Search

Aims To quantify and model the combined effects of temperature ( T) (10-40°C), water activity ( aw) (0·993-0·818) and CO2 concentration (9·4-55·1%, v/v) on the growth rate of Aspergillus niger and Alternaria alternata that cause spoilage during the storage and packaging of dates. Methods and Results The effects of environmental factors were studied using the γ-concept. Cardinal models were used to quantify the effect of studied environmental factors on the growth rates. Firstly, the cardinal parameters were estimated independently from experiments carried out on potato dextrose agar using a monofactorial design. Secondly, model performance evaluation was conducted on pasteurized date paste. The boundary between growth and no-growth was predicted using a deterministic approach. Aspergillus niger displayed a faster growth rate and higher tolerance to low aw than Al. alternata, which in turn proved more resistant to CO2 concentration. Minimal cardinal parameters of T and aw were lower than those reported in the literature. Conclusions The combination of the aw and CO2 effects significantly affected As. niger and Al. alternata growth. The γ-concept model overestimated growth rates, however, it is optimistic and provides somewhat conservative predictions. Significance and Impact of the Study The developed model provides a decision support tool for the choice of the date fruit conservation mode (refrigeration, drying, modified atmospheric packaging or their combination) using T, aw and CO2 as environmental factors. [ABSTRACT FROM AUTHOR]

Highlights: [•] A model associating water transport, deformation and starch gelatinization was developed. [•] Two water population were distinguished according to the state of starch. [•] Model was validated through 3 independent ways (microscopy, gravimetry and volumetric changes). [•] Microscopic gelatinization front thickness kinetics were predicted from degree of starch gelatinization profiles. [•] The model was able to predict water redistribution after cooking. [ABSTRACT FROM AUTHOR]

Abstract: Fry-drying process of wood involves intense water vaporization. The pressure at a sample core increases over 250kPa. Under such pressure conditions, vapour transport driven by Darcy''s law should be considered as the prevailing phenomenon in a simplified heat and mass transport model. The latter was developed in the absence of mechanical deformation and oil penetration, in a 2D rectangular geometry and solved numerically with commercial finite element software. Free and bound water were distinguished in the energy equation. Despite the directions of vapour flux being orthogonal to the simulation plane, the use of only two adjusted permeabilities (9×10−15 and 9×10−16 m2) allowed the characterisation of a large amount of wood, regardless of sample size and permeability variability. The model was experimentally validated with local pressure and temperature measurements at the core, temperature alone at three locations and with overall water loss. Beech (Fagus silvatica), oak (Quercus pedonculae) and maritime pine (Pinus pinaster) were considered at both laboratory (0.3m in length) and industrial (2m in length) scales in the temperature range from 103 to 180°C. Evidence of mechanical degrade or cracks was observed at 180°C due to the sudden decrease in water boiling point and by fluctuations in temperature kinetics. [Copyright &y& Elsevier]

The effect of temperature ( T = 55–120 °C) and water content ( X 1 = 1.4–2.0 kg kg −1 dry basis) on the gelatinization and digestibility of plantain flour (Dominico Harton genotype) were investigated. The degree of plantain starch gelatinization ( α ) was measured by DSC and modelled as a function of T and X 1 , using the Weibull model. Rapidly digestible starch ( RDS ) and resistant starch ( RS ) fractions were evaluated for different α values. An appropriate dimensionless variable was introduced to the analyzed and modelled RDS and RS as a function of α . Starch gelatinization begins at a temperature above 59.6 ± 0.5 °C and α is strongly dependent on T in non-limiting water conditions. The combined effects of T and X 1 on the RDS and RS can be explained by α . We demonstrate that various heat treatments and water contents lead to the same α , with the same RDS and RS values. [ABSTRACT FROM AUTHOR]