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Egg Yolk Cholesterol Lowering Effects of Garlic and Tea

Marshall Arebojie Azeke and Kokoete Ekerete Ekpo
 
ABSTRACT
This study was conducted to evaluate the effect of garlic and tea on the performance, egg traits and laying parameters of laying hens. Five groups of black leghorn hens, Yafa breed (five birds per group) and aged 21 weeks were used for this experiment. Each group was fed basal diet (layers mash) supplemented with garlic at 1% garlic powder (group 1), 2% garlic powder (group 2), 1% black tea (group 3), 2% back tea (group 4) and a combination of 2% garlic and 2% tea (making 4% supplementation, group 5). Feeding was done for four weeks after a one week acclimatization period on test and control feeds. The effects of supplementation on the number and weight of eggs layed, the weight of hens and the weight of egg yolk were determined. Also determined were the total triglycerides, HDL-, LDL and total cholesterol content of egg yolk. Feeding of hens for 4 weeks with test and control diets resulted in non-significant changes (p>0.05) in the weights of birds, egg and egg yolk. All the garlic supplemented feeds resulted in significant reductions (p<0.05) of total cholesterol, total triglyceride, LDL- and HDL-cholesterol. With exception of the 1% tea supplemented diet, the other tea supplemented diet resulted in significant reductions in the egg yolk concentration of the cholesterols tested. One percent tea supplementation had no significant effect on LDL-cholesterol concentration of egg yolk (p>0.05). The combination of garlic and tea resulted in significant reductions of total-LDL and HDL-cholesterol (p<0.05) but not total triglycerides (p>0.05). The control diets had in most cases non-significant effects on the lipid parameters tested. The results show that garlic and tea have great potential when low cholesterol egg is desired.
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  How to cite this article:

Marshall Arebojie Azeke and Kokoete Ekerete Ekpo, 2008. Egg Yolk Cholesterol Lowering Effects of Garlic and Tea. Journal of Biological Sciences, 8: 456-460.

DOI: 10.3923/jbs.2008.456.460

URL: http://scialert.net/abstract/?doi=jbs.2008.456.460

INTRODUCTION

The effect of dietary cholesterol and saturated fat in raising plasma cholesterol levels has been identified and verified in numerous metabolic studies. Some cross section population studies have established a correlation between dietary cholesterol and plasma cholesterol levels in humans (Schonfeld et al., 1982). Earlier studies (Grande et al., 1965) suggested that the P/S ratio did not affect the changes in plasma cholesterol in response to dietary cholesterol. However, most studies agree that the fat composition of the diet influences the plasma cholesterol changes in response to cholesterol consumption. Recent studies have focused on the effect of dietary lipids on plasma lipoproteins and apoproteins (Mooradian et al., 2006). These studies have generally shown that dietary cholesterol increases LDL-cholesterol but either is without effect or increases HDL-cholesterol (Weggemans et al., 2001). Most investigators have observed a large inter-individual variability in response to cholesterol and saturated fat-containing diets (Steinberg, 2004).

Animal studies have suggested that garlic supplemented diets may inhibit the synthesis of cholesterol and fatty acids in the liver (Yeh and Liu, 2001). Warshafsky et al. (1993) suggested that a cholesterol-lowering effect of ~ 9% (0.59 mmol L-1) could be achieved by a daily consumption of 1.5-3 g of fresh garlic for 2-6 months. Allicin, which causes the characteristic garlic odour, is believed to be the active lipid-lowering compound in garlic. Also flavonoids from green and black tea, when added directly to isolated LDL, protect against lipid peroxidation induced by free radicals, copper ions and cells (Ishikawa et al., 1997). The effect of tea consumption on the development or regression of atherosclerotic lesions in humans has not been directly examined (Riesmersma et al., 2001).

According to Guéye (2003), egg consumption in Africa is estimated to be around 2.1 kg person-1 year-1. The egg contributes 46% of the daily cholesterol intake of the American diet (McGill, 1979) and several previous studies have used eggs as cholesterol source in human nutritional experiments (Porter et al., 1977). Egg consumption has been associated with increases in LDL-cholesterol and with small or negligible changes in HDL-cholesterol (Weggemans et al., 2001).

Several studies showed that plasma cholesterol lowering drugs, such as statins, were able to reduce significantly the cholesterol concentration of egg yolk (Elkin et al., 1999). The present study was therefore conducted to evaluate the effect of garlic and tea on the performance, egg traits and egg yolk cholesterol concentration of laying hens.

MATERIALS AND METHODS

Preparation of layers mash: The layer’s mash used in this study was prepared at the Hephzibah Integrated Farms, Irrua, in mid-western Nigeria. The feed composition is shown in Table 1. This study was conducted in the 2006.

Preparation of garlic powder, tea and test feed: Garlic was purchased from a local market in mid-western Nigeria. It was initially cut into smaller pieces and then sun dried for about two days. After sun drying, the garlic was milled into a powder. This was stored in closed containers pending usage. The black tea (LIPTON™ tea brand) packaged in 2 g portions was purchased from a local supermarket in mid-western Nigeria. The tea powder was removed from its packaging material and placed in a bowl just before weighing to compound the test feed. The test feed was prepared by weighing out 90 and 180 g of garlic powder and making up to 9,000 g with layer's mash to obtain the 1 and 2% supplementation, respectively. Tea was administered brewed in tap water as 1 and 2% tea powder in water (w/v). This was used in place of water for the tea supplementation group.

Preparation of poultry: The Ambrose Alli University Poultry was used for this study. The experimental poultry cages constructed with compartments for housing a single bird were used. Each compartment had dimensions 35x20x37 cm for length, breadth and height, respectively. The cages and the poultry house were first of all disinfected. Two troughs each were placed in the cage compartment for feed and water/tea, respectively.

Administration of feed: The black leghorn hens, Yafa breed and aged 21 weeks, which were already laying eggs, were used for this experiment. A total of six experimental groups of five birds each were used. They were all allowed to acclimatize on normal layer’s mash for one week before test feeding was commenced. Each bird was given 100 g of feed per day and water/tea was administered ad libitum. One group (control) received layer’s mash and water while the other five groups (test) received test feed. Feeds were supplemented with garlic powder at 1% level (group 1), 2% level (group 2), 1% black tea (group 3), 2% back tea (group 4) and a combination of 2% garlic and 2% tea (making 4% supplementation, group 5).

Table 1: Composition of layer’s mash

Data collection: The quantity of feed left after each day was collected and weighed. The number of eggs layed was also noted on daily basis. The weight of the birds and weight of eggs were recorded on weekly basis. The eggs used for analyses were collected one per hen on day 0, 7, 14, 21 and 28.

Preparation of egg yolk for analyses: The eggs used for analyses were prepared according to the procedure described by Elkin et al. (1999). The eggs were first of all hard-cooked, allowed to cool, after which the weight of the boiled egg was noted. The egg shell was peeled off and also weighed followed by the careful removal of the egg white (albumen). The yolks were separated, weighed and crumbled. A 1 g sample of each yolk was homogenized with 15 mL of chloroform-methanol 2:1 (by volume), thoroughly mixed and filtered. Egg homogenate filtrates were designated egg yolk samples.

Analysis: Total cholesterol, HDL-cholesterol and total triglycerides concentrations of egg yolk were determined using the respective RANDOX® cholesterol assay kit. The kit contained cholesterol assay reagent and standard cholesterol solution, used for calibration curve.

Total cholesterol: One hundred microliter of egg yolk sample and 100 μL of deionized water (reagent blank) were pipetted into separate test tubes. This was followed by 1000 μL of total cholesterol assay reagent. The test tubes were incubated for 15 min at 37°C after which absorbance of sample was read 500 nm against the reagent blank. The various cholesterol concentrations recorded as mg g-1 of egg yolk was computed from values obtained from the various cholesterol standard curves.

HDL-cholesterol: The HDL-cholesterol assay kit (RANDOX®) contained a cholesterol precipitant. Five hundred microliter of egg yolk sample was pipetted into a test tube and 1000 μL of the precipitant was added, mixed and then centrifuged for 15 min. After centrifuging, the supernatant was used for total cholesterol assay as described in preceding section. The difference in value was noted as HDL-Cholesterol in mg g-1 of egg yolk.

Total triglyceride: The Total triglyceride assay kit contained a buffer solution, enzyme reagent and standard triglyceride solution. The working enzyme reagent was constituted by adding 15 mL of buffer to the enzyme reagent. Triglyceride assay was performed as previously described except that test tubes were incubated for 15 min at room temperature.

LDL-cholesterol: LDL-cholesterol was estimated using the Friedewald equation (Friedewald et al., 1972), which is as follows:

LDL-cholesterol = Total cholesterol–(Triglyceride/5+ HDL-cholesterol)

Data analyses: Student’s t-test was used to compare test results obtained after four weeks with results obtained at the start of experiment.

RESULTS AND DISCUSSION

As stated earlier, test and control feeding was done for 4 weeks. It was found that supplementation at test levels did not significantly affect feed consumption and number of eggs layed (p>0.05; data not shown). With the exception of the 1% garlic powder supplementation group, test diet resulted in non-significant changes (p>0.05) in the weights of birds and egg (Table 2). One percent garlic powder supplementation resulted in 10% increase in average weight of bird (p<0.05). Control diet resulted in 6% reduction in bird weight (p>0.05). Only 1% supplementation resulted in slight increase in weight of egg yolk (+6%, p>0.05). Only garlic powder supplementation had a positive effect on the weight of egg shell while other test treatment resulted in non-significant reductions in weight of egg shell (Table 2).

Almost all the test treatment resulted in significant reductions (p<0.05) in the egg yolk concentration of total cholesterol, LDL and HDL-cholesterol and total triglyceride. The exception was the 1% tea supplemented diet, which resulted in a significant increase in LDL-cholesterol concentration in egg yolk. On the other hand control diet resulted in increases in total-cholesterol, LDL- and HDL-cholesterol. Similar patterns were observed for the various egg yolk cholesterols of eggs from hens which received 2% tea, 1 and 2% garlic supplementation as well as combination of 2% tea and 2% garlic powder (Table 3).

The anti-cholesteromic agents found in garlic and in tea flavonoids could be responsible for the reduced cholesterol content of egg yolks. There are lots of research on the clinical use of the hypocholesterolemic effect of garlic and tea in blood plasma. There is, however, scarcity of information on the effect of garlic and tea on egg yolk cholesterol. Yalcın et al. (2006) recently researched on the effect of garlic supplementation on egg yolk total cholesterol. They also reported a significant reduction in total egg yolk cholesterol. They did not, however, report on LDL- and HDL-cholesterol.

The mechanisms underlying the possible lipid-lowering action of garlic are not well understood. Allicin, which causes the characteristic garlic odour, has been suggested to be one of the major sulphur-rich components in garlic that may contribute to its hypocholesterolemic effect. Animal studies have suggested that garlic supplemented diets may inhibit the synthesis of cholesterol and fatty acids in the liver (Yeh and Liu, 2001). Although the results from two earlier meta-analyses (Warshafsky et al., 1993) suggested a hypocholesterolemic effect of garlic, they did not provide strong evidence for the usefulness of garlic as a hypocholesterolemic agent because of methodological shortcomings of many of the studies included.

Table 2: Changes in weight of layers and some egg characteristics after four weeks feed administration
Results are means of at least 3 determinations±SD; *A total of 4% supplementation comprising 2% each of garlic powder and black tea, **Values in brackets represent (%) change after 4 weeks of feed administration

Table 3: Changes in cholesterol contents (mg g-1) of egg yolk after four weeks feed administration
Results are means of at least 3 determinations±SD; *A total of 4% supplementation comprising 2% each of garlic powder and tea, **Values in brackets represent (%) change after 4 weeks of feed administration

Not all the included trials provided information about the subjects’ dietary intakes and body weights, or about the comparability of the smell or taste of the placebo and garlic preparations. In the meta-analysis performed by Warshafsky et al. (1993), only 5 randomized, placebo-controlled trials of the 28 identified trials were included. The reason for the lack of effect of garlic on the lipid and lipoprotein profile in recent well designed studies is unclear. It is possible that the allicin released from the garlic preparations, despite standardization was not optimal (Zhang et al., 2001). Garlic preparations are often designed to release allicin enzymatically from alliin after consumption. It seems that the enzyme alliinase quickly denatures at a low gastric pH (Ackermann et al., 2001).

Flavonoids from green and black tea, when added directly to isolated LDL, protect against lipid peroxidation induced by free radicals, copper ions and cells (Ishikawa et al., 1997). There is substantial evidence that oxidized LDL is central to early events leading to atherosclerosis (Riesmersma et al., 2001). The effect of tea consumption on the development or regression of atherosclerotic lesions in humans has not been directly examined. A typical cup of tea (200 mL) contains 24-40 mg catechin, 8-15 mg flavonols, plus flavones, ~85 mg thearubigins and 7-15 mg of theaflavins, which together amount to 166-193 mg per cup (Riesmersma et al., 2001). This makes tea one important source of phenols. Tea polyphenols, catechins and flavonols scavenge reactive oxygen species (Rice-Evans et al., 1996) and chelate transition metal ions in a structure dependent manner (Brown et al., 1998). Flavonoids found in tea scavenge NO and peroxynitrite produced from superoxide radical and NO (Pannala et al., 1997). The ways and means by which these events lead to a reduction in the levels of cholesterol in egg yolk should be the focus of further research. The results of this study, however, show that garlic and tea have great potential when low cholesterol egg is desired in the diet.

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