The effect of salts on the retention of ethyl butyrate by gellan gels

The effect of gellan gels with different texture on the retention of ethyl butyrate was investigated by Static Headspace Gas Chromatography. Calcium induced gels enriched with 400 ppm of the volatile showed not significantly different aroma release for calcium concentrations up to 40 mM, whereas higher concentrations exhibited greater partition coefficient values not significantly different from each other. Aroma release was not controlled by the mechanical properties when 1000 ppm of ethyl butyrate was added. When mixtures of calcium and potassium chloride, at a total molar concentration of 80 mM, were used to induce gelation, aroma release became greater with increasing calcium concentration in the mixtures. Moreover, elevated concentrations of the aroma compound (400-1000 ppm) added to gellan matrices, gelled by 10 mM calcium chloride, resulted in increased aroma release. For all samples, the percentage of retention was also calculated and both positive and negative values were determined.     

Retention of selected aroma compounds by gelatine matrices

The retention of various aroma compounds (linalool, limonene, ethyl butyrate, butyl acetate, isobutyl acetate, pentyl acetate, isopentyl acetate, hexyl acetate) by gelatine gels (2.5, 5, 10 and 20 wt%) was investigated by Static Headspace Gas Chromatography. Prior to analysis the samples were left to equilibrate at 37 °C for 24 h. The selected volatiles differed in their hydrophobicity and structure. One of the major conclusions was that increased hydrophobicity, in volatiles within the same homologous series, resulted in increased release. Branched volatiles gave greater partition coefficient values than their linear counterparts. When volatiles without the same functional group were compared, no correlation between hydrophobicity and retention was observed. The different mechanical properties of the matrix, as a result of different protein concentration, also affected the aroma retention. The effect of equilibration temperature on partition coefficients was also studied. Increased temperature resulted in higher partition coefficient values, probably due to the increased volatility of the aroma compound. Both positive and negative percentage of retention values were calculated suggesting varying protein-volatile interactions.     

Retention of trans-anethole by gelatine and starch matrices

The retention of trans-anethole by gelatine gels (2.5, 5, 10 and 20 wt.%) and starch solutions (10 and 20 wt.%) was investigated by Static Headspace Gas Chromatography. Prior to analysis the samples were left to equilibrate for 24 h at 5 and 37 °C, respectively. Higher partition coefficients were obtained at the higher temperature, probably due to the increased volatility of the aroma compound. The effect of freeze drying of the matrices in the presence of trans-anethole was also evaluated. No significant effect on the partition coefficient values was observed. However, the changes in the nature and the concentration of the matrix were not of great importance on the retention of trans-anethole.     

硫酸氢钾催化合成正丁酸异戊酯的研究

以硫酸氢钾为催化剂，正丁酸和异戊醇为原料合成了正丁酸异戊酯。考察了催化剂用量、醇酸物质的量比、反应时间及催化剂重复使用性等因素对收率的影响。结果表明：硫酸氢钾是高效、经济且环境友好的酯化催化剂，具有工业化前景。适宜反应条件为：正丁酸0．15mol，醇酸物质的量比1．50，催化剂1．50g，反应时间40min，收率82．2％。     

Retention of aroma compounds in food matrices of similar rheological behaviour and different compositions

Two matrices with a similar rheological behaviour but with a different composition have been developed: one containing carbohydrates (d-glucose, pectin and starch) and in the second one, called complex matrix, a lipid (triolein) was added. The release of six aroma compounds is quantified by using the measurements of partition coefficients at thermodynamic equilibrium. The role of lipid (triolein) on the retention of all the aroma compounds was pointed out. The effect of carbohydrates was more complex: in comparison with water, ethyl hexanoate and trans-2-hexenal were more retained whereas diacetyl, 2-pentanone and cis-3-hexenol were “repulsed” from the matrix. The kinetic study of the release from these matrices had shown a decrease of the initial rate of release by reference with water. From carbohydrates matrix, the decrease of the release for three compounds (ethyl acetate, ethyl hexanoate, 2-pentanone) seemed to arise from the variation of diffusion and/or retention by carbohydrates. For the three other aroma compounds (diacetyl, cis-3-hexenol and trans-2-hexenal) no variation of the initial rate was registered. The comparison of the release rates from carbohydrate and complex matrices indicated the role of lipids and the comparison of the release rates from water and complex matrix showed the combined effects of texture and lipids. The decrease of initial release rate was more important in presence of lipids than in presence of carbohydrates. The most important decrease was observed with the most hydrophobic compound.     

The influence of gelation rate on the physical properties/structure of salt-induced gels of soy protein isolate–gellan gum

The cold-set gelation of soy protein isolate (SPI)-gellan gum was induced by the addition of salts (KCl or CaCl₂) using two different procedures: the direct addition of salts (fast gelation) or the diffusion of salts through a membrane (slow gelation). The mechanical properties, syneresis and microstructure of the mixed gels were evaluated, as well as for gellan and SPI gels. The mixed gels induced by calcium diffusion were stronger and more deformable than gels induced by the direct addition of calcium, while the opposite occurred for potassium-induced gels. All the mixed gels were macroscopically homogeneous, but at the microscopic level two independent networks could be observed. These two separate networks were more evident for the calcium-induced gels, and the structural characteristics depended strongly on the concentration of the protein and the polysaccharide. However an organized microstructure with the formation of microtubes surrounded by other network was only observed for the mixed gels induced by calcium diffusion at the higher protein/polysaccharide (10:1) ratio. Thus besides the composition and concentration of the biopolymers, the results showed that the type of salt and its velocity of incorporation led to gels with different structures and consequently different mechanical properties.     

NaCl存在下结冷胶以及结冷胶/明胶共混凝胶质构和熔点的研究

研究了不同浓度NaCl(1％～3％,w/v)、结冷胶(0.1 5％～0.35％,w/v)和明胶(1％～3％,w/v)对结冷胶和结冷胶明胶共混凝胶质构特性和熔点的影响.目的是得出结冷胶明胶复配胶凝胶特性,为复配胶在成味食品中的应用提供参考结果表明,共混凝胶硬度和熔点随NaCl浓度增加而增大,当NaCl浓度高于1.5％时,硬度和熔点均下降;结冷胶和明胶浓度对共混凝胶硬度影响较大;结冷胶形成的凝胶弹性差,与明胶复配使用,弹性显著提高,并且共混凝胶弹性随结冷胶浓度增大而降低,随明胶浓度增大而增大;结冷胶浓度决定了共混凝胶的熔点结冷胶和明胶复配可以弥补各自单独使用的不足,且复配胶兼具高熔点和入口即化的特性.     

白酒中香味物质的顶空一气相色谱／质谱联用分析

研究建立了一种快速简单的检测白酒中的香气成份的检测方法,即顶空一气相色谱／质谱联用分析方法,该方法采用静态顶空进样,GC-MS分离鉴定,总离子流色谱的峰面积归一化定量分析白酒中酯类和醇类等香气成份,方法操作简单,定性可靠准确。     

Diffusion of probe polymer in gellan gum solutions during gelation process studied by gradient NMR

The diffusion coefficients of pullulan added in gellan gum solutions as a probe polymer were measured using pulsed-field-gradient stimulated-spin-echo (PFG-Ste) ¹H NMR in order to investigate the gelation mechanism and gel structure. The echo intensity of gellan was steeply decreased at around the gelling temperature T_gel indicating stiffening of the gellan chains upon aggregation and formation of the network. The diffusion coefficient of pullulan D_pull increased with decreasing temperature below T_gel. This result suggests that the decrease in concentration of solute gellan in the interspaces of the network below T_gel, as evidenced by the decrease in its echo intensity, leads to an overall decrease of hydrodynamic interactions between gellan and pullulan. The characteristic hydrodynamic shielding length ξ was calculated from the relation D_pull/D_pull,0 = exp(−R_h/ξ), where D_pull,0 is D_pull in dilute solution and R_h is the hydrodynamic radius of pullulan. The temperature dependence of ξ, which was investigated for varying concentrations of several cations, was found to follow closely the gelling temperature, and in particular, showing a very similar thermal hysteresis.     

Headspace concentration of selected dry-cured aroma compounds in model systems as affected by curing agents

The effect of curing agents (sodium chloride, nitrate, nitrite, glucose, and ascorbic acid) on the headspace concentration of six volatile compounds (2-methyl-butanal, 3-methyl-butanal, 2-pentanone, hexanal, methional, and octanal) has been studied. These volatile compounds were selected based on their presence and contribution to the flavour of typical Spanish dry-cured meat products. The release of volatile compounds to the headspace has been studied by using solid-phase microextraction (SPME) and gas chromatography analysis. The main effect was produced by sodium chloride, because it produced a salting-out effect on all the volatile compounds studied. Furthermore, the presence of nitrite, nitrate, and ascorbic acid in the solution also produced an increase in the headspace concentration of the volatile compounds while glucose decreased the headspace concentration of octanal and hexanal. The changes in the relative proportions of volatile compounds due to the effect of curing agents should be taken into account as they may change the flavour perception of dry-cured meat products.     

Acid gelation of low acyl gellan gum relevant to self-structuring in the human stomach

The aim of this study was to investigate the in vitro acid-induced gelation of low acyl gellan gum. Various metabolically relevant pH environments and hydrocolloid concentrations were investigated. These resulted in very different acid structures, which were characterised by texture analysis, with Young’s and bulk moduli and work of failure being reported. The structures of the acid gels were shown to depend upon the pH and hydrocolloid concentration (c) used during their production, with a maximum in gel strength between pH 3 and 4. Both the Young’s and bulk moduli data suggest that there is a critical concentration for gelation to occur, and both parameter values displayed a gradual increase (which appears to be lower than a c² dependency) as the gellan concentration was increased.     

Effect of gellan,alone and in combination with high-methoxy pectin,on the structure and stability of doogh,a yogurt-based Iranian drink

Doogh is a traditional Iranian drink prepared by fragmentation and dilution of yogurt, with addition of salt and flavouring. In the present work, we have used viscometry, microscopy, particle-size analysis and measurements of serum separation to explore the effect of very low concentrations of gellan gum (0.01, 0.03 and 0.05 wt %), alone or in combination with 0.25 wt % high-methoxy pectin (HMP), on its structure and stability. HMP is known to prevent association of casein particles in acidic milk drinks by steric stabilisation, forming a protective layer bound electrostatically to the surface of the particles. Doogh incorporating 0.25 wt % HMP alone showed satisfactory stability on storage for ∼10 days at 5 °C, but after 15 days there was obvious separation into a dense sediment and a much clearer upper layer that occupied more than 80% of the total volume, which we attribute to progressive sedimentation of individual sterically-stabilised particles. Samples incorporating gellan (with or without HMP), by contrast, showed rapid development of a clear serum phase, with little further separation at longer times (up to ∼1 month), suggesting expression of fluid by contraction of a gel network (i.e. syneresis rather than sedimentation). Particle size increased dramatically (more than 10-fold) with increasing concentration of gellan, and at the highest concentration studied (0.05 wt %) a continuous network of casein-rich strands was observed by phase-contrast microscopy. The concentration of NaCl used in the doogh samples (0.5 wt % ≈ 85 mM) is known to be sufficient to maintain gellan in its ordered (double-helix) conformation, which has higher charge density than individual molecules of HMP. We suggest that network structure is formed by electrostatic attachment of gellan to fragments of acid-casein gel, thus increasing particle size and inhibiting surface-coverage by HMP, with weaker associations between gellan helices allowing the samples to flow. Observed decrease in serum volume with increasing concentration of gellan is attributed to formation of progressively stronger coupled networks with greater resistance to syneresis. Stabilisation of doogh with 0.05 wt % gellan in combination with 0.25 wt % HMP had no adverse effect on organoleptic acceptability, and reduced serum volume on protracted storage to ∼10% (in comparison with over 80% for the same concentration of HMP alone), suggesting that gellan could be of practical value in extending the shelf-life of doogh (and related acidic milk drinks).     

Determination of partition coefficient of migrants in food simulants by the PRV method

Partition coefficients of six migrants between four simulated foods (water, 10% ethanol, 3% acetic acid, 95% ethanol) and air were determined by the phase ratio variation (PRV) method using headspace analyses by gas chromatography. The migrants were ethyl acetate, methyl ethyl ketone, propyl alcohol, butyraldehyde, acetaldehyde and acetonitrile. The results showed that migrant absorption by the four food simulants was highly dependent on the physicochemical properties of migrants and foods, such as polarity, solubility and hydrogen-bonding.     

助留剂在瓦楞原纸生产中的应用试验

本文介绍了助留剂在瓦楞芯纸生产过程中的应用试验,分析了试验过程单程留着率和白水浓度的变化趋势以及添加助留剂对纸页强度的影响。     

Effect of high‐pressure homogenisation on the retention of selected aroma compounds in model dairy emulsions

The aim of this work was to investigate the effects of high‐pressure homogenisation on the aroma retention of mixed sodium caseinate–whey protein (2% + 2% w/v) emulsions. For this purpose, raw and pasteurised emulsions, with different fat contents (5%, 8% and 15% w/v) and subjected to different homogenisation pressures (0, 18, 100 and 150 MPa), were produced. The retention of seven aroma compounds (hexanal, benzaldehyde, diacetyl, ethyl butyrate, isoamyl acetate, ethyl hexanoate and ethyl octanoate) was evaluated by static headspace gas chromatography. Results showed that aroma release was affected by the presence and the quantity of the lipid phase. As regards homogenisation, an increase in the retention of hexanal with homogenisation pressure was observed and interactions between hexanal and caseinate were suggested. Benzaldehyde showed significant changes in headspace partition with increasing pressure only in the 5% fat content emulsions, whereas no homogenisation effect on aroma retention was observed for diacetyl or esters.     

Modelling and optimization of ethyl butyrate production catalysed by Rhizopus oryzae lipase

Response surface methodology was used to model and optimise the production of ethyl butyrate, catalysed by Rhizopus oryzae lipase immobilised in a hydrophilic polyurethane foam. Experiments were carried out following a central composite rotatable design, as a function of reaction temperature (T: 22–38 °C) initial butyric acid concentration (A: 0.031–0.619 M) and initial molar ratio ethanol/acid (MR; 0.257–2.443). After 48 h reaction time, the production of ethyl butyrate could be fitted to a surface described by a second-order polynomial model. A maximum ethyl butyrate concentration of 0.106 M, corresponding to 47% conversion into ester and a productivity of 2.21 μmole/mL h, is expected at initial reaction conditions of T, A and MR of 33 °C, 0.225 M and 1.637, respectively. This maximum was experimentally confirmed.     

Simultaneous kinetic-spectrophotometric determination of maltol and ethyl maltol in food samples by using chemometrics

A fast and accurate procedure has been researched and developed for the simultaneous determination of maltol and ethyl maltol, based on their reaction with iron(III) in the presence of o-phenanthroline in sulfuric acid medium. This reaction was the basis for an indirect kinetic spectrophotometric method, which followed the development of the pink ferroin product (λ_max = 524 nm). The kinetic data were collected in the 370–900 nm range over 0–30 s. The optimized method indicates that individual analytes followed Beer’s law in the concentration range of 4.0–76.0 mg L⁻¹ for both maltol and ethyl maltol. The LOD values of 1.6 mg L⁻¹ for maltol and 1.4 mg L⁻¹ for ethyl maltol agree well with those obtained by the alternative high performance liquid chromatography with ultraviolet detection (HPLC-UV). Three chemometrics methods, principal component regression (PCR), partial least squares (PLS) and principal component analysis–radial basis function–artificial neural networks (PC–RBF–ANN), were used to resolve the measured data with small kinetic differences between the two analytes as reflected by the development of the pink ferroin product. All three performed satisfactorily in the case of the synthetic verification samples, and in their application for the prediction of the analytes in several food products. The figures of merit for the analytes based on the multivariate models agreed well with those from the alternative HPLC-UV method involving the same samples.     

硅溶胶微粒助留系统在纸机上的应用实践

论述了硅溶胶助留系统在造纸厂的应用实践,湿部纸浆电荷需求对助留效果的影响,调节电荷需求的方法及PCD仪器的使用.     

纳米TiO2微粒助留系统在新闻纸中应用初探

本文探讨了纳米胶体TiO2作为一种新型的微粒子助留系统应用在新闻系统中的可行性,主要考察了该纳米TiO2胶体溶液在pH值和离子强度变化的情况下其表面Zeta电位和表面电荷的变化情况,以及在浆料中pH值变化情况下其对新闻纸系统助留效果的影响,并且与CPAM的助留效果进行了比较.