eChapter Name: Biosurfactants
9789390083237
eBook Name: NOVEL FOOD PROCESSING TECHNOLOGIES
by Gurpreet Kaur, Savita Sharma, Poonam A Sachdev
13.1 Introduction
A surfactant or surface-active agents are the compounds that lower the surface tension between the two liquids or between a liquid and a solid. Surfactants may act as detergents, wetting agents, emulsifiers, foaming agents and dispersants. Surfactants are normally organic compounds that are amphiphilic, meaning they contain both hydrophobic groups or hydrophilic groups. Therefore a surfactant contains both a water insoluble component and a water soluble component. Surfactant will diffuse in water and adsorb at interfaces.
The interfacial free energy is the minimum amount of work required to create that interface and the interfacial tension between two phases is determined as the interfacial free energy per unit area. The interfacial (or surface) tension is also a measure of the variance in nature of the two phases meeting at the interface (or surface). The greater the dissimilarity in their natures, the greater the interfacial (or surface) tension between them. A surfactant is therefore a substance that changes the amount of work required to expand those interfaces. Surfactants usually act to reduce interfacial free energy.
Surface active agents in the form of emulsifiers have a long history of use and are widely used in many products being used in everyday life. An extensive basic research is required to understand the reason of instability and methods to prevent the breakdown of emulsions. Emulsifiers can function as dough conditioners by improving tolerance to variations in flour quality, better gas retention resulting in lesser yeast requirements, increased uniformity in cell size, a finer grain, more resilient texture and improved slicing. Also, the characteristics of freshly baked bread like soft crumb can be retained longer, if the appropriate emulsifiers are added. Commonly used surface active agents in bread production are propylene glycol mono- and diesters, polyoxyethylene sorbitan monostearate, ethoxylated mono- and diglycerides, succinylated monoglycerides and Diacetyl tartaric acid, esters of monoglycerides. Cookie characteristics like top grain, volume and spread ratio can also be improved. Here surfactants used are sodium stearoyl fumarate, sucrose fatty acid esters, sodium stearoyl lactylate, sorbitan fatty acid esters, polysorbates and ethoxylated monoglycerides. In dairy products like Ice cream surface active agents play some important functions like to improve fat dispersion and control fat agglomeration, facilitation of fat– protein interactions, facilitate air incorporation, give smoother texture due to smaller ice crystals and air cells, increase resistance to shrinkage, improve melt-down and reduce whipping time. In candy products, the elimination of “bloom,’’ i.e., the transition of fat crystals is a key reason for the addition of surface active agents. In mixtures of triglycerides, surfactants like sorbitan esters (Spans) and ethoxylated sorbitan esters (Tweens) can control product viscosity in chocolates and in cream fillings and modify the crystal structure. Surface active agents have been utilized in the production of meat analog products also. In margarine, Emulsifiers fulfil several functions like modification of crystal structure in the vegetable fat, assistance in emulsion formation and antispattering. Here, a mixture of citric acid monoglycerides and monoglycerides or lecithin can be used. The properties and mode of action of these chemical surfactants is discussed in the following sections.