Stéphane Portanguen

Effect of cooking on protein oxidation in n-3 polyunsaturated fatty acids enriched beef. Implication on nutritional quality.

The effect of cooking on protein oxidation was investigated in M. Longissimus thoracis of eight Normand cows fed during a 100 days finishing period with two different diets: a conventional diet (concentrate/straw based diet) and a diet rich in n-3 polyunsaturated fatty acids (PUFAs), obtained by addition to the conventional diet of a mixture of extruded linseed and extruded rapeseed. After 11 days storage, at 4 degrees C under vacuum, meat was cooked by applying jets of steam. Three experimental heating treatments were tested: two with constant surface temperatures of 65 and 96 degrees C during 300s, and one with a continuous increasing surface temperature up to 207 degrees C. Protein oxidation was evaluated by the measurement of carbonyls, aromatic amino acids, and free thiols content. The formation of Schiff bases due to the reaction of proteins with aldehydic products of the lipid oxidation was also evaluated. Cooking resulted in a significant increase of carbonyl groups and Schiff bases as well as a significant degradation of tyrosine and tryptophan. Nevertheless, enrichment of the animal diet in n-3 PUFAs had minor effects on protein oxidation induced by cooking which are unlikely to be of nutritional significance.

Use of meat fluorescence emission as a marker of oxidation promoted by cooking.

Accumulation of fluorescent pigments in cooked bovine meat (M. Longissimus thoracis) was studied in relationship with the heating parameters (time and temperature). Muscles were aged at 4°C for 11days under vacuum before cooking. Meat cooking was performed by applying jets of steam. Three different heating treatments were tested: two with constant surface temperatures of 65 and 96°C for 300s, and one with a continuously increasing surface temperature up to 207°C. After extraction in water/dichloromethane/ethanol, fluorescence pigments were distributed between the apolar phase (emission 420-440nm after excitation at 360nm) and the polar phase, where two emission peaks were seen (emission 410-430 and 515nm after excitation at 360nm). Fluorescence in the two phases was little affected by heating at the two constant temperatures while it increased exponentially after 1min of treatment, as the varying temperature reached 141°C. The maximum fluorescence increases, measured in the extreme conditions of cooking (207°C/300s), were of 5000% in the apolar phase and 1700% in the polar phase. Thiobarbituric acid reactive substances (TBARS) and protein carbonyls were measured in parallel. The correlations between these two parameters and the fluorescence emission demonstrated that the interaction between proteins and aldehyde products of lipid peroxidation was mainly involved in the production of fluorescent pigments in cooked meat.

Combined heat transfer and kinetic models to predict cooking loss during heat treatment of beef meat

A heat transfer model was used to simulate the temperature in 3 dimensions inside the meat. This model was combined with a first-order kinetic models to predict cooking losses. Identification of the parameters of the kinetic models and first validations were performed in a water bath. Afterwards, the performance of the combined model was determined in a fan-assisted oven under different air/steam conditions. Accurate knowledge of the heat transfer coefficient values and consideration of the retraction of the meat pieces are needed for the prediction of meat temperature. This is important since the temperature at the center of the product is often used to determine the cooking time. The combined model was also able to predict cooking losses from meat pieces of different sizes and subjected to different air/steam conditions. It was found that under the studied conditions, most of the water loss comes from the juice expelled by protein denaturation and contraction and not from evaporation.

Dynamic MRI and Thermal Simulation To Interpret Deformation and Water Transfer in Meat during Heating

Understanding and controlling structural and physical changes in meat during cooking is of prime importance. Nuclear magnetic resonance imaging (MRI) is a noninvasive, nondestructive tool that can be used to characterize certain properties and structures both locally and dynamically. Here we show the possibilities offered by MRI for the in situ dynamic imaging of the connective network during the cooking of meat to monitor deformations between 20 and 75 °C. A novel device was used to heat the sample in an MR imager. An MRI sequence was developed to contrast the connective tissue and the muscle fibers during heating. The temperature distribution in the sample was numerically simulated to link structural modifications and water transfer to temperature values. The contraction of myofibrillar and collagen networks was observed at 42 °C, and water began to migrate toward the interfascicular space at 40 °C. These observations are consistent with literature results obtained using destructive and/or nonlocalized methods. This new approach allows the simultaneous monitoring of local deformation and water transfer, changes in muscle structure and thermal history.

Towards models for the prediction of beef meat quality during cooking

Heating of beef muscles modifies the water content, the micronutrient content and the colour of beef meat. Juice expelling and loss of water soluble micronutrients were predicted by combined transfer-kinetics models. Kinetics modeling and crust formation are needed to progress toward a reliable prediction of HAAs formation. HAAs formation in uniformly heated beef meat slices was compared with the values issued from the kinetic models developed in literature in liquid systems. The models of literature were adapted to meat slices but the parameter values were different from those determined in liquid systems. Results in meat slices were confronted to the HAAs formation at the surface of bigger meat pieces subjected to air roasting conditions. The transposition of the results from the meat slices towards the bigger meat pieces was not direct because the formation of HAAs was affected by the thickening of the crust and the migration of precursors.

Quantitative study of the relationships among proteolysis, lipid oxidation, structure and texture throughout the dry-cured ham process.

Temperature, salt and water contents are key processing factors in dry-cured ham production. They affect how proteolysis, lipid oxidation, structure and texture evolve, and thus determine the sensory properties and final quality of dry-cured ham. The aim of this study was to quantify the interrelationships and the time course of (i) proteolysis, (ii) lipid oxidation, (iii) five textural parameters: hardness, fragility, cohesiveness, springiness and adhesiveness and (iv) four structural parameters: fibre numbers, extracellular spaces, cross section area, and connective tissue area, during the dry-cured ham process. Applying multiple polynomial regression enabled us to build phenomenological models relating proteolysis, salt and water contents to certain textural and structural parameters investigated. A linear relationship between lipid oxidation and proteolysis was also established. All of these models and relationships, once combined with salt penetration, water migration and heat transfer models, can be used to dynamically simulate all of these phenomena throughout dry-cured ham manufacturing.

Synchronous front-face fluorescence spectroscopy coupled with parallel factors (PARAFAC) analysis to study the effects of cooking time on meat.

In this study, the potential of synchronous front-face fluorescence coupled with chemometrics has been investigated for the analysis of cooked meat. Bovine meat samples (thin slices of 5 cm diameter) taken from Longissimus dorsi muscle were cooked at 237 degrees C for 0, 1, 2, 5, 7, and 10 min under control conditions. Synchronous front-face fluorescence spectra were collected on meat samples in the excitation wavelength range of 250 to 550 nm using offsets (Delta lambda) of 20, 30, 40, 50, 60, 70, 80, 90, 100, 110, 120, 130, 140, 150, and 160 nm between excitation and emission wavelengths. The synchronous fluorescence landscape containing 360 spectra was analyzed using PARAFAC. The best PARAFAC model presented 2 components since core consistency values for the first 2 components were 100% and the explained variance was 67.98%. The loading profiles of 1st and 2nd components had an optimal Delta lambda of 70 and 40 nm, respectively, allowing to determine the excitation (exc.) and emission (em.) maxima wavelengths of 1st (fluorescence band at about exc.: 340 to 400/em.: 410 to 470 nm, and peak at exc.: 468/em.: 538 nm) and 2nd (exc.: 294 nm/em.: 334 nm) components. As the loading profile of the 1st component of PARAFAC was assigned to Maillard-reaction products formed during cooking, the profile of the 2nd component corresponded with the fluorescence characteristics of tryptophan residues in proteins. Loadings and scores of the PARAFAC model developed from the synchronous fluorescence spectra enabled to get information regarding the changes occurring in meat fluorophores during cooking of meat at 237 degrees C from 0 to 10 min.

Mechanisms of Crust Development at the Surface of Beef Meat Subjected to Hot Air: An Experimental Study

When cooking meat, the development of a crust is an important element for consumer. It is the place of Maillard reactions and development of flavor. It is also where carcinogenic compounds can be formed. To our knowledge, no study has been devoted to the formation of the crust during cooking pieces of meat, so these mechanisms were studied under laboratory conditions. Temperatures were measured close to the surface using a special isolated device that corrects for movements due to meat thermal shrinkage. These temperature measurements were paired with microscopic measurements of the crust thickness and with the measurement of profiles of water content by magnetic resonance imaging to interpret crust formation and structure. Three areas were characterized in the crust, and the thickness of the colored area was proved to vary linearly with time. Images obtained by X-ray microtomography showed a great heterogeneity of the porosity in the crust of the heated samples.

Oil uptake by beef during pan frying: Impact on fatty acid composition

Fat entering food during frying needs to be monitored to control the nutritional properties of the products: fat penetration and fatty acid (FA) composition. The large difference between the apparent diffusion coefficients of lipids and meat fibers allows the use of diffusion-weighted magnetic resonance imaging (DWI) to measure oil uptake profiles. This method, in association with analysis of FAs by gas-liquid chromatography, predicts nutritional changes. Beef samples from finishing cows given control feed or high FA supplemented feed were fried in olive oil at 130 °C and 180 °C. Frying oil penetration was quantified by computing oil signal profiles from 3D DWI. Oil penetration was deeper at 180 °C (5 mm) than at 130 °C (2.5 mm), consistent with oil penetration processes. Oil penetration evaluated with DWI was correlated (R²=0.82) with biochemical analysis of FA composition. These results highlight the predominance of oil uptake over animal feed effects in the first millimeters of in-plane fried meat.

Analysis of the juice and water losses in salted and unsalted pork samples heated in water bath. Consequences for the prediction of weight loss by transfer models

This study has analyzed the effect of different factors on variation of meat weight due to juice loss, and variation of water content of pork samples heated in a water bath. The weight loss (WL) was influenced by initial water content of raw meat which can be connected to meat pH, muscle type, and by pre-salting. WL was also influenced by sample thickness and by nature of the surrounding fluid. These effects were significant at 50°C and in thinner samples but decreased as meat temperature and sample thickness increased. WL showed no significant difference in response to prior freezing, applying a surface constraint during heating or varying meat salt content from 0.8 to 2.0%. The results were interpreted from literature knowledge on protein denaturation, contraction and, transport phenomena. Reliably predicting WL from water content variation during heating hinges on taking into account the loss of dry matter and the possible effects of meat pH, sample size or surrounding fluid.