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Natural Variation in Egg Cholesterol Greater Than Probiotic Effect

by 5m Editor
6 December 2010, at 12:00am

The results of an investigation into effects of feeding bile salt hydrolase-positive Bifidobacterium strains on the cholesterol content in hen's eggs from the Poultry Industry Council of Canada (PIC). The variation between individual birds was greater than the effect of the selected probiotic bacteria in this pilot study.

The Problem

Hypercholesterol is a risk factor for cardiovascular disease, the leading cause of death in many developed countries, and thus preventive measures have been taken through medication, but those medications often resulted in side effects. The cholesterol lowering effects of natural lactic acid bacteria (LAB) and probiotic bacteria have been studied in human, mouse and pig. The deconjugation mechanism of bile salts by strains containing the bile salt hydrolase (BSH) might be responsible for the cholesterol lowering effect of probiotics, but the hypocholesterolemic mechanism of probiotics based on the BSH hypothesis has not yet been sufficiently elucidated. Yet, many yogurt companies have selected the BSH-active bifidobacteria and lactobacillus strains for the commercial production of probiotic yogurts.

To confirm this hypothesis, PIC has studied the detailed genetic analysis of the probiotic bacterial bile salt hydrolases. In the present study, they investigated the role of BSH-active probiotic bacteria in lowering of cholesterol level in serum and subsequently in hen's eggs.

The Research

BSH-active Bifidobacterium longum cells grown in MRS medium with cysteine were harvested and the freeze-dried and heat inactivated (BSH-negative) cells were mixed with the basal diet at low dose and high dose of cells. Ninety white Leghorn layers (21 week old) were housed in individual cages and randomly assigned into treatments of nine hens each. The experiment was conducted from 0 to 12 weeks. The body weight and feed conversion ratio (kg of feed/dozen eggs) was calculated every two weeks. Five eggs of each treatment were weighted and boiled. Total yolk cholesterol content in eggs and blood serum were determined by a colorimetric method using a commercial cholesterol/cholesteryl ester kits.

The different farm parameters (live weight, feed consumption ratio, egg) showed no significant differences in the treatments, that mean a good start in the trials. The viable cell counts (total microbial counts, lactic acid bacteria and bifidobacteria) also showed no significant differences among treatments and different sampling times. However, the lack of significant difference among the samples suggests that there was an important probiotic viability reduction in the feed possibly by heat during mixing, storage in refrigerator, and exposure to environmental oxygen and humidity.

The overall cholesterol concentration in both plasma and egg yolk decreased significantly with time in all treatments. This trend seems to be independent of the treatment and is more pronounced in the first eight weeks. These variations were clearly due to the biological variability as confirmed by comparing the cholesterol concentration change for each individual.

The possible cholesterol-reducing effect of the potential probiotic was masked by other factor such as effect of the feed change at the start of the experiment or even of the hen's age.

The cholesterol-reducing effect of the potential probiotic could not be confirmed at this stage, and other critical parameters must be controlled. Regular poultry feed preparation and handling conditions are too harsh for Bifidobacterium longum, causing an abrupt reduction in cell viability. Also Bifidobacterium longum KL515 did not appear to significantly colonise hen's gastro-intestinal tract. A poor colonisation would severely limit the total BSH activity in the digestive tract.

The Bottom Line

This finding identifies the biological variability of each hen and reduction of cell viability during feed preparation, that require the well controlled studies to confirm the cholesterol-reducing effect of the probiotic bile salt hydrolase in hen's serum and eggs.

December 2010