A role for pectin in the control of cell expansion

Uptake of nutrients and water depends on the growth of roots through elongation of individual cells near the root tip. Many of the numerous components of Type I primary cell walls, those of dicotyledons and monocotyledons other than grasses (Poaceae), have been determined, and many hypotheses have been proposed for the control of cell expansion. This important aspect of plant growth still needs elucidation, however. A model is proposed in which pectin, which occurs as a calcium (Ca) pectate gel between the load-bearing cellulose microfibrils and xyloglucan (XG) chains, controls the rate at which cells expand. It is considered that the increasing tension generated by the expanding cell is transmitted to interlocked XG chains and cellulose microfibrils. The resulting deformation of the embedded Ca pectate gel elicits the excretion of protons from the cytoplasm, possibly via compounds such as cell wall-associated kinases, that weakens the Ca pectate gel, permitting slippage of XG molecules through the action of expansin. Further slippage is prevented by deformation of the pectic gel, proton diffusion, and the transfer of residual tension to adjacent XG chains. Evidence for this model is based on the effects of pH, Ca, and aluminum (Al) on root elongation and on the reactions of these cations with Ca pectate. This model allows for genetic selection of plants and adaptation of individual plants to root environmental conditions.     

芍药不同品种发育过程中花茎细胞壁成分变化

花茎挺直是评判芍药切花品质的重要标准之一,但目前影响芍药花茎直立性的因素尚不完全清楚。为明确直立性不同的芍药品种发育过程中花茎细胞壁成分的变化差异,利用花枝夹角指标将6个品种划分为3个直立等级,将现蕾期到花朵盛开的过程划分成S1~S5共5个阶段,观测不同直立等级品种花茎弯曲发生的关键时期及其5个发育阶段细胞壁组分的动态变化。结果表明,切花品种东方少女和杨妃出浴直立性最好,迟粉等3个品种花茎自S2时期起随发育逐渐变弯,晴雯自S4时期起迅速下垂。比较一致的规律是,3个直立等级的品种木质素含量随发育进程均呈升高趋势,水溶性果胶含量自S2时期起呈下降趋势。相关性分析表明,在发育前期花茎直立性和木质素含量极显著正相关;发育中期花茎直立性和木质素含量极显著正相关,和原果胶含量显著负相关;发育后期花茎直立性和半纤维素含量、木质素含量极显著正相关,和水溶性果胶含量显著负相关。研究为切花芍药品种的选育和栽培调控提供了理论依据。     

利用生物酶降解烟草果胶的研究

研究了果胶甲酯酶、果胶裂解酶、多聚半乳糖醛酸酶、纤维素复合酶处理烟叶,细胞壁物质降解后,烟叶中果胶的含量与结构以及中性糖比例的变化。结果显示:4种生物酶可以有效降低烟叶中细胞壁类物质的含量,最高降幅可达17.8%;果胶甲酯酶和果胶裂解酶处理后的烟样,果胶的甲酯度显著降低,多聚半乳糖醛酸酶处理后果胶甲酯度略有增大;酶处理后果胶中性糖的含量均比对照样增加,但不同种类酶处理的中性糖比例有区别。果胶裂解酶和纤维素酶处理后,烟叶中性香气物质总量(不含新植二烯)分别提高了24.4%和21.9%。     

橘皮中果胶提取工艺研究

以橘皮为原料,用草酸铵萃取高价铁盐沉析法提取果胶。先通过单因素试验探讨草酸铵浓度、提取温度、提取时间、料液比等单因素对橘皮中果胶提取效果的影响,再在该基础上进行L9(34)正交试验,确定橘皮中果胶提取的最佳提取工艺。结果表明:橘皮中果胶提取的最佳提取工艺为:草酸铵浓度0.7%,料液比1∶20,提取时间90 min,提取温度80℃,此条件下果胶的提取率为4.4%。     

超高压下Ca~(2+)与Na~+离子对甜菜果胶结构及流变性质的影响

[目的]研究超高压下不同浓度Ca2+与Na+对甜菜果胶结构及流变性质的影响,为甜菜果胶在食品中的应用提供理论依据。[方法]甜菜果胶用浓度0.05 mol·L-1的Tris-HCl溶液溶解,添加不同浓度Ca2+(2、12和20mmol·L-1)和Na+(0.05、0.1和0.6 mol·L-1),配制成1%(w/v)甜菜果胶溶液后进行超高压处理,然后分别对甜菜果胶分子量、微观结构、黏度和动态粘弹性进行测定。[结果]与常压下相比,在450 MPa条件下处理不同时间(10、20、30和50 min)后,甜菜果胶在1 550 cm-1处均出现新的吸收峰,甜菜果胶溶液的屈服应力σ0显著增加,但不同超高压处理时间之间无显著差异。添加不同浓度Ca2+或Na+的甜菜果胶在450 MPa条件下处理30 min,其结构及流变性的变化有所不同。相对于未添加Ca2+或Na+的甜菜果胶,添加2 mmol·L-1 Ca2+离子使甜菜果胶溶液屈服应力σ0、储能模量G’和损耗模量G"均明显增加,当Ca2+浓度增加到12 mmol·L-1和20 mmol·L-1时,果胶的流变性质变化不显著;添加2 mmol·L-1 Ca2+使甜菜果胶分子发生明显的交联。果胶分子量由只高压处理的2.25×105 Da显著增加到6.07×105 Da,Ca2+的添加浓度增加到20 mmol·L-1,果胶的分子量变为5.99×105 Da,与添加2mmol·L-1 Ca2+时没有显著差异,其流变性质变化亦不显著。相对于未添加Ca2+或Na+的甜菜果胶,添加0.05 mol·L-1 Na+也使甜菜果胶的屈服应力σ0显著增加,并且随着Na+浓度的持续增加,果胶的屈服应力σ0显著增加;而只有当Na+浓度增加到0.6 mol·L-1时,甜菜果胶储能模量G’和损耗模量G"才发生明显增加。添加0.1 mmol·L-1 Na+的甜菜果胶,其果胶分子链相互交联成网状,果胶分子发生明显聚集,果胶分子量显著增加到11.95×105 Da;而当Na+浓度增加到0.6 mol·L-1时,果胶链呈棒状结构,果胶分子量显著降低到5.53×105 Da。[结论]超高压下Ca2+与Na+可能与甜菜果胶分子结合使其结构发生改变,进而影响甜菜果胶的结构及流变性质。     

The effect of storage conditions on chemical content of raw potatoes and texture of cooked potatoes

Summary Texture of boiled potato tubers (cv. Beate) was studied over several months of storage at either 4 or 8 °C, in relation to dry matter content, non-starch polysaccharides (NSP), methyl groups, glucose, starch and amylose. The dry matter content decreased significantly during storage at 4 °C, but increased at 8 °C due to evaporation. The insoluble NSP contained rhamnose, galactose, arabinose, xylose, mannose, fucose and glucose; the first three sugars decreased significantly after the first 7 weeks of storage. Fracturability and percent compression before break increased during storage at 8 °C, particularly percent compression after 15 weeks. The change in fracturability could partly be explained (R²=43.4%) by the content of the NSP and the increase in percent compression by dry matter (R²=91.8%). Changes in texture during storage at 4 °C, however, were not striking, and could not be explained by changes in the potato components that were analysed.     

籽瓜皮果胶的提取工艺研究

为探究提取分离新疆籽瓜皮中果胶的最佳工艺,采用酸提醇析法探讨了原料预处理,萃取剂的种类、浓度和加入量,萃取温度、时间和浓缩比例等因素对果胶产率的影响。在此基础上,运用正交试验对萃取工艺进一步优化。确定最佳工艺条件为:籽瓜皮以细渣状沸水浴灭酶3min,萃取液为硫酸,萃取液pH值为1.5,料液比为1∶15,萃取温度为90℃,萃取次数为2,萃取时间分别为2.5h和1h,浓缩比例为1/4,冷却后经1.5倍的乙醇沉淀,果胶产率为19.5%。     

超声波辅助提取桔皮中果胶的研究

研究了不同因素对超声波辐射萃取法从桔皮中提取果胶的影响通过试验确立了超声波条件下提取桔皮中果胶的最佳工艺条件为:用盐酸调pH值至1.8,用水作溶剂,料液比1:20.超声功率600 W,作用时间40 min,乙醇浓度60%.在此条件下,果胶提取率可达到20.8%并且确定了各因素对提取率的影响顺序为:pH值＜料液比＜超声时间＜乙醇浓度＜超声功率.     

微波法提取柚子皮中果胶的工艺研究

在微波条件下,研究微波加热时间、料液比以及盐酸浓度等因素对柚子皮中果胶提取率的影响,通过正交试验确定最佳工艺参数.结果表明:各因素影响果胶提取率的大小顺序为:微波加热时间>料液比>盐酸浓度,正交试验得出最佳工艺参数为:微波加热7 min,料液比1:15,盐酸浓度0.1 mol/L.与酸提取法相比,微波提取法能大大缩短提取时间,节省能耗,提高果胶的提取率.     

毛酸浆果实中果胶的提取

采用酸法提取毛酸浆果实中的果胶,同时考查了纤维素酶辅助酸法提取果胶的效果,比较了酸法及酶辅助提取果胶的得率及酯化度.结果表明;酸法提取果胶的最佳条件为:料液比1∶4、温度90℃、pH 2.0、时间80 min,在此条件下果胶得率为1.74%,果胶的酯化度为65.1%.纤维素酶浓度选择0.3%、酶解时间90 min,酶解...