Elsevier

Carbohydrate Polymers

Volume 115, 22 January 2015, Pages 613-616
Carbohydrate Polymers

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Aminoacids as non-traditional plasticizers of maltodextrins fast-dissolving films

https://doi.org/10.1016/j.carbpol.2014.09.023Get rights and content

Highlights

Abstract

This study explored the effect of aminoacids as non-traditional plasticizers of maltodextrins fast dissolving films. 5% w/w glycine and proline decreased the glass transition temperature (Tg) of maltodextrins from 102.6 ± 2.0 °C to 73.1 ± 1.4 °C and 76.1 ± 0.7 °C, respectively; meanwhile the binary mixture made with lysine had a Tg value of 83.6 ± 2.2 °C. At the same time, all aminoacids increased the ΔCp values. The shift of the thermal data were due to profound effect on the hydrogen bonding as evidenced by ATR-FTIR spectra since the OH stretching and scissoring bands decreased of about 15–26 cm−1. A linear relationship was found (R2 = 0.9334) between HOH scissoring wavenumbers and Tg values. The addition of glycine and proline resulted effective in reducing the elastic modulus (about 50%) and tensile strength (about three times) and, therefore, can be used to increase the film ductility.

Introduction

Maltodextrins (MDX) are the products of the controlled hydrolysis of starch, and are mixtures of α(1→4) linked glucose oligo- and polysaccharides with occasional α(1→6) branches (Chronakis, 1998). The degree of hydrolysis of the MDX is indicated by the dextrose equivalence (DE) value (Chronakis, 1998), which denotes the percentage fraction of reducing sugars in the sample (DE value of non-hydrolyzed starch is below 1, DE 100 is equivalent to glucose). The DE value, therefore, reflects the number-average molecular weight of the carbohydrate.

A barrier to the development of MDX based films is the brittle nature of the blends. Overcoming this issue can be accomplished with the addition of plasticizers. As plasticizers typically reflect the polarity of the polymers with which they are blended (Sears & Darby, 1982), common plasticizers for MDX include water, glycerol and propylene glycol (Cilurzo, Cupone, Minghetti, Selmin, & Montanari, 2008). A complex behavior was described as a function of the water content since the antiplasticizing and plasticizing behavior of diluents in a glassy carbohydrate depend in a sensitive manner on a balance between the molecular size and the interactions of the diluent molecules with the carbohydrate chains (Roussenova, Murith, Alam, & Ubbink, 2010). At high water content, water is a very effective plasticizer of MDX, but it evaporates easily, leaving an extremely brittle, glassy material. Glycerol, being much less volatile than water, is generally exploited to obtain workable blends which were suitable to produce fast-dissolving films loaded by different drugs (Cilurzo et al., 2010, Cilurzo et al., 2011). It was evident that certain ingredients themselves can act as plasticizer. For example, nicotine or taste-masking agents affected tensile properties compromising the film integrity during the packaging procedures. A class of compounds yet to be investigated for its ability to plasticize MDX is amino acids. It was reported that proline is an exceptionally good plasticizer of standard blends of starch–glycerol (Stein & Green, 1996).

In this study, we report the effect of glycine, proline and lysine on the mechanical properties of MDX films obtained by casting. The transitions occurring during the heating of glassy carbohydrates plasticized with different amino acids were monitored by DSC in conjunction with ATR-FTIR spectroscopy in an attempt to study the molecular origin/fingerprint of the main thermodynamic transitions.

Section snippets

Materials

Maltodextrin having a DE equal to 6 (Glucidex® IT6, MDX) was obtained from Roquette Frères (Lestrem, F). Lysine (K), proline (P) and glycine (G) were purchased from A.C.E.F. (I). Sorbitan monooleate (Span® 80, SO) was gifted by Uniqema (UK) and glycerol (GLY) was obtained by Carlo Erba Reagenti (I).

Preparation of binary blends

Feeds at the concentration of 5% were prepared by dissolving MDX and amino acid in the ratio 95:5% w/w in distilled water. The solutions was spray-dried by a 4M8 spray-dryer (ProCepT, B) using the

Characterization of binary mixture

The residual water content in all binary mixtures was approximately 7%, which is acceptable for this class of materials.

DSC data of MDX revealed a glass transition temperature (Tg) at 102.6 ± 2.0 °C. After blending MDX with amino acids, a single Tg value at lower temperature was detected (Table 2). In particular, glycine and proline caused a drop in Tg to 73.1 ± 1.4 °C and 76.1 ± 0.7 °C, respectively; meanwhile binary mixture made with lysine had a Tg value of 83.6 ± 2.2 °C. ΔCp at the glass transition was

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