Stoichio-Kinetic Modeling of Fenton Chemistry in a Meat-Mimetic Aqueous-Phase Medium.

Fenton reaction kinetics, which involved an Fe(II)/Fe(III) oxidative redox cycle, were studied in a liquid medium that mimics meat composition. Muscle antioxidants (enzymes, peptides, and vitamins) were added one by one in the medium to determine their respective effects on the formation of superoxide and hydroxyl radicals. A stoichio-kinetic mathematical model was used to predict the formation of these radicals under different iron and H2O2 concentrations and temperature conditions. The difference between experimental and predicted results was mainly due to iron reactivity, which had to be taken into account in the model, and to uncertainties on some of the rate constant values introduced in the model. This stoichio-kinetic model will be useful to predict oxidation during meat processes, providing it can be completed to take into account the presence of myoglobin in the muscle.

Effects of pH and NaCl levels in a beef marinade on physicochemical states of lipids and proteins and on tissue microstructure.

Meat slices were incubated for 24h at 10°C in marinade solutions so that their pH reached 6.5, 5.4, or 4.3, and their NaCl contents 0.9% or 2%. The histological modifications were assessed by image analysis using two parameters: mean fibre cross section area (FCSA, µm(2)) and the ratio of the extra-cellular space (ECS, % area). The changes in lipids and proteins were evaluated through oxidation, protein surface hydrophobicity, and protein aggregation by granulometry (size and shape of particles). ANOVA showed that FCSA decreased linearly while ECS increased when pH decreased from 6.5 to 4.3 at either low or high NaCl salt content. Decreasing pH significantly increased TBARS and carbonyl groups, while increasing NaCl level had a significant protective effect on lipids. No marinating effect was observed on free thiols. Protein surface hydrophobicity and aggregation increased significantly with decreasing pH, but were unaffected by NaCl. The effect of these physicochemical changes on the nutritional value of meat is discussed.

Modelling of pepsin digestibility of myofibrillar proteins and of variations due to heating.

Digestibility of myofibrillar proteins by pepsin was determined by in vitro trials and mathematical modelling. A primary model was developed to predict in vitro digestion kinetics, and a secondary model based on the mechanisms of protein denaturation was then added to take into account the effect of meat heating. Model predictions agreed with measurements in the pH and pepsin concentration ranges 1.8-3.8 and 6-50 U mg(-1) respectively. The utility of the model is illustrated by a simple example where meat is assumed to be heated homogeneously, and myofibrillar proteins to be directly in contact with pepsin. The combined effects of heating time, temperature, enzyme concentration and pH modified the digestibility value, which also depends on residence time in the stomach.

Modelling the distribution of a(w), pH and ions in marinated beef meat.

New beef products from low value cuts could be developed using marinating since this process has been shown to improve meat sensorial properties and shelf life. However, to optimise the process mathematical models are needed to predict evolution of the physicochemical properties that determine biochemical and structural changes. Two major works have been carried out to elaborate comprehensive models: (1) Thermodynamic models were adapted to predict water sorption isotherms and pH of beef meat tissue in presence of salts (NaCl, KCl) and organic acids (acetic, lactic, citric and ascorbic acid), (2) Fickian numerical models were set up to predict the migration of ions within meat cuts using apparent diffusivities previously estimated from 1D experiments. Simulation calculations showed reasonable agreement with measurements and can be used to investigate the effect of marinating conditions, product heterogeneity, dimension and shape.

Cooking temperature is a key determinant of in vitro meat protein digestion rate: investigation of underlying mechanisms.

The present study aimed to evaluate the digestion rate and nutritional quality of pig muscle proteins in relation to different meat processes (aging, mincing, and cooking). Under our experimental conditions, aging and mincing had little impact on protein digestion. Heat treatments had different temperature-dependent effects on the meat protein digestion rate and degradation potential. At 70 °C, the proteins underwent denaturation that enhanced the speed of pepsin digestion by increasing enzyme accessibility to protein cleavage sites. Above 100 °C, oxidation-related protein aggregation slowed pepsin digestion but improved meat protein overall digestibility. The digestion parameters defined here open new insights on the dynamics governing the in vitro digestion of meat protein. However, the effect of cooking temperature on protein digestion observed in vitro needs to be confirmed in vivo.

Effect of temperature and cultivar on polyphenol retention and mass transfer during osmotic dehydration of apples.

Several cultivars of apples (Malus domestica) were chosen for their variable concentrations and compositions in phenolic compounds. Cubed samples (1 cm3) were subjected to osmotic dehydration, and the effect of temperature was studied at 45 and 60 degrees C. Water loss, sucrose impregnation, and the evolution of some natural components of the product were followed to quantify mass transfer. Ascorbic acid and polyphenols were quantified by HPLC for several osmotic dehydration times and regardless of the quantity of impregnated sugar. Changes in antioxidant components differed as a function of the nature of molecules. Their concentrations decreased in line with temperature, and few differences were observed between cultivars. Processing at a lower temperature (45 degrees C) caused a total loss in ascorbic acid but allowed the retention of between 74 and 85% of initial polyphenols, depending on the cultivar. Cultivars containing highly polymerized procyanidins (such as Guillevic) experienced less loss. Hydroxycinnamic acids and monomeric catechins displayed the most marked changes. Leaching with water into the soaking solution was the principal mechanism retained to explain these losses.