Effect of thermally treated barley dietary fiber against hypercholesterolemia

Abstract Dietary fiber is a nondigestible constituent of vegetal foods, formed by insoluble and soluble dietary fiber. The intake of dietary fiber, especially soluble dietary fiber, is limited and demands researcher's attention. The modification of cereal's dietary fiber, predominantly insoluble fiber, could be one possible solution. The current study evaluated the comparative effects of several thermal treatments on the modification of insoluble dietary fiber in barley and explored their therapeutic potential in vivo against hypercholesterolemia. The two cultivars of barley, Haider‐93 and Jau‐87, were thermally treated using different techniques, and dietary fiber was extracted. Successively, the intake of these dietary fibers was evaluated for its antilipidemic activity in normal and hypercholesterolemic rats. In the first phase, thermal treatments especially cooking without soaking increased the soluble fiber (68.08%). The roasting all increased the soluble fiber contents, however, at relatively lower rate (53.91%). The results of efficacy study revealed that biochemical parameters in control animals were within the normal clinical ranges, thus appraising the safe status of the experimental diets. The thermally treated barley fiber decreased total cholesterol (12.14%–12.63%), low‐density lipoprotein (14.12%–14.85%), and triglycerides (2.25%–4.32%). The study recorded increasing trends for high‐density lipoprotein in both normal and hypercholesterolemic rats. In the nutshell, thermal modification of dietary fiber increased the ratio of soluble to insoluble dietary fiber that improved its hypocholesterolemic potential. The thermally treated barley dietary fiber is effective in reducing the lipid profile in Sprague–dawley rats than untreated dietary fiber and, therefore, can be considered as a functional food and ingredient to cope different lifestyle diseases.


| INTRODUC TI ON
Functional foods have captured great attention owing to the presence of an array of active ingredients. Among these bioactive compounds, dietary fiber is acknowledged as a major functional ingredient due to its potential to combat different lifestyle disorders (Luithui, Baghya-Nisha, & Meera, 2019;Zhang, Wang, Cao, & Wang, 2018). Hipsley coined the term "dietary fiber" for first time in 1935, indicating the nondigestible constituents of plant cell walls. Dietary fiber is classified in two classes according to its water solubility, that is, insoluble (IDF) and soluble dietary fiber (SDF). The soluble dietary fiber is effective remedy for reducing the cholesterol, triglyceride, and glucose levels in blood. Therefore, SDF is relatively more functional than IDF. Cereals and other grains contain the higher level of insoluble fiber as compared to soluble fiber. Among cereals, barley contains relatively high soluble amounts of dietary fiber. Even if the cereal fiber is of low cost, its use in foods is considered relatively unsatisfactory due to its poor functionality. Therefore, the need for some modification of its characteristics before incorporation into foods is evident (Borderias, Alonso, & Mateos, 2005;Veronese et al., 2018).
Thermal processes are considered as important approaches for the modification of soluble and insoluble fibers ratio and of their physicochemical properties (Zhou, Qian, Zhou, & Zhang, 2012). Different methods are used for thermal modification, such as sterilization, sun drying, steam processing, boiling, frying (mainly deep fat frying), microwave drying, vacuum-belt drying, roasting, and pressure-cooking.
The steam processing of dietary fibers in Polygonatum odoratum revealed the increased oil-holding capacity, whereas sun drying significantly increased the water-holding capacity and swelling power (Lan, Chen, Chen, & Tian, 2012). Similarly, continuous vacuum-belt drying resulted effective in increasing total dietary fiber content in apple pomace at three different temperatures (Yan & Kerr, 2013).
The dietary fiber holds many functional properties that usually correlate with health-promoting perspectives. The soluble fibers due to their higher water absorption capacities form viscous gel that act as sponge structures, thus reducing the digestion and absorption of nutrients. Second, the slow rate of stomach emptying results reduced transit time in small intestine results in cholesterol reduction.
Even, some of the dietary fibers act as prebiotics, thus promoting the growth of intestinal bacteria that in return reduced the synthesis of cholesterol in the body. Barley-derived β-glucan can positively reduce the total cholesterol, low-density lipoprotein (LDL), and triglycerides; however, high-density lipoprotein (HDL) levels remained unchanged (Talati, Baker, Pabilonia, White, &Coleman, 2009. Furthermore, Behall, Scholfield, andHallfrisch (2004) reported that barley dietary fiber significantly reduced the lipid levels in moderately hypercholesterolemic men and woman.
Therefore, it can be postulated that partial conversion of insoluble into soluble dietary fiber can improve the efficacy of the fiber-enriched functional products to cope different lifestyle disorders. The aim of the current study was to evaluate the comparative effect of some thermal treatments on the conversion of insoluble into soluble dietary fiber in two barley cultivars and to evaluate their hypocholesterolemic effects in rodent modeling studies.

| Plant material
Two barley cultivars, Haider-93 and Jau-87, were procured from Ayub Agriculture Research Institute (AARI), Faisalabad. The grains were cleaned to remove any debris or field dirt and sealed in polyethylene bags.

| Extraction, determination, and modification of dietary fiber
The fiber extraction and fractionation was conducted as reported by Southgate (1977)

TA B L E 1 Mean values for dietary fiber content of thermally treated barley varieties
obtaining the whole flour (WF). After grinding, WF was sieved, boiled, and cooked using pressure cooker. In the last stage, both barley cultivars were roasted (Pushparaj & Urooj, 2011). All these samples were collected separately to check the influence of each processing stage.
Later, the four thermal treatments, that is, soaking, cooking and soaking, cooking of nonsoaked barley, and canning were applied following the protocols by Kutos, Golob, Kac, and Plestenjak (2003).

| Extraction of dietary fiber
After thermal treatments, the extraction and fractionation of dietary fibers was carried out as reported by Southgate (1977) with some modifications. The concentrations of acidic solution for the extraction of dietary fiber were adjusted to 1.50% as compared to 1.25% used in the previous studies.

| Animals
Sixty male Sprague-Dawley rats were housed in the Animal Room of Department of Physiology, Government College University, Faisalabad. The research plan was duly approved by "Ethical Departmental Committee" constituted under Office of Research, Innovation, and Commercialization (ORIC) vide Letter No. GCUF/ IFHS-16-EC-05. Initially, the rats were acclimatized by feeding basal diet for one week. During the experiment, the environmental conditions were maintained, that is, Tempt: 23 ± 2.0°C, Relative Humidity: 55 ± 5%, 12 hr light-dark period. At the beginning of trial, some rats were dissected to get the baseline values for the selected traits.

| Feed plans and housing of experimental rats
In the first phase, three iso-caloric experimental diets were prepared, that is, control diet contains corn oil (10%), cornstarch (66%), protein (10%), cellulose (10%), mineral (3%), and vitamin mixture (1%). Mineral and vitamin mixture were prepared according to AIN guidelines. The two experimental diets (T 1 and T 2 ) were prepared by replacing 2.0% cellulose with raw barley dietary fiber (2%) and treated barley dietary fiber (2%), respectively. In the second phase, high cholesterol diet, that is, 1.5% of cholesterol along with cholic acid @ 0.5% was given to induce hypercholesterolemia. Periodic examination of rats was carried out to assess the induction of hypercholesterolemia. Rest of the diet plan was same as that of normal rats and diets were provided to the rats concurrently to synchronize their effect on the respective group. At the end of study (42th day), rats were decapitated, after 12 hr of administered fasting, and blood samples were collected in EDTA-coated tubes. Furthermore, the serum was separated after centrifuging the blood (Rotrofix 32-A Heltich) for 6 min at 4,042 g. The collected sera samples were kept for biochemical evaluation through Rendox Toerauta (RX-Monza Republic of Ireland).

TA B L E 2 Effect of treatments on cholesterol level
Means carrying same letters are significantly identical.

F I G U R E 1 Effect of thermally treated barley fiber on % decrease in cholesterol
and triglycerides (TG) was carried out at mentioned intervals. The cholesterol level of collected sera was measured by liquid cholesterol CHOD-PAP method according to Kim et al. (2011). Serum low-density lipoproteins (LDL) were estimated following the protocol of McNamara, Cohn, Wilson, and Schaefer (1990). Accordingly, the high-density lipoproteins (HDL) were assessed by cholesterol precipitation method (Alshatwi et al., 2010).The triglycerides were measured by liquid triglycerides (GPO-PAP) method as previously described (Kim et al., 2011).

| Statistical analysis
The research trial was repeated twice, and the results were analyzed statistically to draw conclusive inferences. The data obtained for each parameter were subjected to analysis of variance (ANOVA) to determine the level of significance. The means were compared using least significance test (LSD test) to check the variability among diets (Steel et al., 1997).

| Dietary fiber content of barley before and after treatment
The soluble and insoluble fiber contents of the native and the thermally modified barley of the two cultivars were measured and presented as g/100 g dry matter (

| Low-density lipoprotein (LDL)
The results revealed that highly significant differences were observed in case of treatments while the impact of trials was nonsignificant ( Means carrying same letters are significantly identical.

F I G U R E 3
Effect of thermally treated barley fiber on % increase in LDL levels in premenopausal women with no estradiol intake, and the results revealed that dietary fiber intake produced a decrease in the lipoprotein cholesterol levels. Among lipoprotein cholesterol levels, LDL was reduced significantly. Aman (2006) reported that concentrated barley dietary fiber, that is, beta-glucan, was found to be significantly effective in reducing LDL levels when the concentrated beta-glucan-enriched food products were given to hyperlipidemia patients without metabolic syndrome, and after six weeks of beta-glucan administration, LDL was lowered by 15%. Talati et al.
(2009) worked on the relation of serum lipids and barley-derived soluble fiber in hypercholesterolemic subjects and found that the use of barley soluble fiber notably reduced the total cholesterol, LDL, and triglycerides, but no effect was probed against HDL.

| High-density lipoprotein (HDL)
The levels of HDL were significantly influenced by treatments  (Figure 3).

| Triglycerides
Statistical data demonstrated that there was highly significant variation among treatments (  (Figure 4). Ranhotra et al. (1998) reported that the consumption of barley-derived soluble fiber significantly reduced the total cholesterol level, triglycerides, and LDL through its binding capacity with bile acids. Through this binding, reabsorption of bile acids in intestine was prevented and these were carried to colon and excreted. The results of present study were in accordance with the results of previous researches (Aman, 2006;Talati et al., 2009).

| CON CLUS ION
The The large-scale efficacy of modified dietary fiber must be checked in human subjects through clinical trials before warranting their commercial applications.

ACK N OWLED G M ENTS
The authors are thankful to Higher Education Commission, Islamabad, Pakistan for providing financial support for the current study.

CO N FLI C T O F I NTE R E S T
Authors declare no competing financial interests.

E TH I C A L S TATEM ENT
The authors declare that they do not have any conflict of interest.
The research plan was duly approved by "Ethical Departmental