AbstractOur previous studies have demonstrated that histidine supplementation significantly ameliorates inflammation and oxidative stress in obese women and high-fat diet-induced obese rats. However, the effects of dietary histidine on general population are not known. The objective of this Internet-based cross-sectional study was to evaluate the associations between dietary histidine and prevalence of overweight/obesity and abdominal obesity in northern Chinese population. A total of 2376 participants were randomly recruited and asked to finish our Internet-based dietary questionnaire for the Chinese (IDQC). Afterwards, 88 overweight/obese participants were randomly selected to explore the possible mechanism. Compared with healthy controls, dietary histidine was significantly lower in overweight (p < 0.05) and obese (p < 0.01) participants of both sexes. Dietary histidine was inversely associated with body mass index (BMI), waist circumference (WC) and blood pressure in overall population and stronger associations were observed in women and overweight/obese participants. Higher dietary histidine was associated with lower prevalence of overweight/obesity and abdominal obesity, especially in women. Further studies indicated that higher dietary histidine was associated with lower fasting blood glucose (FBG), homeostasis model assessment of insulin resistance (HOMA-IR), 2-h postprandial glucose (2 h-PG), tumor necrosis factor-α (TNF-α), interleukin-1β (IL-1β), interleukin-6 (IL-6), C-reactive protein (CRP), malonaldehyde (MDA) and vaspin and higher glutathione peroxidase (GSH-Px), superoxide dismutase (SOD) and adiponectin of overweight/obese individuals of both sexes. In conclusion, higher dietary histidine is inversely associated with energy intake, status of insulin resistance, inflammation and oxidative stress in overweight/obese participants and lower prevalence of overweight/obesity in northern Chinese adults. View Full-Text
Keywords: dietary histidine; overweight/obesity; insulin resistance; inflammation; oxidative stressdietary histidine; overweight/obesity; insulin resistance; inflammation; oxidative stress►▼ Figures
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Li, Y.-C.; Li, C.-L.; Qi, J.-Y.; Huang, L.-N.; Shi, D.; Du, S.-S.; Liu, L.-Y.; Feng, R.-N.; Sun, C.-H. Relationships of Dietary Histidine and Obesity in Northern Chinese Adults, an Internet-Based Cross-Sectional Study. Nutrients2016, 8, 420.
Li Y-C, Li C-L, Qi J-Y, Huang L-N, Shi D, Du S-S, Liu L-Y, Feng R-N, Sun C-H. Relationships of Dietary Histidine and Obesity in Northern Chinese Adults, an Internet-Based Cross-Sectional Study. Nutrients. 2016; 8(7):420.Chicago/Turabian Style
Li, Yan-Chuan; Li, Chun-Long; Qi, Jia-Yue; Huang, Li-Na; Shi, Dan; Du, Shan-Shan; Liu, Li-Yan; Feng, Ren-Nan; Sun, Chang-Hao. 2016. "Relationships of Dietary Histidine and Obesity in Northern Chinese Adults, an Internet-Based Cross-Sectional Study." Nutrients
Cereals have been associated with food and drinks throughout the history of mankind, and they serve as a major source of energy for millions of people worldwide, to this day. In addition, consumption of whole grain cereals has long been considered to be beneficial to human health. For example, in the early 1970s, Trowell  in a review presented data from various epidemiological and dietary intervention studies that supported the hypothesis that a diet consisting of whole grain cereals may decrease the incidence of ischemic heart disease and hyperlipidemia. Since then, several epidemiological studies have associated consumption of whole grain cereals with decreased risk of chronic diseases such as cardiovascular disease , cancer  diabetes  and obesity . To date, these benefits have been mostly attributed to the content of dietary fiber, essential fatty acids, vitamins and antioxidant phytochemicals including several phenolic compounds in these cereals [6,7]. Different cereals are prevalent in the diets of different communities in the world. Rice is an important cereal amongst Asians, whereas a Western diet is based on wheat, and maize is the major starch food in many parts of Africa. The increasing use of wheat, rice and maize in the human diet has led to a decrease in the consumption of oat and especially barley.
However, both these cereals are still intensively cultivated for other purposes. For example, according to Eurostat statistics, among the cereals cultivated in Europe, wheat is the largest crop, followed by barley, with oats in the third place . The largest producers of oats in 2014 were Poland, Finland and UK, whereas the largest producers of barley were France, Germany and Spain. Data relative to the total production, area under production and average yield of oats and barley in Europe in 2014 has been summarised in Table 1.
Table 1. Production of oats and barley in Europe in 2014.
|Total Production’000 tons||Area’000 hectares||Average Yield tons/hectare|
Barley is usually classified as spring and winter types, two-rowed or six-rowed (depending on the number of rows of seeds on each spike) and hulled or hulless (by presence or absence of hull tightly adhering to the grain) . Based on the grain composition, barley is further classified as normal, waxy or high amylose starch types, high β-glucan and proanthocyanidin free types. Hulless barley, owing to the absence of hull, requires minimal processing and retains most of the germ and endosperm which is occasionally lost in the process of pearling or dehulling. Therefore, it is more suited for human consumption as the whole grain can be directly used to form a meal or milled to flour. Hulless barley on the other hand is preferred for malting and brewing because of contribution of the hull to beer flavour and as a filtering aid during brewing. Waxy barley genotypes not only deliver unique physical properties to food products but also contain higher contents of protein and β-glucan than genotypes with regular starch composition. Oat can be classified into husked or naked type (depending on the presence or absence of a thick fibrous husk) . Husked oat is suitable for feeding to ruminants. However, unlike husked oat, naked oat has increased metabolizable energy content and low amount of fiber thus making it more suitable for human consumption and as a feed for monogastric animals.
About 14% of the oats produced in Europe are used for the purpose of human consumption . Oats are generally regarded as a minor cereal crop when considered in terms of grain produced annually, or areas sown for production. Oats have been mainly used as animal feed crop, but only in the 19th century it won acceptance as a part of the human diet . Today, oat can be found in various food products such as breakfast cereals, beverages, bread and infant foods [12,13]. In Europe, approximately two-thirds of cultivated barley has been used for animal feed, one third for malting, and approximately <1% for food directly . Barley is primarily used as an animal feed, and as grain for malting and brewing in the production of beer and whiskey. However, recently barley is being used to some extent in their whole, flaked and ground form in breakfast cereals, stews, soups, porridge, flat breads etc. [14,15].
Oat (Avena sativa) and barley (Hordeum vulgare), although consumed in considerably lower quantities than rice and wheat, have the advantage that they are normally consumed as whole grain cereals and considered as a ‘health food’ for humans. Whole grains or foods made from whole grains include the outer bran, the endosperm in the middle and the inner germ, in contrast to the refined grains, in which the bran and germ of the grains are removed during the milling process. Whole grain oats and barley are also good potential sources of fiber, vitamins, minerals and bioactive compounds such as phenolics, carotenoids, vitamin E, phytic acid, β-glucan and sterols [7,16]. Furthermore, oats are one of the few grains that have been recommended in the diet of patients suffering from coeliac disease, since they do not contain gluten . The bioactive compounds present in whole grains may provide desirable health benefits beyond basic nutrition, such as a reduced risk of chronic diseases such as coronary heart diseases , type 2 diabetes , and cancer . For example, Tighe et al.  reported 6 and 3 mm Hg reductions in systolic blood pressure and pulse pressure, respectively, among middle aged healthy individuals consuming three servings of whole grain food/day compared with individuals consuming refined grains. This observed decrease in systolic blood pressure is estimated to lower the risk of coronary artery disease and stroke by ≥15% and ≥25% respectively . The health benefits of diets rich in whole grains may be a consequence of the additive effects of nutritional and biologically active compounds present in them . It is clear however that the beneficial properties of oats and barley have attracted much attention from researchers recently. The food industry is also keen on increasing the usage of these cereals as food ingredients and therefore more research is merited in this area.
The bioactive components of oats and barley can be broadly classified into polar and intermediately polar compounds such as β-glucan, phenolic acids, polyphenols, and non-polar compounds such as tocols. A wide variety of techniques have been used over the period of years, for the extraction of these phytochemicals from these cereals. The aim of this article is to provide an insight on the important bioactive compounds that have been extracted from oats and barley. The review discusses the various extraction and characterisation techniques that have been used for identification of these bioactives. The potential shown by novel processing technologies like ultrasound assisted extraction and pressurized liquid extraction in efficiently extracting various bioactives from oats, barley and other related cereals has also been discussed.
Research on oats and barley has intensified arising from the findings that oat and barley bran possess serum cholesterol lowering and hypoglycaemic effects [22,23]. This property has been largely attributed to the soluble fiber fraction of these cereals, in particular to the (1-3, 1-4) β-d-glucan (β-glucan, Figure 1) component. Barley and oat β-glucans, together with other non-starch polysaccharides, occur in the walls of the endosperm cells which enclose starch, matrix protein and lipid reserves of the grain. The extraction of β-glucans usually requires inactivation of endogenous enzymes (β-glucanases and amylases), as leaving these enzymes active may degrade the β-glucan resulting in a low molecular weight β-glucan product. Preserving the molecular weight (MW) of β-glucan is an important factor, as it determines its physicochemical properties such as viscosity, which in turn determines the cholesterol-lowering property of β-glucan .
Figure 1. Chemical structure showing the β-1,3 and β-1,4 bonds of β-glucan.
Figure 1. Chemical structure showing the β-1,3 and β-1,4 bonds of β-glucan.
Wood et al.  were amongst the first authors to investigate factors affecting β-glucan extraction efficiency. They used a dehulled oat variety ‘Hinoat’ to assess the effects of particle size, ionic strength, temperature, pH and obtained an oat β-glucan gum fraction by extraction of 75% ethanol refluxed oat bran, with a sodium carbonate solution at pH 10. Refluxing with ethanol was performed for achieving inactivation of the endogenous β-glucanases. This simple procedure yielded a high viscosity β-glucan gum with 78% purity. Several other extractants for the recovery of β-glucan from hulless barley, waxy hulless barley and commercial oat bran were investigated by Bhatty . The authors reported that the highest enrichment of β-glucan from barley and oats could be obtained by a single extraction using 4% of 1 M sodium hydroxide (NaOH) at room temperature. The purified high viscosity gums contained 72%–81% β-glucan plus pentosans from barley brans and 84% from oat brans. The β-glucan yield or the % total recovered from barley bran and oat bran were 81% and 61% respectively. Later, the same approach was used by Bhatty  for pilot scale extraction. Although ethanol deactivation and extraction at higher pH with NaOH have been found to yield a high viscosity β-glucan gum, these processes are accompanied with a decrease in yield and an added risk of degradation of the β-glucan polymer . Pre-treatment processes such as boiling and ethanol reflux have also been shown to increase starch contamination of the extract, because of its gelatinisation at temperatures around 63 °C. Thereby, reducing the starch content of the extract from refluxed flour, using thermostable α-amylase resulted in significant improvement in purity of the gums . Recently, an enzymatic procedure has been used to obtain β-glucan from Greek barley cultivars wherein, the removal of starch and proteins was achieved enzymatically using thermostable amylase and pancreatin respectively, followed by precipitation of β-glucans using 37% ammonium sulphate . The purity of β-glucan using this procedure was as high as 93%, with some small amount of protein contamination. The MW of β-glucan of these samples varied from 0.45 × 106 to 1.32 × 106 g/mol.
Various research studies have shown that temperature, pH and pH-temperature interaction of the extraction process are important factors in β-glucan recovery and functionality [28,30,31,32]. As temperature increases beyond 60 °C, the starch contamination of the extract increases due to gelatinisation of starch. Dawkins and Nnanna  found that pH/temperature treatment combinations of 9.2/50 °C or 10.5/50 °C/55 °C produced oat gum with little or no starch contamination. Later, Temelli  recommended a pH/ temperature combination of 7.0/55 °C for maximising the β-glucan content, gum yield, emulsion stability and viscosity. The ethanol refluxing step was not employed for this extraction, based on the hypothesis that this step might not be required if extraction was carried out in acidic or alkaline conditions, wherein the enzymes were inactivated during the process itself. This hypothesis was proved when the viscosity of the β-glucan gum was found to increase with an increase in pH of the extract. In 2011, a Taguchi experimental design was used to find an optimal combination of factors that maximise the extraction yield from waxy barley cultivars . At pH close to neutrality and temperature of 55 °C, an extraction yield of (73.4 ± 1.2)% was obtained at the optimal conditions of particle size, 100 μm; solvent:flour ratio of 5; stirring rate, 1000 rpm and extraction time, 3 h. However, molecular weight (MW) of β-glucan or its viscosity was not taken into account in the aforementioned study. Recently Gangopadhyay et al.  obtained similar results on using response surface methodology for optimising extraction of high amount and high MW β-glucan from Irish hulled barley cultivars. Size exclusion chromatography was used for determination of MW of β-glucan. Water used as the extraction solvent at a temperature of 55.7 °C and pH 6.6 were found to be optimal for delivering a high yield (81.5%) and high MW (351.6 kDa) β-glucan product from barley . A technique that has been commercially accepted for making β-glucan from barley flour involves extraction with water followed by freezing the extract . The frozen extract is thawed and the fibrous material is recovered from it by filtration and further washed with water and ethanol before being dried. This β-glucan product known commercially as Glucagel® is a high purity (75% β-glucan) product with MW varying from 62 kDa to 560 kDa depending on the temperature and time used for extraction.
Several techniques have been employed for analysis of the oligosaccharides from enzyme-hydrolysed barley β-glucan. The earliest technique used was paper chromatography , which had the disadvantage of being extremely time consuming taking up to 72 h. Oligosaccharides released from the β-glucans of oat products, barley, wheat and rye have been analyzed by the use of HPLC, but this technique could not adequately resolve the oligosaccharides with a higher degree of polymerisation (DP) . Derivatization using methylation, of oligosaccharides released by lichenase hydrolysis from barley β-glucan, improved the HPLC resolution of the oligosaccharides with higher degree of polymerisation . Wood et al.  successfully applied high-performance anion-exchange chromatography with pulsed amperometric detection (HPAEC-PAD) for analysis of oligosaccharides from barley β-glucan, with DP of 5–19. However, the quantification of oligosaccharides by HPAEC-PAD was limited to the knowledge of weight response factors.
Jiang and Vasantham  were the first to investigate the use of MALDI-MS for the qualitative and quantitative analyses of oligosaccharides, of lichenase-hydrolyzed water soluble β-glucan from barley. The authors concluded that MALDI-MS provides a rapid and sensitive means for the analysis of the oligosaccharides and requires only 1/12 of the sample concentration of that used by HPLC or HPAEC-PAD. A standard addition method was employed to determine both the relative and absolute amounts of each oligosaccharide using the weight concentration relationship. Oligosaccharides from DP 3 to 12 could be detected and quantified by this method. Trisaccharide (DP 3) and tetrasaccharide (DP 4) chain units were indicated to be the main building blocks of water soluble barley β-glucan, accounting for about 95% of the whole polymer, with the molar ratio of tri- to tetrasaccharides ranging from 2.3 to 2.8.
Nuclear magnetic resonance (NMR) spectroscopy is a method that has been widely used for the primary and secondary structural determination of β-glucan. Johansson et al.  used two-dimensional correlation NMR for structural characterization of water soluble β-glucan. They showed that the glucose units are joined with 1,3- and 1,4-linkages only, and that no other linkages exist. Later Johansson et al.  also studied structural differences between oats and barley, and soluble and insoluble β-glucan using FT-IR, 1H-NMR and solid state 13C-NMR. They showed differences in the ratio of oligosaccharides with degree of polymerisation 3 and 4 (DP3:DP4) in oats and barley. The ratio of DP3:DP4 was higher for barley than for oats, indicating a higher number of cellotriose segments in barley. Ryu et al.  linked the structural differences between the barley and oat β-glucan to their rheological and thermal characteristics. It was suggested that oat with a lower DP3:DP4 and thus higher cellotetraosyl units would have improved solution viscosity and gel formation characteristics than barley.