Sugar replacement with zwitterionic plasticizers like amino acids

Summary

In this paper, we investigate the potential of zwitterions like amino acids as alternative (bulking) sugar replacers. Commonly, polyols or oligosaccharides are taken as sugar placers, but they are perceived as less attractive due to laxative problems. The choice of amino acids as alternative sugar replacers is inspired by their presence in Natural Deep Eutectic Solvents (NADES) and compatible solutes, next to carbohydrates. In these compounds, hydrogen bonding plays an essential role similar to sugar (replacers) in food. Because of the novelty of the topic, we first discuss at length NADES as a potential source of alternative plasticizers/sugar replacers. Subsequently, we perform a detailed analysis of their thermodynamic properties, to investigate whether amino acids and related zwitterions indeed have the appropriate properties for sugar replacement. Our analysis shows that several zwitterions indeed have proper thermodynamic properties, which can make them good plasticizers and humectants. However, the use of several zwitterions can be restricted by their poor solubility, except for L-proline. Solubility problems can be circumvented by their use in mixtures of several sugar replacers, which enhances their solubility. The poor solubility makes it also difficult to characterize the glass transition temperatures of the pure solute T_g,g. Consequently, we have estimated them via extrapolation of the viscosity curves, which is shown to scale with T_g∕T. We have taken T_g of the plasticizer solution as a measure of the hydrogen bond density, n_OH,eff. That measure is shown to explain the melting behaviour of biopolymers like egg white and starch in glycine and L-proline solutions, similar to sugar (replacers). However, our measurements of the biopolymer melting show indications of phase separation at high moisture contents for both amino acid solutions as for carbohydrate solutions. Overall, the amino acids and other compatible zwitterions have very similar thermodynamic behaviour as sugars and their carbohydrate-based replacers. In proper combinations with alternative plasticizers, the zwitterionic compatible solutes can well be used in sugar replacement strategies for foods.