Effect of Ethanol and Ultrasound Pretreatments on Pineapple Convective Drying.

Lívia Dias Campêlo De Freitas,Otidene Rossiter Sá Da Rocha,João Henrique Fernandes Da Silva,Shirley Clyde Rupert Brandão,Patrícia Moreira Azoubel

doi:10.17113/ftb.59.02.21.7045

Lívia Dias Campêlo De Freitas, Otidene Rossiter Sá Da Rocha + Show 3 more

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https://doi.org/10.17113/ftb.59.02.21.7045

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Abstract

SUMMARYResearch backgroundDrying represents a viable unit operation for the preservation of food. Convective drying is the most used method for plant materials. However, it can result in negative changes in food nutrient composition, and other quality parameters, besides requiring high energy consumption. Pretreatments can represent an alternative to minimise these negative aspects of dried materials. This work aims to evaluate the use of ethanol and ultrasound before pineapple convective drying and its effect on the product´s colour, water activity, ascorbic acid and total carotenoid contents.Experimental approachFor the pretreatment step, fruit samples were immersed in ethanol solutions of different volume fractions, and experiments were carried out for 10 min with and without using ultrasound (25 kHz). Fruit samples were dried at 60 ºC. A control group (without the pretreatment step) was also dried under the same condition. Semi-theoretical models were used for drying data fitting, and the diffusional model was used to describe the moisture transfer and calculate the effective diffusivity. Water activity, ascorbic acid, total carotenoids and colour analyses were performed.Results and conclusionsThe combination of ethanol and ultrasound as a pretreatment reduced the drying time of pineapple. Higher effective moisture diffusivities were obtained when ethanol and ultrasound were applied before drying. The two-term exponential model presented the best fit for drying experimental data. The dried samples had a darker colour than the fresh sample. The pretreatment with ethanol resulted in increased retention of the studied bioactive components. The satisfactory results of this study represent an improvement in the drying process.Novelty and scientific contributionUltrasound and ethanol as a pretreatment to convective drying are promising. However, each food matrix has a typical structure and composition. Therefore, the application of the pretreatment in other products or using other conditions is still necessary to deeply understand and explain their effect on the process and the quality of the dried products.

Highlights

Drying represents a viable unit operation for the preservation of food, which after dehydration can be directly consumed or rehydrated
The pretreatment with ethanol resulted in increased retention of the studied bioactive components
Convective drying is the most used for plant materials

Summary

Introduction

Drying represents a viable unit operation for the preservation of food, which after dehydration can be directly consumed or rehydrated. The use of hot air can result in negative aspects, as some materials change their appearance, texture, colour, nutrient composition and other quality parameters when dried, which displeases the consumer [1,2]. Non-enzymatic browning (appearance/colour) and degradation of nutritional components (nutritional composition) that are thermodynamically unstable or thermosensitive, which is the case with ascorbic acid present in abundance in pineapples [3], can be considered as some of the main consequences of drying. Convective drying has high energy consumption [4]. To minimise these negative aspects, pretreatments like ultrasound have been used [2,5,6]

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