Elsevier

Food Hydrocolloids

Volume 87, February 2019, Pages 550-560
Food Hydrocolloids

Effect of Persian gum and Xanthan gum on foaming properties and stability of pasteurized fresh egg white foam

https://doi.org/10.1016/j.foodhyd.2018.08.030Get rights and content

Highlights

  • Effect of Persian gum and Xanthan on bulk properties and final foam derived from pasteurized egg white is presented.

  • Importance of choosing appropriate experimental method for foam characterization is discussed clearly.

  • Relation of structural and stability changes as a function of different beating time is demonstrated.

Abstract

Pasteurization process results in undesirable effects on foaming properties and stability of liquid egg white. Persian gum (PG) as native hydrocolloids and Xanthan gum (XG) (in three levels) were added to liquid egg white in order to improve the foaming properties of the final solution prior to pasteurization. The viscosity increment of egg white was the natural consequence of addition of XG and PG. By addition of hydrocolloids to egg white solution, the solution's flow behavior changed from Newtonian to Pseudoplastic and flow curves were fitted to power law model consequently. Both hydrocolloids showed positive effects on foam stability in all levels, yet their negative effect on overrun and foam density was undeniable. High concentrations of XG and PG (0.1%≤) resulted in the improvement of foam texture, while XG exhibited the greatest effect on foam elasticity through physical interaction with unfolded proteins. Analyzing microscopic images of foam bubbles, owing to different bulk viscosity of samples, showed negative effect of over beating for some samples while in some others the whipping time was inadequate to reach the maximum gas phase.

Introduction

Fresh egg white (albumen) is a 10% protein solution containing over than 20 different proteins. Albumen's pH varies from 7.6 to 9.7 depending on the storage time. The pH changes occur due to CO2 diffusion from egg shell during storage time (Belitz, Grosch, & Schieberle, 2009). Owing to the sensitivity of some proteins to surface denaturation (ovalbumin) and also viscosity making protein (ovomucin) along with binding ability of some other proteins (lysozyme), albumen can make a solid, irreversible and semi stable foam which is applied widely in variety of food and bakery products (Abeyrathne et al., 2013, Garibaldi et al., 1968, Hagolle et al., 2000, Stevens, 1991, pp. 1–9). It is noteworthy to mention that none of these proteins can make similar foam individually and egg white foam is a consequence of all these proteins interaction at air/water interface (MacDonnell et al., 1955, Nakamura, 1963). Paying attention to factories requirements, has led the industry to produce liquid egg white, while hygienic standard commitments forced factories to consume pasteurized egg whites for which the heating process of around 60 °C was recommended (Cunningham, Kline, & Lineweaver, 1966).

Normally, some protein-protein interactions take place in fresh egg white including ovomucin-lysozyme interactions through electrostatic forces. This interaction is reversible in native conditions with no negative effect on functional properties of egg white. As this complex goes through the pasteurization process, denatures and consequently as a result, stable, rigid and insoluble complex forms which effectively decreases the foaming properties of egg white, specially whipping time and foam density (Garibaldi et al., 1968). Earlier studies have also confirmed some aggregation formation during egg white thermal treatment, including soluble and insoluble aggregates while more soluble aggregates were observed at higher temperatures (Nicorescu et al., 2011). The same negative effect of pasteurization was also reported by other scientists (Van der Plancken, Van Loey, & Hendrickx, 2007).

Foam is a colloidal system in which gas is dispersed in a liquid, semi liquid or solid continuous phase.

From thermodynamic point of view, foam is an instable system (Schramm, 2005). Considering foam's intrinsic instability along with negative effects of pasteurization process on egg white foaming ability and stability, some additives to counterbalance negative effects are required. Hydrocolloids in food industry are a group of substances which are widely used as stabilizers. Hence at the present research, Xanthan gum (XG) and Persian gum (PG) were applied as stabilizers to compensate the negative effects of pasteurization.

As an extracellular hydrocolloid, Xanthan produces highly pseudoplastic dispersions with high stability over a wide range of pH and temperature (Phillips & Williams, 2000). The gum's structure is considered as a rigid rod while heat treatment (∼82.5 °C) causes conformational changes varying from rigid ordered state to flexible disordered state (Williams, Annable, Phillips, & Nishinari, 1993). Unlike to well-known Xanthan, Persian gum is a newly introduced anionic pseudoplastic exudate gum (The gum's zeta potential at its natural pH is around −25 mV) from trunk and branches of wild almond tree being mainly native to Iran (Hadian et al., 2016). This is a transparent, semi cloudy gum whose color varies from white to brownish red which all can be obtain from one trunk at the same time. The gum's molecular weight (Mw) varies from 4.74 × 106 Da for white fractions to 2.59 × 106 Da for red ones (Fadavi, Mohammadifar, Zargarran, Mortazavian, & Komeili, 2014). The whole gum dispersion is comprised of 70% insoluble and 30% soluble fraction of the whole gum dispersion. The gums dispersion is stable over pH range from 2 to 11 and also a wide range of temperature to 90 °C(Abbasi, 2015 #31; Abbasi, 2017 #56). It is noteworthy to mention that the viscosity of PG dispersion increases with pH increase which makes this hydrocolloid a suitable stabilizer for high pH systems. Persian gum was used as herbal remedy from ancient times. It is in the center of attention in recent years to find industrial applications for this valuable gum. PG was used as replacement of gelatin in confectionery, to improve texture in different dairy food and bakery products, to decrease oil absorption in deep fat frying and showed other emulsifying and stabilizing effect reviewed by Abbasi (2017).

Although food foam is not a new aspect in food science, choosing appropriate experiment procedure for each initial foaming substance, due to their different nature, is necessary. Hence, reliable experiments should be designed to obtain precise results which would be applicable even for food factories. The foam volume is the most important parameter of egg white for confectionery industry. The accurate foam volume measurement poses a big challenge for a scientist because of two major issues; first, after beating, the top surface of the foam is wavy and no careful measurement could be carried out even at scaled containers and the final observed volume is an approximated data. Moreover, when a dry foam with egg white is prepared, a semi solid and brittle texture is derived which could be fragmented into parts during beating and overbeating process, accordingly there would be some bulk air area beneath the foam which results in some miscalculations in the actual foam volume measurement. Therefore, air phase looks to be the best alternative factor for foam volume which represents the foaming ability and foaming capacity of a liquid, meanwhile it can be easily measured with acceptable repeatability.

The foaming ability of a liquid is an indicator of liquids capacity to maintain a specific volume of air in itself (ErÇElebi and IbanoĞLu, 2009). This parameter for a solution is a function of physical properties and chemical nature of the liquid (Stone et al., 2003, Yang and Foegeding, 2011). There are several foam generating techniques of which two are more popular in scientific experiments; gas injection and whipping. Regarding gas injection, foaming capacity is a function of fluids physical properties such as surface tension, film elasticity, fluid viscosity and etc., while the chemical nature of the liquid is ignored. According to the literature, ovalbumin constitutes more than 50% of egg white proteins; and its main functional property is surface denaturation, but the denaturation process for this specific protein initiates with physical tension (Belitz et al., 2009, Zayas, 1997), meaning that, its normal presentation at the air/water interface does not have any effect on its natural conformation (Benjamins, Lyklema, & Lucassen-Reynders, 2006). It should be noticed that it is an irreversible process for ovalbumin (Neurath & Bull, 1936). Since the denaturation process does not happen spontaneously at air/water interface and also gas sparging does not provide such physical tension, the final volume of the foam is not the actual foaming capacity of egg white solution. Therefore, it seems that whipping method is more convenient technique to measure the foaming ability of egg white, while gas injection is still applicable for other proteins such as whey protein whose molecules does not need any physical tension to play a role at surfaces.

The second important factor which is directly related to foam functionality, as it restricts the convenient time of foam applicability, is drainage. Drainage is a function of foam stability and apart from chemical properties of the solution; it alters with variations of air fraction (φ) and the viscosity of initial liquid. Higher air phase leads to increase in the number of bubbles and extends path for liquid to drain out from the foam structure through bubbles lamella (Nakamura and Sato, 1964, Schramm, 2005). To get to the maximum air phase fraction for a specific liquid, determining the optimum whipping time is mandatory, since both over beating and whipping in periods shorter than optimum time have negative effects on foam texture and stability. Due to the descriptions above, the physical properties of foam are considered as convincing evidence for some interactions occurring within foam structure, even between protein molecules. However, a few of previous researches have focused on the effect of hydrocolloids on foaming properties of fresh pasteurized egg white; meanwhile the effect of Persian gum as a native gum in foam systems has not been studied by now; Thus the aims of this research were: a) to investigate the effect of two hydrocolloids on physical properties of pasteurized fresh egg white foam at pH 9, considering mentioned issues and challenges; b) to compare the impact of this native gum on the foaming properties of the egg compared to the performance of commercial Xanthan gum to possibly find a native replacement for commercial gums.

Section snippets

Materials

The pure liquid egg white with standard composition was purchased from Tooka Talaei Paj Company. White PG (protein: 1.05%, fat: 0.8%, dry matter: 89.16%, total ash: 2.3%, crude fiber: 0%, Mw: 4.74 × 106 Da, apparent viscosity for 1% solution at shear 60/s: 45.7 mPa s, Zeta potential at pH 5: −25 mV) was purchased from local herbal store (Shiraz, Iran). Then it was grounded and passed through a sieve (mesh size 60) and stored at sealed vessel. The commercial grade XG (dry matter: 88%, total ash:

Initial liquid properties

Egg white (EW) is a shear-thinning liquid in its original form (Belitz et al., 2009). The filtration process relays a destructive effect on its fibrillar structure which is formed by ovomucin in egg white and results in a smooth proteinous fluid. Pasteurization, stirring and mixing during the process can also have the same effect on the egg white. According to our viscometric experiment data from pasteurized liquid egg white, flow behavior was fitted appropriately to the Newtonian equation

Conclusion

Regarding the week structure of pasteurized fresh egg white, and requests from industrial consumers to improve the physical properties, addition of some additive to achieve a proper foam from egg white seems necessary. Appropriate methods to measure foam overrun and stability should be applied to gain accurate results as much as possible. Although several parameters could affect the physical properties of egg white foam, the whipping time is an absolutely effective factor in foam structure and

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