Chitosan Films in Food Applications. Tuning Film Properties by Changing Acidic Dissolution Conditions.

Elodie Melro,Inês Cruz,Fátima Carvalho,Luís Alves,Filipe E Antunes,Philippe E Ramos,Gabriela J Da Silva

doi:10.3390/polym13010001

Elodie Melro, Inês Cruz + Show 5 more

Open Access

https://doi.org/10.3390/polym13010001

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Abstract

Food contamination due to the presence of microorganisms is a serious problem. New food preservation systems are being studied to kill or inhibit spoilage and pathogenic microorganisms that contaminate food and reduce the shelf life of products. Chitosan films with potential application to food preservation have witnessed great developments during the last years. Chitosan is a cationic polysaccharide with the ability to form films and possess antimicrobial properties. It is water-insoluble but can be dissolved in acidic solutions. In the present work, three different acids (acetic, lactic and citric) were used in chitosan dissolution and both, the resultant solutions and formed films were characterized. It was observed that chitosan water-acetic acid systems show the highest antimicrobial activity due to the highest chitosan charge density, compared to the mixtures with lactic and citric acid. This system showed also the higher solution viscosity compared to the other systems. Chitosan–acetic acid films were also the ones presenting better mechanical properties; this can be attributed to the fact that lactic and citric acids remain in the films, changing their properties, which does not happen with acetic acid. Films produced from chitosan dissolved in water/acetic acid system are resistant, while very fragile but elastic films are formed when lactic acid is used. It was demonstrated that a good selection of the type of acid not only facilitates the dissolution of chitosan but also plays a key role in the properties of the formed solutions and films.

Highlights

Microbial degradation and dehydration of meat products during their shelf life were identified to be the parameters that present a higher influence in meat products quality and consumer acceptance [1]
Acetic acid and lactic acid were acquired from Panreac Química S.L.U., Barcelona, Spain, and citric acid from Merck, Algés, Portugal
The residual weight differences between the samples, which result from the carbonization during the degradation of chitosan above 350 ◦C, are related to the remaining acid quantity in the formed films; the residual amount, in the thermograms, for the film obtained from the solution acetic acid is higher than for the films containing lactic or citric acid, due to the absence of remaining acid in the film

Summary

Introduction

Microbial degradation and dehydration of meat products during their shelf life were identified to be the parameters that present a higher influence in meat products quality and consumer acceptance [1]. Chitosan (poly β-(1→4)N-acetyl-D-glucosamine) is the deacetylated form of chitin [2] and during long time was considered a waste product of the crabbing and shrimp canning industry [3] This linear polysaccharide has attracted considerable interest because is a nontoxic, biodegradable, biofunctional and biocompatible polymer [4,5] and has antimicrobial, antifungal, antitumor and hypocholesterolemic activities [6,7]. Chitosan is a weak base and it is insoluble in pure water and organic solvents [11], but can be solubilized in diluted acidic aqueous solutions, below pH 6.0. This characteristic is due to the presence of amino groups, whose pKa value is ca. We explore the effect of the three acids used in the dissolution of chitosan, and the correlation of the used acid with the properties of the solution, in the films formed and their antimicrobial activity, discussing the possible mechanisms of bacterial inhibition and the effect of the residual acids in the formed films

Materials

Characterization of Chitosan Solutions

Characterization of Chitosan Films

Results

Findings

Conclusions