A Novel and Accurate Method for Moisture Adsorption Isotherm Determination of Sultana Raisins

Jun Li,Man Xiao,Fatang Jiang,Dongling Qiao,Saffa B Riffa,Yuehong Su,Kao Wu,Lei Dong

doi:10.1007/s12161-019-01599-0

Abstract

A novel method (dynamic water transfer–based water activity analyzer (DWT) method) based on Fick’s law of diffusion for the accurate measurement of moisture sorption isotherm (MSI) has been developed and was compared with saturated salt solutions (SSS) method and dynamic vapor sorption (DVS) method. MSIs at 25 °C of sultana raisins obtained by the three methods were analyzed and compared, and four adsorption models (BET, Halsey, GAB, and Peleg) were used to fit the results. The MSI curves obtained by the three methods all showed the similar type III isotherm characteristic, but equilibrium moisture content at the same relative humidity (RH) showed some differences, and the repeatability and accuracy were different. Generally, results obtained by the SSS method may have relatively low accuracy due to the relatively high measurement error; results obtained by the DVS method may lack representativeness due to the small sample size; results obtained by the DWT method may have high representativeness and accuracy at the same time. The fitting results of adsorption models indicated that MSI results obtained by the DWT method had the highest fitting degree with the Peleg model. This study may contribute to deepened understandings on MSI measurement of semi-dried foods.

Highlights

Under the condition of constant temperature, the relationship between equilibrated water content and equilibrium water activity (Aw) can be described graphically in a curve, which is called the moisture sorption isotherm (MSI)
This typical J-shaped MSI curve was similar to prior reports of MSI of sultana raisins determined by saturated salt solution (SSS) method
Moisture adsorption isotherm of sultana raisins determined by dynamic vapor sorption (DVS)

Summary

Introduction

Under the condition of constant temperature, the relationship between equilibrated water content (typically represented by the water in the mass of each unit of dry basis) and equilibrium water activity (Aw) can be described graphically in a curve, which is called the moisture sorption isotherm (MSI). The relation between the dehydration degree of food in the process of concentration and drying and the relative vapor pressure; (2). The determination of what water content can inhibit microbial growth in food; (4). The prediction of the relationship between chemical and physical stability of food and water content (Labuza et al 2006; Almuhtaseb et al 2002; Caballero-Cerón et al.2015; Van den Berg and Bruin 1981). The shape and values of MSI can be very different in foods, as they are related to the components’ properties, physical structure, pretreatment, and temperature (Almuhtaseb et al 2002)

Objectives

Methods

Results

Conclusion