酸法提取青稞麸皮结合酚工艺优化

为了提高青稞的附加利用价值，该文以青稞麸皮为研究对象，考察了提取试剂、酸质量分数、萃取pH值、料液比和提取温度对多酚质量分数和 DPPH·自由基清除能力的影响。采用中心组合设计优化其结合酚提取工艺。结果表明，青稞结合酚提取最优工艺条件为：提取试剂为硫酸，酸质量分数为11.10%，水料比为1：17 g/mL，提取温度为75℃，pH值不作处理，此条件下提取得到的结合酚质量分数达224.33 mg/(100 g)，DPPH·自由基清除能力达9919.28μmol/(100 g)，与预测值多酚质量分数243.80 mg/(100 g)，其DPPH·自由基清除能力9087.02μmol/(100 g)基本一致。高效液相色谱法检测到最优工艺下所得青稞结合酚中含有8种酚酸及8种黄酮类物质，总量达325.104 mg/(100 g)。研究结果为全面评价青稞结合酚含量及青稞麸皮的高效利用提供科学依据。

Optimization of combined phenols extraction with sulfuric acid from hulless barley

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 andβ-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 andβ-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 H2SO4were compared and H2SO4solution 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 g/mL, 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 9 919.28μmol/(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.