Elucidation of the emulsification properties of sugar beet pectin

A protocol has been developed to fractionate sugar beet pectin using hydrophobic affinity chromatography. Three samples eluted from the column using 4 M NaCl as solvent (fractions 1A, 1B, and 1C), two fractions eluted using 2 M NaCl (fractions 2A and 2B), and one fraction eluted using water (fraction 3). The fractions were shown to be very polydisperse, and differences between the GPC refractive index and UV absorbance (214 nm) elution profiles demonstrated chemical heterogeneity. They were found to contain significantly different proportions of protein (1A, 2.79%; 1B, 0.97%; 1C, 0.77%; 2A, 1.41%; 2B, 5.09%; and 3, 5.89%) and ferulic acid (approximately 1A, 0.5%; 1B, 0.5%; 1C, 0.9%; 2B, 1.5%; and 3, 2%). The weight-average molecular mass, M(w), of the fractions also varied (1A, 153 kDa; 1B, 155 kDa; 1C, 306 kDa; 2A, 562 kDa; 2B, 470 kDa; 3, 282 kDa). Three fractions, that is, 1A, 1B, and 3, produced orange oil emulsions with a relatively small droplet size that were stable over a period of weeks. The other three fractions (1C, 2A, and 2B with higher M(w) values) produced emulsions with an initially larger droplet size, and the droplet size increased considerably over time. The increased droplet size may be influenced by the viscosity of the aqueous continuous phase. There was no simple relationship between protein or ferulic acid content and emulsification ability. For example, fraction 1B, which contained the lowest proportion of both protein and ferulic acid, produced stable emulsions of similar droplet size to fraction 3, which contained the largest proportion of protein and ferulic acid. The role of protein in the emulsification process was investigated by measuring the amount of protein in the aqueous phase before and after emulsification. It was clearly demonstrated that proteinaceous material adsorbed at the oil-water interface. It is evident that the emulsification properties of sugar beet pectin are influenced by the accessibility of the protein and ferulic acid groups to the surface of the oil droplets, the proportion of ester groups, and the molecular mass distribution of the fractions.     

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.     

Molecular changes in soy and wheat breads during storage as probed by nuclear magnetic resonance (NMR)

Addition of raw ground almond has been shown to improve loaf quality (e.g., loaf specific volume) of soy bread. To better understand the effects of almond addition to soy bread and to follow these through storage, nuclear magnetic resonance spectroscopy relaxation times and cross-relaxation experiments were performed. Spin-spin relaxation times of water protons were similar for the two soy breads, and therefore changes of water interactions with the other components of the soy breads (with and without almond) were not considered to be major contributors to the differences in loaf quality observed between these breads. Additionally, T2 values of water protons were found to have a similar decreasing trend during storage, especially up to day 3, for all of the products studied. On the other hand, during storage, lipid proton relaxation times exhibited only small changes in wheat and regular soy bread, whereas the soy-almond bread showed a major decrease of lipid proton mobility in particular after day 3 and up to day 10. These findings may indicate that, after a few days of storage, the lipid fraction contributes to better plasticization of the soy bread with almond, which can affect acceptability and storage stability of the final product. Thus, the higher amount of lipids introduced in the almond-enriched soy bread is likely to be responsible for the improved loaf quality and may significantly affect shelf stability of the soy-containing product.     

不同施肥处理土壤胡敏酸及其级分与Fe2+络合特征Ⅱ.胡敏酸级分与Fe2+络合特征

采用酒精沉淀法对不同施肥处理胡敏酸进行分级 ,在研究胡敏酸级分组成变异以及各级分性质变化的基础上 ,研究了胡敏酸各级分与Fe2+的络合特征。结果表明 ,胡敏酸各级分随级分数的增大芳构化度逐渐降低 ,分子结构趋于简单。在所分离的 7个级分中 ,均以级分 3与Fe2+的络合能力最强。从级分 1到级分 3络合能力逐渐增强 ,级分 3到级分 7络合能力逐渐降低。胡敏酸A型级分的络合能力一般大于P型。但若A型级分芳构化度过高 ,也存在A型级分小于P型现象。Rp型级分的络合能力明显比A型、P型级分小。不同施肥处理胡敏酸原样与Fe2+络合能力差异与其级分组成变异以及各级分的络合能力有密切关系     

Fast characterization of industrial soy protein isolates by direct analysis with matrix-assisted laser desorption ionization time-of-flight mass spectrometry

Industrial soy protein isolates (SPIs) due to differences in their processing conditions may differ both in composition and in degree of hydrolysis. As a result, they display different performance in food production and final food properties like consistency and taste. To address this issue, a fast, cheap, and simple method for screening and characterization is required. In this article, the successful analysis of soy protein isolates, a complex mixture of proteins with glycinin and beta-conglycinin as major components, by matrix-assisted laser desorption ionization time-of-flight mass spectrometry (MALDI-TOF-MS) is demonstrated. The preparation implements a fast extraction of the proteins from the raw SPI either under neutral or reducing conditions. The extracts are analyzed subsequently by MALDI-TOF-MS without further purification. Results of the two conditions are compared. Finally, different SPIs from different suppliers are analyzed and compared concerning their consistency. The method could be applied to other plant proteins and mixtures thereof. Since the composition and intactness of different subunits play important roles in functional properties of soy proteins, rapid methods for fingerprinting of different industrial soy protein sources will be valuable tools for successful product formulation.     

Relationships between different hydration properties of commercial and laboratory soybean isolates

Functional properties related to water protein interactions of soy protein isolates depend on the structural and aggregation characteristics of their major components (storage globulins 7S and 11S) that could be modified by the preparation procedure, thermal and/or chemical treatments, and drying methods. Commercial and laboratory isolates with different functionalities resulting from their structural modifications were compared. Isolates with high solubility or excessive thermally induced insolubilization or compact calcium-induced aggregates caused low water-imbibing capacity (WIC) values. The highest WIC results from the balance between intermediate solubility and the formation of aggregates with good hydration properties. The apparent viscosity of dispersions of commercial (spray dried) and laboratory (lyophilized) isolates depends on the WIC, the morphology and size of the particles, and the interaction of the hydrated particles. The hydration properties and viscosity of protein isolate suspensions were strongly determined by the amount and properties of the insoluble fraction.     

Particle Distribution and Composition of Retail Whole Wheat Flours Separated by Sieving

The purpose of this study was to evaluate the differences among four retail whole wheat flours with respect to particle size distribution and composition of fractions separated by sieving. Interestingly, not only were significant differences discovered among the brands for particle size distribution, but lots within two of the brands were significantly different (P < 0.05), suggesting that flour particle size produced by the same company is not always consistent. Starch damage ranged from 4.67 to 7.69%. As expected, darker colors were associated with the larger particle size fractions, and the colors lightened as particle size decreased. This observation suggested that the differences in particle size resulted from differences in the degree to which the bran fraction of the kernel was milled, an observation substantiated by the distribution of ash in each fraction, which ranged from 0.37 to 38.0% of total ash. Distribution of protein ranged from 0.19 to 61.8% of total protein. These data are relevant because differences in particle size distribution and composition affect functionality, sensory acceptability, nutritional properties, and shelf life of whole wheat flour.     

Rheological characterization of a novel functional food: tomato juice with soy germ

The rheological properties of tomato juice containing 1.5% soy germ were compared to plain tomato juice with and without soy protein isolate. This novel product was developed to provide a delivery system of carotenoids, soy protein, and significant isoflavone content without compromising the perceived juice characteristics of tomato product. Rheological tests depicted physical gel characteristics for all three products. Dynamic tests as a function of temperature showed that the stability and the compatibility between tomato juice and soy germ were higher as compared to soy protein isolate. The hydrophobic and electrostatic interactions between pectin and protein in the tomato soy protein isolate system were weakened as the temperature was increased. In the case of tomato juice with soy germ, the viscosity did not change during heating. The addition of soy germ increased the viscosity of tomato juice reinforcing the entire system without major qualitative effects on the rheological properties of plain tomato juice.     

Fractionation, characterization, and study of the emulsifying properties of corn fiber gum

Corn fiber gum (CFG) has been fractionated by hydrophobic interaction chromatography on Amberlite XAD-1180 resin using ionic, acidic, basic, and hydrophobic solvents of different polarities. Characterization, including determination of total carbohydrate, acidic sugar, and protein content, has been done for each fraction together with measurements of molar mass, polydispersity, radius of gyration, Mark-Houwink exponent, and intrinsic viscosity using multiangle laser light scattering and online viscosity measurements. Emulsification properties of all fractions in an oil-in-water emulsion system with 20:1 oil to gum ratio were studied by measuring turbidity over 14 days. The results indicate that CFG consists of different components differing in their molecular weights and carbohydrate and protein contents. The main fraction eluted with NaCl, although low in protein content, has the highest average molecular weight and was determined to be a better emulsifier than the other fractions. The unfractionated CFG, which contains different molecular species, is the best emulsifier.     

Improved storage stability of model infant formula by whey peptides fractions

The purpose of this study was to evaluate the shelf-life stability (6 months) of model infant formula with whey protein hydrolysates or peptidic fractions as carrageenan replacers. Whey protein hydrolysates were prepared with trypsin and followed by ultrafiltration of the hydrolyzed mixture, and peptidic fractions were isolated from the ultrafiltered tryptic hydrolysate by anion- or cation-exchange chromatography. The stability of the model infant formula was evaluated using a stratification method based on fat content differences between the top and bottom strata of the samples. With protein hydrolysate-based formulations, the creaming rate of the fat in the product was slightly higher than in the standard formulation (with carrageenan), which is indicative of lower storage stability. The addition of cationic fractions to model infant formula also resulted in lower product stability, whereas the fat creaming rate was retarded in anionic fraction based formulations. The physicochemical characteristics of certain peptides combined with the reported high emulsifying properties of peptidic sequences found within these fractions may account for their ability to act as carrageenan replacers.     

Functional and structural properties of 2S soy protein in relation to other molecular protein fractions

The purpose of this investigation is to develop a better understanding of the structure-function relationship of the 2S fraction of soy protein that has not been considered in earnest by the research community. Defatted soy flour was used to extract the three major fractions of the protein (2S, 7S, and 11S). It was found that 2S exhibits better foaming and emulsification properties than the other two molecular fractions. Work was extended to structural properties, which were monitored using spectrophotometry, atomic force microscopy, scanning electron microscopy, small-deformation dynamic oscillation on shear, and large-deformation compression testing. An experimental protocol utilizing glucono-delta-lactone (GDL), GDL with N-ethylmaleimide, or GDL with urea was capable of identifying the nature of molecular interactions responsible for gelation. Surprisingly, it was found that in the initial stages of structure formation, 2S fared better than 7S, with 11S exhibiting the highest rates of aggregation. Given time, however, 7S produced a firmer network with a better water-holding capacity than that of 2S. Non-covalent interactions, as opposed to disulfide bridging, were found to be largely responsible for the changing functionality of the molecular fractions throughout the experimentation from the formation of a vestigial structure to that of a mature gel.     

Hydrophobicity of bitter peptides from soy protein hydrolysates

Soy peptides were characterized for flavor, chemical properties, and hydrophobicity to investigate their relationships with bitterness. Five peptide fractions ranging in average molecular mass from 580 to 11300 Da were fractionated by ultrafiltration from two commercial soy protein hydrolysates. The bitterness of fractionated peptides was related to molecular mass, with maximum bitterness observed at approximately 4000 Da for one hydrolysate and 2000 Da for the other. The bitterness increased as the peptide M(w) decreased to 3000 Da for the first hydrolysate and to 2000 Da for the second one and then decreased as the peptide M(w) decreased below 1000 Da. The peptide fraction with molecular mass of <1000 Da showed the lowest bitterness for both. The hydrophobicity data based on Q values do not support Ney's Q rule as a predictor of bitterness for soy peptides.     

Characterization and quantification of proteins in lecithins

Several methods for extraction and quantification of proteins from lecithins were compared. Extraction with hexane-2-propanol-water followed by amino acid analysis is the most suitable method for isolation and quantification of proteins from lecithins. The detection limit of the method is 15 mg protein/kg lecithin, and the quantification limit is 50 mg protein/kg. The relative repeatability limits for samples containing 0-500 and 500-5000 mg protein/kg sample were 12.6 and 7.5%, respectively. The protein recovery ranged between 101 and 123%. The protein content has been determined in different kinds of lecithins. The results were as follows: standard soy lecithins (between 232 and 1338 mg/kg), deoiled soy lecithin (342 mg/kg), phosphatydylcholine-enriched soy lecithins (not detectable and 163 mg/kg), sunflower lecithins (892 and 414 mg/kg), and egg lecithin (50 mg/kg). The sodium dodecyl sulfate-polyacrylamide gel electrophoresis protein patterns of the standard soy and sunflower lecithins are very similar to those of soy flour. The protein profile of the egg lecithin shows several bands with a broad range of molecular masses. The molecular masses of the main proteins of soy lecithins and soy flour have been determined by matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) and ranged from 10.5 to 52.2 kDa. Most of the major proteins from soy and sunflower lecithins identified by MALDI-MS and electrospray tandem MS belong to the 11S globulin fraction, which is one of the main fractions of soy and sunflower seeds. In addition, the seed maturation protein P34 from the 7S globulin fraction of soy proteins has also been identified in soy lecithins. This protein has been reported as the most allergenic protein in soybean.     

Adsorption and dilatational rheology of heat-treated soy protein at the oil-water interface: relationship to structural properties

We evaluated the influence of heat treatment on interfacial properties (adsorption at the oil-water interface and dilatational rheology of interfacial layers) of soy protein isolate. The related structural properties of protein affecting these interfacial behaviors, including protein unfolding and aggregation, surface hydrophobicity, and the state of sulfhydryl group, were also investigated. The structural and interfacial properties of soy protein depended strongly on heating temperature (90 and 120 °C). Heat treatment at 90 °C induced an increase in surface hydrophobicity due to partial unfolding of protein, accompanied by the formation of aggregates linked by disulfide bond, and lower surface pressure at long-term adsorption and similar dynamic interfacial rheology were observed as compared to native protein. Contrastingly, heat treatment at 120 °C led to a higher surface activity of the protein and rapid development of intermolecular interactions in the adsorbed layer, as evidenced by a faster increase of surface pressure and dilatational modulus. The interfacial behaviors of this heated protein may be mainly associated with more flexible conformation and high free sulfhydryl group, even if some exposed hydrophobic groups are involved in the formation of aggregates. These results would be useful to better understand the structure dependence of protein interfacial behaviors and to expand utilization of heat-treated protein in the formulation and production of emulsions.     

Rheological properties and sensory characteristics of set-type soy yogurt

The study examined chemical composition and rheological and sensory properties of probiotic soy yogurt during 28 day storage at 4 degrees C. Soymilk supplemented with 2% (w/v) inulin or 1% (w/v) each of raffinose and glucose was used as a base for soy yogurt manufacture. Viability of probiotic organisms and their metabolic activity measured as production of organic acids and aldehyde content responsible for beany flavor, as well as rheological and sensory properties of soy yogurt, were examined. Inulin or raffinose/glucose supplementation in soymilk increased the bacterial population by one log cycle and the amount of lactic acid. Probiotic bacteria metabolized more aldehyde than yogurt culture and substantially reduced the beaniness in soy yogurt as determined by sensory evaluation. The probiotic soy yogurts showed more viscous and pseudoplastic properties than the control soy yogurts, but the sensory evaluation results showed preference for the control soy yogurts which were slightly less viscous. Control soy yogurt provided better mouth feel than probiotic soy yogurts.     

Antioxidant activity of some protein hydrolysates and their fractions with different isoelectric points

Antioxidant activities of commercially available enzymatic hydrolysates of milk and plant proteins were examined. Among them, soy protein and wheat gluten hydrolysates showed strong 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical scavenging activity and antioxidation activity against linoleic acid oxidation in emulsion systems. Peptide fractions with higher antioxidant activities than crude enzymatic hydrolysates of gluten and soy protein were prepared without toxic solvents and reagents. Peptides in these plant protein hydrolysates were fractionated on the basis of the amphoteric nature of sample peptides by preparative isoelectric focusing without adding chemically synthesized carrier ampholytes, which is termed autofocusing. The acidic fractions from both protein hydrolysates showed stronger DPPH radical scavenging activities than the basic fractions, while the basic fractions strongly suppressed 2,2'-azobis (2-amidinopropane) dihydrochloride-induced oxidation of linoleic acid in an emulsion system. These acidic and basic peptide fractions would be useful to examine the mechanism underlying the antioxidant activities of peptides in food.     

Effects of protein and peptide addition on lipid oxidation in powder model system

The effect of protein and peptide addition on the oxidation of eicosapentaenoic acid ethyl ester (EPE) encapsulated by maltodextrin (MD) was investigated. The encapsulated lipid (powder lipid) was prepared in two steps, i.e., mixing of EPE with MD solutions (+/- protein and peptides) to produce emulsions and freeze-drying of the resultant emulsions. EPE oxidation in MD powder progressed more rapidly in the humid state [relative humidity (RH) = 70%] than in the dry state (RH = 10%). The addition of soy protein, soy peptide, and gelatin peptides improved the oxidation stability of EPE encapsulated by MD, and the inhibition of lipid oxidation by the protein and the peptides was more dramatic in the humid state. Especially, the oxidation of EPE was almost perfectly suppressed when the lipid was encapsulated with MD + soy peptide during storage in the humid state for 7 days. Several physical properties such as the lipid particle size of the emulsions, the fraction of nonencapsulated lipids, scanning electron microscopy images of powder lipids, and the mobility of the MD matrix were investigated to find the modification of encapsulation behavior by the addition of the protein and peptides, but no significant change was observed. On the other hand, the protein and peptides exhibited a strong radical scavenging activity in the powder systems as well as in the solution systems. These results suggest that a chemical mechanism such as radical scavenging ability plays an important role in the suppression of EPE oxidation in MD powder by soy proteins, soy peptides, and gelatin peptides.     

Processing effect on soybean storage proteins and their relationship with tofu quality

Tofu was prepared from 13 soybean varieties according to three different methods (bench, pilot, and production methods). Different soybean varieties showed significant differences in storage protein composition (glycinin and beta-conglycinin). The beta-conglycinin (7S) and glycinin (11S) contents were 7.3-9.9 and 14.1-22.9% on the dry matter basis, respectively. The 11S/7S protein ratio varied from 1.64 to 2.51 among the varieties. Glycinin content and 11S/7S protein ratio of the 13 varieties did not change significantly from soy milk to tofu for the production and pilot methods. Soybean 11S/7S protein ratio positively correlated with the 11S/7S ratio of soy milk and tofu (0.57 < or = r < or = 0.83, p < or = 0.01). The correlation coefficient depended on the processing method. Processing method affected 7S and 11S protein contents of tofu and their contribution to tofu hardness, yield, and sensory quality. This may explain in part the contradictory findings of the relationships between storage proteins and tofu quality because processing methods differed in various studies.     

Characterization of hydrophobic acid fractions in water-soluble organic matter in Dystric Cambisol and in a stream in a small forested watershed: Seasonal and vertical variations in chemical properties

Abstract

Chemical properties of hydrophobic acid (HoA) fractions in water-soluble organic matter in soil and water are concerned with its interactions with mineral soil surfaces and organic pollutants. In 2004 we examined the seasonal and vertical changes in chemical properties of the HoA fraction in a Cambisol profile and compared these properties with those in the HoA fraction of an adjacent stream (aquatic humic substances) in a temperate forested watershed using high performance size exclusion chromatography (HPSEC) and ¹H and ¹³C nuclear magnetic resonance (NMR) spectroscopy. The HoA fractions from Oi, Oe/Oa, A and B horizon soils in summer had lower O-alkyl C proportions than those recorded in samples in other seasons. The proportions of aromatic C in HoA fractions from A and B horizons were highest in summer. These seasonal variations were less significant than variations with soil depth. O-alkyl C proportions in HoA fractions decreased with increasing soil depth from the Oi to the A horizon. The HoA fractions from the B horizon showed a higher alkyl C proportion than samples from other horizons in winter and spring. These changes with soil depth from the Oi to A horizons might result from selective utilization of carbohydrate carbon by microorganisms, whereas those in the B horizon may result from sorption to mineral surfaces. The HoA fractions in the stream were similar in relative molecular weight, distribution of each type of proton and carbon species in HoA fractions from the B horizon, whereas stream HoA fractions collected in summer would be derived from organic horizons. This indicated that vertical changes in the chemical properties of HoA fractions in soil and pathways of water to the stream would largely affect the chemical properties of HoA fractions in the stream.