微波处理对果胶构象的影响

本文主要通过测定特性粘度,结合尺寸排阻色谱-多角度激光散射联用法(SEC-MALLS)、动静态光散射法表征果胶构象,研究微波处理前后果胶的构象变化。结果显示,微波处理5、15、20、30 min,果胶的特性粘度从4.25 dL/g分别降低至3.35、3.10、2.97、2.85 dL/g。SEC-MALLS结果显示,微波处理30 min后,M_W由原果胶的31.38×10⁴ Da降低至4.76×10⁴ Da,表明微波处理会导致果胶的降解;通过对果胶溶液的R_g和M_W的双对数图α值进行分析,可以得出原果胶及微波处理5、15、20 min后果胶分子链构象为无规则线圈,而处理时间延长至30 min后,果胶分子的链构象变为刚性棒状。此结果与动静态光散射法表征得到的果胶构象变化一致。本论文为解释微波处理造成果胶理化性质变化提供一定的理论基础。     

Rheological Properties of High-Methoxyl Pectin and Locust Bean Gum Solutions in Steady Shear

The Cross and Carreau flow models described well the shear rate-apparent viscosity data. The coil overlap parameter, c[η], correlated well with the zero-shear rate specific viscosities of these mixtures. Experimental values of intrinsic viscosities of the mixtures were in good agreement with the prediction based on an additive model of the individual contributions of the gums. From the results obtained for the mixtures of both polysaccharide solutions at similar viscosity, pH and ionic strength, no significant interactions were detected. Hypotheses for this lack of polymer interaction were developed. Results with such model systems are useful in understanding the relation of composition to the properties of complex food systems.     

柿单宁对果胶流变特性的影响

研究不同聚合度柿单宁(DP 26/5)对高酯/低酯(HM/LM)果胶在变剪切速率及变温下稳态和动态流变性的影响。利用TA-DHR2流变仪测定柿单宁-果胶复合物的流变学性质。静态流变特性测试结果表明,柿单宁未改变HM/LM果胶的流体类型,符合Cross模型,表现为剪切变稀,呈假塑性非牛顿流体特征。随着温度的升高柿单宁-果胶复合体系显示出粘度下降的趋势,符合Arrhenius方程。在同等温度条件下,0.2%柿单宁能显著增强HM/LM果胶粘度(p0.001),且柿单宁-HM果胶复合物的粘度值略高于柿单宁-LM果胶复合物的粘度值。柿单宁聚合度对果胶粘度的影响不明显。此外,动态流变性质测试结果表明,DP26/5柿单宁能够缩短HM/LM果胶凝胶化相转变时间,降低其凝胶化相转变温度。柿单宁对果胶流变性质的影响对开发柿单宁-果胶功能性复合配料提供理论依据。     

微波降解果胶对其流变性质的影响及动力学

对不同质量浓度(0.5、1.0、1.5、2.0 g/100 m L)的果胶溶液微波处理不同时间(0、1、3、5、8、15、20、30 min)后的流变性质及动力学进行考察。结果表明,随着果胶溶液质量浓度降低、微波处理时间延长、剪切速率增大,样品的表观黏度和特性黏度[η]均降低。用牛顿幂律方程描述溶液的流体行为,果胶溶液是剪切稀化的假塑性非牛顿流体,在低质量浓度时,微波处理对溶液的流体行为影响最大。根据特性黏度对样品进行反应动力学拟合,发现果胶的微波降解遵循反应一级动力学,在质量浓度0.5 g/100 m L时降解速率最快,质量浓度1.5 g/100 m L时降解速率最慢。经与沸水浴无微波的空白组对比,发现微波降解果胶的过程还存在非热效应。     

Sugar replacement in sweetened bakery goods

This review presents the state‐of‐the‐art concerning the application of natural and artificial high‐intensity sweeteners, fructans and bulking agents such as polyols as sugar replacers in sweet‐baked goods and their effects on product characteristics. The recent much publicised attention given to weight gain of the population and its consequences on the occurrence of diet‐related diseases in developed countries has influenced the food manufacturers attempts to provide the consumer with reduced energy products. The replacement of sucrose in sweet bakery products by alternative natural or artificial sweeteners can be a challenging issue. Sucrose as a main ingredient in sweet bakery products contributes, aside from providing sweetness, to numerous processing and product characteristics. Intense sweeteners have a high sweetness compared with sucrose but lack in their contribution to the body of the product, whereas the replacement of sucrose with bulking sweeteners may result in products with a similar body but a lack in taste and flavour.     

小麦淀粉的特性黏度

以15种小麦淀粉为原料,在极稀的淀粉溶液中对比浓黏度-浓度做图,外推到浓度为零处,由截距得到淀粉的特性黏度。     

高效液相色谱-串联质谱法同时测定调味品中8种人工合成甜味剂

目的 建立一种高效液相色谱-串联质谱法(HPLC-MS/MS)同时测定调味品中8种人工合成甜味剂(安赛蜜、甜蜜素、糖精、阿斯巴甜、阿力甜、纽甜、三氯蔗糖、新橘皮苷二氢查耳酮).方法 样品用水提取,提取液用甲醇沉淀水溶性大分子化合物,离心后取上清液经过中性氧化铝固相萃取柱分离色素,采用C18色谱分离柱,以10 mmol/L甲酸铵溶液-乙腈进行梯度洗脱,电喷雾负离子模式下多反应监测(MRM)模式检测.结果 线性范围分别为糖精于0.05～5μg/ml,三氯蔗糖于0.1～ 10 μg/ml,其它甜味剂于0.01～1μg/ml,线性关系良好,r2＞0.990.在3个添加水平下,样品平均回收率为82.7％～117.9％,RSD为0.6％～10.6％.甜味剂于液体及半固体基质中的检出限均为0.01 ～0.1 mg/kg,于固体基质中的检出限为0.1～1 mg/kg.结论 本方法选择性强、灵敏度高、处理方法简单,可用于调味品中8种人工合成甜味剂的测定.     

羟乙基纤维素水溶液粘度特性的研究

在本实验中,羟乙基纤维素(HEC)的水溶液为剪切变稀的非牛顿流体.其表观粘度随溶液浓度非线性增大,表明在该水溶液中除HEC分子主链间有相互作用外,还存在较少量的HEC分子侧链间的弱缠结;其水溶液的特性粘度为0.9488.在HEC水溶液达到初始粘度后,最初HEC分子链由于受到水分子的较大作用而造成粘度急剧下降.随之,HEC分子链间的作用与HEC与水分子间的相互作用会产生一个暂时平衡,使其溶液的粘度趋于平稳.其后,HEC分子链的运动加速,同时水分子与HEC链间较强的相互作用破坏了HEC分子侧链的缠结,使溶液体系的粘度进一步下降直到趋于平衡.     

苹果果胶的结构、单糖组分和稳定性研究

对苹果果胶的结构、单糖组分及稳定性进行研究。采用傅立叶变换红外光谱仪测定苹果果胶的结构,毛细管气相色谱法测定果胶多糖的单糖组分,粘度法测定果胶在不同浓度的糖、盐、过氧化物存在时粘度的变化。结果表明:苹果果胶中含有部分甲氧基和少量乙酰基,具有一般果胶结构,果胶多糖中含有8种单糖。葡萄糖和麦芽糖对苹果果胶还原粘度起促进作用,而糊精相反。盐能降低果胶粘度,低浓度的盐作用最显著。过硫酸铵由于改变了果胶液的离子强度和pH,因而能增大果胶粘度。      

Dynamic Rheological Measurement of Structure Development in High-methoxyl Pectin/Fructose Gels

Incipient structure development (SD) in 65% fructose—0.5, 0.75, and 1% high—methoxyl (HM) pectin gels (pH 2.7) being cooled (50–10°C) were measured in terms of dynamic viscosity (η*) at 1Hz. SD rates (poise/min) were higher at lower temperatures, higher pectin concentrations, and when pectin was hydrated for 16 hr. Below the gel temperature, SD rates in 1% gel followed the Flory-Weaver model. SD in stored 0.5% gels during 22 days was strongly affected by storage temperature (2–38°C) and pH. SD rates in pH 2.7 gels were positive above, but negative below 18°C.     

Characterisation of gold kiwifruit pectin isolated by enzymatic treatment

Pectin was extracted from gold kiwifruit by four commercial enzyme preparations (Celluclast 1.5 L, Cytolase CL, Cellulyve TR 400 and NS33048). The chosen enzymes were used either in single or in combination, with and without protease addition. The recovered pectin was characterised and compared for the yield, total nonstarch polysaccharide and neutral sugar composition, protein and ash, pectin, molecular weight distribution and the viscosity. Results indicated that enzyme‐extracted gold kiwifruit pectin was rich in galacturonic acid. Purified pectin yield, and their physicochemical composition and rheological property (viscosity), was significantly affected by the type of enzyme used. The pectin extracted by Celluclast 1.5 L demonstrated to be the most viscous and recorded the highest in molecular weight (M_w) (1.65 × 10⁶ g mol^–1) compared with the other extracts. The extract M_w and their distribution were discussed and related to their viscosity behaviour.     

苹果梨果胶理化特性的研究

采用酸解法从苹果梨疏果和成熟果榨汁后的果渣中提取果胶,并对果胶纯度、色度、甲氧基含量、酯化度、黏度和相对分子质量进行测定。结果表明：用酸解法结合沉析法提纯的苹果梨果胶纯度在70% 以上,疏果期果胶颜色为浅棕色,成熟期果胶颜色为白色。苹果梨成熟期果胶的特性黏度和相对分子质量分别为1.51 × 10-7Pa·s 和6.96 × 105,均高于疏果期果胶,两者均为高酯果胶,其中疏果期果胶为慢凝型果胶,成熟期果胶为速凝型果胶。     

Component Analysis of Disaggregation of Pectin During Plate Module Ultrafiltration

Concentration of commercial lime and citrus was carried out by plate module ultrafiltration with a 300K cut-off membrane with small changes in intrinsic viscosity and 48 and 55% recoveries. Subsequent ultrafiltration of permeates with a 100K cut-off membrane yielded pectins from retentates with lower viscosities and recoveries of 34 and 39%. Component analysis was applied to concentration and viscosity response curves from high performance size exclusion chromatography. Results suggested viscosity loss was due to passage through the membrane of small pectin molecules and/or aggregates released from breakdown of larger pectin aggregates during 300K ultrafiltration. Concentration of pectin with minimum loss of viscosity requires ultrafiltration which insures retention of small pectin aggregates. Improved component analysis was developed for characterizing solution behavior of pectin during processing.     

山楂果胶的黏度特性及其与化学构造的关联性

山楂果实中含有大量的果胶,其果胶溶液的黏度高于同等条件下市售柠檬果胶的黏度.山楂果胶与柠檬果胶黏度不同的主要是由山楂果胶与柠檬果胶中中性糖组分(Hf1、Lf1)的化学组成与化学构造的不同以及山楂果胶中存在而柠檬果胶中不存在的酸性糖组分(Lf2)所引起的.对山楂果胶中中性糖组分Hf1的化学构造特征进行分析的结果表明,Hf1是一种含有Glc(1→3)Xyl与Xyl(1→6)Glc这两种键合样式的Arabinoxyloglucan.     

Pectin and Raspberry Concentrate Effects on the Rheology of Stirred Commercial Yogurt

The influence of pectin (0.0–0.5%) and raspberry concentrate (64°B; 0–10%) on the rheological characteristics of commercial stirred yogurt was evaluated using a computer-controlled rotational viscometer. All upward flow curves (shear rate vs shear stress) followed the Herschel-Bulkley model while downward curves showed a linear relationship. The consistency coefficient (upward flow) and apparent viscosity (downward flow) showed a continuously increasing trend with increasing pectin and raspberry concentrate. The rheology of flavored yogurt could be fabricated by post-incubation mixing of stirred yogurt with pectin and raspberry concentrate.     

贮藏期间芦荟果胶含量变化及影响果胶粘度因素的研究

果胶作为由植物中提取的天然添加剂,具有良好的胶凝化和稳定化作用。从具有保健作用和药用价值的芦荟中提取果胶已广泛应用于食品工业、化妆品、医药等领域。本文对贮藏期间芦荟果胶含量态变化进行研究,并确定影响果胶粘度的因素,对芦荟果胶提取具有指导意义。本文采用酸水解醇析法提取芦荟中的果胶,确定提取果胶醇析过程中的最优pH和温度,并明确贮藏0～60d芦荟中果胶含量,此外还确定各种影响因素对果胶成品粘度的影响。结果表明,醇析过程中的最佳pH3.5,最佳温度为50℃。果胶成品的pH2.79（符合国标）,甲氧基含量为8.518%,属于高甲氧基果胶。贮藏0～60d库拉索芦荟中的果胶含量在贮藏10d时达到峰值。而后果胶含量随贮藏时间的延长而降低,并且在20d之后明显下降。因此,最适宜芦荟果胶提取和加工的时间为0～20d。所得芦荟果胶粘度与温度、柠檬酸和氯化钠添加量呈负相关,而与果胶浓度和蔗糖添加量呈正相关。