Model discrimination for drying and rehydration kinetics of freeze‐dried tomatoes

Abstract

The aim of this work is to investigate the effect of a highly interconnected porous microstructure on the quality of rehydrated tomatoes by (a) designing a freeze-dried cycle that ensure product integrity (i.e., no collapse, no puffing) (b) characterizing both freeze-drying and rehydration kinetics. Fresh tomatoes were first freeze-dried and subsequently rehydrated to get generate kinetics data. Afterwards, six thin-layer drying models and four rehydration models were fitted using regression analysis to the experimental data.The goodness-of-fit was evaluated according to root mean squared error, adjusted R 2 , Akaike information criterion, and Bayesian information criterion. The most accurate representations of the system kinetics were observed using the Page model for freezedrying and the exponential and Weibull models for rehydration. Rehydration capacities and equilibrium moisture contents of the rehydrated samples were found to increase with temperature, and the corresponding activation energy values were calculated. Practical applicationsFreeze-dried porous microstructures can enhance water absorption and transport, contributing to restore the fresh product functional properties and leading to higher quality rehydrated products, especially in highly heat-sensitive food products as vegetables and fruits. The use of mathematical models to (a) design freeze-drying cycles and (b) characterize and/or predict drying and rehydration kinetics in cellular freezedried microstructures is then key for processing and optimization of convenience and ready-to-eat foods, which represents the main application of dried foods/powders and also a growing market. This approach to the manufacture of freeze-dried products also presents potential to set the basis of an alternative decentralized supply scenario for high-quality dried products, where freeze-dried foods will be manufactured and shipped and finally rehydrated closer to the consumption point.

Freeze-Dried Gellan Gum Gels as Vitamin Delivery Systems: Modelling the Effect of pH on Drying Kinetics and Vitamin Release Mechanisms

“…The kinetics of moisture loss during freeze-drying of the loaded gellan gum gels were described by five empirical models commonly employed to characterise drying kinetics in foods [15,16]: Newton, Page, Henderson and Pabis, logarithmic and Wang and Singh. Table 1 lists them all alongside their expressions.…”

“…The effect of pH on drying kinetic parameters has been determined by analysing the values of the constants in Newton (Table Equation 1) and Henderson and Pabis (Table Equation 3) models. These two models are derived from Newton's cooling law and Fick's Second law [16], respectively, so their constants enclose physical meaning-as opposite to the Page and Wang and Singh models that are purely empirical [16].…”

“…Parameters k 1 (Newton) and k 3 (Henderson) in Table 2, both time constants (h −1 ), characterise the drying rates of the system, while a 1 (Henderson) is a dimensionless parameter related to the shape and structural properties of the samples [16].…”

“…Experimental drying curves were fitted to five common food drying models [15] (i.e., Newton, Page, Henderson and Pabis, logarithmic and Wang and Singh), and the effects of different pHs on freeze-drying kinetics were assessed. In addition, Information Theory criteria (Akaike and Bayesian information criteria) were used to discriminate the models [16] attending to their accuracy and complexity (i.e., number of parameters involved). The effect of pH on vitamin release (at ambient temperature) has been also studied using the classical Korsmeyer-Peppas model [17,18], and corresponding delivery mechanisms revealed.…”

Model-Based Real Time Operation of the Freeze-Drying Process

“…Such particular processing conditions are key to delivering high-quality, shelf-stable dried products. For example, low processing temperatures avoid the degradation of heat-sensitive compounds (e.g., pharmaceutical active principles or nutrients and flavors in foods), while freezing and subsequent sublimation create highly porous microstructures that enhance rehydration/dissolution of food [5][6][7] and drug powders [8]. Characteristic low moisture contents make freeze-drying both time-consuming-cycles are typically over 24 h-and energy intensive [9,10].…”