The extension of shelf-life of eggs contributes to the reduction of food losses and decreases the use of refrigeration, energy demand, production costs, and consequently avoid the increase in the price of the final product. The rice protein concentrate (RPC) and plus Brazilian green propolis (GP), were used in the manufacture of coatings used to extend the shelf-life of eggs during storage for 6 wk at 20 oC. The coatings based on RPC and GP delayed the loss of internal egg quality, since avoided moisture loss through the pores of the eggshell. The improvement of the quality attributes showed the potential of using coatings, such as the RPC and GP coatings analyzed in this research.
Material and methods
The materials used in this work were: rice protein concentrate (RPC), Brazilian green propolis (GP), Glycerol and Fresh eggs. The fresh eggs were divided into four groups: 1 – the uncoated group as the control, 2 – a RPC group, 3 – a GP coated group (10% solution), 4 – a last group with RPC combined with GP (at 10%). The edible coating solution was prepared by mixing RPC (8%) and glycerol (16%) in 100 ml distilled water. Dry extract of GP was dissolved in alcohol and distilled water to prepare the propolis solution. All eggs were washed with water at 42 oC and chlorine (50 ppm) was used as a sanitizer. The eggs were immersed for 1 min each followed by drying time of 5 min. The clean eggs were individually submerged in the coating solutions at 24 oC for 1 min, so that the coating visibly covered the entire shell surface. The uncoated and coated eggs were placed in polystyrene trays and were then dried at room temperature. At the end of the procedure, the eggs were stored at a room with controlled temperature (20 oC) for up to 6 wk and analyses were realized on 0, 7, 14, 21, 28, 35, and 42 day. Six eggs per treatment were analyzed on 0 and 42 d for Salmonella spp. presence.
To characterize eggs with zero days of storage, twelve fresh eggs from each group were randomly chosen and evaluations of quality parameters were carried out. Some analyzes were performed weekly: weight loss, Haugh unit, albumen, and yolk pH and yolk index. The variables of eggshell breaking strength (twelve eggs/treatment), the color (6 eggs/treatment), and the electron microscopic structure of the shells (three eggs/treatment) were evaluated at the end of the experiment. The eggs were weighed individually on a precision digital scale (Bel, Mark M 214A, Italy). The weight loss was calculated weekly in relation to the respective egg weight on day zero. After separation of the yolk and albumen, the dense and the fluid albumen were homogenized for 20 s, and then the pH (albumen and yolk) was determined using a digital pH meter. A digital caliper (TMX PD – 150, China) was used to measure the yolk width (mm) and the yolk index. Eggs with a smooth shell surface and without imperfections were selected for color measurements. The eggshell breaking strength (puncture strength) was performed using a texture analyzer. The eggshells were drilled using a firing force of 3 g, at the top using a die probe and constant speed in compression mode.
Results
No Salmonella spp. colonies were detected in all noncoated and coated eggs before and after 6 wk of storage at 20 oC. In the analysis of the responses weight loss, Haugh unit, albumen and yolk pH and yolk index, a significant interaction was observed between treatments and storage time. In general, the eggs that were coated showed better quality, maintaining the integrity of the eggs over 6 wk of storage. In the end of the storage time, the coated eggs had the lowest weight loss. For all eggs, the weight loss gradually increased with increased storage periods and the eggs from the control group (uncoated) had the highest weight loss and eggs coated with RPC, GP, or RPC þ GP showed less weight loss. Haugh unit (HU) decreased over the storage period. Treatments RPC þ GP and GP were similar among them and both were higher than in uncoated eggs. Eggs coated with GP, was able to maintain quality for longer, maintained grade AA up to 6 wk compared to control. The albumen pH gradually increased, the initial average albumen pH of the eggs was 8.03 and this value increased to 9.51 after 6 wk in the uncoated eggs. Coated and uncoated treatments differed in albumen pH early from the 1st wk up to the end of the study. The treatments RPC, GP, or RPC þ GP showed similar albumen pH at the end of storage time.
Yolk index (YI) of the coatings tested had a higher YI compared to the control treatment. After 6 wk of storage, the YI of the uncoated eggs decreased from 0.48 to 0.33. This was the lowest result observed, followed by eggs coated with RPC, GP, and RPC þ GP. In general, it can be said that the egg quality decreased according to the increase in storage time. The eggs coated with GP and PRC þ GP showed higher b* values than the control and RPC-coated treatments. The eggshell breaking strength did not differ between uncoated eggs (4.49 kg force) and eggs coated with RPC (4.78 kg force), GP (5.12 kg force), and RPC þ GP (5.25 kg force) after 6 wk of storage, probably due to the high value of variation coefficient (14.16) with a minimum observed value of 3.48 kg force and a maximum of 6.47 kg force.
Conclusions
The work was focused on the assessment of the effects of rice-protein and green propolis coating. The results highlight the potential of the coating to act as a moisture loss barrier, providing evidence that coating can extend egg shelf-life and reduce food losses. The results indicate that egg weight loss, albumen pH, Haugh unit, and Yolk index are variables that are greatly influenced by coating and storage time. The study confirms that measurements of weight loss and albumen quality (pH) are excellent indicators of egg freshness. This study demonstrated the use of coatings could preserve albumen quality for 2–3 wk longer compared to uncoated eggs. Based on these assessments, future research should focus on sensorial analysis and consumer acceptance.
Reference:
da Silva Pires, P.G., Bavaresco, C., da Silva Pires, P.D., Cardinal, K.M., Leuven, A.F.R. and Andretta, I., 2021. Development of an innovative green coating to reduce egg losses. Cleaner Engineering and Technology, 2, p.100065.
