- Open Access
Effects of different cooking methods of oatmeal on preventing the diet-induced increase of cholesterol level in hypercholesterolemic rats
© Ban et al. 2015
Received: 22 September 2015
Accepted: 16 October 2015
Published: 24 October 2015
The aim of present study is to investigate the influences of brewing and boiling on hypocholesterolemic effect of oatmeal in rats fed with a hypercholesterolemic diet.
Fifty-six male Sprague–Dawley rats were divided into 5 groups of 8 rats each with similar mean body weights and serum cholesterol concentrations. Rats were fed with the experimental diets containing 10 % of oatmeal from two Chinese oat varieties which were brewed or boiled for 30 days. The lipids levels in serum, liver, and faeces were determined.
The effects of feeding boiled oatmeal on lowering lipid concentrations in plasma and liver were more significant than that of brewed oatmeal (P < 0.05). Feeding boiled oatmeal was also more efficient in increasing fecal total lipids, cholesterol and bile acids as compared to feeding brewed oatmeal (P < 0.05). Boiled oatmeal had higher apparent viscosity and soluble β-glucan content than the brewed oatmeal did (P < 0.05).
These results indicated that the capability of boiled oatmeal in improving cholesterol metabolism is better than that of brewed oatmeal, which is mainly attributed to its higher soluble β-glucan content and apparent viscosity.
Dietary oat effectively lowers the plasma total cholesterol and low-density lipoprotein (LDL)-cholesterol concentrations and, hence, reduces the risk of cardiovascular disease in animal models and hypercholesterolemic subjects [1, 2]. The health benefits of oat are mainly attributed to its high content of nutritional components, including 2.0 ~ 7.5 % of β-glucan , 2 ~ 12 % of crude fat , 13 ~ 20 % of protein  and around 60 % of starch . Previous studies have also shown that dietary full-fat from oat bran could promote excretions of fecal lipids and bile acids. Oat oil has high tocotrienols and sterols contents and, hence, hypocholesterolemic effect. As a result, oat bran with high lipids content lower serum total cholesterol and LDL-cholesterol concentrations  as well as the concentrations of rat plasma total cholesterol, LDL-cholesterol the cholesterol, free cholesterol, cholesterol ester and triglyceride levels of liver .
According to Wolever et al. , dietary oat β-glucan reduces plasma cholesterol total cholesterol and LDL-cholesterol levels by increasing intestinal viscosity, which lowers the reabsorption of bile acids, leading to lower plasma lipids levels. Wood et al.  reported that there was a significant correlation between the peak levels of blood glucose concentration and the viscosity of β-glucan. Therefore, it is nutritionally favorable for β-glucan to have a high viscosity. On the other hand, as reported by Tong et al. , dietary hull-less barley β-glucan could reduce the concentration of plasma LDL cholesterol in hypercholesterolemic hamsters. However, this hypocholesterolemic effect was weaker than that of oat β-glucan because of the higher viscosity and prebiotic activity of oat β-glucan. Previous study demonstrated that the viscosity and hypocholesterolemic effect of β-glucan was positively correlated with its molecular weight, namely, the molecular weight of β-glucan may influence the hypocholesterolemic effect .
Thermal, physical and enzymatic treatments had significant effects on the water solubility and molecular weight of β-glucan and, thereby, could affect the viscosity of hull-less barley . In addition to molecular weight of β-glucan, the soluble β-glucan content can also affect the lipids-lowering effect of oat or hull-less barley because soluble β-glucan can formhighly viscous solutions, which seems to be responsible for reducing the plasma cholesterol in humans and animals [14–16]. In China, brewing and boiling are the most common cooking methods for oatmeal. However, few publications can be found reporting the relationship between the cooking methods and the health impacts of oatmeal, especially the lipid-lowering activity.
The aim of this study was to investigate the effects of oatmeal cooking methods including brewing and boiling on cholesterol metabolism of Sprague–Dawley rats fed with two different varieties of oatmeal. The apparent viscosity, soluble β-glucan and other index of brewed and boiled samples were determined, in order to clarify the differences in their hypocholesterolemic abilities.
Materials and methods
Oatmeals (Avena sativa L., Bayou NO.1 and Bayou NO.8) were provided by Beijing Lipid-lowering Oats Products Development Co. Ltd. Oatmeal Bayou NO.1 contained 12.9 % protein, 75.9 % total starch, 5.6 % crude lipid and 5.6 % crude fiber. Oatmeal Bayou NO.8 contained 16.7 % protein, 68.8 % total starch, 5.5 % crude lipid and 9.0 % crude fiber. The compositions of oatmeals were determined using the methods of AACC-32-23 (2000), AOAC 996.11, GB/T5511-2008, GB/T5512-2008, GB6193-86, and GB/5009.3-2010, respectively.
To obtain brewed oatmeal sample, 250 g of oatmeal was mixed with 1 L of 100 °C hot deionized water, and then cooled at room temperature with constant stirring. Boiled oatmeal sample was prepared by cooking 250 g of oatmeal in 1 L of 100 °C hot deionized water with constant boiling for 5 min using an electronic cooker (Povos-PIB07, Shanghai POVOS Electric Works Co. Ltd., Shanghai, China), and then cooling at room temperature.
The heat treated oatmeal samples were filtrated through a 100 mesh filter cloth, respectively. The apparent viscosity of the filtrate was measured by a digital viscometer (Model NDJ-9S, Shanghai Precision and Scientific Instruments Co., Ltd., Shanghai, China) using a 3# rotor at a shear rate of 3 r/min and 25 °C.
Soluble β-glucan concentration
The β-glucan concentration in the filtrate of treated oatmeal was determined by an enzymatic method using a mixed-linkage β-glucan assay kit (Megazyme International Ireland, Ltd., Wicklow, Ireland).
Protein dispersibility index
Animals and diets
Diet composition (g/1000 g diet)
Brewed Bayou No.1
Boiled Bayou No.1
Brewed Bayou No.8
Boiled Bayou No.8
This study was carried out according to the P.R. China legislation regarding the use and care of laboratory animals and was approved by the Animal Ethics Committee of Northwest A&F University (Yangling, China).
Analysis of metabolic parameters in rats
The concentrations of plasma lipids were measured using an Automatic Chemistry Analyzer (7020, Hitachi, Tokyo, Japan) at Biochemical Clinical Laboratory, Yangling Demonstration Zone Hospital, Yangling, China. The liver lipids extracted by tissue lysate from tissue lipids assay kits were chemically measured using the method as the kits described. The concentrations of liver lipids were measured by a Tissue triglyceride assay kit, E1003-2; Tissue total cholesterol assay kit, E1015; and Tissue free cholesterol assay kit, E1016 (Applygen Technologies Co., Ltd, Beijing, China). Liver was made to be paraffin sections, and its structure was observed by H&E staining method. The fecal total lipids contents were measured by Soxhlet method. The cholesterol and fecal bile acids contents were measured using the Tissue total cholesterol assay kit, E1015 (Applygen Technologies Co., Beijing, China) and Rat Bile Acid ELISA Kit (Nanjing Sen Shellfish Gamma Biotechnology Co., Ltd., Nanjing, China), respectively.
The data were expressed as the mean ± standard errors (SE) and analyzed by SPSS (Version 12.0 for Windows, SPSS Inc., Chicago, IL, USA) using Tukey-Kramer’s multiple comparison post hoc test and t-test. Statistical significance was defined as P < 0.05.
Growth parameters of rats
Effects of eating methods on the growth parameters of Sprague–Dawley rats fed with a hypercholesterolemic dieta
25.1 ± 0.4
25.2 ± 0.5
25.3 ± 0.4
25.0 ± 0.3
25.4 ± 0.3
19.8 ± 0.4
18.9 ± 0.5
19.0 ± 0.5
19.0 ± 0.5
19.8 ± 0.4
Initial body weight
281 ± 5
279 ± 6
277 ± 4
283 ± 5
279 ± 7
Final body weight
327 ± 9
333 ± 10
332 ± 9
323 ± 13
323 ± 10
Body weight gain
56 ± 9
54 ± 8
55 ± 5
50 ± 7
54 ± 8
10.7 ± 0.3
10.9 ± 0.8
11.0 ± 0.6
10.9 ± 0.5
11.3 ± 0.2
Effects of eating methods on the fecal parameters of Sprague–Dawley rats fed with a hypercholesterolemic diet1
Fecal weight (g/day)
2.50 ± 0.21
2.55 ± 0.23
2.61 ± 0.17
2.58 ± 0.19
2.66 ± 0.11
Fecal lipids (mg/day)
91 ± 9a
132 ± 11b
197 ± 10c
136 ± 8b
241 ± 22d
44 ± 5a
59 ± 6b
90 ± 8c
64 ± 7b
117 ± 13d
57 ± 3a
67 ± 5b
93 ± 4c
89 ± 5c
121 ± 11d
Chemical and physical characteristics of oatmeal
Numerous studies have revealed the cholesterol metabolism of oats in animal models and hypercholesterolemic subjects may play the beneficial effects, and thereby reduce the risk of cerebrovascular disease [1, 2, 19, 20]. So far, a large number of studies have focused on the effects of oat functional ingredients and its mechanism, but the effect of cooking method of oatmeal on cholesterol-lowering activity is still unknown. In present study, boiling methods has been demonstrated to be a more efficacy cooking method for oatmeal for improving its effects in lowering plasma lipid concentration. Boiled oats (both two varieties) lowered the concentrations of plasma total cholesterol, LDL-cholesterol and triglycerides more significantly than the brewed oatmeal. In addition, the ability of boiled oatmeal to lower liver lipids concentrations was stronger than that of brewed oatmeal (P < 0.05). The findings were new because the effects of cooking methods on oatmeal cholesterol-lowering activity was not reported much elsewhere. We also found that Bayou No.8 had better lowering effect of plasma lipids than Bayou No.1. It was in agreement with the reports that the cholesterol-lowering effect was attributed to its β-glucan content [9, 21].
It has been widely reported that dietary oats reduces the plasma lipids concentrations by promoting the excretion of fecal total lipids and bile acids, and regulating the activities of 3-hydroxy-3-methyl glutaryl-coenzyme A reductase and cholesterol 7-α hydroxylase CYP7A1 . In present study, the fecal total lipids, cholesterol and bile acids excretion were increased in all of oatmeal groups compared with the control group (P < 0.05). The capability of boiled oatmeal to increase fecal lipids excretion was stronger than that of brewed oatmeal (P < 0.05). The results indicate that the boiling method contributes to decrease plasma and liver cholesterol concentrations by strengthening the inhibition of cholesterol absorption in intestine through high intestinal viscosity provided by high soluble β-glucan content.
Studies have shown that the highly water-soluble β-glucan plays the better role in lowering cholesterol than β-glucan with the low water-solubility [10, 12]. The soluble β-glucan shows the capacity of forming highly viscous solutions which seems to be responsible for the reduction of plasma cholesterol by increasing intestinal viscosity [14–16]. In addition, the soluble β-glucan is fermented by the intestinal microflora to produce the short chain fatty acids (SCFAs) which also results in the decrease of cholesterol . Bell et al.  reported that these SCFAs, absorbed through the portal vein, improved cholesterol metabolism by increasing catabolism of LDL-cholesterol or regulating the related enzymes activities. The boiled oatmeal had higher soluble β-glucan content (Fig. 4a) and apparent viscosity (Fig. 4b) than the brewed oatmeal (P < 0.05), which might be related to the higher efficacy of boiled oatmeal in lowering lipids. Our study was in agree with Izydorczyk et al.  which involved in hull-less barley. The boiled oatmeal showed higher starch gelatinization and PDI compared with the brewed oatmeal (P < 0.05) (Fig. 4c, d). Because the boiling applied more thermal energy which results in the increase of starch gelatinization and PDI, boiled oatmeal has a loose organizational structure. This may be the reason why boiling increases soluble β-glucan content of oatmeal, thus showing better lipid-lowering effectiveness than brewing.
The present study clearly revealed that cooked oatmeal can lower plasma and liver lipids concentrations in Sprague–Dawley rats fed with a hypercholesterolemic diet, and boiled oatmeal is more effective than the brewed one. The boiled oatmeal improved cholesterol metabolism by enhancing the excretions of fecal total lipids, cholesterol and bile acids. Furthermore, the better hypocholesterolemic effect of boiled oatmeal was proven to be positively correlated to its higher soluble β-glucan content and apparent viscosity as compared to the brewed oatmeal.
This research was funded by the Chinese Agricultural Research System (grant number: CARS-08-D-3). We appreciate Beijing Lipid-lowering Oats Products Development Co. Ltd for their kindy support to this work.
Open AccessThis article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated.
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