| Tibetan hull-less barley(Hordeum vulgare L, var. nudum hook. f.)(THB) has been grown in the Qinghai-Tibet Plateau for thousands of years. It contains high levels of proteins, dietary fibers and vitamins, and low levels of fats and carbohydrates. Because of the extreme growing conditions-cool temperature, hypoxia and intense UV radiation Tibetan hull-less barley is unique for research. Steam explosion is a processing method extensively used for pre-treatment of structural components in plant biomass. The principle of steam explosion treatment is the use of steam hydrolysis at high temperature and pressure followed by sudden reduction of the pressure to break down the molecular structures to produce low molecular weight substance. This technology has a large potential to be applied in natural products research.Nowadays, whole grains are drawing a great amount of attention around the world for their many potential benefits. Thus, it is instructive to explore the local whole grains in China. The primary objective of this study was to investigate the health benefits and mechanisms of whole THB. The secondary objective was to investigate the possibilities of infusing cereal products with high contents of nutrients using steam explosion. Main conclusions are as follows,I) Three varieties grown in Tibet and one variety grown in plain were collected from Lhasa and Tianjin. The barleys were polished into five fractions. Total soluble phenolic content (TSPC), total antioxidant capacity (TAC) and their correlation were investigated. Results showed that TSPC decreased from the outer to the inner fractions. TSPC and TAC were highly and positively correlated (r=0.9583-0.9710).Compared to plain variety, the outer layer of THB, which accounts for20%of the whole mass ratio, has more than50%of total phenols. In the outermost layer, the THB’s average TSPC is5867μg gallic acid equivalent·g flour-1, which is twice the amount in common varieties. The extreme growing conditions have influenced the distribution of phenols in the barleys. Therefore, THB bran extracts are valuable sources of bioactive components. 2) A steam explosion pre-treatment process followed by methanol extraction has been applied for releasing and extracting phenols, as well as other effective components, from barley bran. The steam explosion treatment was performed at different temperatures and residence times. The results indicated that under optimum conditions the water soluble carbohydrates were5times that in the untreated samples. Also, compared with untreated samples, the TSPC reached1686.4gallic acid equivalents mg/100g dry weight, which was8.83fold higher. The yields of ferulic acid in its free and conjugate forms were increased by about59.0and8.45times, respectively. Meanwhile, the corresponding increases of p-coumaric acid were47.6and7.25times. Moreover, the TSPC and TAC obtained were highly positively correlated (r=0.918～0.993), which meant that the increase of TAC for the steam explosion pre-treated barley bran extracts was due, at least in part, to the increase of TSPC in the methanol soluble fraction. It can be concluded that a proper and reasonable steam explosion pre-treatment could be applied to release the bound phenolic compounds and enhance the antioxidant capacity of barley bran extracts.3) The effects of steam explosion on whole THB components were studied and compared with those of roasted or extrusion cooked barleys. TSPC, total flavonoids content (TFC), water soluble carbohydrates and TAC of whole THB digesta were evaluated. Significant increases in TSPC (6.4%) and in TFC (30.5%) were observed after steam explosion. The content of ferulic acid in steam exploded samples was3times and2.3times as much as that in untreated and extrusion cooked samples, respectively. Additionally, steam explosion led to the decrease of water soluble carbohydrates and increase of free amino acids.4) The THB pre-and post-treated with steam explosion was prepared as high fat and high sucrose experimental diets. The long-term metabolic effects of diets supplemented with whole untreated or treated THB and refined wheat flour on high-fat high-sucrose diet induced metabolic syndrome (MS) in the SD rats were studied. After15weeks, rats fed with refined wheat flour showed obvious symptoms of MS. Compared with those rats fed with refined wheat flour, rats fed with THB untreated or treated with steam explosion had ameliorated MS symptoms including reduced plasma lipid disorder, higher insulin sensitivity and less fatty liver. Moreover, untreated THB reduced body weight and adiposity in rats fed with high-fat high-sucrose diet.5) The underlying mechanisms of THB on MS were investigated in different aspects such as oxidative stress, adipokines secretion, signal transduction in insulin action and adipose cell apoptosis. It was revealed that THB induces adipose cell apoptosis. Treated and untreated THB both led to decreased mRNA levels of resistin in adipose cells. Furthermore, they both enhanced PPAR-y mRNA expression and activated the activity of PPAR-y to promote expression of GLUT4mRNA in adipose cells.In summary, steam explosion had an obvious effect on releasing active compounds from THB. In addition, THB has an advantage in product development for that intake of THB whole grains could prevent the occurrence of high-fat high-sugar diet induced MS. Due to the large amount of consumption of THB, it is of great significance to research its effects and mechanisms on health promotion. |
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