Biochemical and microbial studies on the efficiency of some coating materials for egg preservation

Abstract

Five coating materials (paraffin oil, starch, gelatin, dextrin and formaldehyde-urea polymer) have been selected to seal the eggshells of eggs laid by white Balady hens (a native Egyptian breed). The uncoated and coated eggs were stored at room temperature (30 ± 2d`C) and in a refrigerator (5 ± 1d`C), and periodically examined microbiologically and chemically. The number of total microorganisms located on the outer surface of uncoated and coated eggs was slightly increased with increasing the storage period up to 30 days. Thereafter, a decrease occurred on the total microbial count from 30 to 60 days in all cases except in eggs coated with gelatin. On the other hand, no bacterial growth was detected in the whole internal egg constituents. The chemical parameters (acid value, free amino acids, total reducing sugars and hydrogen sulfide) were generally increased with time during storage of uncoated eggs at room temperature. The mode of reaction type, i.e. gradual increase or an autocatalytic, for the production of free fatty and amino acids, mono- and oligosaccharides and hydrogen sulfide was entirely dependent upon the storage temperature (30 d`C or 5 d`C). Sensory scores for the uncoated and coated eggs during storage were in accordance with the data of hydrogen sulfide. Storing eggs in a refrigerator and coating minimised the increase of these values considerably. In general, paraffin oil was the superior coating material for maintaining egg quality.