Effects of water activity and lipid addition on secondary structure of zein in powder systems

The effects of water activity (A(w)) and lipid addition on the secondary structure of powdery zein were investigated using Fourier transform infrared spectroscopy. Two fatty acid esters, i.e., the linolenic and eicosapentaenoic acid ethyl esters (LAE and EPE), were mixed with the zein powder. The powders were stored in the "dry" state (with silica gel) and the "humid" state (A(w) = 0.9). The powdery zein without the lipids was shown to have a high content of the intermolecular hydrogen-bonded beta-sheet in the "dry" state, indicating the presence of protein aggregates. An increase in A(w) induced a decrease in this beta-sheet, concomitant with increases in the alpha-helix and beta-turn structures. The addition of LAE caused decreases in the alpha-helix and intermolecular hydrogen-bonded beta-sheet of zein when the powder was stored in the "humid" state, suggesting the strong interaction of LAE and zein molecules. However, LAE did not affect the secondary structure of zein in the "dry" state. The addition of EPE hardly influenced the secondary structure of zein, irrespective of A(w). These results are discussed in relation to the antioxidative activity of zein in the powder system, which had studied previously.     

Myowater dynamics and protein secondary structural changes as affected by heating rate in three pork qualities: a combined FT-IR microspectroscopic and 1H NMR relaxometry study

The objective of this study was to investigate the influence of heating rate on myowater dynamics and protein secondary structures in three pork qualities by proton NMR T2 relaxation and Fourier transform infrared (FT-IR) microspectroscopy measurements. Two oven temperatures at 100 degrees C and 200 degrees C corresponding to slow and fast heating rates were applied on three pork qualities (DFD, PSE, and normal) to an internal center temperature of 65 degrees C. The fast heating induced a higher cooking loss, particularly for PSE meat. The water proton T21 distribution representing water entrapped within the myofibrillar network was influenced by heating rate and meat quality. Fast heating broadened the T21 distribution and decreased the relaxation times of the T21 peak position for three meat qualities. The changes in T21 relaxation times in meat can be interpreted in terms of chemical and diffusive exchange. FT-IR showed that fast heating caused a higher gain of random structures and aggregated beta-sheets at the expense of native alpha-helixes, and these changes dominate the fast-heating-induced broadening of T21 distribution and reduction in T21 times. Furthermore, of the three meat qualities, PSE meat had the broadest T21 distribution and the lowest T21 times for both heating rates, reflecting that the protein aggregation of PSE caused by heating is more extensive than those of DFD and normal, which is consistent with the IR data. The present study demonstrated that the changes in T2 relaxation times of water protons affected by heating rate and raw meat quality are well related to the protein secondary structural changes as probed by FT-IR microspectroscopy.     

Reducing the brittleness of zein films through chemical modification

Zein protein is a major coproduct of biofuel from corn. To reduce the brittleness of zein films, a new type of zein-based biomaterial, was synthesized by chemical modification of zein with lauryl chloride through an acylation reaction. The final products were confirmed by (1)H NMR, FT-IR analysis, and SDS-PAGE. Thermal analysis detected no microphase separation in the synthesized polymer matrix. As the content of lauryl moiety increased, the glass transition temperatures of modified zein decreased by as large as 25.8 °C due to the plasticization effect of the lauryl moiety. In addition, mechanical and surface properties of cast films from acylated zein were also investigated. The elongation at break of modified zein sheet was increased by about 7-fold at the high modification level with some loss of mechanical strength. The surfaces of modified zein films were as uniform as unmodified zein film but more hydrophobic, further suggesting that no microphase separation happened during the film formation process. This work indicated the potential of these new biomaterials in the development of biodegradable food packaging materials and delivery systems.     

Formation and stabilization of antimicrobial delivery systems based on electrostatic complexes of cationic-non-ionic mixed micelles and anionic polysaccharides

Lauric arginate (LAE) is a cationic surfactant that is of great interest to the food industry because of its strong antimicrobial activity. However, its application within foods and beverages is currently restricted because of its limited solubility in aqueous solutions and its bitter taste, which have been associated with its cationic nature. This study examines whether electrostatic complexes between cationic LAE mixed micelles and anionic polysaccharides could be used to improve LAE functionality. Two types of pectin (high and low methoxyl) were titrated into buffer solutions containing either LAE micelles or LAE/Tween 20 mixed micelles (pH 3.5, 50 mM citrate buffer). The electrical characteristics of the micelles or micelle/pectin complexes were assessed by microelectrophoresis measurements, while their stability to aggregation was evaluated by light scattering measurements. LAE micelle/pectin complexes formed large aggregates that rapidly sedimented. On the other hand, mixed micelle/pectin complexes (1:1 LAE/Tween 20, w/w) were stable to aggregation and formed clear solutions. The electrical charge of mixed micelles changed from +8 to -15 mV when the pectin concentration was increased (0.00-0.05 wt %), indicating an electrostatic interaction between anionic pectin molecules and cationic micelles. Lower concentrations of low methoxyl pectin were required (0.01 wt %) to change the net charge of mixed micelles from positive to negative than high methoxyl pectin (0.025 wt %). Our results suggest that the addition of pectin to mixed LAE/Tween 20 micelles leads to the formation of electrostatic complexes that may be useful as functional ingredients in food and other products.     

Heat-induced changes in myofibrillar protein structures and myowater of two pork qualities. A combined FT-IR spectroscopy and low-field NMR relaxometry study

Low-field NMR T(2) and Fourier transform infrared (FT-IR) measurements were performed on meat samples of two qualities (normal and high ultimate pH) during cooking from 28 degrees C to 81 degrees C. Pronounced changes in both T(2) relaxation data and FT-IR spectroscopic data were observed during cooking, revealing severe changes in the water properties and structural organization of proteins. The FT-IR data revealed major changes in bands in the amide I region (1700-1600 cm(-)(1)), and a tentative assignment of these is discussed. Distributed NMR T(2) relaxation data and FT-IR spectra were compared by partial least-squares regression. This revealed a correlation between the FT-IR peaks reflecting beta-sheet and alpha-helix structures and the NMR relaxation populations reflecting hydration water (T(2B) approximately 0-10 ms), myofibrillar water (T(21) approximately 35-50 ms), and also expelled "bulk" water (T(2) relaxation times >1000 ms). Accordingly, the present study demonstrates that definite structural changes in proteins during cooking of meat are associated with simultaneous alterations in the chemical-physical properties of the water within the meat.     

Effects of heat treatment and pectin addition on beta-lactoglobulin allergenicity

The specific effects of heat treatment and/or addition of low/high-methylated pectin (LMP/HMP) on the allergenicity of beta-lactoglobulin (beta-Lg) and its hydrolysis products were investigated through a two-step in vitro digestion approach. beta-Lg was first hydrolyzed by pepsin and then by a trypsin/chymotrypsin (T/C) mixture done in a dialysis bag with a molecular weight cutoff of 1000. The protein digestion was followed by SDS-PAGE electrophoresis performed on each digestion product, and their in vitro allergenicity was analyzed by immunoblotting. Such procedure was applied on beta-Lg samples mixed with the two kinds of pectin before or after heating (80 degrees C, 25 min) to determine the respective impact of heat treatment and pectin addition. Heat denaturation improved significantly the susceptibility of beta-Lg against the pepsin and the T/C. This effect, which was coupled to a reduction in immunoreactivity of the digested beta-Lg, appeared to be distinctively modulated by LMP and HMP. Through nonspecific interaction with the beta-Lg, pectin could reduce the accessibility of cleavage sites and/or epitope sequences. This mechanism of action is discussed in relation to the intra- and intermolecular interactions between beta-Lg and pectin initiated under the experimental conditions.     

Conformational study of globulin from common buckwheat (Fagopyrum esculentum Moench) by Fourier transform infrared spectroscopy and differential scanning calorimetry

Fourier transform infrared (FTIR) spectroscopy and differential scanning calorimetry (DSC) were used to study changes in the conformation of globulin from common buckwheat (Fagopyrum esculentum Moench) (BWG) under various environmental conditions. The IR spectrum of the native BWG showed several major bands from 1691 to 1636 cm(-1) in the amide I' region, and the secondary structure composition was estimated as 34.5% beta-sheets, 20.0% beta-turns, 16.0% alpha-helices, and 14.4% random coils. Highly acidic and alkaline pH conditions induced decreases in beta-sheet and alpha-helical contents, as well as in denaturation temperature (Td) and enthalpy of denaturation (DeltaH), as shown in the DSC thermograms. Addition of chaotropic salts (1.0 M) caused progressive decreases in ordered structures and thermal stability following the lyotropic series of anions. The presence of several protein structure perturbants also led to changes in IR band intensities and DSC thermal stabilities, suggesting protein unfolding. Intermolecular antiparallel beta-sheet (1620 and 1681 cm(-1)) band intensities started to increase when BWG was heated to 90 degrees C, suggesting the initiation of protein aggregation. Increasing the time of the preheat treatment (at 100 degrees C) caused progressive increases in Td and pronounced decreases in DeltaH, suggesting partial denaturation and reassociation of protein molecules.     

Monitoring of denaturation processes in aged beef loin by Fourier transform infrared microspectroscopy

We present the results of a Fourier transform infrared (FT-IR) microspectroscopic study using conventional FT-IR microscopy and FT-IR imaging to detect the denaturation process during four different heating temperatures (raw, 45, 60, and 70 degrees C) spatially resolved in bovine cryosections from longissimus dorsi muscle. FT-IR imaging, employing a focal plane array detector, which allowed the simultaneous collection of spectra at 4096 pixels, enabled the investigation of the heat-induced changes in the two major meat constituents, i.e., myofibrillar and connective tissue proteins, spatially resolved. The infrared spectra of both compounds revealed that the major spectral changes involved an increase in beta-sheet and a decrease in alpha-helical structures, which appeared to be much more pronounced for the myofibers than for the connective tissue. These conformational changes could be correlated to the denaturation of the major meat proteins, such as myosin, actin, and collagen.     

Inhibition against heat coagulation of ovotransferrin by ovalbumin dry-heated at 120 degrees C

Ovalbumin (OVA) was aggregated stepwise by dry heating at 120 degrees C with a gradual increase in its heating times (10 min-6 h). The inhibiting effects of DHOVAs (OVAs dry-heated for various times up to 6 h) on the heat coagulation of ovotransferrin (OT) were studied. DHOVAs and OT were solubilized at 5% (w/w) concentration with 10 mM sodium phosphate buffer, pH 7.4. Their solutions were mixed at the volume ratio of 1:1 and reheated at 60 degrees C for 3. 5 min. Some remarkable differences according to dry-heating time were observed: coagulum formations were greatly inhibited in the solutions mixed with DHOVAs treated for more than around 2.0 h, with decreasing turbidity as dry-heating time increased. In addition, the effects of reheating time and temperature, as well as those of pH and ionic strength, were also examined on coagulum formation and turbidity development in connection with dry-heating time. Thus, the inhibiting effects of dry-heated egg white on the heat coagulation of fresh egg white previously described were confirmed on the molecular level of OVA and OT.     

Effect of supramolecular structures on thermoplastic zein-lignin bionanocomposites

The effect of alkaline lignin (AL) and sodium lignosulfonate (LSS) on the structure of thermoplastic zein (TPZ) was studied. Protein structural changes and the nature of the physical interaction between lignin and zein were investigated by means of X-ray diffraction and Fourier transform infrared (FT-IR) spectroscopy and correlated with physical properties. Most relevant protein structural changes were observed at low AL concentration, where strong H-bondings between the functional groups of AL and the amino acids in zein induced a destructuring of inter- and intramolecular interactions in α-helix, β-sheet, and β-turn secondary structures. This destructuring allowed for an extensive protein conformational modification which, in turn, resulted in a strong improvement of the physical properties of the bionanocomposite.     

Real-time monitoring of thermal flavor generation in skim milk powder using atmospheric pressure chemical ionization mass spectrometry

The feasibility of monitoring volatile flavor compounds formed by thermal treatment of skimmed milk powder in real time by atmospheric pressure chemical ionization mass spectrometry (APCIMS) was established. Skim milk powder samples were heated isothermally (70 to 120 degrees C) at different moisture contents (2.2 and 12.7 g water/100 g dry solids). Headspace was sampled and analyzed continuously in full scan mode (30-180 amu) by APCIMS. The identity of the volatile compounds monitored by APCIMS was confirmed by coupled GC-EI-APCIMS. The concentration measured by the APCIMS was the net effect of three processes, namely formation of the compound, partition from the skim milk powder into the gas phase, and dilution due to the headspace sampling method used. Preliminary experiments established that the technique could follow the effects of heating temperature and moisture content on the formation of selected compounds from skim milk powder.     

Effect of Dry Heating on Physicochemical Properties of Pregelatinized Rice Starch

Japonica and indica rice starches (10% w/w) were pregelatinized in a boiling water bath for 5 or 10 min and subsequently heat‐treated in a dry state for 0, 1, 2, or 3 h at 130°C to examine the effects of dry heating on pasting viscosity, paste clarity, thermal properties, X‐ray diffraction pattern, and gel strength of pregelatinized starches. Heat treatment obviously changed the physicochemical properties of pregelatinized rice starch. The pregelatinized rice starches had higher peak viscosity and final viscosity than the corresponding native rice starches. Heat treatment of pregelatinized rice starch for 1 h increased the peak viscosity, but treatment for 2 or 3 h decreased the peak viscosity compared with the unheated pregelatinized rice starch. The indica rice starch exhibited more substantial changes in pasting viscosity than did japonica rice starch during heat treatment. The melting enthalpy of the endothermic peak occurred at 90–110°C, and the intensity of the X‐ray diffraction peak at 20° was increased by dry heating, possibly owing to the enhanced amylose‐lipid complexes. The dry heat treatment of pregelatinized starch caused an increase in paste clarity and a decrease in gel strength.     

Denaturation and aggregation of myosin from two bovine muscle types

The thermal behaviors of myosin from bovine vastus intermedius (VI, predominantly red muscle) and semimembranosus (SM, predominantly white muscle) at pH 6.05 (ultimate pH of VI muscle) and 5.50 (ultimate pH of SM muscle) were compared. Differential scanning microcalorimetry and turbidity measurements were used to monitor changes in myosin during heating from 25 to 80 degrees C at 1 degrees C/min. VI and SM myosin heavy chain isoforms were identified on gradient SDS-PAGE. Endotherms of VI myosin at pH 6.05 had three transition temperatures (T(m)) of 45, 53, and 57 degrees C, whereas at pH 5.50 two transitions were observed at 42 and 59 degrees C. SM myosin had two T(m) values of 46 and 58 degrees C at pH 6.05 and T(m) values of 43 and 62 degrees C at pH 5.5. SM myosin at its ultimate pH was less heat stable than VI myosin at its ultimate pH; however, when SM and VI myosin were compared at the same pH, VI myosin was less stable.     

LED补光和根区加温对日光温室起垄内嵌式基质栽培甜椒生长及产量的影响

田间条件下采用起垄内嵌式基质栽培(soil ridged substrate-embedded cultivation,SRSC)方法,研究了日光温室LED冠层补光和电热线根区加温对甜椒生长和产量的影响。该试验设不加温不补光对照(CK)、根区加温15℃处理(T15)、根区加温18℃处理(T18)、单一补光处理(L)、根区加温15℃+补光处理(T15+L)、根区加温18℃+补光处理(T18+L),共6个处理。结果表明,与对照相比,根区加温均能提高SRSC甜椒根区的温度,但根区温度仍呈现出随环境温度变化而变化的趋势,T18的根区全天保持较高温度。根区热通量的变化与根区温度变化相对应,T15和T18处理的根区热通量昼夜变化较CK剧烈,其根区侧面白天向内传热滞后,晚间侧面向外传热提前,传递量增加;根区垂直方向白天向内传热滞后,传递量减少,晚间垂直向外传热提前,但传递量增加。T15和T18均显著提高了甜椒的株高、冠层厚度和冠层直径,且T18比T15效果更明显。T15对甜椒的地上及地下干鲜重没有显著的提升作用,而T18的提升效果显著。根区加温补光处理的甜椒生物量普遍高于单一根区加温或补光处理,其中T18+L处理提升效果显著优于T15+L处理。T15、T18和L相对CK均提高了甜椒单产,单产分别提高30.74%、53.0%和14.81%。而根区加温和LED补光协同作用比单一的根区加温或冠层补光都能表现更好的增产效果,T15+L和T18+L分别比T15和T18的产量分别提升32.86%和15.50%,分别比L产量提升51.29%和53.87%。总之,根区加温与LED补光是日光温室甜椒增产有效的调控措施,两者在增加单株产量上存在显著的协同效应,二者共同作用比单一作用效果更加明显,且根区加温对甜椒生长和产量的促进效果比冠层补光更加显著,在实际生产中具有重要的指导意义。     

Impact of melting conditions of sucrose on its glass transition temperature.

The impact of the melting conditions of sucrose crystals on the glass transition temperature (T(g)) of the sucrose melt was studied. Final temperature, heating rate, and the residence time at the final temperature were the experimental conditions considered. The glass transition temperature of the different glasses was measured by differential scanning calorimetry, and the degradation of sucrose during the thermal treatments was studied by high-performance liquid chromatography. The results showed that the T(g) is sensitive to the degradation of sucrose: T(g) decreases with the appearance of small molecules and then increases with the appearance of polymerization products. Thus, the choice of thermal treatment is of the utmost importance for the determination of the T(g) of pure sucrose.     

Analysis of protein structures and interactions in complex food by near-infrared spectroscopy. 1. Gluten powder

The potential of near-infrared (NIR) spectroscopy in detailed food analysis was tested in a model system consisting of gluten powder treated with moisture and heat. Second-derivative transformation and extended multiplicative signal correction were applied for improving the band resolution and removing physical and quantitative spectral variations. Subsequent chemometric analyses gave loading spectra, which were interpreted as spectral effects of altered protein structures, induced by the treatments. Moistening of the gluten powder resulted in shifts and intensity changes in the protein bands, which could be explained by a combination of minor secondary structure changes, water binding, and changed microenvironments of the amino acid side chains. Heat denaturation induced increases at 2209 nm and decreases at 2167-2182 nm, indicating an alpha-helix to beta-sheet transformation, in agreement with the expectations.     

粉-气混合流润滑试验装置及摩擦学特性

为了研究粉气混合流在摩擦副间的润滑状况,采用空气压缩机及油水分离器提供高压干燥空气,并结合粉末流化和喷粉设备构建了向环块摩擦副间输送粉气混合流的粉末润滑试验装置。基于Timken摩擦磨损试验机,用石墨粉末进行一系列润滑试验。结果表明:此供粉装置能提供稳定持续的粉气混合流;石墨粉气混合流能进入到环块摩擦副中,使其保持良好的线接触并起到良好的润滑作用,摩擦系数在载荷达到450N时还不足0.1,并且随着载荷增大有减小趋势;摩擦力随着载荷的提高而增大,但总体上相对较小;磨损量也比较小,试件块的磨痕呈细细的条状;石墨粉气流通过环块摩擦副时将环块表面间的摩擦转换为石墨颗粒间的摩擦,并通过空气流将大部分热量带走,从而有效降低摩擦副的温度。     

Water sorption properties of extruded zein films

Water interactions in extruded zein films were investigated through moisture sorption isotherms. Sorption isotherms of zein products were affected by composition and structure morphology. Zein powder showed moisture sorption hysteresis, which was not observed in extruded samples. Extruded samples held less moisture than zein powder, while films containing oleic acid showed further reduction in moisture uptake. Brunauer, Emmett, and Teller (BET) and Guggenheim, Anderson, and De Boer (GAB) models fitted well the moisture sorption isotherms of zein products. Monolayer values estimated by BET and GAB models were consistent with predictions based on zein structural models. Water vapor permeability (WVP) of zein films was affected by the relative humidity of testing environment. Higher relative humidity resulted in higher WVP.     

Influence of aging and salting on protein secondary structures and water distribution in uncooked and cooked pork. A combined FT-IR microspectroscopy and 1H NMR relaxometry study

Fourier transform infrared (FT-IR) microspectroscopy and low-field (LF) proton NMR transverse relaxation measurements were used to study the changes in protein secondary structure and water distribution as a consequence of aging (1 day and 14 days) followed by salting (3%, 6%, and 9% NaCl) and cooking (65 degrees C). An enhanced water uptake and increased proton NMR relaxation times after salting were observed in aged meat (14 days) compared with nonaged meat (1 day). FT-IR bands revealed that salting induced an increase in native beta-sheet structure while aging triggered an increase in native alpha-helical structure before cooking, which could explain the effects of aging and salting on water distribution and water uptake. Moreover, the decrease in T2 relaxation times and loss of water upon cooking were attributed to an increase in aggregated beta-sheet structures and a simultaneous decrease in native protein structures. Finally, aging increased the cooking loss and subsequently decreased the final yield, which corresponded to a further decrease in T2 relaxation times in aged meat upon cooking. However, salting weakened the effect of aging on the final yield, which is consistent with the increased T2 relaxation times upon salting for aged meat after cooking and the weaker effect of aging on protein secondary structural changes for samples treated with high salt concentration. The present study reveals that changes in water distribution during aging, salting, and cooking are not only due to the accepted causal connection, i.e., proteolytic degradation of myofibrillar structures, change in electrostatic repulsion, and dissolution and denaturation of proteins, but also dynamic changes in specific protein secondary structures.     

Differential scanning calorimetry study of glass transition in frozen starch gels

The effects of initial water content, maximum heating temperature, amylopectin crystallinity type, and annealing on the glass transition of starch gels were studied by differential scanning calorimetry (DSC). The glass transition temperatures of the frozen gels measured as the onset (T(g,onset)) or midpoint temperature (T(g,midpoint)), heat capacity change during the glass transition (deltaC(p)), unfrozen water of starch gels, and additional unfrozen water (AUW) arising from gelatinization were reported. The results show that T(g,onset) and T(g,midpoint) of the partially gelatinized gels are independent of the initial water content, while both of the T(g) values of the fully gelatinized gel increase as the initial water content increases. These observations might result from the difference in the level of structural disruption associated with different heating conditions, resulting in different gel structures as well as different concentrations of the sub-T(g) unfrozen matrix. The amylopectin crystallinity type does not greatly affect T(g,onset) and T(g,midpoint) of the gels. Annealing at a temperature near T(g,onset) increases both T(g,onset) and T(g,midpoint) of the gels, possibly due to an increase in the extent of the freeze concentration as evidenced by a decrease in AUW. Annealing results in an increase in the deltaC(p) value of the gels, presumably due to structural relaxation. A devitrification exotherm may be related to AUW. The annealing process decreases AUW, thus also decreasing the size of the exotherm.