Moisture Sorption Isotherms and Isotherm Model Performance Evaluation for Food and Agricultural Products

Abstract

Moisture sorption characteristics of agricultural and food products play important roles in such technological processes as drying, handling, packaging, storage, mixing, freeze-drying and other processes that require the prediction of food stability, shelf life, glass transition and estimation of drying time and texture and prevention of deteriorative reactions. They are useful in the computation of thermodynamic energies of moisture in the products. An understanding of moisture sorption phenomena in products, moisture sorption isotherm (MSI) determination techniques and moisture sorption isotherm model evaluation procedures would be useful in the development or selection, modeling and controlling as well as optimization of appropriate processes to make for enhanced efficiency. The phenomena addressed in this chapter are equilibrium moisture content (EMC)-water activity (a w) relationships and MSI types, temperature influence on isotherms and occurrence of moisture sorption hysteresis. MSI measurement techniques highlighted are the gravimetric, vapor pressure manometric (VPM), hygrometric and inverse gas chromatographic and the use of AquaLab equipment. Commonly used moisture sorption isotherm models (BET, GAB, modified GAB, Hailwood-Horrobin, modified Hailwood-Horrobin, modified Halsey, modified Henderson, modified Chung-Pfost and modified Oswin) were selected, and their evaluation procedures using moisture sorption data were outlined. Static gravimetric technique involving the use of saturated salt solution appears to be the most widely used and recommended method of determining the EMC of agricultural and food products. Most of the MSI models can be fitted to moisture sorption data thorough linearization by logarithmic transformation, while others can be solved using such expression as second-order polynomial. Model goodness of fit can be determined using standard (SE) error of estimate, coefficient of determination (R 2), mean relative percentage deviation (P) and fraction explained variation (FEV). The acceptance of a model depends on the nature of its residual plots. A model is considered acceptable if the residual plots show uniform scatter around the horizontal value of zero showing no systemic tendency towards a clear pattern. A model is better than another model if it has lower SE, lower P, higher R 2 and higher FEV. Although it appears as if a generalized MSI model is yet to exist, it is recommended that the Ngoddy-Bakker-Arkema (NBA) model should be given thorough going and extensive testing on the MSI of different categories of food as it could prove true to its generalized model posture due to the fundamental nature of its derivation.

Physicochemical, thermal, and flow properties of ice cream powder as influenced by moisture content

“…About 1 ± 0.0001 g of powder was spread as a thin layer in 25 ml beakers, which were placed inside 50 ml beakers (to reduce the condensation of moisture and splashing of salt solutions) and transferred to desiccators containing the salt slushes for moisture equilibration at 10°C, 25°C, and 40°C for 45 days. Water activities of 0.113–0.982 at 10°C, 0.113–0.973 at 25°C, and 0.112–0.964 at 40°C were maintained using suitable salt slushes (Aviara, 2020). The moisture contents of six replications were fitted to various classical sorption models described by Pushpadass, Emerald, Chaturvedi, et al.…”

The Freeze-Drying of Foods—The Characteristic of the Process Course and the Effect of Its Parameters on the Physical Properties of Food Materials

“…The third form of water corresponds to a water activity greater than 0.5. It is relatively free water, fills the capillaries, and complies with Raoults’ law [ 69 ] in primary drying. The freeze-drying process removes water that mainly corresponds to the first two forms of water.…”

“…Therefore, in this state, the bioactivity of the ingredients can significantly change. For this reason, secondary drying significantly determines the characteristics of the freeze-dried material [ 68 , 69 , 73 ].…”

Effect of maturity on the moisture sorption isotherm of chili pepper (Mareko Fana variety)

“…Full understanding of the behavior of the moisture sorption isotherm of chili pepper is important information for the design and optimization of the drying process, packaging, storage and shelf life of the product and to control moisture migration of the products ( Kaymak-Ertekin and Sultanoglu, 2001 ; Singh and Prasad, 2015 ; Aviara, 2020 ). Different chili pepper varieties throughout the world have been described using different sorption isotherm models ( Table1 ).…”