【作者】 张勤良；

【导师】 王璋；

【作者基本信息】 江南大学 ， 食品科学， 2005， 硕士

【摘要】 随着生物技术的发展,木聚糖酶的应用领域正在逐渐扩大。目前,木聚糖酶己成功应用于制浆造纸、食品、医药等工业中。在食品工业中,虽然木聚糖酶有着广阔的应用前景,但是目前应用性研究还不够深入,范围也不够大,有待于进一步研究。本文在研究中性木聚糖酶酶学性质的基础上,研究了中性木聚糖酶在面包制作中的应用和在速溶焦大麦饮料生产中的应用。本文首先测定了中性木聚糖酶制剂中中性木聚糖酶的活力和其他可能存在的一些酶的活力,结果表明:以桦木木聚糖为底物,pH6.4、温度50℃条件下采用DNS法测定液态中性木聚糖酶制剂中木聚糖酶活力,其活力为4460±65 U/g;液态中性木聚糖酶制剂中,果胶酶和纤维素酶活力极低,可以忽略不计。在此基础上,研究了中性木聚糖酶的部分酶学性质,结果表明:中性木聚糖酶的最适温度为55℃、最适pH为pH6.4;温度为25℃时,中性木聚糖酶在pH3.2～6.4范围内稳定(10hr),pH7.2～10.4范围内,中性木聚糖酶失活速率常数k随着pH的上升增加,但是失活速率均不大;中性木聚糖酶在30～50℃稳定,温度在50℃以上,随着温度的上升失活速率显著加快,70℃时在5min内几乎完全失活。根据中性木聚糖酶的一些基本性质,探讨了中性木聚糖酶作为面包焙烤添加剂的可行性。根据粉质曲线,在中性木聚糖酶合适的添加范围内,可以明显改善面团的揉制,缩短揉制时间,当酶的添加量为30ml/100kg面粉时,面团的形成时间降低50%左右,从而加快揉面的速率,提高生产效率。在适当的添加范围内(5～42ml/100kg面粉)中性木聚糖酶可以明显地增加面包的体积和比容,减小面包皮的硬度,同时改善面包心的弹性、硬度以及柔软性。中性木聚糖酶具有明显的抗老化作用,添加范围为5～42ml/100kg面粉能明显改善面包在贮存过程中的品质,贮藏7天后,面包的硬度和弹性没有明显变化,因而大大延长了货架寿命。这些结果表明,中性木聚糖酶作为焙烤添加剂是可行的,添加范围可以在5～42ml/100kg面粉,其中30ml/100kg面粉的添加量最佳。将中性木聚糖酶与淀粉酶和蛋白酶复合用于生产速溶焦大麦饮料。首先,采用大麦焙炒设备焙炒含水量为10±0.20%的大麦,大麦最佳焙炒温度和时间分别为178℃、24min。然后,将中性木聚糖酶与淀粉酶、蛋白酶复合,同时添加以液化焦大麦粉生产焦大麦饮料。通过单因素实验确定焦大麦的最佳酶解工艺为料水比1:9,酶解pH6.5,酶解温度60℃,酶解时间60min,而中性木聚糖酶、蛋白酶和淀粉酶三种酶最适添加量(E/S)分别为1.0%、1.0%和1.5%,在最佳工艺条件下可使焦大麦总固形物提取率达64～66%。接着,焦大麦酶解提取液经浓缩后按雾化器转盘空气压力0.25Mpa、进风温度180℃、出风温度80℃的条件进行离心喷雾干燥,喷雾干燥后的样品速溶性较好,润湿性、分散性和溶解性分别为53.50±2.17S、12.33±0.58S和93.66±0.03%,堆积密度为0.4279±0.0034g/ml。当焦大麦被复合酶液化时,体系黏度在前10min快速下降,平均粒径前30min减小比后30min明显。酶解过程中体系中可溶性组分的相对分子质量逐渐减小,酶解及灭酶后体系中短肽的重均相对分子质量大部分小于1,500Da,而可溶性糖的重均相对分子质量为1,582Da。比较添加与不添加中性木聚糖酶更多还原

【Abstract】 With the development of bio-technology, the application of xylanase has progressivelyexpanded. Nowadays, xylanase is successfully applied in the paper-making, food andpharmaceautical industries. By virtue of its application in the food industry, the need for it to bestudied extensively. This paper reports studies on partial characterization of neutral xylanase and itsapplication in bread making and instant baked barley beverage making.Initially, the activities of neutral xylanase, pectinase and cellulase were determined in theenzyme preparations. The activity of neutral xylanase as determined by DNS method was foundto be 4460±65 U/g at pH 6.4 and 50℃ with birch xylan as substrate;however, the activities ofboth pectinase and cellulase were less. Next, partial properties of neutral xylanase such as itsoptimal temperature, optimal pH, temperature stability and pH stability were investigated. Theoptimal temperature and pH of the neutral xylanase were 55℃ and pH 6.4, respectively. Xylanasewas stable in the range of pH 3.2～6.4 at 25℃ over a 10hr period. However, in the pH range from7.2 to 10.4, its inactivation rate increased slowly, although all the inactivation rates were small.Neutral xylanase was heat-stable in the temperature range 30 to 50℃ but was completelyinactivated at 70℃ in 5min. Moreover, the rate of enzyme denaturation increased rapidly withcorresponding increase in temperature above 50℃.Based on its partial characterization, the feasibility of application of neutral xylanase as bakingadditive was studied. The farinograph showed that as baking additive its use could improve mixingand enhance the velocity of mixing since dough forming time was reduced by about 50% with30ml/100kg flour addition. Moreover, neutral xylanase not only markedly improved the quality ofbaking and the baked bread, it also led to an increase in the volume and specific volume of bread.Additionally, its use led to a decrease in the hardness and springiness of crumb as well assignificantly reducing retrogradation and staling during the storage period thus prolonging the shelflife of the baked product. The added amount ranged from 5 to 42 ml/100kg wheat flour amongwhich the optimal addition was 30ml/100kg wheat flour.Neutral xylanase combined with amylase and proteinase was employed to liquefy baked barleyfor instant beverage. Initially, the barley containing 10±0.20% water was baked by the modifiedbarley-baking equipment;indicating that the optimum condition of baked barley was 178℃ for24min. Next neutral xylanase compounded by amylase and proteinase was added to liquefy bakedbarley. The optimal doses of amylase, xylanase, proteinase were determined to be 1.0%, 1.0% and1.5% ([E]/[S]), respectively;whereas the ratio of sample to water 1:9, pH 6.5, 60℃ and 60minwere the optimal processing parameters. The extraction yield of soluble components of bakedbarley rose to 64～66% based on these optimal processing conditions. After that, instant bakedbarley beverage was prepared by concentration and centrifugal spray drying in order. The dryingconditions were: atomizer air pressure of 0.25Mpa, inlet temperature of 180℃ with an outlettemperature of 80℃. The product had good instantizing property. The wetness, dispersibility, bulkdensity and solubility of the instant beverage were 53.50±2.17S, 12.33±0.58S, 0.4279±0.0034g/ml and 93.66±0.03%, respectively.During the enzymatic degradation of baked barley, the relative viscosity markedly decreased inthe first 10min, the average size of suspended particles in enzymatic degradation system decreasedmore quickly in the first 30min and less quickly in the final 30min. Moreover, the relativemolecular weight of the soluble ingredients evidently decreased. In the soluble ingredients afterenzymatic degradation, the relative molecular weight of most peptides was less than 1,500Da andthe mean relative molecular weight of soluble sugar was 1,582Da. Compared with xylan contents oftwo other samples with/without use of neutral xylanase, the results indicated that the contents ofwater-extractable xylan in beverage of baked barley could be enhanced more than 3 times afterliquefaction when it (neutral xylanase) was employed giving the beverage more functionality.The flavor profile of instant baked barley beverage was caramel and sweet-like aroma. The keyvolatile compounds in the instant beverage were aldehyde (hexanal, nonanal etc.), ketone(3-hydroxy-2-butanone, 1-hydroxy-2-butanone, 3-methyl-1,2-cyclopentanedione etc.), acid (aceticacid, 2-methyl-propanoic acid, 3-methyl-butanoic acid, etc.), pyrazine (methyl pyrazine,2,5-dimethyl pyrazine, 2,3-dimethyl pyrazine, etc.), furan (5-methyl-2(3H)-furanone,2-furan-methanol, 2(5H)-furanone, 5-methyl-furfural, etc.), pyrrole (5-methyl-1H-pyrrole-2-carbox-aldehyde, etc.). The volatile compounds of three samples, including baked barley,enzyme-extracted solution and instant beverage, were compared. It was found that flavor precursors,for example aldehyde, ketone, pyrazine and furan produced in the course of baking of the barleyand that aroma could increase in the course of enzymatic degradation of baked barley since theconcentration of heterocyclic compounds increased markedly. Lastly, the pleasant instant beverageflavor was formed after spray drying of enzyme-extracted solution. Owing to evidence of therelease of xylose and arabinose when xylan was degraded by xylanase, xylanase could enhance theflavor of instant baked barley beverage.更多还原