Tough, dry, stale, leathery, tasteless...These are words that describe baked goods without emulsifiers. The processing, distribution and storage of these products necessitates the use of food additives to maintain the quality and freshness that consumers expect.

Emulsifiers, a subset of surfactants, are commonly used in many food products. An emulsion is a dispersion of small droplets of one immiscible liquid within another. Emulsifiers keep the droplets from coalescing. Although these food additives may offer some degree of emulsification, they perform more important functions in baked goods, such as starch complexing, protein strengthening and aeration.

The bakery industry is the largest user of food emulsifiers, according to industry sources. Recent figures indicate that about 400 million pounds of emulsifiers were used by the food industry; approximately two decades ago about half as much was used. The bakery industry accounts for 50% of the total food emulsifier market, and it is estimated that the growth of emulsifiers used in the baking industry will be about 3% per year.

This article explores the functionalities of and misconceptions about emulsifiers used in the two most common bakery systems: yeast-raised and chemically leavened products. Some guidelines and caveats for using emulsifiers in baked goods are presented, and the future of emulsifiers in the bakery industry is discussed. For information on emulsion chemistry and other applications of food emulsifiers, please refer to the October 1995 and May 1992 issues of Food Product Design.

Yeast-raised products

Emulsifiers are incorporated into bread formulas to improve dough handling and the product's overall quality. They result in significant improvements in machinability, shelf life and loaf volume. Emulsifiers have two major functions in yeast-raised products: dough conditioning/ strengthening; and shelf life extension, or "crumb softening."

Dough conditioners/strengtheners (protein interaction)

Emulsifiers function as dough conditioners by improving the binding of wheat flour gluten strands to each other. After gas produced by the yeast escapes through weak sections of the gluten film, part of the gluten matrix collapses. Although the mechanism is not fully understood, dough strengtheners increase the amount of binding sites that gluten strands have to each other and/or form bridges to supplement disulfide linkages which results in a stronger gluten film. Dough conditioners provide the following benefits:

Generally, the higher the moisture content of fresh baked goods, the greater the effects of staling. Yeast-raised products and cakes are more susceptible to staling than cookies and crackers.

Bill Knightly of Emulsion Technology Inc., Wilmington, DE, has worked with emulsifiers since the late 1950s and has written many papers to prove the difference between crumb softening and staling. He explains, "The term 'crumb softener' is a misnomer. As bread is baked, water becomes bound or entrapped in gelatinized starch, which is a soft gel. As bread begins to stale, the starch network closes and the starch is transformed from this soft state into a firm, crystalline state. The bound water previously entrapped in this three-dimensional network gets squeezed out and becomes free water which then migrates to the crust, making the crust leathery."

Although one cannot soften bread with emulsifiers, it is possible to slow the rate of staling. Knightly states that enzymes such as alpha-amylases can be considered true softeners. Enzymes cleave portions of the amylose chains in the dough, thereby disrupting the crystalline network in retrograded starch, reducing the rigidity and increasing the shelf life. He cautions that one must exert proper control over en-zyme activity in doughs, otherwise gummy, sticky products result.

One of the best starch-complexing agents is a dispersible form of monoglycerides (saturated types), typically used at 0.5% to 1.0% of the flour weight. Other good starch complexers include CSLs, SSLs, DATEMs, and SMG. Most bakeries use a blend of "crumb softeners" and dough strengtheners.

Chemically leavened products

Consumers prefer cakes that are light, tender and moist. Without emulsifiers, cake batter appears greasy and shiny with the fat dispersed in very large, coarse, irregularly shaped particles. Incorporation of certain emulsifiers provides aeration, foam stabilization, emulsification, and crumb softening to cake systems.

Aeration/foam stability

Cake batter is a mobile foam, while baked cakes are rigid foams. Emulsifiers coat the air cells in foams to provide foam stabilization. In addition, emulsifiers increase the amount of air that can be whipped into the batter by decreasing the surface tension of the aqueous phase, thereby increasing the whipping rate of batters.

Carbon dioxide gas, a leavener, does not spontaneously form bubbles in cake batters. By adding emulsifiers, more uniform air cells are generated and these act as nucleation sites for the dissolved gas. The result is a cake with improved grain, more even cell structure, and increased volume.

Monoglycerides, lactic acid esters, propylene glycol esters, polyglycerol esters, and polysorbates are emulsifiers that provide aeration and foam stabilization.

Emulsification

Cake batter is also an oil-in-water emulsion, with shortening or oil as the dispersed phase and water as the continuous phase. Emulsifiers, especially hydrophilic types, aid in mixing the fat phase with other ingredients. They aid in fat dispersion by breaking the fat into a large number of smaller particles.

The integrity of the foam walls, formed by proteins, determines cake volume and uniform appearance. Shortening is an antifoam that tends to disrupt the foam cells. Emulsifiers coat the fat particles' exterior surface, providing protection to the protein film cell walls and eliminating film disruption. Because of this protection, bakers can incorporate plastic shortenings, as well as vegetable oils - notorious antifoams - in their formulations. Not only is vegetable oil easier to use because of its pumpability at room temperature, but 25% less fat is required in oil-containing bakery formulations compared with those that contain plastic shortening. Vegetable oil also enhances the moistness.

Crumb softness

Crumb softening in cakes involves moisture retention and efficiency of shortening action, as well as starch complexing. A sponge cake with emulsifiers will have higher volume, a more tender and uniform crumb, better crust appearance and increased shelf life.

Choosing an emulsifier for a cake system depends on the type of fat used, production equipment available, and labeling issues. Emulsifiers for cake systems are usually added into the shortening at levels ranging from 4% to 14%. The most common emulsifier used in cake mixes is 10% to 14% propylene glycol monoesters (PGME), on a shortening basis. Typically, emulsifiers such as monoglycerides, polyglycerol esters, or SSLs are used in combination with "alpha-tending" emulsifiers such as PGME, acetylated mono glycerides, or lactylated monoglycerides.

In vegetable oil formulations, one may choose a dispersible blend of PS-60, SSL, sorbitan monostearate, and monoglycerides or a fluid shortening containing lactic acid esters of monoglycerides. A traditional system still used by bakers contains a plastic shortening with 5% to 10% mono- diglycerides.

Selecting emulsifiers

"First, food product designers should identify the problem to determine what they want to solve by using emulsifiers," notes Harold Kazier, applications and technical services manager for Quest International, Hoffman Estates, IL. "Second, determine what the emulsifier can do for you. Third, by examining the functionality you need in the system, decide if an emulsifier will solve that problem. Finally, pick the emulsifier or emulsifier system and optimize usage levels."

Keep the following considerations in mind when selecting emulsifiers:

Future outlook

Although emulsifiers will continue to be functional ingredients in baked goods, several factors will play a role in how they are used:

Low fat

Low-fat products will continue to benefit from the incorporation of emulsifiers. "Most developers of low-fat foods are investigating many different formulation options," says Knightly. "In baked goods, we may eventually see two main categories of ingredients for low-fat products such as both carbohydrate- and protein-based gel formers, since they do not add fat calories; and emulsifiers such as mono- and diglycerides."

Enzymes and emulsifiers

Enzymes are true crumb softeners, as previously mentioned. "If you want to use an enzyme, first use the normal levels (0.50% to 0.75% based on flour weight) of M-DG for dough conditioning and antistaling," advises Knightly. "If this isn't satisfactory or you need extra shelf life, then add enzymes. For some baking applications where increasing the level of M-DG is costly, adding a small amount of enzymes is more cost effective.

"The average consumer doesn't realize that M-DGs are naturally occurring in all foods that contain fats," Knightly continues. "Whenever you have a fatty food in its natural state it contains M-DG, lecithin, lipoproteins and glycolipids. They all have their functional value. Although more enzymes will be used in the future, they will not be replacing M-DG; rather, they will be used together for the best product performance and cost effectiveness."

According to Wulf Doerry, director of cereal technology, American Institute of Baking, Manhattan, KS, "Enzymes will have a definite impact on the future of the baking industry." Although enzymes are currently used to some extent for crumb softening, Doerry indicates that their use will increase in the future.

"Overseas companies, especially in Germany and Japan, are way ahead of us technologically. They are willing to invest the time, resources, and money to research new products and processes," he notes.

Microencapsulated emulsifiers

Emulsifiers such as monoglycerides are being tested in a convenient, cost-effective, microencapsulated form, and will be available soon.

Extended shelf life

Emulsifiers help retard staling in baked goods, thereby prolonging the shelf life. Two main factors are attributed to this need for extended shelf life: the smaller size of families today, and longer shipping distances. With smaller families, consumption time of baked products increases. It may take up to a week for some consumers to finish a loaf of bread. Therefore, bread must have a total shelf life of seven to 10 days.

Recent changes in the baking industry include consolidation and/ or elimination of personnel, closure of obsolete plants, and use of larger, more efficient existing state-of-the-art facilities. This has direct impact on distribution patterns - i.e., shipments of baked goods may need to travel farther in order to reach their final destination. This adds another one to two days extra shelf life. It is cheaper to increase the shelf life of baked goods by adding emulsifiers and shipping them farther, rather than rebuilding old plants. For the emulsifier market, this means that food product developers should use the maximum level of M-DG that is economically feasible together with the proper enzyme.

Healthy and ethnic products

In tortillas, emulsifiers increase flexibility and extend shelf life.

A client of Knightly recently approached him regarding the quality of their tortillas. "Before scaling up their operation to include sophisticated production equipment, Mexican ladies hand-stretched the tortillas out 360 degrees. Such equipment does not provide the stretching action needed for flexibility. The tortillas cracked when rolled up to make a burrito," says Knightly.

This problem was solved by the addition of M-DG. Today, packaged tortillas need a seven-day shelf life in supermarkets.

Other products such as bagels showed a 57% increase in sales last year, with bagels as the largest growth item in the bakery industry, according to Knightly. Emulsifiers help to prolong the shelf life of bagels, which can harden very quickly.

Change in consumption patterns

U.S. consumers are now eating bread like the Europeans - i.e., they are purchasing a variety of freshly baked "upscale" breads such as multi-grain, rosemary, and sourdough, and consuming them the same day. One in-store bakery manager of a large East Coast supermarket chain comments that people are paying between $2.29 per loaf for "Olde World" sourdough bread and $4.99 per loaf for olive bread. All of these breads include emulsifiers in their formulations.

As the trend continues toward healthier products that contain less fat, sugar and sodium, more fiber and no bromate, emulsifiers will play an important role as functional ingredients in baked goods. Food product designers should keep in mind that no single emulsifier or combination of emulsifiers is right for every formulation.

HLB still has a place

The hydrophilic/lipophilic properties of emulsifiers are sometimes expressed in terms of hydrophilic/lipophilic balance (HLB). Ranging from zero to 20, this scale indicates attraction to either oil or water. Emulsifiers that are predominantly lipophilic will have low HLB values and tend to form water-in-oil emulsions.

In the past, HLB was a common property used to select emulsifiers for actual bakery formulas. The system has drawbacks, however, because HLB values reflect the emulsifier's ability to influence surface tension in a simple system only. Because emulsifiers perform multiple functions in bakery foods, this limits the HLB's usefulness. Still, HLB does offer a starting point for emulsifier selection in products such as cakes where emulsification is important.

The cell structure of a cake is formed by proteins. The integrity of these walls determines cake volume and uniform crumb appearance. Through their emulsification properties, emulsifiers align themselves at the surface of fat droplets and prevent the fat from disrupting the protein film. Finding the ingredient with the correct emulsification properties -- including the HLB -- will, therefore, directly contribute to cake quality.