The nutritive value of egg by‐products and their potential bactericidal activity: in vitro and in vivo studies
Technical‐grade egg albumen (TA) and whole egg (WE) by‐products are produced in substantial quantities by egg‐breaking facilities across North America. TA and WE products are recovered during processing but are not approved for human consumption. Both products are known to be rich in fat, maternal antibodies, protein and lysozyme, a bactericidal enzyme. The objective of this research was to explore the potential for egg by‐products to be used as a valuable protein, energy and bactericidal supplement in animal nutrition. To improve the nutritive value of TA and WE, spray‐dried samples were heat treated at various temperatures and their digestible protein content was determined in vitro using a pepsin/pancreatin digestion/dialysis system. In addition, enhancement of lysozyme activity towards Gram‐negative bacteria (GNB) by heat or irradiation was examined. Optimal protein digestibility for TA averaged 80% following heat treatment at 105–110 °C for 10 min. In contrast, protein digestibility of spray‐dried TA was only 55%. Heat treatment (100–122 °C) of spray‐dried WE or hot room storage of spray‐dried TA and WE products at 70 °C for up to 14 days had a minimal effect on protein digestibility in vitro. Heat treatment or γ‐irradiation of lysozyme for at least 20 min at 80 °C or 0.5 kGy, respectively, increased antimicrobial activity towards GNB. When compared with either the heat or radiation control treatments, reductions in Escherichia coli and Salmonella enterica serovar Typhimurium populations increased by at least 1 and 0.5 log10, respectively. In contrast, the effect of irradiation (2 kGy) on the antimicrobial activity of spray‐dried TA was less pronounced. In a feeding trial, rats fed spray‐dried TA and spray‐dried TA subjected to either radiation (1.8 kGy) or heat (80 °C, 20 min) treatment exhibited a body weight gain and protein utilisation equal to or higher than the control (casein diet). In contrast, feeding spray‐dried WE or TA and WE previously maintained in a hot room (70 °C) for 3 days had a negative effect on rat growth and protein utilisation. In the case of WE products this was substantiated by poor digestibility of essential amino acids, including lysine, threonine and, to some extent, methionine. When compared with the control treatments, inclusion of heat‐treated or irradiated TA in the rat diets reduced the population of Enterobacteriaceae. Copyright © 2006 Society of Chemical Industry
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Document Type: Research Article
Publication date: 2007-02-01
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