Water transport in parchment and endosperm of coffee bean

Abstract

International audienceThis paper aims at contributing to identify the eventual regions where fungus Aspergillus ochraceus could grow and produce ochratoxin A (OTA) during drying of coffee beans. Internal structure of coffee bean was analyzed by optical microscopy for endosperm and parchment. From the expression of the dissipation in the grain due to the water transport, we show that a relationship formally analogous to an equation of diffusion governs the water transport. Three structures with mass transfer resistance potential are studied: parchment, silver skin and endosperm. An experimental technique to study the water transfer into the parchment was proposed. In the endosperm, for moisture contents above 65%, a constant transport coefficient controls the drying kinetics of the whole bean. Below this moisture content, water transport coefficient (with and without silver skin) were significantly lesser than those for the whole bean. This is firstly due to the reduction of the pore space occupied by water and second to the increasing bonding energy between solid structure and water as moisture content decreases. The contribution of parchment to the protection of the endosperm is highlighted

Characterization of Two Different Stumps of <i>Spirulina platensis</i> Drying: Assessment of Water Transport Coefficient

“…The overall shape of curves is identical to those obtained by [11] with Spirulina platensis. The variation of desorption isotherm between 25˚C and 50˚C is similar to the one underlined with various food products such as banana, apple, coffee and pasta [18] [41]- [43]. It is noteworthy that the sorption behaviour is not sensitive to the geographical origin, i.e., both samples cultivated in different areas lead to nearly identical measures.…”

“…One can note a sharp increase of the transport coefficient above a water content of w = 2. This tendency has already been observed with rubber [45], Agar gel [47], clay [48], coffee [18] and wood [31]. This variation is attributed to the contraction of the porous microstructure and the reduction of pore size distribution that lead to a decrease of water permeability.…”

“…The evolutions of porosity and density during drying experiments were determined by kinetic analysis [8] [14]. In the literature, the water transport coefficients of some food products such as the papaya [15], beef meat [16], coffee [17] [18] and Okra [19] were determined by analytical models [20] [21]. Crank (1975) [22] focused on very simplifying assumptions which mask the contribution of certain parameters at water transport, particularly the shrinkage of the solid structure and the heterogeneity of the water content.…”

Hydric Properties Evolution of <i>Spirulina platensis</i> during Drying: Experimental Analysis and Modeling

“…There is a sharp decrease in the transport coefficient for water contents above 2 kg w /kg dm and a low decrease for low water contents. This trend has already been observed with rubber [30], agar gel [31] [32], clay [33], coffee [34] and wood [35]. W = 2 kg w /kg dm represents a critical mean value from which the contribution of solid shrinkage to water transport is negligible.…”

Moisture dynamic sorption isotherms and thermodynamic properties of parchment specialty coffee (Coffea arabica L.)

“…Reis, Franca and Oliveira (2013) also mentioned that carbohydrates exhibit several absorption bands in the 1500-700 cm −1 region. For the parchment FTIR spectrum, cellulose exhibits strong bands at 1059 and 1033 cm −1 (ring vibration) (Craig et al, 2018) (presented as a strong peak at 1017 cm −1 in this work) which can be associated with the lignocellulose composition of the parchment (Ramírez-Martínez et al, 2013), being ∼ 57% cellulose and ∼ 22% lignin (Collazo-Bigliardi;Ortega-Toro;Chiralt, 2018).…”