Emulsifier-Carbohydrate Interactions

Abstract

Emulsifiers are a diverse group of amphiphilic, surfactant compounds that interact by various mechanisms with carbohydrates, another diverse group of compounds present in foods. Some emulsifiers interact with starches, a carbohydrate fraction that is ubiquitous in foods, via a hydrophobic (lipophilic) bonding that results in the formation of reversible starch/surfactant inclusion complexes. The functional properties of food starches are attained when heated in the presence of water, allowing the starch granules absorb water and swell, and inducing some level of starch gelatinization. Pasting, an empirical rheological measurement, is the net effect of the competing events of granule swelling and disintegration, and a peak viscosity is commonly measured during pasting. Surfactants added to foods tend to stabilize the swollen starch granule during cooking and can also affect the properties of starch gels that form during cooling. A wide range of emulsifiers, capable of a variety of interactions with other molecules, are used in food products. Each emulsifier tends to be best suited for one or two functions. No single emulsifier exhibits a high level of all common functional characteristics, and the impact is not always predictable. The interactions between exogenous emulsifiers and starches resulting in inclusion complex formation is often used to deliberately control properties of the starches. These interactions have a significant, practical impact on food products containing starch. For example, the increase in firmness and loss of flavor in staled bread are caused by retrogradation of the amylopectin fraction of wheat starch. Control or modification of amylopectin retrogradation by incorporation of surfactants is an important application for surfactants in the food industry. Studies have also shown that starch/surfactant complexes modify in vitro and in vivo hydrolysis and digestion of starch, an interesting phenomenon with potential implications to carbohydrate digestibility. In addition to using emulsifiers to modify starch characteristics during processing, potential use of pre-formed amylose/surfactant complexes as potential temperature controlled release agents for lipids or reduced Glucose Index carbohydrates have been proposed. Other common carbohydrates in food such as simple sugars and most hydrocolloids are not amphiphilic due to the absence of a lipophilic group, so do not directly form complexes with emulsifiers. Emulsifiers can, however, influence the functionality of non-starch carbohydrates due to interfacial activity or competition for water.

Amylose-lipid complexes are formed under a range of common processing conditions for starch-based foods. Some process parameters, such as time of addition of an emulsifier, can be varied to significantly modify the food properties. When studying these interactions, some traditional methods of starch analysis, such as iodine binding capacity may not be sensitive enough to be useful in selection or optimizing emulsifier performance for a specific matrix, especially with high amylopectin starch matrices. However, the functionality of emulsifiers in starch-containing food systems can be demonstrated by measuring the impact of emulsifiers on other ingredients or food systems. Examples include data from starch pasting profiles and enzymolysis. In addition, directly measuring the physical properties of starch/surfactant complexes has provided valuable insights into their identification, and has broadened the understanding of the functionality of surfactants in starch-containing food systems. Techniques, such as X-ray diffraction, differential scanning calorimetry, nuclear magnetic resonance, electron spin resonance, rheology and microscopy have proven especially useful. The bimolecular interactions that emulsifiers participate in continue to be studied and better understood. Correlation of these data to ingredient behavior in complicated food formulations can be quite difficult, however, and further efforts to refine predictive cause-effect relationships for practical application in complex food matrices are needed. The best understanding comes from using multiple approaches including empirical and direct methods of measurement.