitutes fraud. The aim of this study was to design a method for distinguishing frozen–thawed livers from fresh livers. For this, the spectral fingerprint of liver proteins was acquired using Matrix-Assisted Laser Dissociation Ionization-Time-Of-Flight mass spectrometry. The spectra were analyzed using the chemometrics approach. First, principal component analysis studied the expected variability of commercial conditions before and after freezing–thawing. Then, the discriminant power of spectral fingerprint of liver proteins was assessed using supervised model generation. The combined approach of mass spectrometry and chemometrics successfully described the evolution of protein profile during storage time, before and after freezing-thawing, and successfully discriminated the fresh and frozen–thawed livers. These results are promising in terms of fraud detection, providing an opportunity for implementation of a reference method for agencies to fight fraud.

Evolution of liver fattening and foie gras technological yield during the overfeeding period in mule duck

In foie gras production the technological yield after the cooking process is one of the main issues of processors as it is closely linked to the cooking melting rate. This rate is subjected to strict laws and regulations since it directly affects the organoleptic and technological qualities of this gourmet product. The objective of the study was to better understand the liver fattening and the technological yield decrease during the overfeeding kinetics. A flock of 210 mule ducks was reared and then overfed during 12 D with 2 overfeeding programs; in the test group the amounts of corn in the first meals were higher than in the control group (+430 g during the whole period). Ducks were slaughtered at the end of the rearing period (D0, n = 15) and every other day (D2 to D12, n = 15 by group). Duck performances, anatomical dissections and physical and biochemical liver characteristics were registered. The performances were equivalent in the groups (P > 0.1). The evolution of the liver weight was then analyzed in detail in relation with the evolution of its biochemical composition. A two-step evolution occurred in the liver metabolism, first a main glycogen storage and then a strong lipid storage. A model to predict the liver weight was established with only BWs and feed intakes (R² = 0.83). The technological yield was determined on foie gras weighing more than 300 g (D6 to D12). The melting process was high during the last 2 D. The technological yield reached 72% at D12, for 758 g foie gras, and a strong negative correlation was observed with liver weight (−0.83; P < 0.001). A model to predict the technological yield was established with the liver weight and the liver color parameters (R² = 0.71). This study highlights the compromise between foie gras weight and its quality.

Metabolomic study of fatty livers in ducks: Identification by 1H-NMR of metabolic markers associated with technological quality

The control of fatty liver fat loss during cooking is a major issue. Previous studies showed that fat loss was influenced by bird production factors and liver technological treatments. However, part of the variability in fat loss remained uncontrolled. To provide enhanced insights into the determinism of fatty liver quality, liver hydrophilic metabolite profiles were measured by nuclear magnetic resonance of the proton ((1)H-NMR). The study aimed at i) comparing fatty livers with extreme fat loss values and ii) at characterizing the effect of postmortem evolution of livers during chilling. A group of 240 male mule ducks (Cairina moschata × Anas platyrhynchos) was reared and overfed. Their livers were sampled at 20 min and 6 h postmortem. Of these birds, 2 groups of ducks were built with extreme values on the technological yield (TY; TY = 100 - % fat loss; the low-fat-loss group, TY = 89.9%, n = 13; and the high-fat-loss group, TY = 68.3%, n = 12, P < 0.001). The (1)H-NMR analyses showed that the high-fat-loss livers were more advanced in postmortem biochemical and structural changes than low-fat-loss livers early postmortem. The high-fat-loss livers were characterized by hydrolysis of glycogen into glucose, worse integrity of cell membrane with diminution of compounds of phospholipids, and higher catabolic processes. The accelerated postmortem processes may be the origin of the differences in fat loss during cooking. During the early postmortem period, the adenosine triphosphate amount in liver cells was strongly reduced and lipolysis of triglycerides seemed to be enhanced. The glycogen stored in liver was first converted into glucose, but contrary to what happens in postmortem muscles, glucose was not converted into lactate.

Protein matrix involved in the lipid retention of foie gras during cooking: a multimodal hyperspectral imaging study

Denaturation of the protein matrix during heat treatment of duck foie gras was studied in relationship to the amount of fat loss during cooking. A low fat loss group was compared with a high fat loss group by histochemistry, FT-IR, and synchrotron UV microspectroscopy combination to characterize their protein matrix at different scales. After cooking, the high fat loss group showed higher densification of its matrix, higher ultraviolet tyrosine autofluorescence, and an infrared shift of the amide I band. These results revealed a higher level of protein denaturation and aggregation during cooking in high fat loss than in low fat loss foie gras. In addition, the fluorescence and infrared responses of the raw tissue revealed differences according to the level of fat losses after cooking. These findings highlight the importance of the supramolecular state of the protein matrix in determining the fat loss of foie gras.

Relationship between Proteolytic Activities and Cooking Loss Variability in Liver Issued from Force-Fed Mule Ducks

We investigated liver protease activities to better understand the mechanisms responsible for losses during the cooking of Mule ducks' fatty livers. Fatty livers of similar masses (520 g) were randomly selected among a large flock of overfed male Mule ducks and divided into two groups on the basis of their cooking loss rate, L+ (high cooking losses, 36%) and L- (low cooking losses, 21%). In addition to dry matter and total lipid contents, main hepatic protease (matrix metalloproteinase 2, cathepsins, and calpains) activities were measured by zymography. The results show that L+ samples present higher total relative proteolytic activity (6.15 ± 1.07 vs 4.46 ± 0.52 for L+ and L- samples, respectively) and total lipid content (61.0 ± 3.03% vs 53.7 ± 3.22% for L+ and L- samples, respectively) than L- samples. The results imply that proteases could be involved in the fragilization of the hepatocyte structure, resulting thus in higher cooking losses in L+ samples.