Inhibition of non-enzymatic browning of white and whole egg powder by enzymatic treatment and pH change: effect on physicochemical and sensory properties

Introduction: Effective factors for increasing the quality of dried egg products have been studied by various researchers (Bergquist, 1995). Non-enzymatic browning (Millard) is the reaction between amino group (proteins/amino acids) and glucose that occurred during production of egg powder, leading to undesirable color and lower nutritional values (Sisak et al., 2006). In order to remove negative effect of glucose from liquid egg before producing the powder, glucose oxidase enzyme is applied to prevent non-enzymatic browning. This enzyme catalyzes the oxidation of glucose to gluconolactone and hydrogen peroxide, which is followed by the production of gluconic acid (Wang et al., 2008). In addition, the hydrogen peroxide produced in the reaction can also kill or inhibit the growth of microorganisms (Dobbenie et al., 1995).
Materials and Methods: Eggs were washed, disinfected and separated to be ready for treating and processing. Liquid whole egg and egg white are transferred into glass jars and mixed to become homogeneous. Citric acid treatment (10% solution) and glucose oxidase-catalase mixture were used to eliminate or minimize the effect of glucose in all samples. In enzymatic method, liquid whole egg (pH 7.6) and liquid egg white (pH 9) was treated with glucose oxidase-catalase (30°C-6 h) for removing glucose effect. In the acidic method, citric acid was applied to adjust pH of liquid whole egg on 7.6 (control), 6.6, 5.6 and 4.6 and liquid egg white, on 9 (control), 8, 7 and 6 and then they were pasteurized by water bath (65°C- 2.5min). Pasteurization of white and whole egg was evaluated based on inactivation of alpha-amylase (S. senftenbarg 557W). The measured parameters were pH, non-enzymatic browning color, foaming volume, pasteurization adequacy, sensory properties. Experiments were conducted in completely randomized design with three replicates.
Results and Discussion: Powdered eggs should retain maximum physicochemical, appearance color and sensory properties of the fresh egg. The pasteurization index in white and whole egg was based on the killing S. senftenbarg 557W pathogenic bacterium. Therefore, adequacy of pasteurization is measured based on the inactivation of alpha-amylase enzyme (65°C-2.5 min) (da Silva et al., 2017). Evaluation of alpha-amylase activity is a rapid test (starch-iodine complex) to evaluate the pasteurization efficiency of liquid egg products. Decreasing the pH of liquid whole egg from pH 7.6 (control) to pH 4.6 using citric acid (10% solution) resulted in lighter color of the samples. The results showed that after drying pasteurized eggs, the samples with pHs of 7.6 (control) and 6.6 had the darkest color due to maximum non-enzymatic browning reaction. In contrast, samples with pH 5.6 had a moderate color, while samples with pHs of 7.6 (enzymatic treatment) and 4.6 had the brightest color. The results indicated that foaming ability of reconstituted whole egg powders were higher at pHs 5.6 and 4.6 in compared to other pHs. The sample with pH 4.6 and pH 7.6 showed the highest (72%) and the lowest (55%) foaming capacity, respectively. The enzyme-treated sample (pH 7.6) had moderate foaming capacity. Semi-trained sensory assessors were used to evaluate sensory attributes such as color, thermal stability and clotting of egg powder during reconstruction. In terms of moisture according to the national standard of Iran (National Standard 2487, 1396), all samples with different pHs had the standard moisture range (4.5-5%). Regarding the physicochemical properties of egg white, decreasing pH of the samples from pH 9 (control) to 6 pH with citric acid (10% solution), caused the brighter color of the samples. The results showed that sample of egg white dried with pH 9 (control) had the darkest color due to the maximum non-enzymatic browning reaction in contrast the samples with pHs 9 (enzymatic treatment), 8, 7 and 6 lightest color (minimum color reaction). The foaming ability of the reconstituted white powder was higher at pHs 6 and 8 as compared to other pHs such as control and enzymatic treatment, while the foaming capacity was moderate at pH 7. The samples with pH 6 and control (9 pH) had the highest (82%) and the lowest (65%) foaming, respectively. Semi-trained sensory assessors were used to evaluate sensory attributes such as color, thermal stability and clotting of white powder during reconstruction. In terms of moisture according to the national standard of Iran (National Standard 2487, 1396), all samples with different pHs had a standard moisture range (4.5-5%).
Conclusion: Glucose is the main problematic component in production of egg powders, which mainly affects the appearance of products and its negative effect is through the non-enzymatic browning reaction. Acidic methods (citric acid) is applied to reduce pH and minimize the effect of glucose as a rapid method and also enzymatic treatment (glucose oxidase-catalase) applied to remove glucose and inhibit the reaction of non-enzymatic browning and subsequently discoloration of powdered samples. The foaming ability of reconstituted powder products was good at low pHs. In contrast, properties such as thermal stability and clotting displayed different behavior at different pHs.