No abstract

Specific heat (Cp) and effective thermal conductivity (λ) of native maize starch (NS) were measured by DSC and transient heat transfer method, respectively, at different moisture contents and temperatures. The dependency of temperature (T) and moisture content (W) on the two parameters were investigated. The thermophysical properties of treated starch (TS) by four hydrothermal processes (RP-HMT, IV-HMT, DV-HMT and FV-HMT) were measured and compared to native strach. Hydrothermal treatments were performed at 3 bars (133°C) for 10 min. For Cp and λ measurements, moisture content varied for NS from 5 to 21.5% d.b. and from 8.8 to 25% d.b., respectively, and was fixed at 6% d.b. for TS. Empirical models were developed to specific heat and effective thermal conductivity, using a multiple regression algorithm with subsequent statistical analysis. The proposed models for NS based on T and W predict Cp and λ with a mean absolute error of 3.5% and 1.3%, respectively. Large differences in specific heat were observed between TS and NS. In a temperature range of 40 to 160°C, Cp values varied from 1.964 to 2.699 for NS and 1.380 to 2.085 (J.g -1 .°C -1 ) for TS. In contrast, the conductivity of NS was almost identical to that of treated starch by FV-HMT, followed in an increasing order by those treated by DV-HMT, RP-HMT, and IV-HM processes. These processes differ by the water content, temperature and processing time used. The two major hydrothermal processes largely cited by the literature that modify the physicochemical properties of starch, without destroying the granules are annealing [1-3] and Heat-Moisture Treatment (HMT) [4][5][6][7]. Annealing process occurs under large excess of water (50 to 60%) and relatively low temperatures, below the gelatinization temperature while HMT process is conducted under restricted moisture content (10-30%) and higher temperatures (< 140°C), above its glass transition temperature and below the gelatinization temperature for times of few minutes [8] to hours [7,[9][10]. As the HMT treatments lead to more or less significant changes in the structure and the functional properties of starches, many works were focused on the study of physicochemical properties of starch granules after HMT treatment but limited investigations are available on the effect of these treatments on changes in thermophysical properties and taking into account modifications of structural properties. Starch is considered as a reactive porous media, composed of a discontinuous solid phase which plays an important role in internal transports by canalizing flows and developing the thermophysical bonds with the fluid phases [11]. In presence of water and temperatures above 60°C, the physico-chemical properties of starch change due to modifications in its semi-crystalline structure. Bahrani et al. [12] have already shown during the steaming of standard maize starch (SMS) by three HMT processes that the heating of starch granules is the result of transfer of latent heat of steam condensation by direct contact with saturated...

The objective of this study is to prepare, evaluate, and understand carrageenan gelation. By using these properties of κ‐carrageenan, beads are created by thermal gelation. A warm κ‐carrageenan solution is extruded dropwise into a cold air column; the particles are collected. The relationship is studied between the process variables on the shape and size of κ‐carrageenan drops after gelation is established with the aid of image analysis. Thanks to these measurements, a model is developed to present satisfactory performance in industrial application. Mathematical models for κ‐carrageenan prilling, its simulated results, the parameters of equipment for the innovated process, and its application are addressed.

Checking is a recurring problem in the dry cereal products industry which involves hydromechanical and thermomechanical phenomena. This study focuses on the hydromechanical problem at constant temperature. The objective is to develop a model giving access to stress and the resulting strain fields in a rusk undergoing moisture equilibration during a 7‐day storage period in closed packaging to understand how checking occurs. A model was developed and implemented with Comsol Multiphysics. The effect of cells and the shape of the rusk on the stress field is investigated. Set‐ups were designed to determine the model parameters. Simulations showed that the rusks undergo shrinkage caused by moisture equilibration. Stresses reached maximal values around the cells of the matrix. The stress field varied significantly with the shape of the rusk. Practical Applications Checking in dry cereal products is a recurrent problem that has not yet been solved for many products, as it depends on the formulation of the latter and the processes used. Rusks, in particular, are subject to this phenomenon. This work provides elements for understanding the checking mechanism. It provides guidance to manufacturers on how to modify their processes to reduce the proportion of rusks that crack during storage.