Retention of ethyl butyrate by gellan gels in the presence of potassium ions

The air/biopolymer partition coefficient (K) and percentage of retention (R%) of ethyl butyrate (400 ppm) added to gellan gels were determined, using static headspace gas chromatography. Potassium chloride (40–120 mM) was used to induce gellan gelation. When 5 g of sample were left to equilibrate at 37 °C for 2 and 24 h, the coefficient values initially decreased with salt concentration to a certain value after which they raised again. The lower coefficient values, for the 24 h period, were observed at higher salt concentration than for the 2 h. Moreover, for both time periods, the lower coefficient values were found for the gellan gels with the greater strength and rigidity and were accompanied by positive percentages of retention. When 15 g of sample were used, after equilibration at 37 °C for 24 h, no significant changes in aroma release were observed. Moreover, negative percentages of retention values were calculated for all salt concentrations.     

Compression of gellan gels. Part I: effect of salts

Gellan gels, in the presence of potassium and calcium ions and their mixtures, were tested using large deformation compression experiments. Characterisation was based on stress and strain at failure along with Young’s modulus. Samples prior to compression were refrigerated at 5 °C for 1, 2 and 24 h. In the case of potassium, the strongest gel was obtained for a cation concentration of 80 mm . Increasing concentrations of calcium resulted in decreased gel strength. Brittleness values for potassium and calcium gels fluctuated around ～0.5 and ～0.3 respectively. The strength for both, potassium and calcium, gels did not increase significantly over time. For each cation, Young’s modulus and stress at failure showed the same variation. In the case of mixtures, strength was determined by calcium as its progressive replacement by potassium was actually similar to reducing its concentration. Potassium determined the remaining properties.     

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.     

Rheological analysis of emulsion-filled gels based on high acyl gellan gum

Emulsion-filled gels are widely used in cosmetic, food, and pharmaceutical industry. As rheological properties of these systems are strongly dependent on the properties of the gelled polymer network, rheological characteristics of gels containing high and low acyl gellan gum were analyzed. Under the processing conditions low acyl emulsions were unstable, thus in the present work the influence of oil and hydrocolloid concentrations on the viscoelastic behavior of emulsion-filled gels containing high acyl gellan gum was studied. Increasing gellan concentration (from 0.1 g/100 g to 0.5 g/100 g) produced stronger gels, while oil fraction (10 g/100 g–30 g/100 g) slightly affected the elastic behavior of the emulsions reinforcing the structure and the elastic characteristics of the gellan matrix. Sauter diameter (d₃₂) was measured for all emulsions and an average value of 12 μm was obtained. Rheological data (oscillatory and creep–recovery tests) were successfully modeled to interpret the structural characteristics of the gelled emulsions. The broadened Baumgaertel–Schausberger–Winter spectrum was used to represent the linear viscoelastic behavior of the continuous phase and the emulsified system, showing that the rheological behavior of the systems was controlled by the highly structured continuous phase rather than the contribution of filler lipid droplet in the emulsion. Relaxation spectra were validated using creep–recovery experiments. Regardless of hydrocolloid concentration, creep compliance of the gel emulsions decreased compared with their respective gels, showing that the inclusion of oil droplets produced a reinforcement of the structure and the gel strength of the matrix.     

Effect of inulin on texture and clarity of gellan gels

The effect of inulin on the gelation of 0.5 wt% low acyl gellan in the presence of increasing concentrations of potassium chloride was investigated by large deformation compression experiments and visible light absorbance. The sugar and salt concentrations varied from 0 to 15 wt% and 40-100 mM, respectively. Stress and strain at failure along with Young’s modulus were calculated from each compression curve. Samples prior to compression were refrigerated at 5 °C for 24 h. Reduced gel strength and firmness were observed for all inulin and salt concentrations. Increasing amounts of inulin resulted in an increase in gel strength which was greater for higher potassium concentrations. Elasticity values did not exhibit great diversion. Inulin at concentrations of 5 and 10 wt% led to less turbid gels than those with only gellan. Samples containing 15 wt% inulin gave absorbance readings greater than 1.     

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.     

Effect of salts and sugars on the clarity of gellan gels

The effect of glucose, fructose and sucrose (0–15 wt%) on the clarity of low acyl gellan gels (0.5 wt%) in the presence of potassium chloride (40–100 mm ), calcium chloride (10–80 mm ) and their mixtures at a total molar concentration of 80 mm , was investigated by light absorbance experiments (490 nm). The effect on gel clarity (at 100 mm KCl) of all sugar combinations, at a final concentration of 15 wt%, was also investigated. All gels with potassium were less turbid than the ones with calcium. In the case of salt mixtures, increasing concentration of calcium in the mixtures resulted in decreased clarity. In addition, turbidity increased with increasing salt concentration. Moreover, and at the higher salt concentrations, the presence of sugars resulted in clearer gels. When mixtures of sugars were added, all combinations resulted in increased clarity compared to the individual sugars.     

Nanofiltration of glucose solution containing salts: Effects of membrane characteristics,organic component and salts on retention

The understanding on nanofiltration especially the rejection of uncharged solutes, charged solutes and mixture of solutes is crucial for its application in food industry. This is because process streams in food industry usually contain organic components without charge and salts. In this work, DK and CK membranes were utilized for the separation of multi-component feeds containing glucose, NaCl and multivalent salts (MgCl₂ or Na₂SO₄). Glucose rejection is slightly affected by salt concentration which may due to pore swelling of CK membranes at high concentration of NaCl. Meanwhile, rejection of NaCl is reduced by the increment of glucose and NaCl concentration which causes concentration polarization. The addition of multivalent salts even induces negative rejection of NaCl in DK membranes. However, both membranes show high rejection of multivalent salts with or without the presence of glucose. The rejection behavior follows the pattern expected from the structural and electrical properties of the membranes.     

Effect of polymer ratio and calcium concentration on gelation properties of gellan/gelatin mixed gels

Gelation properties of gellan/gelatin mixed solutions were studied using dynamic viscoelastic testing at eight different ratios of gellan (1.6–0.2% w/v) to gelatin (0–1.4% w/v) and seven different calcium levels (0–30 mM). The gelation temperature and gelation rate of the mixed gels were significantly affected by the ratio of gellan to gelatin as well as concentration of calcium. Addition of calcium at low levels resulted in an increase in gelation temperature and gelation rate compared to gels with no added calcium. Further increases in calcium increased the gelation temperature, but caused a decrease in gelation rate of the mixed gels. In addition, the presence of gelatin generally had a negative influence on gelation rate, especially at high proportions and when the solution had a high gelling temperature, probably by physically hindering the growth and development of gellan crosslinks. It appeared that in the presence of calcium, gellan formed the continuous gel matrix, with gelatin present as a discontinuous phase. Gellan/gelatin mixtures can form gels over a wide temperature range by varying the ratio of the two polymers as well as the calcium concentration.     

Effect of temperature on the dielectric properties of low acyl gellan gel

Gellan gum is an increasingly popular and a naturally occurring hydrocolloid. It is widely used in the food, chemical, and pharmaceutical industries as a stabilizer, emulsifier, thickener, and gelling agent. The gel is also used as a model material to study microwave heating dynamics of biological materials in the food processing industry. In this study, baseline data on dielectric properties of 1% gellan gel containing 0.17% and 0.3% CaCl₂ were collected at frequencies between 0.2 and 20 GHz and temperatures between 10 and 100 °C. These data are compared with those of distilled water containing similar ionic concentrations. Models describing the behavior of the dielectric constant, loss factor, loss tangent and the penetration depth for 0.2–3.2 GHz were developed. These models can be effectively used in microwave food processing applications of gellan gel, which will save considerable time and effort often used in empirically determining the dielectric spectra.     

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.     

微粒助留助滤体系对烟草薄片浆料助留助滤性能的影响

在造纸法烟草薄片的生产中,利用食品安全级的阳离子壳聚糖和瓜尔胶与膨润土和胶体二氧化硅组成二元微粒助留助滤体系,研究其对烟草浆料助留助滤性能的影响。研究结果表明：使用壳聚糖／膨润土或瓜尔胶／膨润土组成的二元微粒助留助滤体系能明显改善烟草浆料的留着率和滤水性能。壳聚糖（用量为0．1％）与膨润土（用量为0．4％）所组成的二元微粒体系与只添加0．1％的壳聚糖相比,烟草浆料单程留着率和填料留着率分别提高14％和12％,20s内滤水量提高200g。     

丁酸钠对副溶血性弧菌毒性的影响及机制研究

目的 探究丁酸钠对副溶血性弧菌毒性的影响及机制.方法 通过测定丁酸钠对副溶血性弧菌生物膜形成能力及黏附宿主细胞能力,评估其对副溶血性弧菌毒性的影响;通过傅里叶变换红外光谱法(Fourier transform infrared spectroscopy,FT-IR)和拉曼光谱法检测胞外成分变化;逆转录聚合酶链反应(re...     

有机硅-酚醛树脂共聚物的合成与应用研究

该文利用酚醛树脂与有机硅化合物的接枝共聚反应制备了有机硅改性酚醛树脂,并将其与聚氧化乙烯(PEO)组成双元助留体系,应用于废纸脱墨浆的助留实验。实验结果表明,该双元体系能显著提高细小组分的一次留着率,而影响助留效果的主要因素有助剂的用量、有机硅改性酚醛树脂与PEO的比率、剪切力等。     

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).     

Flobind微粒助留系统在超成形纸机上的应用

Flobind微粒助留体系在超成形纸机上应用效果明显,提高了细小纤维和填料的留着率,提高了纸料的滤水性,改善纸机湿部抄造环境.同时,又可获得良好的纸页匀度.生产综合成本降低.     

助留剂在我国的发展简史

造纸助留剂在我国的应用历史不到30年,随着中国造纸工业快速发展,助留剂在最近10年里发生了根本性的变化,从单元助留直接进入微粒助留.本文对造纸助留剂在中国的发展过程做了评述.     

Effect of physico‐chemical properties of tropical starches and hydrocolloids on rice gels texture and noodles water retention ability

The links between the physico‐chemical properties of rice flour (RF), cassava (CS), sago (SS), canna (CaS), sweet potato (SPS), and mung bean (MS) starches, and the gelling properties of rice flour blends with these starches in different proportions (0, 20, 40, 60, 80, and 100% pure starches) and with xanthan (XG) and carrageenan (CG) gums were studied. Water retention ability of starches and hydrocolloids blends in noodle systems during drying at 40°C was also investigated. The mean granule diameter and AM content values of RF, CS, SPS, SS, CaS, and MS were in the range of 12.8–41.0 µm and 21.9–39.4%, respectively. Thermal properties showed significant differences (p < 0.05) between the starches in terms of gelatinization temperature and enthalpy, as well as retrogradation tendency. Different starches produced gels with a wide range of textural properties. Results confirmed the role of AM content in determining the gel strength, and indicated a possible role of retrogradation in increasing the dissipation of mechanical energy during compression and relaxation tests, which can have an effect on mouth feel. Blends of RF with other starches and hydrocolloids generally improved the characteristics of RF‐based gels, by increasing gel strength. In particular, the use of MS markedly increased the strength of RF‐based gels. Addition of hydrocolloids significantly reduced the drying rate of noodles, although overall water retention ability was reduced only to a limited extent. This may be used to produce starch‐based products, especially noodles, in a range of desired characteristics.     

Development of a headspace trap HRGC/MS method for the assessment of the relevance of certain aroma compounds on the sensorial characteristics of commercial apple juice

A reliable and simple method was developed for the completely automatised analysis of apple juice aroma compounds. In total 26 flavour compounds could be measured by headspace trap gas chromatography/mass spectrometry (GC/MS). We used the method to analyse 85 commercially available apple juices, of which 67 apple juices were not from concentrate. Our results show that apple juices not from concentrate are mainly characterised by flavour compounds responsible for fruity, ripe, and sweet aroma impressions, such as 1-butanol, 2-methyl-1-butanol, ethylbutyrate, and ethyl-2-methylbutyrate. On the contrary, apple juices made from concentrate were dominated by acetaldehyde, E-2-hexenal, 3-methyl-1-butanol, ethyl acetate, and hexanal, which are mainly responsible for sensory impressions, such as ‘green, fresh, estery’. According to our data, neither of the single compounds nor indexes calculated thereof as suggested by some authors could be used for the reliable assessment of apple juice quality. Thus, these results suggest that sensory evaluation remains the ultimate mean to reliably assess apple juice quality.     

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.