Jean-Dominique Daudin

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.

Water transfer analysis in pork meat supported by NMR imaging.

NMR proton density imaging was used to study isothermal and unidirectional drying of pork semi membranosus muscle samples at temperatures of 12, 16 and 20 °C. An independent calibration of the transversal relaxation time T(2) as a function of the moisture content was carried out to convert the signal amplitude into moisture content. Due to spatial heterogeneity in drying, 2D images were needed to assess the evolution of 1D moisture profiles. The relationship between the effective water diffusivity (D) was calculated in function of water content (X) using the Boltzman transformation which needs no a priori on the relationship D=f(X); the effect of lipid content, temperature and fibre direction on this relationship were also studied. In all cases a decrease in water content brought about a decrease in D. A slight increase in lipid content led to a dramatic decrease in D. The fibre direction relative to water movement had a negligible effect. No significative differences in D between the three temperatures were observed, due to variability in the chemical composition of the samples.

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.

Development of a new method for fast measurement of water sorption isotherms in the high humidity range validation on gelatine gel

Abstract A fast and accurate method has been set up to measure sorption isotherms of solid foods in the water activity range 0.9–1. In a purpose-built device thin slices of the studied material are submitted to an air flow of very high velocity (more than 10 m s−1), at any temperature between 4°C and 40°C. Air relative humidity is controlled by a reduction in pressure of a saturated air. This method was validated over the range 0.7–0.9 using gelatine gel samples by comparison with the standard saturated salt method. Results obtained at two temperatures (3.5°C, 20°C) and three values of pH (4, 5.2 and 8) were used to test the ability of different fitting models.

Heat and mass transfer coefficients at the surface of a pork hindquarter

Abstract Heat and mass transfer coefficients were measured at the surface of a pork hindquarter for common air flow properties encountered in chillers and dryers. Air velocity and turbulence intensity ranged from 0.4 to 5.0 m s −1 and 1.3% to 30%, respectively. The local values of the transfer coefficients can be verydifferent from one location to another at the body surface. An inversion of the air flow direction slightly affects the value of the mean transfer coefficients. The effect of turbulence intensity on the mean transfer coefficients is important, but complex and different from what happens on cylinders. An increase in turbulence intensity from 1.3% to 6% decreases the mean transfer coefficients values while a further increase in Tu increases those values. One relation has been established to describe the experimental data for Tu >- 6%.

Modelling of temperature and weight loss kinetics during meat chilling for time-variable conditions using an analytical-based method — I. The model and its sensitivity to certain parameters

Abstract A mathematical model for the calculation of meat chilling is presented; it allows the prediction of both the weight loss kinetics and internal temperature profile evolution. The model is based on analytical solutions of unsteady heat transfer in infinite cylinders. These solutions were adapted to account for: (1) product surface water evaporation to avoid fitting the effective heat transfer coefficient; and (2) the variable chilling conditions that exist in industrial chillers. Calculation time is around 25 s on a microcomputer. The sensitivity of the calculations to physical phenomena, physical constant values and possible measurement errors in validation experiments is discussed. This model can easily be transposed to other elementary shapes.

Three-dimensional CFD calculations for designing large food chillers

In industry solid foods such as vegetables and meat are mostly air-chilled and stored in refrigerated rooms. Plant performance depends on heat and water exchanges between the air and the products and thus on the spatial distribution of the air parameters: velocity, turbulence intensity, temperature and relative humidity. In theory the transient behaviour of chillers could be calculated using computational fluid dynamics (CFD) codes, but current computer capacity and the inaccuracy of models for evaluating heat and mass transfer coefficients make them inapplicable to very large rooms containing hundreds of individual products. To overcome these limits a four-step calculation is proposed to assess how changes in chiller design and operating conditions affect chilling kinetics: (1) 3D calculation of the air velocity field with a CFD code, (2) deduction of an average air velocity map, (3) determination of heat and mass transfer coefficients in relation to the air velocity map using independent measurements, and (4) calculation of the product chilling kinetics using specific software. This procedure was applied to a pork chiller containing 290 carcasses. Two design cases differing in inlet air direction and flow rate, and two functioning modes, batch and continuous, were analysed. A fairly good agreement was observed between the calculated and measured air velocities. It was shown from temperature and weight loss kinetics that with this type of design, batch chilling can only be achieved overnight at the cost of overcooling for low weight carcasses, and increased weight losses.

Heat and mass transfer in chilling and storage of meat

Abstract The kinetics of temperature and weight loss for meat or phenolic foam ‘model’ samples were measured during chilled storage. The results were analysed by considering the basic equations which describe the simultaneous heat and mass transfer through the boundary layer and used to evaluate the average heat and mass transfer coefficients and the water activity of the meat surface. The mass transfer coefficient was found to be independent of the temperature (2°C to 15°C) and the relative humidity (52% to 87%) of the air in chilled storage conditions and proportional to the square root of the air velocity in the range of 0·25 to 1·5 m/s. A relationship which takes into account radiative heat transfer is given to enable the heat transfer coefficient to be predicted from the mass transfer coefficient. The water activity of the meat surface was observed to fall slowly when the initial drying rate was greater than 15 × 10 −6 kg/s m 2 .

Assessment of meat fat content using dual energy X-ray absorption.

Fat content is an essential component of meat quality. Fat content and fatty tissue content were determined by dual energy X-ray absorption on 3 types of meat: pork meat (mixture of longissimus dorsi and fat) and beef meat (longissimus dorsi and pectoralis profondus). The measurements were carried out with a medical densitometer, the SOPHOS L-XRA usually used for osteodensitometry. The results from the dual energy X-ray absorption and the chemical analysis were compared and the correlations were good to very good (R(2) values from 0.7 to 0.97). The residual standard deviations were in the range 2.75-4.89%. The routine use of dual energy X-ray absorption would though suppose a previous calibration.

Water activity and dielectric properties of gels in the frequency range 200 MHz–6 GHz

Abstract Dielectric spectroscopy gives information on a molecules chemical relations with its surroundings while water activity (aw) is the thermodynamic measure linked with water bonding to the food matrix. Thus, it should be possible to access information on aw via dielectric measurements, which could be very interesting, in practice, regarding easiness of dielectric measurements. Forty-five model samples of animal gelatin gel of various water and NaCl contents (aw from 0.91 to 1) were characterised in terms of aw and dielectric properties. To analyse the variations of water activity with water and salt contents, over a larger moisture content range, isothermal sorption curves were determined. This investigation provides correlations between aw and some dielectric properties, such as relaxation frequency. Results of this first investigation are encouraging but lead to some questions about influence of NaCl on dielectric measurements, the possibility of associating dielectric measurements with sorption isotherms and problems concerning measurements on real food products.