Comparison of functional and structural properties of native and industrial process-modified proteins from long-grain indica rice

Rice proteins, as a cheap plant protein source from the by-products of rice dreg processing, could potentially replace commonly used proteins such as soy and whey proteins in selected food products. In this study, the functional properties, surface hydrophobicity (H₀), sulfhydryl and disulfide bond contents, thermal properties, as well as secondary structures of native rice endosperm protein (REP) and processed rice dreg protein (RDP) extracted from long-grain indica rice, were compared. RDP was found to have a higher solubility associated with its relatively higher emulsifying and foaming properties than REP, as well as its water/oil holding capacity, although it was a denatured protein. The emulsifying properties were dependent on the solubility and H₀, while solubility was also related to the disulfide bond contents. Distinct differences in H₀, thermal properties, and disulfide bond contents between REP and RDP could be due to the conformational changes, as the industrial processing steps in the production of rice syrups caused an increase in β-turns at the expense of β-sheets and random coils of REP, leading to the unfolding of β-sheets into higher-ordered supramolecular structures for RDP, which could be responsible for its better functional properties.     

Functionality and characterization of kafirin-rich protein extracts from different whole and decorticated sorghum genotypes

The study of food-grade isolated kafirin proteins has increased recently due to the interest of their potential applications in gluten-free products. However, functionality of extracted proteins and fractions have been poorly characterized. In this investigation, kafirins were extracted from whole or decorticated sorghum genotypes (white-regular, white-waxy, red-regular and high-tannin) with 70% aqueous ethanol with metabisulfite. Chemical composition, color parameters, functionality and molecular characterization of kafirin extracts were determined. When kafirin extracts were obtained from decorticated sorghums, higher protein purities (81.5–93.3%), lower lipid contents (1.9–12.6%), better color parameters, and higher yields were obtained compared to counterparts extracted from whole caryopses. Functional properties of the extracted kafirins showed low water solubility, free amino nitrogen, and emulsifying activity, but adequate water holding and fat absorption capacities and in vitro protein digestibility. Differences in functionality were attributed to sorghum genotype. SDS-PAGE showed extraction of α₁-, α₂-, β-, and γ-kafirins with no contamination of other protein fractions. FTIR indicated a reduction in α-helix:β-sheet after extraction, especially in proteins obtained from decorticated sorghums. High correlations found from Pearson analysis could be used to optimize protein yield and the functionality (emulsifying activity and solubility) of the extracted proteins to be applied in gluten-free food systems.     

Functional properties of protein from Lesquerella fendleri seed and press cake from oil processing

This investigation determined the functional properties of protein in Lesquerella fendleri seed and press cake from oil processing. L. fendleri seeds were heat-treated at 82 °C (180 °F) during 120 min residence time in the seed conditioner, and then screw-pressed to extract the oil. Unprocessed ground, defatted lesquerella seeds and press cakes were analyzed for proximate composition and protein functional properties. Protein from unprocessed lesquerella seed showed the greatest solubility (≥60%) at pH 2 and 10 and was least soluble (25%) at pH 5.5–7. Unprocessed lesquerella protein also had high surface hydrophobicity index (S_o), as well as, excellent foaming capacity and stability, emulsifying properties, and water-holding capacity (WHC) at pH 7. Protein solubility profile of the press cake showed up to 50% reduction in soluble proteins at nearly all pH levels, indicating heat denaturation during cooking and screw-pressing. Foaming capacity of the press cake protein decreased slightly, but foam stability was completely lost. Press cake protein also had markedly reduced values for S_o, emulsifying properties and WHC, further confirming lesquerella protein’s sensitivity to heat treatment.     

Digestibility and Structural Properties of Thermal and High Hydrostatic Pressure Treated Sweet Potato (Ipomoea batatas L.) Protein

This study assessed the effects of thermal (40, 60, 80, 100 and 127 °C) and high hydrostatic pressure (HHP, 200, 400 and 600 MPa) treatments on the in vitro digestibility and structural properties of sweet potato protein (SPP). The results showed that the in vitro digestibility of SPP increased significantly with increasing heating temperature and heating time (0–60 min), while HHP treatment had little or no effect. Native SPP denaturation temperature (T _d ) and enthalpy change (ΔH) were 89.0 °C and 9.6 J/g, respectively. Thermal and HHP treated SPP had T _d of 84.6–88.9 °C and 86.4–87.6 °C, respectively. ΔH of thermal treated SPP was 3.6–6.4 J/g, while that of HHP treated SPP was 5.9–7.8 J/g. The differential scanning calorimetry (DSC) results demonstrated that HHP and thermal treatments both significantly reduced SPP thermodynamic stability. Circular dichroism analyses revealed that native SPP contains α-helixes, β-sheets and random coils (4.3, 48.0 and 47.7 %, respectively). After thermal treatment at 127 °C for 20 min, the content of α-helixes and turns increased significantly (13.2 and 27.6 %, respectively), whereas the content of β-sheets decreased significantly (12.3 %). In contrast, HHP treatment increased the content of β-sheets, but decreased the content of random coils. This study suggested that the SPP structure changes might be the main reason affecting the in vitro digestibility of SPP, and thermal treatment was more effective at changing SPP secondary structures and improving in vitro SPP digestibility than HHP treatment.     

Impact of amylose content on starch retrogradation and texture of cooked milled rice during storage

Milled rice from 11 varieties, with amylose levels from 1.2 to 35.6% dry base, were collected to study the impacts of amylose content on starch retrogradation and textural properties of cooked rice during storage. The relationship between amylose content and different properties was determined using Pearson correlation. Starch retrogradation enthalpy (ΔH_r) of cooked rice was determined by differential scanning calorimetry. ΔH_r values were found to be positively correlated with amylose content (0.603 ≤ r ≤ 0.822, P < 0.01) during storage. Textural properties were determined by a Texture Analyser. The hardness of cooked rice showed a positive correlation with amylose content (0.706 ≤ r ≤ 0.866, P < 0.01) and a positive correlation with ΔH_r of cooked rice (r = 0.650, P < 0.01) during storage. The adhesiveness showed a negative correlation with amylose content (−0.929 ≤ r ≤ −0.678, P < 0.01) and a negative correlation with ΔH_r of cooked rice (r = −0.833, P < 0.01) during storage. Hardness showed a negative correlation with adhesiveness (r = −0.820, P < 0.01). These results indicated that amylose content has significant effects on starch retrogradation and textural properties of cooked rice. The cooked rice with high amylose content is easy to retrograde, the cooked rice with low amylose content retrograded slowly. Sarch retrogradation contributes to the changes of textural properties of cooked rice during storage.     

Impact of proteins on pasting and cooking properties of waxy and non-waxy rice

Changes of RVA viscosity and texture properties of waxy rice (n=9) and non-waxy rice (n=10) were analyzed through protein removal or disulfide bond disruption. Protease or DTT had similar effects on the pasting behavior of the waxy rice, but affected differently that of non-waxy rice. For all waxy rice flour treated with DTT or protease, the peak, breakdown and consistency viscosity values all significantly decreased, and the viscosity curves barely rose from the baseline. Pre-incubation of flours with a protease increased RVA pasting temperatures, decreased viscosities along all the points of the curves and the slopes of the linear parts of the curves for all non-waxy cultivars. DTT decreased RVA pasting temperatures and peak viscosities of all non-waxy flour, but increased breakdown viscosities in six non-waxy rice cultivars. With DTT-added cooking water, the hardness of cooked waxy and non-waxy rice, as determined by Instron, generally decreased. With DTT-added cooking water, the adhesiveness of all cooked waxy rice significantly decreased, while it increased significantly or remained the same in all cooked non-waxy rice. The above results indicated that the protein agent of a network linked by disulfide bonds increased the RVA gelatinized paste rigidity, the hardness and adhesiveness of cooked rice of all waxy cultivars, while in non-waxy cultivars, both the network and the increase of the gelatinized paste concentrations resulting from protein hydration contributed to the enhancements of the RVA paste rigidity and the cooked rice hardness.     

Characterisation and functional properties of Australian rice protein isolates

Albumin, globulin, glutelin and prolamin fractions were isolated from an Australian rice variety (cv. Langi) and characterised by yield, protein content and molecular weight profile using both capillary electrophoresis (SDS-CE) and sodium dodecyl sulphate polyacrylamide gel electrophoresis (SDS-PAGE). The influence of pre-extraction enzymatic hydrolysis of starch and heating to 70 °C was also investigated, as was the extraction of the glutelin fraction without prior removal of the albumin and globulin fractions. Pre-extraction treatment affected mainly the albumin fraction, increasing dry matter yield but reducing protein content. SDS-CE was able to separate the protein fractions over a wider molecular weight range than SDS-PAGE, and the peaks from SDS-CE showed slightly higher molecular weight compared to equivalent bands from SDS-PAGE. The glutelin fraction extracted without prior removal of albumin and globulin fractions had different characteristics compared to those obtained by conventional extraction methods. Pre-extraction hydrolysis of starch did not significantly affect the emulsifying, foaming and gelling properties of extracted protein. Although rice glutelin had poor solubility, emulsifying and foaming properties in aqueous systems, it had good gelling properties which could be important for food applications.     

Influence of amylopectin structure on rheological and retrogradation properties of waxy rice starches

A set of 13 waxy rice genotypes prepared by chemical-induced mutation of rice variety TNG67 and 7 waxy rice varieties widely grown in Taiwan were compared for structural, rheological and retrogradation characteristics of starches. Wide differences in retrogradation enthalpy (ΔH_ret), gel firmness and storage modulus (G’_ret) were observed for 2-week stored gels of 20 starches. Ratio of short-to-long amylopectin chains was significantly higher (p < 0.05) in starches from mutant genotypes than in commercial varieties. ΔH_ret and G’_ret of starch pastes stored over 4 weeks showed stronger correlation with amylopectin chain-profile compared to those stored for 2 weeks. Amount of long amylopectin chains was correlated positively (p < 0.05) with ΔH_ret and gel firmness. Overall, ratio of short-to-long amylopectin chains affected almost all the rheological and retrogradation parameters. Results of this study can be useful to plant breeders and food industry for quality improvement and selection of waxy rice mutants for various applications.     

Composition and molecular structure of polysaccharides released from barley endosperm cell walls by sequential extraction with water,malt enzymes,and alkali

Isolated and purified endosperm cell walls (CW), used in this study, were derived from a Canadian malting barley variety, AC Metcalfe, grown in three different environments in Canada in 2003, and varying in grain protein and β-glucan contents, as well as in grain hardness. The CW were initially extracted with water at 45 °C and subsequently digested with barley malt crude enzyme extract resulting in two fractions designated CW-WE45 and CW-MD, respectively. The remaining non-digested cell wall material (CW_ND) was further fractionated by sequential extraction with water at 95 °C (CW_ND-WE95), saturated barium hydroxide (CW_ND-BaE), and 1 N sodium hydroxide (CW_ND-NaE) at 25 °C. Composition and molecular structure analyses were carried out for all fractions including the remaining cell wall residue (CW_RES). Extraction of CW with water followed by digestion with malt crude enzyme extract solubilized the majority of β-glucans (∼55–70%) and glucomannans (∼60–80%) but only a small portion of arabinoxylans (∼20–30%) present in the intact CW. The CW-WE45 and CW_ND-WE95 fractions consisted mostly of β-glucans exhibiting high average molecular weights (M_w) (2–3 × 10⁶), whereas the CW_ND-BaE consisted mainly of arabinoxylans with M_w about 1–1.5 × 10⁶. The CW_ND-NaE contained almost equal amounts of β-glucans and arabinoxylans and a small amount of glucomannans, whereas the CW_RES contained approximately equal proportions of β-glucans, arabinoxylans and glucomannans. β-Glucans in CW_ND-WE95, CW_ND-NaE, and CW_RES exhibited a higher ratio of 3-O-β-d-cellobiosyl-d-glucose to 3-O-β-d-cellotriosyl-d-glucose (DP3/DP4) compared to β-glucans in CW-WE45 and CW-MD. β-Glucans in CW_ND-NaE showed the highest level of long cellulosic oligosaccharides with DP ≥ 5, whereas those in the CW_RES had the highest DP3/DP4 ratio. The CW-MD was fractionated by ultrafiltration into high (CW-MD_HMW) and low-molecular weight (CW-MD_LMW) sub-fractions, with weight-average M_w of ∼150–350 × 10³ and <10 × 10³, respectively, as confirmed by size-exclusion chromatography. The monosaccharide composition of the sub-fractions indicated a more extended enzymic degradation of β-glucans and glucomannans than arabinoxylans. Some differences in composition and molecular structure of the cell wall constituents among the three barley samples were related to their solubility and enzymic digestibility.     

Dehydration of gluten matrix as a result of dietary fibre addition – A study on model flour with application of FT-IR spectroscopy

Nowadays, consumers demand dietary fibre-enriched products of appropriate taste, texture, smell and appearance. Unfortunately, addition of the dietary fibre supplements to bread significantly reduces its quality which is connected with changes in the structure of gluten proteins. Structural changes as well as changes in the water state of gluten matrix induced by eight dietary fibres were observed by using Fourier transform infrared spectroscopy. To facilitate this the difference spectra were calculated by subtraction of the control (gluten only) infrared spectrum from the spectra of gluten-fibre mixtures. The presence of positive bands at ca. 1597 and 1235 cm⁻¹ indicated aggregation of gluten proteins into hydrogen bonded β-sheets. These β-sheets can be formed by other β-sheets, antiparallel-β-sheets, β-turns and/or α-helices. The aggregation is probably induced by partial dehydration of gluten matrix due to competition for water molecules between gluten proteins and fibre polysaccharides. This assumption is confirmed by the presence of the negative band at 3237 cm⁻¹ and decrease in the intensity of the band at 3051 cm⁻¹. These bands are assigned to the weak and strong H-bonds in the gluten matrix, respectively. The results indicated that both weak and strong H-bonds are necessary to dough formation of adequate rheological properties.     

Oat protein solubility and emulsion properties improved by enzymatic deamidation

Oat protein produced by a dry milling process was enzymatically deamidated by a food-grade protein-glutaminase (PG), and the effects on structure, solubility and emulsifying properties of oat proteins were studied. The reactions were conducted at neutral pH and low salt concentration conditions. Oat proteins were deamidated up to a deamidation degree of 59%. The solubility of proteins doubled. Oil-in-water emulsions prepared with the native and deamidated oat proteins differed as the emulsions prepared from oat proteins with high deamidation degree had a more uniform oil droplet particle size and longer stability. Fourier transform infrared (FT-IR) analysis demonstrated that oat protein secondary structure became more flexible by deamidation. Protein-glutaminase mediated deamidation appeared to be a promising technique to improve oat protein functionality such as emulsifying ability and solubility.     

Physiological and Proteomic Analyses Reveal Effects of Putrescine-Alleviated Aluminum Toxicity in Rice Roots

The effects of putrescine on improving rice growth under aluminum(Al) toxicity conditions have been previously demonstrated, however, the underlying mechanism remains unclear. In this study, treatment with 50 μmol/L Al significantly decreased rice root growth and whole rice dry weight, inhibited Ca~(2+) uptake, decreased ATP synthesis, and increased Al, H_2O_2 and malondialdehyde(MDA) contents, whereas the application of putrescine mitigated these negative effects. Putrescine increased root growth and total dry weight of rice, reduced total Al content, decreased H_2O_2 and MDA contents by increasing antioxidant enzyme(superoxide dismutase, peroxidase, catalase and glutathione S-transferase) activities, increased Ca~(2+) uptake and energy production. Proteomic analyses using data-independent acquisition successfully identified 7 934 proteins, and 59 representative proteins exhibiting fold-change values higher than 1.5 were randomly selected. From the results of the proteomic and biochemical analyses, we found that putrescine significantly inhibited ethylene biosynthesis and phosphorus uptake in rice roots, increased pectin methylation, decreased pectin content and apoplastic Al deposition in rice roots. Putrescine also alleviated Al toxicity by repairing damaged DNA and increasing the proteins involved in maintaining plasma membrane integrity and normal cell proliferation. These findings improve our understanding of how putrescine affects the rice response to Al toxicity, which will facilitate further studies on environmental protection, crop safety, innovations in rice performance and real-world production.     

CO2-defatted oats: Solubility,emulsification and foaming properties

Functional properties of conventional oat materials are relatively poor with respect to foam and emulsion formation and stabilization. This is largely due to the poor solubility of oat proteins and the presence of lipids in aqueous extracts of oats. In the experimental part of this study, extracts were prepared from different type oat flours (oat endosperm flour, oat fine flour, CO₂-defatted whole oat flour and CO₂-defatted oat flour) with a buffered aqueous extraction procedure at acidic (pH 4.5 and 6.5) and basic (pH 8.5 and 10.5) regions. The solubility of proteins was the highest at pH 10.5 and NaCl concentration of 2%. Among the extracts, CO₂-oat flour showed improved foaming and emulsifying properties at basic pH values. The presence of 0.1% NaCl resulted in the lowest foam volumes, but the emulsion activity and stability values being the highest. Sucrose addition resulted in increased foam and emulsion stability of suspensions. Heat treatment at 80 °C impaired foam properties, whereas the stability of emulsions increased with the increase in temperature from 20 °C to 80 °C. CO₂-extracted oats can be useful raw materials in beverages and other aqueous applications where protein functionality plays an important role.     

转小麦 TaPDI-A、 TaTRXh-A和 TaPP2Ac-D基因拟南芥植株的主要抗旱性研究

核氧还蛋白（nucleoredoxin,NRX）可通过还原目标蛋白的二硫键来调控其生物活性,在植物的生长发育和抗逆境胁迫中发挥着重要作用。蛋白质二硫键异构酶（protein disulfide isomerase,PDI）、h型硫氧还蛋白（h-type thioredoxin,TRXh）和蛋白磷酸酶2A催化亚基（protein phosphatase 2A catalytic subunit,PP2Ac）是小麦核氧还蛋白TaNRX1的互作蛋白。为了明确TaNRX1互作蛋白的抗旱性功能,本研究在拟南芥中过表达了小麦 TaPDI-A、 TaTRXh-A和 TaPP2Ac-D基因,对野生型和转基因拟南芥的表型和抗旱相关生理指标进行了鉴定。结果表明,干旱胁迫处理后,转 TaPDI-A、 TaTRXh-A和 TaPP2Ac-D基因拟南芥的根长、存活率、脯氨酸含量均大于野生型,离体叶片失水率、丙二醛（MAD）含量均小于野生型。二氨基联苯胺（diaminobenzidine,DAB）对H₂O₂组织定位染色结果表明,干旱胁迫处理后,转 TaPDI-A、 TaTRXh-A和 TaPP2Ac-D基因拟南芥的H₂O₂含量均低于野生型。上述结果说明,TaNRX1的互作蛋白基因 TaPDI-A、 TaTRXh-A和 TaPP2Ac-D增强了拟南芥对于干旱胁迫的抵抗能力。本研究可为小麦抗旱育种提供候选基因和理论基础。     

Characterizing the pigmented traditional rice cultivars grown in temperate regions of Kashmir (India) for free and bound phenolics compounds and in vitro antioxidant properties

The purpose of the research was to identify the phenolic and flavonoid compounds of seven different traditional pigmented whole rice cultivars grown in the temperate regions of Kashmir so as to study their relationship with in vitro antioxidant capacities. The completely pigmented rice cultivars were found to have higher phenolic, flavonoid, anthocyanin contents and exhibited higher antioxidant capacities than the light colored and sparely colored rice cultivars. A total of 40 compounds had been identified in the analyzed rice cultivars that were found to be distributed in 6 major categories with 6-phenolics, 6-flavonoids, 11-hydroxycinnamic acid derivatives, 7-hydroxybenzoic acid derivatives, 3-anthocyanins and 7-flavonoid glucosides of different flavonoid compounds. Among the free and bound fractions for each cultivars the light and sparsely colored depicted higher content of phenolics and in vitro antioxidant properties in bound faction, while the completely pigmented cultivars showed higher antioxidant properties in free fractions. The anthocyanins quercetin-3-O-galactoside, cyanidin-3-O-rutinoside and pelargonidin-3-O-diglucoside had been identified by LC-MS existing in the free fractions of the analyzed rice cultivars whereas, the free fraction of acetone + H₂O possessed higher percentage of phenolic compounds as compared to methanolic extracts and bound fractions. The black colored cultivars possessed higher DPPH scavenging activity and lipid peroxidation inhibition.     

QTL mapping for crude protein and protein fraction contents in rice (Oryza sativa L.)

Improvement of rice storage proteins is important in rice breeding for high nutritional quality. Seventy-one recombinant inbred lines (RIL) derived from a cross between japonica variety Asominori and indica variety IR24 were used to study the inheritance of crude protein and protein fraction contents in rice. A total of 16 QTL were identified and mapped on eight chromosomes. Several QTL affecting contents of different protein fractions were mapped in the same chromosomal region. In particular, two QTL with a significant contribution were identified to simultaneously affect prolamin and glutelin contents. One QTL denoted as qCP-12 affecting crude protein content (CP) was located in the same region as QTL qGLT-12 affecting glutelin content, in agreement with the positive correlation between glutelin level and protein content. QTL with larger genetic effects were further confirmed using two sets of chromosome segment substitution lines (CSSL), where Asominori and IR24 were used as the recurrent parents. By QTL comparative analysis, two QTL for CP, three for globulin content and one for prolamin content were located in the vicinity of CP QTL previously identified in polished rice. Application of these results in rice breeding is discussed.     

Total phenolics,flavonoids, antioxidant capacity in rice grain and their relations to grain color,size and weight

Total phenolics, flavonoid contents and antioxidant capacity from a wide collection of rice germplasm were measured, and their relations to grain color, grain size and 100-grain weight were investigated. Highly significant genotypic differences were observed in total phenolics, flavonoid contents and 2,2-azino-bis-(3-ehylbenzothiazoline-6-sulphonic acid) diammonium salt (ABTS) radical cation antioxidant capacity. They displayed an increasing order in the white rice, red rice and black rice, yet several white rice had higher phenolics and flavonoids contents than the red rice. Significant positive pair-wise correlations were found among the phenolics, flavonoid contents and antioxidant capacity, and the coefficient between the phenolic contents and antioxidant capacity was extremely high (r = 0.96). Among all rice accessions, the grain color parameters had negative correlations with the phenolics, flavonoid contents and antioxidant capacity (p < 0.001). The negative correlation between a* and antioxidant capacity, and the positive correlation between H° and antioxidant capacity were consistent within the respective white rice and red rice groups. Flavonoid contents had positive correlation with grain length and length to width ratio, and had negative correlation with the 100-grain weight among all rice accessions. It was also found that 100-grain weight still had negative correlations with phenolics, flavonoid contents and antioxidant capacity within the white rice genotypes. These relationships may serve as indexes to indirectly select breeding lines high in the phenolics, flavonoids and antioxidant capacity. Principal component analysis including the information for phenolics, flavonoids, antioxidant capacity, grain color parameters, grain size and 100-grain weight extracted five principal components that explained 83.7% of the total variances. The results of this study may provide new opportunities for rice breeders and eventually commercial rice growers to promote the production of rice with enhanced nutritional quality.     

Characterization and In Vitro digestibility of rice protein prepared by enzyme-assisted microfluidization: Comparison to alkaline extraction

Microfluidization followed by density-based separation was employed to extract protein from broken rice by disrupting protein-starch agglomerates. Follow-up enzyme treatments (amylase and glucoamylase) were performed to further improve the purity of the protein-rich fraction. High protein recovery (81.87%) and purity (87.89%) were obtained. The protein composition, solubility, structural properties, and in vitro digestibility of rice proteins prepared by enzyme-assisted microfluidization (EM-RP) and alkaline extraction (AE-RP) were compared. EM-RP was mainly composed of glutelin, which had low solubility and native structure. By contrast, large quantities of prolamin and globulin appeared in the AE-RP except glutelin, leading to the richness of glutamic acid/glutamine, leucine, aromatic and charged amino acids in the AE-RP. Compared to AE-RP, EM-RP showed higher digestibility due to the richness of glutelin (an easy-to-digest protein), as evidenced by higher nitrogen release during pepsin-trypsin digestion. The presence of prolamin (an indigestible protein) in AE-RP decreased protein digestibility although alkaline extraction improved its hydrolysis. These results suggest that enzyme-assisted microfluidization could be an effective technique to non-destructively and selectively extract rice glutelin.     

The effect of sodium chloride on gluten network formation and rheology

Gluten samples were obtained from two wheat flours with different levels of total protein in the presence or absence of sodium chloride (2% flour base). The dynamic oscillation rheology, large extensional deformation, confocal laser scanning microscopy (CLSM), transmission electron microscopy (TEM) and chemical analysis of disulfide bond linkages and the ratio of polymeric glutenins and monomeric gliadins were used to investigate the effect of salt on the structure and rheological properties of gluten. CLSM and TEM images showed that NaCl caused the gluten to form fibrous structure. The presence of NaCl increased non-covalent interactions and β-sheet structure, measured by FTIR, in gluten proteins. The gluten matrix formed with salt resulted in higher tan δ values corresponding to a less elastic network when measured using oscillatory rheometry. Large deformation extensional measurements showed that the maximum force to fracture were lower for the gluten samples prepared in the presence of NaCl. The results from this study indicate that changes in the solvent quality due to the presence of NaCl during dough mixing result in different molecular conformation and network structure of gluten proteins which contributed to the differences in the rheological properties.     

双氧水脱色对油茶粕蛋白结构和功能特性的影响

为了除去油茶粕蛋白的色素,添加体积分数为4%的双氧水在40℃下作用蛋白提取液1h可取得较好的脱色效果,但双氧水脱色对油茶粕蛋白结构和功能的影响需要进一步研究。本文通过测定变性温度、表面疏水性和巯基的含量,分析红外光谱、X射线衍射峰、微观形貌等研究脱色前后油茶粕蛋白结构和功能的变化。结果显示:双氧水脱色使油茶粕蛋白的表面疏水性上升,巯基含量下降,二硫键含量基本不变;通过红外光谱分析,双氧水脱色减弱了油茶粕蛋白化学键强度,但没有影响油茶粕蛋白基本骨架,微观结构基本相似,油茶粕蛋白的X射线衍射峰的位置和强度基本一致,热变性温度升高,双氧水没有改变油茶粕蛋白的等电点,但油茶粕蛋白的溶解度、乳化性、乳化稳定性、起泡能力和泡沫稳定性均下降,持油性和持水性上升。本研究结果表明双氧水脱色未明显改变油茶粕蛋白的结构,但其功能性质受到一定影响。