Optimization of a rapid microbiological method for the assessment of lysine bioavailability of animal feed proteins

Abstract

Achieving nutritional requirements can be a difficult hics. task with the wide variety of protein sources utilized in the feed industry. Assessing the biological availability of amino acids in protein sources rapidly is essential to satisfy dietary requirements and for least cost feed formulation. Of the amino acids, lysine is of key importance due to it being first or second limiting in poultry diets. Therefore, a deficiency or absence of lysine can halt protein synthesis in the animal hindering proper growth and maintenance. The standard method to quantitate the biological availability of lysine is to perform animal growth or digestibility assays, but such assays do not provide a cost effective, timely and reliable determination of lysine availability. Microbiological assays are a rapid and cost effective alternative to animal bioassays. Auxotrophic mutants of Escherichia coli have been shown to be an accurate indicator of amino acid availability in various protein sources when compared to animal and chemical data. The objective of this research is to develop a more rapid in vitro amino acid bioassay for lysine utilizing an E. coli lysine auxotroph that is comparable to conventional in vitro assays for lysine bioavailability. This involves (1) developing a standard medium for lysine assessment of protein sources that will eliminate background microform from protein sources (2) developing a standardized enzyme digest step that can be used on a wide variety of protein sources and (3) developing a luminescent lysine auxotroph strain of E. coli for more rapid lysine assessment. Completion of these objectives will allow the rapid determination of lysine availability and potentially replace animal bioassays resulting in improvements in nutritional quality and cost effectiveness of diets for animal consumption.