一种热凝胶多糖的制备及其应用的研究进展

凝胶多糖是由粪产碱杆菌在限制氮源的条件下发酵产生的一种微生物胞外多糖,它几乎完全由葡萄糖残基通过β—D-1,3键结合成。这种多糖不溶于水,易溶于NaOH溶液。由于它独特的流变学特性和热凝胶特性,应用非常广泛,引起国内外学者的广泛关注。从菌种选育、发酵条件、提取、应用四个方面综述了热凝胶多糖的最新研究进展。     

In vitro release of propranolol from oil/water microemuisions

Oil/water (o/w) microemulsions containing propranolol were studied. Isopropylmyristate was used as the oil, Tween 60 as a surfactant, butanol as a co-surfactant and a buffer of pH 6.5 for the continuous phase. The lipophilicity of propranolol was enhanced by formation of lipophilic ion-pairs to obtain a disperse phase that could act as a reservoir; octanoic acid was used as counter-ion. The diffusion rates of propranolol from microemulsions through a hydrophilic membrane decreased as the concentration of octanoic acid increased. The apparent permeability constant, determined at the beginning of the experiment, was 2.9 × 10⁻⁹ cm s⁻¹ for propranolol alone and diminished until 3.5 × 10⁻¹⁰ cm s⁻¹ in the presence of octanoic acid, at a concentration of 16.4 times that of propranolol.     

热凝胶多糖及其衍生物的研究现状

概述了一种新的热凝胶多糖(curdlan)及其衍生物结构和功能性研究现状，探讨了几个研究热点问题，包括其生产过程的强化，凝胶机理，功能性，消化性，在分散介质中的性质变化，硫酸化衍生物的结构和功能性等。随着这些问题的解决，必将拓展其功能性应用领域。     

Curdlan协同Alcalase嫩化生鲜调理牛肉工艺优化

以新鲜牛肉为原料,分析不同浓度的Curdlan及Alcalase对生鲜调理牛肉剪切力、蒸煮损失及感官品质的影响,并研究该体系下肌浆蛋白质及肌原纤维蛋白质的分解情况,优化生鲜调理牛肉嫩化加工工艺。结果表明:体系中Curdlan对生鲜调理牛肉剪切力、蒸煮损失及感官品质均有显著的影响(P0.05),但是对牛肉中蛋白质无明显的分解作用;Alcalase对肌原纤维蛋白质及肌浆蛋白质有明显的分解作用。另外,不同的Curdlan及Alcalase添加量对生鲜调理牛肉的剪切力、蒸煮损失均有显著的影响(P0.05);并且Curdlan、Alcalase对生鲜调理牛肉感官品质有显著的促进作用;通过响应曲面试验二次回归法优化生鲜调理牛肉工艺,得到工艺条件为Curdlan添加量5.43 mg/g,Alcalase添加量4.29 U/g,腌制时间73.4 h,以该工艺进行验证实验后得到产品剪切力为(0.960±0.006)kg,蒸煮损失为(19.96±0.36)%,感官评分为92.81±0.75,与理论值相比,相对误差小于5%,该工艺准确可靠,可以用于生鲜调理牛肉的嫩化加工处理。     

Antimicrobial activity of nobiletin and tangeretin against Pseudomonas

The inhibitory activities of two polymethoxylated flavone (PMFs) monomers (nobiletin and tangeretin) have been investigated against Pseudomonas fluorescens and Pseudomonas aeruginosain vitro. The effects on cell morphology, the release of cell constituents, the synthesis of proteins and the activities of key dehydrogenase were examined to elucidate their antibacterial mechanism. The concentration of transaminase and reducing sugar in bacterial solutions increased significantly when treated with nobiletin and tangeretin. Electron microscopy showed that the structure of the bacterial cells was destroyed and accompanied with induced cells plasmolysis. Nobiletin and tangeretin also inhibited the activities of succinate dehydrogenase (SDH) and malate dehydrogenase (MDH), and reduced proteins synthesis in bacterial cells. It is proposed that nobiletin and tangeretin destroyed the permeability of the cell membrane, with release of the cell constituents, leading to metabolic dysfunction, inhibition of protein synthesis, and eventually to cell pyknosis and death.     

Effects of composition on fat rheology and crystallisation

The crystallisation behaviour of three fat blends, comprising a commercial shortening, a blend of fats with a very low trans fatty acid content (“low-trans”) and a blend including hardened rapeseed oil with a relatively high trans fatty acid content (“high-trans”) was studied. Molten fats were lowered to a temperature of 31 °C and stirred for 0, 15, 30, 45 and 60 min. Samples were removed and their rheological properties studied, using a controlled stress rheometer, employing a frequency sweep procedure. Effects of the progressive crystallisation at 31 °C on the melting profile of fat samples removed from the stirred vessel and solidified at −20 °C were also studied by differential scanning calorimetry (DSC).     

Effect of honey high-temperature short-time heating on parameters related to quality, crystallisation phenomena and fungal inhibition

The effect of a unique high-temperature short-time heating treatment on natural honeys to produce both a fungi inhibition and a crystallisation delay simultaneously was evaluated. As responses to treatments, hydroxymethylfurfural content, diastase activity, fungi and yeast development, and crystallisation starting time were measured. Besides, moisture, fructose, glucose and acidity were determined.Heating can produce a decrease in honey quality, which is made evident by a simultaneous reduction in the diastase activity, referred to as diastase number, and an increase in the hydroxymethylfurfural content. Considering the minimum admissible diastase number and the maximum admissible hydroxymethylfurfural content values, according to honey present regulations, several thermal treatment tests were performed on selected honey samples without exceeding those values. Tested conditions were: heating between 140°C and 80°C at times between 60 to 15 s and 30 to 10 s during both transient and isothermal heating stages, respectively. In all tests the diastase number was the most heat-sensitive parameter. The boundary thermal treatment, assumed as the most severe conditions able to produce a permissible quality loss, was found to be 140°C, during 15 s in the transient stage and 30 s in the isothermal stage. Beyond those values, an unacceptable diastase number reduction was produced. On the other hand, it was found that a 80°C heating, during 60 and 30 s in transient and in isothermal stages, respectively, destroyed all microorganisms responsible for quality damage without spoiling honey. This was considered to be the mild or more suitable treatment condition. Twenty-six naturally contaminated honey samples heated at such conditions showed a null capacity to develop fungi and yeast. Besides, according to the storing temperature, and moisture and glucose contents, a crystallisation beginning delay between 4 and 9 weeks was obtained on four selected honeys, according to the thermal treatment applied. Several parameters previously proposed that characterise honey crystallisation tendency as fructose/glucose, glucose/moisture and (glucose-moisture)/fructose ratios were related to the time in which crystallisation starts. A new parameter, (fructose/glucose)·moisture was proposed.     

Physico-chemical studies on a wide composition range of low-moisture glucose–fructose mixtures: rates of crystallisation

The crystallisation rates of low-moisture (from 2% to 10% w/w) glucose–fructose mixtures were investigated at a variety of storage temperatures (from 0 to 60 °C). It was found that d -fructose considerably retards the rate of crystallisation. High storage temperatures induced a decrease in the 'threshold' moisture content, which is necessary for the initial nucleation and further development of the glucose and/or fructose crystals. This knowledge of crystallisation rates can be exploited in terms of storage of confectionery products containing d -glucose, d -fructose or both of them, and honey.     

Fermentation of date palm juice by curdlan gum production from Rhizobium radiobacter ATCC 6466™: Purification, rheological and physico-chemical characterization

The present study was undertaken to investigate the possibility of using date palm juice byproducts for curdlan production by Rhizobium radiobacter ATCC 6466™ in batch experiments. A number of operational parameters, namely pH value, temperature range, inoculum ratio, agitation speed, carbon concentration, nitrogen source, and fermentation time, were investigated in terms of their optimal values for as well as individual and synergistic effects on curdlan production. The findings indicated that the strain exhibited a high ability to use the natural substrate under investigation. A curdlan production yield of 22.83 g/l was obtained in 500-ml agitated flasks (50 ml) when the strain was cultivated in the optimal medium (pH, 7; ammonium sulphate concentration, 2 g/l; date glucose juice concentration, 120 g/l) operating at 30 °C with an inoculum ratio of 5 ml/100 ml, an agitation speed of 180 rpm, and a fermentation period of 51 h. The purified date byproducts-curdlan (DBP-curdlan) had a molecular weight of 180 kDa, a linear structure composed exclusively of β-(1,3)-glucosidic linkages, a melting temperature (T_m) and glass transition temperature (T_g) of 1.24 and −3.55 °C, respectively. The average measured heights of its molecules were noted to fluctuate between 14.1 ± 0.07 and 211.73 ± 0.6 μm.     

Controlling fat bloom formation in chocolate – Impact of milk fat on microstructure and fat phase crystallisation

The partial replacement of cocoa butter (CB) with milk fat (MF) strongly influences micro-scale topographic evolution and fat phase crystallisation in milk chocolate. Adding MF reduces the incidence of large surface crystals and the number and diameter of amorphous, welled CB deposits (‘cones’), with a concurrent decrease in initial surface roughness (p < 0.05) and rate of surface coarsening. Presence of MF also slows the solidification of the cones into disorganised crystalline masses. Finally, MF reduces the initial solid fat content, and slows the rate of change in whiteness index, as well as the form V to VI polymorphic transition. Fat crystal growth is accelerated by repeated temperature-cycling (26–29 °C) compared to isothermal conditioning (26 °C). However, cone hardening occurs more rapidly when isothermally-stored. Irrespective of fat composition and storage conditions, fat crystal growth, welling and ultimately fat bloom begin only at specific locations on the chocolate surface, suggesting that chocolate’s microstructural heterogeneity is responsible for distinct surface fat crystallisation pathways.     

杀铃脲缓释微胶囊制备表征及缓释性能的研究

为了提高农药在生态环境中的持效性和生物安全性,采用层层自组装技术,构建了杀铃脲微胶囊,并对其性能进行表征。结果表明:利用正交实验确定杀铃脲微胶囊制备的最优工艺条件为:3.0g/L海藻酸钠,2.0g/L壳聚糖,1.0g/L杀铃脲和2.0g/L CaCl2,其中,壳聚糖的浓度对包埋微胶囊效果影响最大,所得杀铃脲微胶囊的包封率和载药量分别为77.4%和75.2%;通过激光共聚焦显微镜（CLSM）与扫描电镜（SEM）对杀铃脲微胶囊进行表征,晶体形状良好,表面光滑,没有药物溶出,平均粒径为6μm,Zeta电位为-12.5mV,通过体外缓释实验的研究证实随着包覆层数的增加,杀铃脲微胶囊的缓释性能明显增强。      

Effects of high pressure level and holding time on properties of duck muscle gels containing 1% curdlan

The effect of high pressure processing (HPP) on properties of duck muscle gels (DMG) containing 1% curdlan was investigated. The application of > 300 MPa could result in the decrease of cooking loss of DMG in water binding capacity, the increase of L value and the decrease of a value and b value in color, the increase of hardness, springiness, cohesiveness and chewiness in textural parameters (P < 0.05), while the pressure-holding time had no obvious influence. Those experimental results could be attributed to the interactions among protein molecules and the interactions between protein molecules and curdlan molecules created or enhanced by HPP. Overall, the use of curdlan instead of fat and the application of HPP may provide a novel approach to achieve low-fat (< 6% fat) and low-salt (1% salt) DMG products with good properties and high yields.

Industrial relevance

To provide healthier meat foods like low-fat (< 6% fat) and low-salt (about 1% salt) duck meat products, the application of HPP might be of great interest for industrial manufacture and can yield the products bearing high water binding capacity and good textural properties.     

Tripalmitin and monoacylglycerols as modifiers in the crystallisation of palm oil

An exhaustive analysis of the crystallisation behaviour of palm oil was performed using low-resolution magnetic pulsed nuclear resonance, differential scanning calorimetry, polarised light microscopy and X-ray diffraction. The aim of this study was to characterise the changes induced in the crystallisation of palm oil by the addition of two different levels of tripalmitin and two different types of monoacylglycerols. The addition of monoacylglycerols led to the formation of a large number of crystallisation nuclei without changing the final solids content, accelerating the process of crystal formation, leading to the formation of smaller crystals than those found in the refined palm oil. Higher levels of tripalmitin produced crystals with larger dimensions, reducing the induction period and resulted in a higher level of solids at the end of the crystallisation period. The addition of monoacylglycerols and tripalmitin induced the formation of a polymorphic β-form.     

Effect of sugar, cocoa particles and lecithin on cocoa butter crystallisation in seeded and non-seeded chocolate model systems

The effect of major chocolate ingredients (sugar, cocoa particles and lecithin), in combination with the two pre-crystallization techniques, seeding and non-seeding, was investigated with respect to the kinetics of cocoa butter crystallisation and the resulting microstructure. Confocal laser scanning microscopy (CLSM) was used to monitor microstructural evolution under dynamic thermal conditions. DSC measurements and image analysis were also applied in order to quantify the impacts of processing and formulation on microstructure. All ingredients and pre-crystallisation techniques considered proved to have a large impact on fat crystallisation kinetics and the resulting microstructure. Seeded samples tended to form multiple nucleation sites, inducing rapid growth of a crystal network. The non-seeded samples showed an altering structure, with some domains developing large spherical crystals while in other domains a more heterogeneous microstructure resulted. Lecithin showed a remarkable impact on crystallisation kinetics in both the seeded and non-seeded samples. For the seeded samples, the effect was most noteworthy in samples containing cocoa butter and sugar, where lecithin significantly reduced the induction time. In the absence of seeds, lecithin itself acted as the nucleation site for fat crystallisation.     

Evaluation of various salt contents on quality characteristics with or without curdlan of pork myofibrillar protein gels and the development of low-salt pork sausages

The objective of this study was to evaluate the gelling properties of pork myofibrillar protein (MP) gels at various salt concentrations with or without curdlan, and its application to model sausages with reduced salt levels. When curdlan was incorporated into MP mixtures, cooking yield (CY) at 0.15 m salt was similar to that of 0.45 m salt (P > 0.05). Gel strength of MPs at 0.45 m salt was highest among other salt concentrations. Increased salt concentration tended to be high shear stress values, regardless of the presence of curdlan (P < 0.05). MP gels with increasing salt concentration showed fewer pores and swollen structures. Addition of curdlan improved CY and expressible moisture of low-fat model sausage with increased salt levels. The addition of curdlan at 1.0% salt reduced the hardness and gumminess, and similar to those at 1.5% without curdlan. These results indicated that curdlan improved the water-holding capacity and textural properties of low-fat and low-salt sausage.