【作者】 李玥；

【导师】 麻建国；

【作者基本信息】 江南大学 ， 食品科学， 2008， 博士

【摘要】 高纯度的大米淀粉具有颗粒小、比表面积大、色泽白、易消化等独特的优良品质。研究高效、环保、经济的大米淀粉制备方法,是工业化生产高品质大米淀粉的前提,研究大米淀粉功能特性与分子结构之间的关系,开发出具有高附加值的大米淀粉产品,不仅具有理论价值,还能指导大米淀粉的深加工,拓宽其应用。本论文首先比较了碱法、表面活性剂法和酶法制备的大米淀粉的各项理化性质,确定了制备低破损率大米淀粉的工艺,建立了使用流变仪测定淀粉糊化特性的方案。结果表明,三种制备方法除蛋白的能力相近,但酶法制备的大米淀粉其糊化特性与天然大米粉相似,而碱法和表面活性剂法制得的淀粉其糊化峰值温度低于天然大米粉;流变学特性参数显示,用酶法制得的大米淀粉经糊化后具有较高的弹性、表观粘度及抗剪切能力;淀粉破损率的数据显示,酶法制得的三种大米淀粉的破损率均在2%左右,而碱法和表面活性剂法制得的大米淀粉的破损率在2.4-3.9%之间,说明酶法分离提取大米淀粉工艺对淀粉颗粒的破坏程度最小;粒径分布图显示,酶法制备的大米淀粉具有最小的颗粒粒径,颗粒平均粒径在5μm左右。通过对不同品种蛋白酶除蛋白效果的比较,筛选出两种能有效分离提取大米淀粉的蛋白酶,分别为:Alcalace碱性蛋白酶和Protease N中性蛋白酶。通过工艺优化,确定最终酶法制备大米淀粉的条件为:纤维素酶60U/mL,pH5.0,50℃,反应2小时,之后将pH调至10.5或8.5加入100U/mL的Alcalace或ProteaseN反应4小时,制备得到的淀粉中残余蛋白含量分别为0.53%和0.52%,淀粉破损率分别为2.01%和1.86%。差式扫描量热仪(DSC)测得的热力学参数显示两种蛋白酶结合不同的处理方法制备的大米淀粉具有相似的热特性;扫描电子显微镜显示两种蛋白酶结合纤维素酶制备的大米淀粉的颗粒形态基本没有差别,与天然大米粉相比,经酶法分离以后的大米淀粉颗粒显著变小;糊化特性曲线显示由Protease N或Protease N结合纤维素酶制备的淀粉较好的保持了天然大米淀粉的糊化特性,而由Alcalase或Alcalase结合其他方法制备的淀粉其糊化谷底和最终粘度都在0.10 Pa.s和0.24 Pa.s以下,明显低于天然大米粉的0.30 Pa.s和0.57Pa.s。选择了具有不同直链淀粉含量的大米,分别使用Protease N和Alcalase蛋白酶进行大米淀粉的分离提取,对制得的大米淀粉的理化性质、颗粒形态以及分子量分布等作了系统的比较。结果显示:由Alcalase蛋白酶制备的大米淀粉不仅其糊化谷底粘度和最终粘度低于Protease N蛋白酶制备的淀粉,而且糊化以后的淀粉糊的流变学参数G’,σ_o和η_o也是前者明显低于后者。而两种蛋白酶制备的淀粉的扫描电镜图、X-射线衍射测图谱、热特性以及重均分子量均无发现任何区别,表明Protease N和Alcalase这两种蛋白酶在水解大米蛋白、制备大米淀粉的过程中并不会破坏淀粉的分子结构。但经过糊化以后,由Protease N蛋白酶制备的淀粉的重均分子量要明显高于Alcalase蛋白酶制备的淀粉,当添加少量Alcalase或Protease N蛋白酶于大米淀粉,并一起糊化后,添加了Alcalase的大米淀粉的重均分子量显著降低,表明Alcalase制备的大米淀粉中残余的少量蛋白酶在大米淀粉加热糊化过程中水解部分淀粉分子,最终影响淀粉的糊化和流变学特性。选择蛋白酶提取大米淀粉时,除了要考虑到除蛋白的效果和淀粉提取效率之外,还必须注意蛋白酶对淀粉的分子结构和品质特性的影响。研究了酶法制备的大米淀粉的糊化特性。通过研究大米淀粉颗粒和溶出的直链淀粉对糊化过程中淀粉糊粘度的影响得出:糊化过程中淀粉糊粘度的升高主要是由淀粉颗粒的膨胀引起的,即淀粉颗粒所占的体积百分数对淀粉糊粘度的变化起主导作用,而加热过程中溶出的直链淀粉以及大米的品种对淀粉糊化粘度的升高影响不大;糊化初期大米淀粉颗粒的吸水膨胀是直链淀粉溶出的必要条件,而淀粉颗粒中的直链淀粉的存在会对颗粒的糊化膨胀起到阻碍作用,直链淀粉通过影响淀粉颗粒的吸水膨胀,间接的影响淀粉的糊化粘度。通过X-射线衍射和傅里叶红外光谱两种测量手段跟踪大米淀粉糊化过程中结晶程度的变化,结果显示:大米淀粉被加热至起始糊化温度以后其晶体结构很快被破坏;直链淀粉不仅能够抑制淀粉颗粒的糊化膨胀,还能阻止淀粉的结晶区结构在加热糊化过程中的破坏;尽管红外光谱测量法和X-射线衍射法对“结晶度”的定义不同,但对于淀粉结晶程度的测定具有相关性和可比性。使用流变仪控制大米淀粉的升温糊化过程,用浸出法分离直链淀粉,结合高效液相分子排阻色谱(HPSEC)、多角度光散射仪(MALLS)及折光检测器(RI)连用系统,测得直链淀粉的重均分子量范围为3.65×10~5-4.48×10~6,得出:同一品种的大米淀粉在不同温度下浸出的直链淀粉分子的重均分子量(Mw)与分子旋转半径(RMS)都没有显著的差异;大米淀粉中直链淀粉含量高,则Mw与RMS较小。将大米淀粉用于可食性淀粉膜的制备和研究,结果表明:大米淀粉形成的可食用膜的阻氧性、阻水性、溶解性、抗拉强度和储能模量与大米淀粉中直链淀粉的含量均呈现相关性。与玉米和土豆淀粉相比,由大米淀粉制备的可食用膜具有较高的阻氧、阻水和溶解性,但大米淀粉膜的抗拉强度和弹性模量要低于玉米和土豆淀粉膜。采用CMC对淀粉进行干热变性处理能显著改善大米淀粉可食用膜的机械性能,并进一步提高淀粉膜的阻氧、阻水性。实验测定了大米淀粉干热处理前后的糊化特性参数和粒径变化情况,结果显示:与CMC干热反应后,大米淀粉的粒径比干热前明显增大。淀粉分子的羟基基团与CMC分子中的羧基基团在干热处理过程中发生交联,大米淀粉糊化特性的改变取决于二者的反应程度,这与参与反应的淀粉和CMC的比例有关,也与CMC胶的种类有关。可以通过控制离子胶的类型和用量得到具有不同性质的改性大米淀粉。更多还原

【Abstract】 Rice starch is unique in its small granule size,large specific surface area,white color and good digestibility.To develop an efficient,environmental and economical isolation process of rice starch from milled rice is the precondition to product high quality rice starch in industry. To study the relationship between rice starch functional properties and molecule structure and develop the rice starch products with high qualities can provide theoretical basis for rice starch investigation and guide further processing and application of rice starch.The physicochemical properties of rice starches isolated from Alkaline steeping(NaOH), sodium dodecyl sulfate(SDS) and enzymatic process were compared.The rice starch isolation process from milled rice with low damage to starch granules was established.The pasting property measurement was set up using a rotational rheometer instead of Rapid Visco Analyzer(RVA).The results indicated that the pasting curve of the rice starch from enzymatic isolation was similar to that of native rice flour,while the pasting peak temperature of the starches isolated from NaOH or SDS treatments was significant lower than that of native rice flour,which suggested that the nature structure of rice starch granules was retained using enzymatic process.The starch pastes from enzymatic treatments were more elastic and viscous at low shear stresses.The damaged starch content showed that the rice starch from enzymatic isolation was around 2%,while it was from 2.4-3.9%for the starches isolated from NaOH or SDS treatments.The enzymatic isolation also produced the smallest granule size of rice starch,which was around 5μm.The efficiency of starch isolations from milled rice with different protease preparations was evaluated.Alcalase and Protease N "Amano"(Protease N) were found to provide for a better separation of the rice starch from protein.The preferred condition for producing the rice starch with low residual protein content was 60 units/mL Cellulase pre treatment for 2 h followed by the treatment with 100 units/mL Alcalase at initial pH 10.5 or 100 units/mL ProteaseN at initial pH 8.5 and digestion for 4 h at 50℃.The residual protein content was 0.53%with the damaged starch content of 2.01%for Alcalase treatment,and 0.52%residual protein content with 1.86%damaged starch content for Protease N treatment.There were no notable differences in terms of the thermal properties among isolated rice starches obtained from different protease treatments as determined with DSC.The granule size of the rice starches isolated with the two proteases was smaller than that of the native rice flour and no apparent surface damage was found.In evaluating the pasting quality of the starches,it was found that Protease N treatments produceu rice starch with similar pasting viscosities to the native rice flour,while the trough and final viscosities of 0.1 Pa.s and 0.24 Pa.s were dramatically lower than those of rice flour,which were 0.3 Pa.s and 0.57 Pa.s,respectively.The effects of Alcalase and Protease N treatments on the physicochemical properties, granule structure and molecular weight distributions of rice starches with different ratios of amylose to amylopection were studied.The rice starches produced from Protease N exhibited higher pasting trough and final viscosities than those produced from Alcalase.The hot pastes of the starches produced from Protease N also showed higher elastic moduli,zero-order Newtonian viscosities and yield stresses than those produced from Alcalase.No differences were found in the crystalline pattern,thermal properties,granules appearance,and average molecular weight(Mw) of the rice starches between the two proteases treatments.It indicated that neither Alcalase nor Protease N would damage the structure of the rice starch during the isolation process.But the Mw of the pasted starch produced from Protease N was significantly higher than that produced from Alcalase.When additional protease was added to the isolated starches and the mixture pasted,the Mw of the starches pasted with added Alcalase was 47-92%lower than that of the pasted starches without protease.The reduction in molecular weight suggested that Alcalase had modified the starch molecules,hydrolyzed part of the starch molecule during pasting,resulted in the reduce in pasting viscosity and elastic moduli.Although protease treatments provide an effective method for the purification of native rice starches,commercial protease should be selected carefully in order to avoid the damage to the starch structure by the contamination in the protease during or after isolation process.The pasting properties of rice starches isolated from protease treatment were studied.The effects of starch granules and leached amylose on the viscosity of rice starch dispersions during heating were investigated.It was found out that starch granule swelling increased rice starch dispersion viscosity during heating.The viscosities of the starch dispersions during heating were principally dependent of granular volume fraction and independent of starch variety and leached amylose.Granular swelling was necessary before amylose leaching.High initial amylose concentrations in starch granules reduced swelling during heating thereby reducing rice dispersion viscosities.Amylose played an indirect role in affecting rice dispersion viscosity during heating by reducing granular swelling.The change of crystallinity of rice starches during pasting was investigated using attenuated total reflectance Fourier-transform IR spectroscopy(FTIR) and X-ray diffraction(XRD).The results indicated that the loss of crystallinity for the starch granules was significant when the temperature reached the pasting onset temperature.The amylose would inhibit the disruption of the crystalline areas of rice starch granules during pasting.Although the definitions of "crystallinity" were different for FTIR and XRD,the results were correlative and comparable and could provide useful information for the study of starch pasting.Aqueous leaching of amylose from rice starch at different temperatures during pasting was carried out using rotational rheometer.The molecular structure of amylose from rice starch was analyzed by a high performance size exclusion chromatography system.The range of average molecular weight(Mw) of amylose from different rice starches is from 3.65×10~5 to 4.48×10~6.There are no significant differences in Mw and RMS of the amylose leached at different temperatures.The Mw and RMS correlated negatively to the amylose content in the rice starch.The application of rice starch to edible film was investigated.It indicated that the water vapor and oxygen permeability,the solubility the tensile strength and G’ of rice starch-based films were correlated to the amylose content in the rice starch of the rice starch edible films were natively correlated to the amylose content in rice starch.Both water vapor and oxygen permeability were smaller of rice starch-based films as compared to those of corn or potato starch-based films.The solubility of rice starch-based films was higher than those of corn or potato starch-based films.But the tensile strength and elastic module of rice starch-based films were lower as compared to other starch-based films.In order to improve the mechanical properties of rice-starch based film,the rice starch was heat-treated in a dry state after being impregnated with carboxymethylcellulose(CMC).The modified rice starch-based films showed higher tensile strength and elastic module and lower water vapor and oxygen permeability than other modified starch-based films.In order to address the reaction mechanism between the rice starch and CMC,pasting properties and particle size distributions of rice starches before and after modifications were determined.It indicated that the starch particle size increased after heat treatment with CMC.The ester bonds were supposed to be formed between the hydroxyl groups in amylopectin branches of rice starch and carboxylate acid groups of CMC.The change in pasting properties of the modified rice starch depended on the reaction level of the combination between the starch and CMC.It suggested that crosslinkage occurred between the starch and CMC.The crosslinkage level depended on the amount of CMC and starch,which participated in the forming of ester linkage,as well as the viscosity of CMC.The heating process with different types of CMC at different concentrations could be used as a modification method for rice starch and provide desirable properties of starch-based films.更多还原