Ultrasonic spectroscopy and differential scanning calorimetry of liposomal-encapsulated nisin

The thermal stability of phosphatidylcholine (PC) liposomes (colloidal dispersions of bilayer-forming polar lipids in aqueous solvents) in the presence and absence of the antimicrobial polypeptide nisin was evaluated using differential scanning calorimetry (DSC) and low-intensity ultrasonic spectroscopy (US). PC liposome mixtures with varying acyl chain lengths (C16:0 and C18:0) were formed in buffer with or without entrapped nisin. Gel-to-liquid crystalline phase transition temperatures (T(M)) of liposomes determined from DSC thermograms were in excellent agreement with those determined by ultrasonic velocity and attenuation coefficient measurements recorded at 5 MHz. The dipalmitoylphosphatidylcholine (DPPC) T(M) measured by DSC was approximately 41.3 and approximately 40.7 degrees C when measured by ultrasonic spectroscopy. The T(M) of distearoylphosphatidylcholine (DSPC) and DPPC/DSPC 1:1 liposomes was 54.3 and 54.9 degrees C and approximately 44.8 and approximately 47.3 degrees C when measured by DSC and US, respectively. The thermotropic stability generally increased upon addition of nisin. Analysis of the stepwise decrease in ultrasonic velocity with temperature indicated an increased compressibility corresponding to a loss of structure upon heating.     

Effect of freezing and frozen storage of doughs on bread quality

The effects of freezing and storage in frozen conditions on bread quality, crumb properties, and aggregative behavior of glutenins were analyzed. The effect of different additives on bread quality was also studied. The results obtained showed that freezing and storage at -18 degrees C decreased the bread quality. Samples stored in frozen conditions supplemented with diacetyl-tartaric acid ester of monoglycerides, gluten, and guar gum produced breads of greater volume and more open crumb structure than those prepared with the base formulation (without additives). All additives analyzed increased the proof time. Crumb firmness increased with dough frozen storage and bread aging time at 4 degrees C. A decrease in the amount of glutenin subunits of high molecular mass was observed by electrophoresis analysis of the SDS-soluble proteins aggregates extracted from the frozen dough. This result suggested that the protein matrix of bread underwent depolymerization during storage in frozen conditions.     

Analysis of leaf and needle litter decomposition by differential scanning calorimetry and differential thermogravimetry

Summary Changes in the physicochemical properties of three kinds of litter (Prunus serotina leaves, Carpinus betulus leaves, and Pinus sylvestris needles) were analyzed by differential scanning calorimetry and differential thermogravimetry after decomposition for 12 to 27 months under field conditions. As expected, holocellulose was always decomposed to a larger extent than the corresponding lignin components, leading to an enrichment of lignin in the residue. These lignins were more or less modified depending on the plant species. Moreover, the results suggest that energy-rich crystalline cellulose accumulates during decomposition at the expense of easier degradable amorphous cellulose and hemicelluloses. The quotient Q, from the corresponding calorimetry and thermogravimetry values, was introduced to estimate the specific energy content as a measure for the decomposition of litter components.Dedicated to the late Prof. Dr. W. Kühnelt     

Combined effect of sourdough lactic acid bacteria and additives on bread firmness and staling

The effect of various sourdoughs and additives on bread firmness and staling was studied. Compared to the bread produced with Saccharomyces cerevisiae 141, the chemical acidification of dough fermented by S. cerevisiae 141 or the use of sourdoughs increased the volume of the breads. Only sourdough fermentation was effective in delaying starch retrogradation. The effect depended on the level of acidification and on the lactic acid bacteria strain. The effect of sourdough made of S. cerevisiae 141-Lactobacillus sanfranciscensis 57-Lactobacillus plantarum 13 was improved when fungal alpha-amylase or amylolytic strains such as L. amylovorus CNBL1008 or engineered L. sanfranciscensis CB1 Amy were added. When pentosans or pentosans, endoxylanase enzyme, and L. hilgardii S32 were added to the same sourdough, a greater delay of the bread firmness and staling was found. When pentosans were in part hydrolyzed by the endoxylanase enzyme, the bread also had the highest titratable acidity, due to the fermentation of pentoses by L. hilgardii S32. The addition of the bacterial protease to the sourdough increased the bread firmness and staling.     

Kinetic analysis of nonisothermal differential scanning calorimetry of 1,3-dipalmitoyl-2-oleoylglycerol

The crystallization of fats has been extensively studied because of its importance in the processing of food and food ingredients. Differential scanning calorimetry (DSC) is widely used in such studies. The aim of this study was to examine the determination of kinetic parameters from nonisothermal DSC crystallization of a model fat, 1,3-dipalmitoyl-2-oleoylglycerol. We applied peak and isoconversional methods to determine activation energies and compared these techniques with a nonparametric method, which separates the temperature dependence and degree of crystallization dependence of the crystallization rate. The Johnson-Mehl-Avrami-Erofeyev-Kolmogorov (JMAEK) model provided the best fit to the data, while the temperature dependence of the rate constant was best explained by a Vogel-Fulcher relationship, where the reference temperature was the melting point of the crystallizing species.     

Elucidation of the effect of formaldehyde and lipids on frozen stored cod collagen by FT-Raman spectroscopy and differential scanning calorimetry

The effect of frozen storage (-10 and -30 degrees C), formaldehyde, and fish oil on collagen, isolated from cod muscle, was investigated. Salt- and acid-soluble collagen fractions as well as insoluble collagen indicated changes in solubility on frozen storage. Differential scanning calorimetry (DSC) showed a highly cooperative transition at 28.2 degrees C for isolated collagen. Changes in the thermodynamic properties of collagen were observed on frozen storage at -10 degrees C compared with the control at -30 degrees C because of changes in structure. In the presence of formaldehyde, there were no changes in the DSC collagen transition; however, in the presence of fish oil there was an increase in enthalpy and an extra peak was observed at 44.6 degrees C, indicating collagen-fish oil interaction. Structural changes resulted in a decrease in the solubility of collagen in salt and acid solution. FT-Raman spectra obtained for collagen at -10 degrees C and -30 degrees C confirmed the alteration of the conformation of collagen not only at -10 degrees C but also in the presence of formaldehyde and fish oil.     

Changes in litter properties during decomposition: A study by differential thermogravimetry and scanning calorimetry

To verify the paradigm that organic matter (OM) quality (q) decreases with decomposition it is necessary to define q in strictly chemical, operational terms. We suggest defining q as the result of a balance between the energy stored in OM and the external supply of energy needed to release it. We apply this concept to the study of litter decomposition in four European pine forests: boreal, cool Atlantic, Mediterranean and warm Atlantic. Intact litter cores were taken and transported to the laboratory, where needles were sorted into six classes that summarize the main facts of the decomposition: melanisation, fragmentation and perforation by mesofauna. Each class was analyzed by both differential thermogravimetry and differential scanning calorimetry to obtain its spectra of weight loss and energy release.In the non-decomposed needles, two peaks of weight loss and energy release appear: a labile peak at about 350 °C, and a recalcitrant peak at about 450 °C. During decomposition, both peaks (but especially the recalcitrant one) move to lower temperatures, and their shapes change from well defined to flattened. In Mediterranean litters, a third peak appears at about 500 °C, due probably to refractory products of neoformation. There is a continuous increase in the energy stored in the remaining litter (in Joules per unit OM): this increase is concentrated in both the most thermolabile fractions (lost at temperatures <350 °C) and the most thermostable ones (>450 °C). With decomposition OM becomes more recalcitrant (i.e., it is lost at higher temperatures), but its stored energy becomes more available (i.e., it is released at lower temperatures). Overall, the energetic benefit/cost ratio increases. Thus, our results to date do not agree with the current paradigm that q decreases with decomposition; rather, they suggest that, at least in the first phases we studied, q is maintained or even increases.     

Interaction of resveratrol and its trimethyl and triacetyl derivatives with biomembrane models studied by differential scanning calorimetry

The interaction of resveratrol (trans-3,5,4'-trihydroxystilbene) and two of its derivatives (3,5,4'-tri-O-methylresveratrol and 3,5,4'-tri-O-triacetylresveratrol) with biomembrane models, represented by dimyristoylphosphatidylcholine (DMPC) multilamellar vesicles (MLV), has been studied by differential scanning calorimetry (DSC). The analysis of MLV prepared in the presence of increasing molar fraction of such compounds has been carried out to reveal their maximum interaction with biomembrane models. The results from these studies have been compared with kinetic experiments results, in order to detect the entity and rate of compound absorption by the biomembrane models. The findings indicate that the compounds affected the thermotropic properties of DMPC MLV by suppressing the pretransition peak and broadening the DMPC main phase transition calorimetric peak and shifting it to lower temperatures. The order of effectiveness found was resveratrol > trimethylresveratrol > triacetylresveratrol. The kinetic experiments reveal that in an aqueous medium the absorption of resveratrol by the biomembranes models is allowed, whereas the absorption of its derivatives is hindered; in contrast when a lipophilic medium is employed, all three compounds are easily absorbed.     

Effects of alpha-amylases from different sources on the firming of concentrated wheat starch gels: relationship to bread staling

The firming and carbohydrate fractions of concentrated starch gels supplemented with four alpha-amylases from different sources were evaluated. Correlations were found between the firmness data and results for the carbohydrate fractions extracted from the gels. The thermostable (TBA) and intermediate temperature stability (ISBA) bacterial alpha-amylases were most effective in decreasing the rate of firming. The cereal alpha-amylase at the high level (CAH) was also effective. The CAH produced the largest quantity of dextrins at storage time zero and the thermostable bacterial alpha-amylase at the high level (TBAH) after storage for 5 days. None of the maltooligosaccharides appeared to be responsible for the decreased rate of firming of the gels. The results indicated that the TBA and ISBA most effectively inhibited firming because they degraded the external branches and the intercluster regions of amylopectin during storage. Consideration of previously reported differential scanning calorimetry and X-ray crystallography results leads to the conclusion that the antifirming action of the TBA and ISBA is due to their ability to degrade the amylopectin and amorphous regions of the gels during storage, which inhibits the formation of double helices and decreases the strength of the starch gel matrix. Gels supplemented with the TBA and ISBA were most crystalline but firmed to a lesser extent. These results are similar to those previously reported by other researchers for bread and strongly suggest that starch retrogradation plays a primary role in bread staling.     

Effect of alpha-amylases from different sources on the retrogradation and recrystallization of concentrated wheat starch gels: relationship to bread staling

Concentrated starch gels were supplemented with four alpha-amylases from different sources. The retrogradation and recrystallization of the gels were evaluated using differential scanning calorimetry (DSC) and X-ray crystallography. Correlations between the retrogradation data and the carbohydrate fractions extracted from these gels were determined. The thermostable (TBA) and intermediate temperature stability (ISBA) bacterial alpha-amylases were most effective in decreasing the rate of retrogradation of the starch in the gels. The cereal alpha-amylase at the high level (CAH) was also effective. Supplementation with the alpha-amylases increased the crystallinity of the gels. Gels supplemented with TBA or ISBA were most crystalline and retrograded to a lesser extent. The results indicated that DSC gives not only a measure of recrystallized amylopectin but also a measure of total order (recrystallized amylopectin and double-helical content). The maltooligosaccharides produced by the enzymes did not appear to be responsible for the reduced rates of retrogradation, but they appeared to be an expression of the degree of starch modification that was responsible for the inhibition of retrogradation. The crystallinity and retrogradation data were similar to results reported for bread and strongly suggest that bread staling is caused by the retrogradation of starch. The results also indicate that alpha-amylases decrease the rate and extent of retrogradation of starch gels by inhibiting the formation of double helices.     

Analysis of the retrogradation of low starch concentration gels using differential scanning calorimetry,rheology, and nuclear magnetic resonance spectroscopy

The retrogradation of 5, 10, 15, and 25% corn starch gels was measured using differential scanning calorimetry (DSC), rheology, and an array of NMR spectroscopy techniques. During the initial (<24 h) stage of retrogradation, an increase in G' corresponding to an increase in the number of solid protons participating in cross-relaxation (M(B)(0) was observed for all four concentrations studied. During the latter (>24 h) stage of retrogradation, amylopectin recrystallization becomes the dominant process as measured by an increase in deltaH(r) for the 25% starch gel, which corresponded to a further increase in. A decrease in the molecular mobility of the liquid component was observed by decreases in (17)O T(2), (1)H D(0), and T(2A). The value for T(2B) (the solid transverse relaxation time) did not change with concentration or time indicating that the mobility of the solid component does not change over time despite the conversion of the highly mobile starch fraction to the less mobile solid state during retrogradation.     

Impact of redox agents on the extractability of gluten proteins during bread making

The gluten proteins gliadin and glutenin are important for dough and bread characteristics. In the present work, redox agents were used to impact gluten properties and to study gliadin-glutenin interactions in bread making. In control bread making, mixing increased the extractability of glutenin. The level of SDS-extractable glutenin decreased during fermentation and then further in the oven. The levels of extractable alpha- and gamma-gliadin also decreased during bread baking due to gliadin-glutenin polymerization. Neither oxidizing nor reducing agents had an impact on glutenin extractabilities after mixing. The redox additives did not affect omega-gliadin extractabilities during bread making due to their lack of cysteine residues. Potassium iodate (0.82-2.47 micromol/g of protein) and potassium bromate (1.07-3.17 micromol/g of protein) increased both alpha- and gamma-gliadin extractabilities during baking. Increasing concentrations of glutathione (1.15-3.45 micromol/g of protein) decreased levels of extractable alpha- and gamma-gliadins during baking. The work not only demonstrated that, during baking, glutenin and gliadin polymerize through heat-induced sulfhydryl-disulfide exchange reactions, but also demonstrated for the first time that oxidizing agents, besides their effect on dough rheology and hence bread volume, hinder gliadin-glutenin linking during baking, while glutathione increases the degree of covalent gliadin to glutenin linking.     

Conformational study of red kidney bean (Phaseolus vulgaris L.) protein isolate (KPI) by tryptophan fluorescence and differential scanning calorimetry

Fluorescence and differential scanning calorimetry (DSC) were used to study changes in the conformation of red kidney bean (Phaseolus vulgaris L.) protein isolate (KPI) under various environmental conditions. The possible relationship between fluorescence data and DSC characteristics was also discussed. Tryptophan fluorescence and fluorescence quenching analyses indicated that the tryptophan residues in KPI, exhibiting multiple fluorophores with different accessibilities to acrylamide, are largely buried in the hydrophobic core of the protein matrix, with positively charged side chains close to at least some of the tryptophan residues. GdnHCl was more effective than urea and SDS in denaturing KPI. SDS and urea caused variable red shifts, 2-5 nm, in the emission λ(max), suggesting the conformational compactness of KPI. The result was further supported by DSC characteristics that a discernible endothermic peak was still detected up to 8 M urea or 30 mM SDS, also evidenced by the absence of any shift in emission maximum (λ(max)) at different pH conditions. Marked decreases in T(d) and enthalpy (ΔH) were observed at extreme alkaline and/or acidic pH, whereas the presence of NaCl resulted in higher T(d) and ΔH, along with greater cooperativity of the transition. Decreases in T(d) and ΔH were observed in the presence of protein perturbants, for example, SDS and urea, indicating partial denaturation and decrease in thermal stability. Dithiothreitol and N-ethylmaleimide have a slight effect on the thermal properties of KPI. Interestingly, a close linear relationship between the T(d) (or ΔH) and the λ(max) was observed for KPI in the presence of 0-6 M urea.     

Anhydrous goat's milk fat: thermal and structural behaviors studied by coupled differential scanning calorimetry and X-ray diffraction. 2. Influence of cooling rate

Crystallization and melting properties of triacylglycerols (TGs) in anhydrous goat's milk fat (AGMF) are investigated by X-ray diffraction as a function of temperature (XRDT) coupled with high-sensitivity differential scanning calorimetry (DSC), using synchrotron radiation and Microcalix. The polymorphic behavior of AGMF was monitored by varying the cooling rates between 5 and 1 degrees C/min from 45 to -20 degrees C with their subsequent melting at 1 degrees C/min. Quenching of AGMF at -20 degrees C was also examined to determine the metastable polymorphic form of AGMF. At intermediate cooling rates, TGs in AGMF crystallize, from about 18 degrees C in two different lamellar structures with triple chain length 3Lalpha stacking of 72 A and a double chain length 2Lalpha stacking of 48 A, which are correlated to two overlapped exothermic peaks recorded by DSC. A reversible transition sub alpha <--> alpha was observed. Subsequent heating at 1 degrees C/min shows numerous structural rearrangements before final melting. At fast cooling of AGMF (5 degrees C/min), similar unstable crystalline varieties are formed while three endotherms are recorded. Several new unstable lamellar structures are observed after quenching. All of these data are compared to those previously reported at slow cooling (0.1 degrees C/min) showing a relative stability of the structures formed. In spite of general similitude, the thermal and structural behavior of the goat's milk is more complex than that of the cow's milk.     

Characterization of soluble amaranth and soybean proteins based on fluorescence, hydrophobicity, electrophoresis, amino Acid analysis, circular dichroism, and differential scanning calorimetry measurements.

Intrinsic fluorescence (IF), surface hydrophobicity (S(o)), electrophoresis, amino acid analysis, circular dichroism (CD), and differential scanning calorimetry (DSC) were used to study folded and unfolded soluble proteins from Amaranthus hypochondriacus (A. h.) and soybean (S). Globulin (Glo) and albumin subfractions (Alb-1 and Alb-2) were extracted from A. h. and S and denatured with urea. Electrophoretic and functional properties indicated a significant correlation between soluble protein fractions from soybean and amaranth. The protein fractions shared some common electrophoretic bands as well as a similar amino acid composition. The larger percent of denaturation in protein fractions, which is associated with enthalpy and the number of ruptured hydrogen bonds, corresponds to disappearance of alpha-helix. The obtained results provided evidence of differences in their secondary and tertiary structures. The most stable was Glo followed by the Alb-2 fraction. Predicted functional changes in model protein systems such as pseudocereals and legumes in response to processing conditions may be encountered in pharmaceutical and food industries. These plants can be a substitute for some cereals.     

Localization of puroindoline-a and lipids in bread dough using confocal scanning laser microscopy

Puroindolines are lipid-binding proteins from wheat flour that play a significant role in bread crumb texture. The localization of wheat flour lipids and puroindoline-a (PIN-a) in bread dough was studied by confocal scanning laser microscopy (CSLM). Wheat lipids were located around gas cells (GC) and embedded within the protein-starch matrix (SPM) of the dough. PIN-a was mainly located in the matrix of dough, where it was associated with lipids. In contrast, in defatted dough, PIN-a was found around GC. Addition of puroindolines in bread dough induced a defatting of the gas bubble surface and a decrease of the lipid vesicles and/or droplet size embedded within the SPM. Therefore, puroindolines control the lipid partitioning within the different phases of dough, a phenomenon that should have important consequence on the gas bubble expansion and GC formation in the further stages (fermentation, baking) of the bread-making process.     

The question of high- or low-temperature glass transition in frozen fish. Construction of the supplemented state diagram for tuna muscle by differential scanning calorimetry

The thermal behavior of fresh tuna muscle, rehydrated freeze-dried tuna muscle, and tuna sarcoplasmic protein fraction was studied by three types of differential scanning calorimetry (DSC): conventional DSC, alternating DSC, and sensitive micro-DSC. The relationship between glass transition temperature, T(g), and water content was established. Only a low-temperature glass transition was detected for fresh tuna and freeze-dried tuna rehydrated to high water contents, whereas for sarcoplasmic protein fraction both a low-temperature and an apparent high-temperature glass transition were detected for samples of high water content. Construction of the supplemented state diagrams for whole tuna muscle and for tuna sarcoplasmic protein fraction confirmed the low-temperature transition to be glass transition of the maximally freeze-dehydrated phase. The apparent upper transition of sarcoplasmic protein fraction was shown not to be a glass transition but rather to originate from the onset of melting of ice, and the temperature of this event should be denoted T(m)'. The glass transition temperature and the concentration of the maximally freeze dehydrated tuna muscle are -74 degrees C and 79% (w/w), respectively.     

Differential scanning calorimetry and circular dichroism spectrometry of walleye pollack myosin and light meromyosin

The thermodynamic properties of myosin and its C-terminal fragment, light meromyosin (LMM), from walleye pollack, a typical cold-water fish efficiently utilized on an industrial scale, were analyzed by using differential scanning calorimetry (DSC) and circular dichroism (CD) spectrometry. Recombinant walleye pollack LMM expressed in Escherichia coli was also subjected to DSC and CD measurements for reference. The two proteins prepared from frozen surimi showed three endothermic peaks, the transition temperatures (T(m)) of which were quite similar, although overall DSC patterns differed considerably from one another. Their alpha-helical contents determined by CD were low compared to values reported before for other species. On the other hand, recombinant LMM gave four endothermic peaks at 27.4, 30.8, 36.5, and 43.4 degrees C in DSC and showed an alpha-helical content of approximately 80%. The peak at 27.4 degrees C could not be observed in walleye pollack LMM prepared from frozen surimi and thus was possibly attributed to its C terminus, because this extreme C-terminal region is supposedly truncated during preparation of LMM by tryptic digestion.     

Water absorption of freeze-dried meat at different water activities: a multianalytical approach using sorption isotherm, differential scanning calorimetry, and nuclear magnetic resonance

Hydration of freeze-dried chicken breast meat was followed in the water activity range of aw=0.12-0.99 by a multianalytical approach comprising of sorption isotherm, differential scanning calorimetry (DSC), and nuclear magnetic resonance (NMR). The amount of frozen water and the shape of the T2-relaxogram were evaluated at each water content by DSC and NMR, respectively. Data revealed an agreement between sorption isotherm and DSC experiments about the onset of bulk water (aw=0.83-0.86), and NMR detected mobile water starting at aw=0.75. The origin of the short-transverse relaxation time part of the meat NMR signal was also reinvestigated through deuteration experiments and proposed to arise from protons belonging to plasticized matrix structures. It is proved both by D2O experiments and by gravimetry that the extra protons not contributing to the water content in the NMR experiments are about 6.4% of the total proton NMR CPMG signal of meat.     

Differential scanning calorimetry evidence of the enhancement of beta-sitosterol absorption across biological membranes mediated by beta-cyclodextrins

beta-Sitosterol is a plant sterol that has received much attention because of its effectiveness in reducing the absorption of dietary cholesterol, as well as in offering protection from cardiovascular diseases and cancer development. Thus, the knowledge of the interaction of beta-sitosterol with biological membranes can help in understanding its mechanism of action. In the present paper, the differential scanning calorimetry technique has been used to study the interaction of beta-sitosterol with a biomembrane model constituted by dimyristoylphosphatidylcholine multilamellar vesicles. Furthermore, kinetic experiments have been carried out to follow the uptake of beta-sitosterol by biomembranes and the effect of beta-cyclodextrins on such a process. Our results indicate that opportune concentrations of beta-cyclodextrins improve the uptake of beta-sitosterol by phospholipid membranes.