Egg Quality and Food Safety of Table Eggs

This study is an update of data presented previously (Roberts & Chousalkar, 2012) from a study which investigated egg quality at different stages of lay. Although eggs produced in Australia are considered medium to low risk for food borne illness, the egg industry in Australia is periodically implicated in cases of food poisoning. Egg shell defects may potentiate the movement of bacteria into the egg. Two egg shell characteristics were targeted: the extent of cuticle cover and the incidence of translucency. Eggs were collected from commercial caged layer flocks at different stages of lay: early (<25-40 wks), mid (40-55 wks), late (55-65 wks) and very late (>65 wks). Eggs were candled and scored for translucency. Cuticle cover was estimated using MST cuticle stain and a Konica Minolta hand-held spectrophotometer (L*a*b* colour scale). Traditional measures of egg quality were determined using specialised equipment (TSS, U.K.) Shell ultrastructural features were scored following plasma ashing of shell samples and viewing under a benchtop scanning electron microscope. Translucency score increased in late lay and then decreased in the very late flocks, which had been moulted (Table 1). As flock age increased, egg shell quality and egg internal quality decreased although quality was improved to some extent in late lay flocks following an induced moult. Cuticle cover, as measured by a* or the single score (Leleu et al., 2011) was not significantly affected by flock age although the difference between before and after staining, ?a*, was highest for the mid and late lay flocksindicating a trend to better cuticle cover at these ages. The incidence of unfavourable shell ultrastructural features was higher for older flocks and the incidence of favourable ultrastructural features was lower. The differences in mammillary layer characteristics among flock ages is consistent with the findings of previous researchers (Brackpool, 1995; Solomon, 1991) and with the traditional measures of shell quality. The limited number of correlations between egg shell translucency scores and the scores obtained from examination of the mammillary layer of the egg shells suggest that the ultrastructure scoring system only partly accounts for the phenomenon of shell translucency. Cuticle blue dye was a reliable indicator of the presence of cuticle.

Table 1 - Egg Quality Measurements

 

ACKNOWLEDGEMENT: This research was conducted within the Poultry CRC, established and supported under the Australian Government's Cooperative Research Centres Program. The participation of Rowly Horn and egg industry producers is very much appreciated. 

Leleu S, Messens W, De Reu K, De Preter S, Herman S, Heyndrickx M, DE Baerdemaeker J, Michiels CW, Bain M (2011) J. Food Prot. 74(10), 1649–1654.

Roberts JR, Chousalkar KK (2012) Proc. Aust. Poult. Sci. Symp. 23, 241-244.