Abstract
Abstract: Hulless barley belongs to the genus Hordeum in the family Gramineae, and it is the mutation of cultivated barley in botany. It is also called naked barley because its lemma and palea are separated from caryopsis and its grain exposes. Hulless barley is the most characteristic crop on the Tibetan Plateau, and it has a high value in nutrition and health care. In addition to some well known functional ingredients, like dietary fiber and β-glucan, hulless barley also contains a variety of phenolic compounds, such as tocol, flavonoids, and anthocyanins. As important dietary antioxidant components, these substances play a prominent protective effect on human cardiovascular disease, diabete, obesity and cancer. The content of phenolic compounds in barley is much higher than other cereals. Currently, researches on hulless barley are mainly focused on the feed industry, traditional food processing industry, wine making industry and β-glucan. Phenols, which are important functional components, have not received enough attention, so the related studies about the phenolic in hulless barley are of great significance. Free form, soluble combined form and insoluble combined form are the 3 main states of polyphenols in grain, and combined form is the most common state of polyphenols in grain. Research found that when respectively using acid and alkaline hydrolysis to extract combined phenols from lychee, different type and content were obtained, and the total phenolic content and antioxidant capacity of the former were higher than the latter; a similar result was also obtained when using wheat as raw material, but related researches on combined phenol of hulless barley have not yet been reported. In order to further develop the most characteristics crop on the Tibetan plateau, taking hulless barley as the raw material, central composite design was used to optimize the extraction process of combined phenols based on the single factor experiments in this paper. Different extraction reagents, NaOH, HCl and H2SO4 were compared and H2SO4 solution was selected as the best extraction reagent. Acid concentration, extraction pH value, solid-liquid ratio, and extraction temperature were studied with combined phenols content and DPPH radical scavenging capacity as indices. Solid-liquid ratio, acid concentration and extraction temperature were selected as 3 factors when using Box-Behnken central composite design to optimize the extraction parameters. Results showed that the optimum extraction parameters should be as follows: solid-liquid ratio of 1:17, acid concentration of 11.10%, and extraction temperature of 75 ℃. Under the condition, polyphenol content was 224.33 mg/(100 g) and DPPH radical scavenging capacity was 9 919.28 μmol/(100 g) which were consistent with predicted values and significantly better than rice, wheat and oat. High performance liquid chromatography was used to detect this optimum extract and 8 kinds of phenolic acids and 8 kinds of flavonoids were found using acid method , such as, gallic acid, 2,4-dihydroxy benzoic acid, syringic acid, 4-coumaric acid, rutin, ferulic acid, salicylic acid, naringin, hesperidin, benzoic acid, adjacent coumaric acid, myricetin, quercetin, veratric acid, naringenin, kaempferol, and total content was up to 325.104 mg/(100 g). By comparing the difference of different reagents in the extraction of combined phenol from hulless barley and optimizing the extraction parameters, this paper provides a scientific basis and method for the developing and utilization of hulless barley as health food.
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