Pressure is growing on food manufacturers to find alternatives to eggs and egg products as ingredients. Recent outbreaks of avian influenza throughout the world have resulted in price volatility, with significant spikes in cost. The growth in demand for ‘free-from’ or allergen-free foods continues (Crane, 2016).
Eighty-four percent of consumers consider them to be healthier, natural and less processed (Mintel, 2015). Also on the rise is the demographic of vegans, who require egg-free food products. Furthermore, increased concern about the environmental footprint of food production is pushing food manufacturers to look for functional, economical and nutritional egg replacers.
WHAT DO EGGS DO?
The protein composition of eggs gives them the solubility, emulsification, foaming and gelation properties that are needed by formulators. Eggs are said to be ‘polyfunctional’ – in other words, they can contribute more than one functional property at the same time (Pomeranz, 1991; Yang and Baldwin, 1995). Depending on the functionality required, eggs can be used whole, or as white and yolk fractions.
EGGS AND PULSES, PROTEIN & FUNCTIONALITY
Eggs contain 6% protein, of which 12% are globulins and 71% are albumins. Pulses are 23% protein, with 50-80% globulins and 15-25% albumins. Albumins are water soluble and undergo rapid denaturation with heating. In contrast, globulins are insoluble in water but are soluble in dilute salt solutions.
Protein solubility is the most critical property because other characteristics, including emulsification, foaming, and gelation, are dependent on it (Vaclavik and Christian, 2008). Solubility can be altered by freezing, heating, drying, and shearing (Vaclavik and Christian, 2008).
The solubility of protein will change in response to alterations in pH, temperature and ionic strength. This applies equally to pulse proteins and egg proteins.
An emulsifier is an ingredient that allows oil and water to form a stable mixture, without separating into two layers. For example, mayonnaise is a food emulsion that is stabilized by egg yolk. Egg yolk prevents oil and water from separating by creating an ‘interfacial film’ between them. It is the low-density lipoproteins in egg yolk that enable it to be used as an emulsifier.
Although these proteins are not found in pulses, recent research has shown that it is possible to use pulse flour to make an egg-free mayonnaise. Thus, pulse flours appear to contain a protein that is capable of creating an interfacial film between two immiscible liquids.
The foaming properties of egg proteins are highly valued in the preparation of cakes and meringues. The protein must have high solubility in the liquid phase, as well as an ability to quickly form a film around the air bubbles (Kinsella, 1981). For foam stability, the interfacial film needs to be rigid so that it prevents the entrapped air from escaping. The protein also needs to have the ability to form strong chemical bonds including hydrogen bonding and hydrophobic interactions. To maintain its viscosity and rigidity, the protein must be able to resist denaturation (Kinsella, 1981).
Egg white has superb foaming properties due to the various proteins present. Ovalbumin (Smith and Back, 1965; Du et al, 2002), ovomucin (Yang and Baldwin, 1995; Omana et al, 2010), and globulins (MacDonnell et al, 1955) all play different roles in foam formation and stabilization.
Recent trials have shown that a blend of BEST Whole Navy Bean Flour and water can be used to replace the eggs in meringues and macarons. It is thought that the protein and carbohydrate in the navy bean flour provide the foam volume and stability, respectively.
Protein gelation involves the aggregation of protein molecules to form insoluble networks. The texturization of foods such as cakes and sauces is dependent on protein to form gel networks when the ingredients are heated (Kiosseoglou and Paraskevopoulou, 2003). In the case of egg whites, this process occurs via the rapid
denaturation of albumin in egg whites and the formation of gel when egg white is heated (Coultate, 2009). Egg yolk proteins can also form gels.
Pulse proteins have a similar ability to form protein gels (Boye et al, 2013). Recent trials have shown that BEST Whole Navy Bean Flour can be used to make egg-free cookies and muffins, as well as to replace starches in sauces.
It has also been shown that pulse flours can be used as binders in meat systems, replacing both the egg and breadcrumbs (Balakrishnan and Dudley, 2016).