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In a number of tropical countries, the expansion of cassava processing is tied to the development of small-scale, energy-efficient pneumatic dryers used to dry flour and starch. To facilitate this development, in this study a model of the pneumatic drying of starch particles was developed, to be fitted to measurements taken from large cassava processing factories. After that, numerical simulations were performed to analyse the effects of geometry and operating conditions on the energy efficiency and pipe length required to dry the product. The results clarified the influence of processing capacity, air inlet conditions and starch particle size, emphasizing that air velocity, as well as the dilution of the starch, should be minimised. In light of the findings described here, we offer guidelines for the design of efficient small-capacity flash dryers.

A 1D mechanistic model was developed to describe water, deformation, amylose transport and starch gelatinization inside rice grains during cooking. Four migrating species were considered: two water populations according to the state of the starch, soluble amylose and an insoluble solid phase network. Three coupled mass transport PDE were formulated assuming diffusional mass transport and using a Lagrangian-Eulerian framework. The model integrates the convective effect of a water flux on the transport of soluble amylose. Rice grain deformation was the result of both water-induced swelling and erosion of the surface of the solid phase, assuming a zero-order kinetic process. The model was adjusted on a milled Chil-bo rice cultivar steeped in excess water at 75 °C and 95 °C. After 30 min at 95 °C, which is the standard cooking time, water uptake, leaching of soluble amylose and the amount of eroded material were 3.15 kg kg−1 db, 5.0% and 15.5% (w/w) respectively. Using the predicted distribution of species within the grain, the model could help to control the texture of cooked rice. (Resume d'auteur)

An isothermal model of rice cooking process was developed that accounts for the impact of starch phase transition on water transfer and swelling, using an arbitrary Lagrangian–Eulerian framework. Two water populations were distinguished: water in native starch and excess water absorbed by starch since it starts to gelatinize. The model was solved by FEM. Water apparent diffusivities in native and gelatinized starch were 3.6 × 10 −10 and 2.8 × 10 −10 m 2 s −1 respectively. The model was validated on the Chil-Bo rice cultivar using experimental water uptake and microscopy measurements of the gelatinization front. At 50 °C, 75 °C and 95 °C, the volume gains were 0.3, 4.8 and 8.3 m 3 m −3 respectively. The model adequately reproduces swelling as its extent corresponds to the amount of water absorbed (±4% v/v). Both water and gelatinization profiles over time would be of tremendous benefit for the optimization of cooked rice properties such as texture.

A space-and-time dependent model describing the impact of heat transfer on insect survival rate was developed for analyzing the heat disinfestation process of dates. A 2D axial-symmetric domain was defined with five sub-domains: the bulk date pulp, a thin air layer and the date pit, a larva (located in the air layer) and eggs (on the date surface). The model included convective heating and microwave heating (915 MHz). Dielectric properties of the date pulp, egg and larvae were measured. The model predictions showed good agreement with experimental results in the case of the “biological model” (Ephestia kuehniella Zeller) in dates subjected to hot air treatment (70 °C). Sensitive analysis showed that the date size and water content greatly affected the heating time process, during hot air and microwave treatments. Moreover, regarding the eggs’ specific surface, it is advisable to combine convective hot air with microwave heating to induce egg mortality on the date surface.

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. (Resume d'auteur)

The effects of heat treatment on the survival of isolated Ephestia kuehniella Zeller larvae were examined. Larvae were treated in a specific device at a temperature range of 46 to 70 °C. Statistical analysis of the data demonstrated that the thermal survival kinetics was best represented by a 2-parameter Weibull model above 50 °C. The mortality of larvae only occurs beyond a critical temperature of 41.6 °C ± 2.5 °C. A 2D axial-symmetric model of heat transfer (convection, microwave at 915 MHz) was developed for cocoa bean and date palm. It was combined with the survival rate of larvae (Weibull model) and some z -values (from literature) are used for calculating a “food quality index” degradation kinetics. The intensive heating/convection process may not be adaptable for food products at low water activity due to high surface product temperatures. The use of microwave heating for date fruits and conventional hot air treatments for cocoa beans is recommended.

Water activity is the main criterion for characterizing the storage and drying behavior of biological products. As current standardized devices are expensive, a cheaper apparatus was designed and built. After preliminary tests, functional specifications were determined. This gravimetric device was tested and validated on microcrystalline cellulose and then used for the characterization of various tropical products. This operational equipment, easy to handle, robust, and four times cheaper than the reference apparatus, was able to obtain accurate sorption isotherms.

This paper describes the adaptation of a one-dimensional rice cooking model including water transfer, starch phase transitions and swelling to simulate both milled and brown Chu-cheong and Chil-bo rice cultivars cooked in excess water or in limited amounts of water. The pericarp was found to play a temperature-dependent role during steeping of brown rice. At 50 °C, surface mass-transfer resistance was identified whereas from 75 °C the pericarp ruptured. Despite pericarp rupturing, apparent water diffusion coefficients for brown rice (∼1.9 × 10 −10 m 2 s −1 ) were lower than for milled rice (∼3.3 × 10 −10 m 2 s −1 ). This was due to the mechanical constraining effect of pericarp with respect to water uptake. In the limited-water cooking mode, predicted water and gelatinization profiles of four selected cooking procedures explained the texture of cooked rice. Indeed, the highly hydrated gelatinized periphery of the cooked grain resulted in high “initial starchy coating” sensory scores whereas the uncooked core increased instrumental firmness.

In this paper, we report on the water vapour desorption isotherms, at 25°C, of eleven date ( Phoenix dactylifera ) varieties, from different locations, collected at full ripeness: Mech-Degla, Deglet-Nour and Haloua (Algeria), Barhi, Fardd, Khadrawi, Khalass, Madjol, Rizaz (Saudi Arabia), Madjhoul (Israel) and Kentichi (Tunisia). The static gravimetric method was used, according to the COST 90 recommendations. The overall shape of the curves describing the water content as function of the water activity was typical of sugar-rich materials. Experimental data were analysed using the Guggenheim–Anderson–Brunauer (GAB) and Brunauer–Emmett–Teller (BET) models, through direct non-linear regression without any transformation of data. Both models correctly fit the whole set of data, for water activity ranking from 0.11 to 0.90, but the BET model was preferred since the values of its parameters were more realistic.