Multiscale structures of lipids in foods as parameters affecting fatty acid bioavailability and lipid metabolism.

On a nutritional standpoint, lipids are now being studied beyond their energy content and fatty acid (FA) profiles. Dietary FA are building blocks of a huge diversity of more complex molecules such as triacylglycerols (TAG) and phospholipids (PL), themselves organised in supramolecular structures presenting different thermal behaviours. They are generally embedded in complex food matrixes. Recent reports have revealed that molecular and supramolecular structures of lipids and their liquid or solid state at the body temperature influence both the digestibility and metabolism of dietary FA. The aim of the present review is to highlight recent knowledge on the impact on FA digestion, absorption and metabolism of: (i) the intramolecular structure of TAG; (ii) the nature of the lipid molecules carrying FA; (iii) the supramolecular organization and physical state of lipids in native and formulated food products and (iv) the food matrix. Further work should be accomplished now to obtain a more reliable body of evidence and integrate these data in future dietary recommendations. Additionally, innovative lipid formulations in which the health beneficial effects of either native or recomposed structures of lipids will be taken into account can be foreseen.

Modelling the behaviour of Listeria monocytogenes in ground pork as a function of pH, water activity, nature and concentration of organic acid salts.

AIMS: to study and model the effect of sodium acetate, sodium lactate, potassium sorbate and combination of acid salts on the behaviour of Listeria monocytogenes in ground pork. METHODS AND RESULTS: Water activity (a(w)), pH and concentration of acid salt of the meat were adjusted. The behaviour of inoculated L. monocytogenes was studied and modelled according to physicochemical parameters values. Whatever the acid salt concentration used, we observed an inhibition of the growth of L. monocytogenes at pH 5.6 and a(w) 0.95. At pH 6.2 and a(w) 0.97, addition of 402 mmol l(-1) of sodium lactate or 60 mmol l(-1) of potassium sorbate was required to observe a slower growth. CONCLUSIONS: The inhibitory effect of acid salts was a function of pH, a(w), as well as of the nature and concentration of acid salts added. When one acid salt was added, the Augustin's model (Augustin et al. 2005) yielded generally correct predictions of either the survival or growth of L. monocytogenes. SIGNIFICANCE AND IMPACT OF THE STUDY: The suggested model can be used for risk assessment concerning L. monocytogenes in pork products.

Effects of halothane genotype and pre-slaughter treatment on pig meat quality. Part 2. Physico-chemical traits of cured-cooked ham and sensory traits of cured-cooked and dry-cured hams.

Forty-eight castrated F(2) offspring of Piétrain and Large White pigs were allocated to a 3×2 factorial design in order to study the interactive effect of halothane genotype (NN, Nn and nn) and pre-slaughter treatment (referred to as 'Experimental' (EXP) and 'Commercial-like' (COL) conditions; the latter involving short transportation, mixing unfamiliar pigs and slaughtering shortly after transport) on the qualities of cured-cooked and dry-cured hams. At 24 h post mortem, the hams were collected and assigned to cured-cooked (right ham) and dry-cured (left ham) ham processing. A sample of M. semimembranosus (SM) was collected before cooked ham processing, was used for chemical composition analysis, cured and then cooked at various temperatures. Cooking losses and compression tests were carried out after cooking on these SM samples. The water and collagen content of SM muscle was significantly higher in nn pigs compared with the two other genotypes. At all cooking temperatures (60, 65 and 70 °C), SM muscles from nn pigs showed higher cooking losses and instrumentally assessed toughness than the other genotypes, the heterozygous pigs being intermediate. The technological yield of cured-cooked ham processing was lower in nn, compared with NN and Nn animals. Cooked hams from nn pigs were drier, tougher, stringier and less smooth than NN and Nn pigs. The heterozygous pigs were similar to normal pigs for all texture characteristics with the exception of toughness for which they got a significantly higher score than NN pigs. The pigs slaughtered under the COL conditions had a better slice cohesiveness and a significantly lower dryness, than pigs slaughtered under the EXP conditions. The effect of HAL genotype on slice cohesiveness was significant only when pigs were slaughtered under the EXP conditions. Dry-cured hams from nn pigs showed significantly more visual defects, but were less tough, smoother and more fondant (softer) than NN and Nn pigs. The dry-cured hams from pigs slaughtered under the COL conditions had a better cohesiveness between muscles and a more intense yellow colour of fat than those from pigs slaughtered under the EXP conditions. COL pigs were also judged significantly less tough, smoother and more fondant than EXP ones. Overall, the effects of pre-slaughter treatment were small compared with those of the HAL genotype. The effects of HAL genotype on the sensory traits of cured-cooked ham were similar to those reported for fresh meat. However, the good textural characteristics of dry-cured ham processed from HAL positive pigs are somewhat surprising and need to be confirmed.

Tracing of Salmonella spp. in two pork slaughter and cutting plants using serotyping and macrorestriction genotyping.

AIMS: The origin of Salmonella contamination of pork products is not well established. In order to further this knowledge, the transmission of Salmonella spp. from live pigs to pork cuts was investigated in two pork slaughter and cutting plants. METHODS AND RESULTS: Salmonella spp. were isolated from both pork (pigs, carcasses, cuts) and the environment before and during slaughterhouse activities. Eight serotypes were identified. XbaI and SpeI macrorestriction distinguished 20 genotypes of Salmonella Typhimurium and 16 genotypes of Salmonella Derby. A major cluster of Salmonella Typhimurium genotypes was common to both plants and all pig-related genotypes, while a predominant pig-related Salmonella Derby genotype was common to both plants. CONCLUSION: None of the Salmonella strains persisted for long periods in the pork-processing environments. SIGNIFICANCE AND IMPACT OF THE STUDY: This work shows that contaminated live pigs, because of bacterial spread due to the process and ineffective cleaning procedures, are involved in Salmonella contamination.

Physicochemical surface properties of five Listeria monocytogenes strains from a pork-processing environment in relation to serotypes, genotypes and growth temperature.

Physicochemical surface properties, related to electrostatic, van der Waals and Lewis acid-base interactions, of five Listeria monocytogenes strains isolated from pork-processing environments were determined after two subcultures at 37 degrees C and a final culture at three temperatures: 37, 10 and 4 degrees C. Three strains (Lm1, Lm114 and Lm191) were genetically related while two were unrelated (Lm25 and Lm74) according to ApaI-macrorestriction and pulsed-field gel electrophoresis (PFGE) typing. Listeria monocytogenes cell surfaces were generally negatively charged regardless of pH and tended to be hydrophilic due to a basic character. However, variable physicochemical surface properties of the five Listeria monocytogenes isolates were observed after growth at 37 degrees C. After growth at 10 degrees C, the three genetically related isolates exhibited similar surface properties and were slightly more hydrophilic and basic than the others. After growth at 4 degrees C, the five isolates displayed the same weak affinity for all kinds of solvents and low electrophoretic mobility values. A sharp decrease of temperature and subsequent growth of various Listeria monocytogenes strains resulted in loss of the physicochemical surface property variability, which may suggest the role of common chill adaptation mechanisms affecting surface properties.

Effects of animal and muscle characteristics on collagen and consequences for ham production.

The effect of biological and technological factors on ham production were studied by analyzing collagen pyridinoline cross-linking and the thermal stability of type I collagen. The type of muscle affected hydroxylysylpyridinoline (P>0.01) and lysylpyridinoline (P<0.001) cross-linking, total intramuscular collagen concentration (P<0.0001), and the slope of type I collagen solubility as a function of time. pH (P<0.05) and genetic line (P<0.0001) affected lysylpyridinoline cross-linking. In ham production, muscle type, pH(24), nitrite salt concentration and pasteurization value affected type I collagen solubility (P<0.0001). There was a relationship between pyridinoline cross-linking and soluble type I collagen levels and between technological yield and soluble type I collagen concentration (P<0.0001). There was also a relationship between collagen pyridinoline cross-linking and technological yield if the nitrite salt (1.5%) and pH(24) (<5.55) were kept constant. Thus collagen solubility and pyridinoline content are two indicators of meat quality in ham production.

Listeria monocytogenes in pork slaughtering and cutting plants. Use of RAPD, PFGE and PCR-REA for tracing and molecular epidemiology.

In order to determine the origin of pork cuts contamination by Listeria monocytogenes, 287 isolates, collected from five French pork slaughtering and cutting plants, from live pigs to pork cuts, were characterised using three molecular typing methods: random amplification of polymorphic DNA (RAPD) carried out with five different primers, genomic macrorestriction using ApaI with pulsed-field gel electrophoresis (PFGE) and a PCR-restriction enzyme analysis (PCR-REA) based on the polymorphism existing within the inlA and inlB genes. Results obtained from RAPD and PFGE were closely related and distinguished respectively 17 RAPD types (r1-r17) and 17 PFGE types (a1-a17) among the 287 isolates, whereas the PCR-REA analysis only yielded two profiles (p1 and p2). Considering the combined results obtained with the three molecular typing methods, 19 Listeria monocytogenes genotypes (1-19) were distinguished. Serotyping led at least four serotypes being distinguished: 1/2a, 3a, 1/2c and 3c. The application of genotyping identified the predominance of a Listeria monocytogenes strain of type (1) and other very closely related ones (5, 9, 10, 12, 13, 14, 16 and 19) which were present on pork as well as in the environment within the five investigated plants. This study also pointed out the presence of these closely related Listeria monocytogenes strains over a 1-year period in the environments of two plants, even after cleaning and disinfection procedures. This highlights the possibility for some Listeria monocytogenes strains to persist in pork processing environments and raises the problem of the efficiency of cleaning and disinfection procedures used in pork slaughterhouses, chilling and cutting rooms.

[Residual content of nitrite and nitrates in cooked French meat products]. / Teneurs résiduaires en nitrites et nitrates des produits cuits français.

1 256 french meat products samples belonging to the most popular types: 435 saucissons cuits (course ground cooked sausage); 226 saucisses de Strasbourg and 165 saucisses de Francfort (both finely comminuted Frankfurter type sausages); 430 pâtés de Campagne (country-type meat loafs) were analysed. For each type of product contents in nitrite and nitrate are given respectively for products sent by meat plants, handicraft firms and consumers. The average values lie significantly under permitted levels, but many vary in a wide range, especially as far nitrate is concerned.

[Residual nitrite and nitrate content in French cooked hams and shoulders]. / Les teneurs résiduaires en nitrites et nitrates des jambons et épaules cuits Français.

The test laboratory of the "Centre technique de la salaison, de la charcuterie et des conserves de viandes" has evaluated the nitrite and nitrate salts contents of 1 468 cooked hams and shoulders. 90,5 p. 100 of sample have a sodium nitrite content of less than 150 mg/kg. 81,5 p. 100 have a potassium nitrate content of less than 500 mg/kg. The measured contents show a wide scattering. The nitrite mean content is of 61 mg/kg with a standard deviation of 95. The nitrate mean content is of 292 mg/kg with a standard deviation of 382. There were no significant variations between the various categories of cooked hams and shoulders.

[State of nitrite in meat products]. / Etudes sur l'état du nitrite dans les produits de viandes.

The authors search the form under which nitrite is in cured products. Nitrate formation found by official methods is not confirmed by qualitative characterization. The calculations, according to the chemical equations, show the total breakdown of nitrite in nitroge oxide: NO, bound by many substances which are in meats. The distillation experiments confirm the calculations, the characteristic photometric spectra get in sulfitic medium and the modified Zambelli's reaction. These results lead to estimate that both technologic and toxicologic actions impute to nitrite is dominated by the idea of NO more or less bound, according to the medium composition.