Sorption isotherms of osmo-dehydrated fruits and vegetables. Experimental values and prediction equations

R.H. MASCHERONI

Buenos Aires

Congreso; WCCE11 11TH WORLD CONGRESS OF CHEMICAL ENGINEERING; 2023

World Chemical Engineering Council

Osmotic dehydration (OD) is used for the partial elimination of water from fruits and vegetables that will be later finishdried, refrigerated, frozen or directly used in prepared foods like breakfast or soup mixtures, ice creams, jams, cerealbars or tarts. The main advantage of OD is that it is performed at almost ambient temperatures, meaning an importantenergy saving respect to other dehydration methods. Besides - in most cases and with the adequate osmotic solution -it maintains most of the quality characteristics of the fresh product [1]. In many of the cited uses, OD products interactwith environment or materials of different relative humidity or water activity with the possibility of water exchange. Thereis a wide variety of OD agents: aqueous solutions of natural sugars or of different degrees of hydrolyzed corn syrup,mixtures of sugars and salt, polyalcohols, honey, wine must, etc. This fact, together with the ample variety of foodstested (type, variety, whole or peeled, etc.) lead to very different characteristics of sorption isotherms. But very fewpublished reports refer to sorption isotherms of OD fruits and vegetables, and no one of them reviews in deep theexisting literature and evaluate different prediction equations [2].Therefore, this work – as a first stage to further experimental data generation and systematization – presents a detailedreview of the existing experimental data of sorption isotherms of OD foods and tests diverse prediction models forsorption isotherms of foods, evaluating their adequacy for the different foods and treatments.Published literature on sorption isotherms of fruits and vegetables mostly refers to fresh or partially dehydrated foods(banana, apple, pear, peach, avocado, grape, apricot, mango, pineapple, date, papaya, cherry, kiwi, quince, blueberry,strawberry, blackberry, gooseberry, cassava, carrot, potato, squash, pepper, mint, sage, verbena). Experimental resultsshowed that most fruits had sigmoid shape type III isotherms, typical of their high sugar contents. Tested equation weremostly GAB and BET, also Oswin and very recently the NRTL-solid-liquid-mixture (NRTL-SLM) model [2]. In most cases,GAB equation had the higher accuracy in fitting experimental data.For OD foods few data are available: apple, apricot, strawberry, mango, quince, pineapple, pear, sweet cherry,gooseberry and squash; most of them dehydrated in sucrose solutions at different concentrations and temperatures.Isotherms follow the sigmoid shape in the solute concentration and temperature ranges tested. There is very little dataon the use of glucose, concentrated apple juice and fructo-oligosaccharides. GAB equation adjusted adequatelyexperimental results. No paper compares the possibility of changes in isotherms in function of the sugar used in the ODsolution.This paper analyzes the fitting accuracy of the aforementioned prediction models, applied to the different foods for whichadsorption/desorption data are available, and the influence of different solutes in solution on water equilibrium, as donein previous papers with other physical properties of OD fruits.References1. Rodríguez, M.M., Rodriguez, A., Mascheroni. R.H. (2015). Color, texture, rehydration ability and phenolic compounds ofplums partially osmodehydrated and finish-dried by hot air. Journal of Food Processing and Preservation, 39, 2647–2662.2. Zhang, L., Grace, P.M., Sun, D-W. (2021). A new theoretical model for moisture sorption isotherms and its application inderiving a hygroscopicity index for food products. Journal of Food Engineering, 315, 110817.