Precursors for Formation of 2-Pentyl Pyridine in Processing of Soybean Protein Isolates

ABSTRACT: Using stable isotopic ¹³C-2,4-decadienal and ¹⁵N-ammonia, both compounds were confirmed as precursors in the formation of 2-pentyl pyridine (2-pp) in processing of soybean protein isolates (SPI). The yields of 2-pp were higher when adding 2,4-decadienal and ammonia together than the yields when adding 2,4-decadienal only for soybean cultivars Stress land, LOX null, Edison, and KS4694. Arginine, lysine, asparagine, and glutamine increased 2-pp when added together with 2,4-decadienal, whereas aspartic acid, glutamic acid, glycine, and histidine had no effects. In both buffer and defatted soybean slurry, the highest level of 2-pp was found at pH 9, followed by pH 7, then pH 4.5. The results indicate that the synthesis of 2-pp may be a spontaneous reaction.     

Binding Properties of 2-Pentyl Pyridine to Soy Protein as Measured by Solid Phase Microextraction

ABSTRACT: The binding properties of 2-pentyl pyridine (2-pp) were investigated for soybean protein isolates (SPI) and the beta-conglycinin and glycinin soy protein fractions. The glycinin fraction had the highest binding affinities for 2-pp, followed by beta-conglycinin fraction, and then SPI. More 2-pp was bound by SPI and beta-conglycinin or glycinin fractions under alkaline conditions than under neutral conditions, which exhibited more binding than acidic conditions. More 2-pp was also bound at high temperature (74 °C) than at 25 °C, but greater binding affinity of 2-pp was observed at 4 °C than at 25 °C. With increased NaCl concentrations, the binding affinity of 2-pp decreased. Exposure to UV light increased binding of 2-pp to all types of soy protein.     

Comparative studies on protein fractions and amino acid composition from sorghum and pearl millet

A defatted flour sample of sorghum and pearl millet were separated into three fractions. These procedures involve extracting the defatted flour with aqueous sodium hydroxide (pH 11.9) followed by precipitation with diluted HCl acid (pH 4.8). The two protein fractions I (soluble at pH 4.8) and II (insoluble at pH 4.8) along with the remaining residues (fraction III) were lyophilized separately. The amino acid composition of the original flour and the three fractions were determined. Lysine seems to be the most deficient amino acid in the original flour and the remaining residues. Fraction I and II, in which the lysine accumulated, have essentially better amino acid profile and consequently nutritionally better quality than the protein of the original defatted flour. The recovered protein-rich fractions I and II should be useful as a protein ingredient in foods. The remaining residues can be extruded into convenience foods.     

Survival of Listeria innocua after Isoelectric Solubilization and Precipitation of Fish Protein

ABSTRACT:  Protein wasted by the disposal of fish processing by-products may be recovered using isoelectric solubilization and precipitation. Extreme pH shifts are used to solubilize the protein and then it is recovered by precipitation and centrifugation. Microbial survival after this process is unknown; therefore, the purpose was to see if Listeria innocua would survive extreme pH shifts during the protein recovery process. Fresh rainbow trout fillets were inoculated with L. innocua , homogenized, and brought to the target pH of 2, 3, 11.5, or 12.5 by the addition of concentrated hydrochloric acid or sodium hydroxide. The proteins were allowed to solubilize at 4 °C for 10 min, centrifuged, and the lipid and insoluble components (bones, skin, insoluble protein, and so on) were removed. A 2nd pH shift (pH 5.5) and centrifugation was used to separate the precipitating protein and water fractions. Each constituent (lipid, protein, water, insoluble components) was analyzed for bacterial content using growth and selective media. The sums of the surviving L. innocua in these constituents were compared to the initial inoculum. There were no significant differences in recovery on growth or selective media ( P > 0.05). The greatest loss occurred when the pH was shifted to 2, with a 3.1-log reduction in the combined fractions of the trout fillets and a 3.8-log reduction in the protein fraction. There were no significant losses when the pH was adjusted to 11.5 ( P > 0.05). Future studies will continue to look at the effects of using organic acid, rather than inorganic, for protein solubilization.     

Nutritional and functional properties of Vicia faba protein isolates and related fractions

The goal of this research was the characterisation of Vicia faba (broadbean) protein isolates and related fractions in order to determine whether this grain legume could be used for production of high quality protein products and other fractions rich in functional components. Alkaline extraction of the defatted seed flour, followed by precipitation at the isoelectric pH, yielded a 92% protein isolate with a high oil absorption capacity. The contents of the favism-inducing glycosides, vicine and convicine, in the isolate were reduced by more than 99% as compared to the original flour, although the amino acid composition was similar to that of the flour. Some of the by-products of protein isolate production may also be of interest from a nutritional and functional point of view. Thus, the oil resulting from hexane extraction of the flour is rich in unsaturated fatty acids, and polyphenols (resulting from extraction of the defatted flour with acetone) showed a high ABTS radical-scavenging activity. In addition, the solid residue (resulting from protein solubilisation) was high in fibre and showed good water absorption. These results show good nutritional and functional properties in V. faba protein isolates and related fractions, which may favour the revalorisation of this traditional bean crop.     

Functional Properties of Improved Glycinin and β-nglycinin Fractions

ABSTRACT: Glycinin and β-conglycinin have unique functionality characteristics that contribute important properties in soy foods and soy ingredients. Limited functionality data have been published for glycinin and β-conglycinin fractions produced in pilot-scale quantities. Protein extraction conditions were previously optimized for our pilotscale fractionation process to maximize protein solubilization and subsequent product recovery. Glycinin, β-conglycinin, and intermediate (mixture of glycinin and β-conglycinin) fractions were prepared using optimized-process (OP) extraction conditions (10:1 water-to-flake ratio, 45°C) and previous conditions termed Wu process (WP) (15:1, 20°C). Viscosity, solubility, gelling, foaming, emulsification capacity, and emulsification activity and stability of the fractionated proteins, and soy protein isolate (SPI) produced from the same defatted soy white flakes were compared to evaluate functional properties of these different protein fractions. Differential scanning calorimetry, sodium dodecylsulfate-polyacrylamide gel electrophoresis, and surface hydrophobicity data were used to interpret functionality differences. OP β-conglycinin had more glycinin contamination than did the WP β-conglycinin. OP and WP solubility profiles were each similar for respective glycinin and β-conglycinin fractions. Emulsification activities and stabilities were higher for OP β-conglycinin and OP intermediate fractions compared with respective WP fractions. β-Conglycinin and SPI emulsification capacities (ECs) mirrored solubility profile, whereas glycinin ECs did not. OP glycinin had a higher foaming capacity than WP glycinin. OP and WP intermediate fraction apparent viscosities trended higher than those of other protein fractions. β-Conglycinin dispersions at pH 3 and 7 produced firm gels at 80°C, whereas glycinin dispersions formed weaker gels at 99°C and did not gel at 80°C.     

菜籽蛋白水解物体外和细胞内抗氧化性评价及氨基酸分析研究

以“双低”油菜籽秦优7号为原料,碱溶酸沉法获得菜籽分离蛋白后进一步用Alcalase2.4L酶解得到菜籽蛋白水解物（rapeseed protein hydrolysates,RPHs）;采用聚丙烯酰胺葡聚糖凝胶柱（Sephacryl S-100HR）对RPHs进行分离纯化,得到3 个组分;采用抗氧化能力指数（oxygen radical absortion capacity,ORAC）方法以及细胞抗氧化活性（cellular antioxidant capacity,CAA）的方法分析筛选得到抗氧化性最好的组分3。结果表明组分3的ORAC值为（1610.38±112.51）μmol TE/g;CAA值为（124.66±2.18）μmol QE/g,EC50值为（57.84±3.38）μg/mL;在此基础之上,对组分3进行氨基酸分析以及电泳分析,表明其抗氧化性与分子质量分布及氨基酸组成可能存在一定关系。     

Comparative study of the emulsifying and foaming properties of defatted coriander (Coriandrum sativum) seed flour and protein concentrate

Emulsifying and foaming properties were determined for coriander protein products (defatted flour and protein concentrate) at pH 4.0, 7.0 and 9.0 and the results compared with those obtained for defatted soybean flour. Mean oil droplet size and interfacial protein concentration was smallest for emulsions (∼17% oil, v/v) stabilized by the coriander protein concentrate, when compared to the coriander and soybean flours. Polypeptide composition of the interfacial protein membrane of the emulsions was different from the polypeptide composition present in the respective coriander flour and protein concentrate. In contrast, soybean flour-stabilized emulsions contained similar polypeptide composition to that of the flour. Soybean flour formed the greatest amount of foams at pH 4.0, 7.0 and 9.0 followed by the coriander flour, which had greater amounts of foam at pH 4.0 and 5.0. The foam stability of both the coriander flour and protein concentrate were significantly (P⩽0.05) less than those of the soybean flour. It was concluded that the reduced level of non-protein components in the coriander protein concentrate favoured increased surface activity at the oil–water interface but not at the air–water interface.     

Sulfite Formation in Isolated Soy Proteins

ABSTRACT: Defatted soybean flour contained 2820 parts per million (ppm) inorganic sulfate. The corresponding laboratory isolated soy proteins (ISP) contained 1364 ppm sulfate bound to a greater than 3000 molecular weight fraction. Defatted soy flour contained 0.98 nmoles of adenosine triphosphate (ATP) per 0.1 g. ATP levels decreased when the defatted flour was hydrated under a variety of conditions. Neither adenosine-5'-phosphosulfate or 3'-phosphoadenosine-5'-phosphosulfate could be detected in defatted soybean flour or in aqueous extracts of defatted flour. Defatted soy flour contained 1034 ppm reduced glutathione and 647 ppm reduced homogluatathione. These levels dropped to 62 and 13 ppm, respectively, immediately after the isoelectric precipitation step of ISP processing. No oxidized glutathione or homoglutathione were detected. Defatted flour contained 106 ppm cysteine-S-sulfonate, alkaline extracts of defatted flour contained 329 to 579 ppm and ISP contained 0 to 43 ppm. Neither sulfite nor methanethiol were detected until after the soluble components at pH 4.6 were separated from the precipitated soy proteins. These findings indicate that cysteine-S-sulfonate is present in defatted flour and increases during ISP processing. Also, the formation of sulfite during the final stages of ISP processing corresponds to elevated methanethiol levels.     

Faecal Composition and Nitrogen Excretion of Rats Fed on Diets Containing Sweet Lupin (Lupinus angustifoliusL) or its Fractions

Five N balance studies were conducted to determine the faecal composition and N excretion of feeding raw Lupinus angustifolius seed meal and its fractions for growing rats using a semi-synthetic lactalbumin-based diet as control. Diets were formulated to have equal amounts of energy. The protein was incorporated at the level of 10% bulk and contained unsupplemented lupin seed meal (LMU) and fully supplemented lupin seed meal (LMFS) at 360 g kg⁻¹ diet, aqueous extract non-dialysed (LPAND) at 196 g kg⁻¹ aqueous extract dialysed soluble at pH 7·0 (LPAD) at 148 g kg⁻¹ aqueous extract dialysed insoluble at pH 7·0 (LPADI) at 124 g kg⁻¹, buffer dialysed soluble at pH 7·0 (BUSOL) at 136 g kg⁻¹, buffer dialysed insoluble at pH 7·0 (BUDI) at 119 g kg⁻¹ and lupin meal residue after aqueous and buffer extraction (LMR) at 170 g kg⁻¹ diet. Rats were pair-fed for 10 days with all the above diets which had been supplemented with essential amino acids up to the target requirements for rats. Faecal wet and dry weight were increased in rats fed on LMU, LMPS and LMR diets compared to those obtained from the control diet based on lactalbumin (milk protein) LACT. The higher faecal weight was largely due to water content. The higher faecal N excretion observed in LMU, LMFS, LPAND, LPAD, BUSOL, BUDI and LMR compared to that of LACT diet was significantly lower and thus which was assumed not to be due to a decrease in the digestibility of the dietary protein, which was over 90% as compared to that in the control group. Analysis suggested that an increase in endogenous N excretion is involved in the rise of its excretion in the faeces, and indicates a long-term effect of this seed as a protein and or fibre source in monogastrics.     

Effects of oxidizing agents and defatting on the electrophoretic patterns of flour proteins during dough mixing

3 ) or ascorbic acid at levels of 50, 100 and 150 mg/kg. The effects of mixing, lipid extraction and additives on dough proteins were studied using electrophoresis. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis results for the 50 % 1-propanol insoluble fractions of both varieties showed that the relative band intensities of the flours were more intense than those of the optimum mixed control doughs. KBrO₃ did not affect the extractability of protein in optimum mixed dough, while ascorbic acid reduced the extractability. Generally, overmixing caused a decrease in relative band intensities. The reductions in the relative band intensities were especially noticeable in the oxidant-added doughs. The relative band intensities of the defatted samples were more intense than those of the undefatted ones. Received: 7 December 1999 / Revised version: 14 February 2000     

苦荞蛋白质的低消化性研究Ⅰ——热处理、还原二硫键及添加芦丁对其体外消化率的影响

采用Osborne分级分离的方法从苦荞粉中制备得到清蛋白、球蛋白、醇溶蛋白和谷蛋白。体外消化率测定结果表明,四种蛋白组分的消化率均低于对照-小麦胚分离蛋白和大豆分离蛋白,并且四种组分的体外消化率也存在不同程度的差别:清蛋白最高,谷蛋白最低。热处理可以明显提高苦荞粉四种蛋白组分的体外消化率。添加芦丁不但没有降低四种蛋白组分的体外消化率,反而均有一定程度的提高。二硫键的破坏,除醇溶蛋白得以提高之外,对于其它三种组分只是提高了初始水解速度,最终体外消化率没有明显提高。体外消化实验后,四种蛋白组分所剩的残渣蛋白SDS-PAGE分析结果表明:这些残渣蛋白的谱带存在相似之处:在20kDa处有一条很窄的谱带,在14～10kDa处的谱带较宽。     

The effect of using citric or acetic acid on survival of Listeria monocytogenes during fish protein recovery by isoelectric solubilization and precipitation process

Isoelectric solubilization and precipitation (ISP) is a protein recovery process effective at reducing Listeria innocua, a nonpathogenic bacterium typically used as a surrogate for L. monocytogenes in recovered trout protein. The response of L. monocytogenes to ISP processing was determined and compared to the response of L. innocua. Headed and gutted rainbow trout were inoculated with L. monocytogenes (10.16 log CFU/g), homogenized, and pH-adjusted with granular citric acid (pH 2.0 and 2.5) or glacial acetic acid (pH 3.0 and 3.5). Proteins were solubilized and centrifugation was used to remove insoluble components (skin, insoluble protein, so on). The supernatant was returned to the protein isoelectric point (pH 5.5) with NaOH and centrifuged to remove precipitated protein. Microbial load was enumerated on both growth and selective media; recovery was not significantly different (P > 0.05). Surviving cells from each component (protein, insoluble, and water) were compared to initial inoculum numbers. Significant reductions were detected at all pH (P < 0.05). The greatest reductions were at pH 3.0 with acetic acid, with a mean log reduction of 3.03 in the combined components, and a 3.53 log reduction in the protein portion. Data were compared to results from a previous study using L. innocua. Significant differences (P < 0.05) in recovery were found between the 2 species at pH 2.0 and 3.0 with greater recovery of L. monocytogenes, regardless of processing pH or acid type. These results demonstrate the variability in resistance between species and indicate that L. innocua is not an appropriate surrogate for L. monocytogenes for ISP processing with organic acids.     

On the functional properties of globulin and albumin protein fractions and flours of African locust bean (Parkia biglobossa)

Albumin (ALBa) and globulin (ALBg) fractions of African locust bean were isolated and the functional properties were compared with its defatted (ALBdf) and undefatted flours (ALBf). Albumin had minimum % solubility (56.7%) at pH5, while minimum solubility was observed at pH4 for globulin and the flours. In all the samples studied, maximum solubility was observed at pH 10. A pH-dependent gelation study revealed that all of the samples had the highest least gelation concentration at pH10 apart from ALBf which had 16% w/v LGC at pH 2. Initial increase in ionic strength of the medium, to 0.4 and 0.6 M, enhanced the gelation capacity of protein fractions and flours, respectively, while further increase in ionic strength reduced it. Oil absorption capacity was maximal in ALBa while ALBf had the least value of 1.05 ml/g. Initial increase in ionic strength, up to 0.4 M, increased the water absorption capacity (WAC) of albumin fractions while WACs of the globulin fraction and flours were reduced when the ionic strength of the media reached 0.4 M. Foam capacity increased as the concentration of protein solution increased but was reduced by 6% w/v in ALBf. Initial increase in ionic strength enhanced both foam capacity and stability. Maximum EA was observed at pH 10 in all samples apart from ALBf, which reached a peak EA value at pH 2. ES (emulsion stability) was maximal at pH 10 for ALBa and ALBg while the same values were observed for ALBdf and ALBf at pH 2 and 10. Increasing the ionic strength, to 0.4 M, enhanced the EA and ES of ALBa while further increase in ionic strength, to 0.7 M, improved EA of ALBf but reduced the ES. Both EA and ES of ALBf reached peak values in 0.2 M solutions but no fixed pattern was observed in the response of ALBdf to various ionic strengths of the solutions.     

Storage Proteins of Glandless Cottonseed Flour

The salt-soluble storage protein isolate of defatted glandless cottonseed flour was separated by gel filtration column chromatography into six fractions (I to VI). Column and thin-layer gel filtration showed that these fractions had molecular weights of >600,000, 280,000, 127,000, 63,500, 10,700, and <2,000, respectively. Treating fraction I protein with dilute alkali dissociated a component that migrated upon gel filtration with fraction VI. Both fractions I and VI were yellow and the color intensified at alkaline pH, suggesting the presence of bound flavonol and gossypol pigments. Because of its large size and low (16.6%) protein content, fraction I was thought to be fragments of membrane and aleurone gram globulins. Gradient polyacrylamide gel electrophoresis (PAGE) showed that the proteins in each fraction being completely recovered from column chromatography were represented in the pattern of the initial isolate. The proteins in fractions II and III have similar ammo acid compositions, except that III is low in methionine, cystine and tryptophan and II is low in tyrosine and phenylalanine. The amino acid composition of fraction I was also similar to fractions II and III, while unique patterns were noted for fractions V and VI. Fraction VI was rich in lysine and arginine.     

Detection of Mustard, Egg, Milk, and Gluten in Salad Dressing Using Enzyme-Linked Immunosorbent Assays (ELISAs)

ABSTRACT:  Enzyme-linked immunosorbent assay (ELISA) is a commonly used method for the detection of trace amounts of potentially allergenic protein residues in foods. However, food matrices and processing conditions can affect the detection of protein residues. The effects of acidity on the detectability of several allergenic proteins commonly found in salad dressing using ELISAs was investigated. First, recovery experiments were performed on salad dressing formulated with 0 to 1000 ppm mustard flour (mustard). The mean percent recovery for mustard from the salad dressing was only 7.7%± 1.6%. When the pH of the salad dressing was adjusted to pH 7 prior to spiking with mustard, recovery improved to 94.1%± 7.6%. However, if the pH was adjusted to pH 7 after spiking and extraction, the recovery was only 11.1%± 1.7%. When vinegar was spiked with mustard flour at pH 3, 3.5, and 4, detectability of mustard was lowest at pH 3. Basic extraction of mustard proteins from salad dressing did not improve the mustard detection. Acidic salad dressing matrices reduced the detectability of mustard by the mustard ELISA probably because of acid precipitation of mustard proteins that renders them insoluble and nonextractable. Commercial salad dressings containing 100 ppm (mg/kg) of egg, milk, or gluten were analyzed every 2 to 4 d for 90 d using 3 commercially available ELISAs. A decrease in the detection of the egg, milk, and gluten in the salad dressing upon storage was observed. Our study highlighted the importance of evaluating the utility of various ELISAs for specific food matrices and the recovery as a function of product storage.     

氧化咖啡酸交联乳清蛋白膜的物理性能

咖啡酸氧化后与乳清蛋白交联成膜,对膜的机械性能、吸水性能、浸出率及其浸出物分子质量进行测试。结果显示：氧化后的咖啡酸能够作为交联剂提高乳清蛋白膜拉伸强度、杨氏模量及膜材料的吸水率,但对膜的断裂伸长率没有显著影响。蛋白膜在pH 3～5的Mc Ilvaine缓冲液浸出率略微降低,而在pH 6和pH 7条件下则显著提高;SDS-PAGE实验表明,在pH 6时,浸出物主要是由二硫键支配的聚合物。     

亚临界水水解脱脂高温芝麻饼粕中蛋白与糖类研究

亚临界水是一种绿色化学反应介质,已经应用于农副产品加工。为拓展芝麻饼粕的利用途径,采用亚临界水将脱脂高温芝麻饼粕中的水不溶性蛋白与糖分别水解为水溶性小分子物质。以上清液中蛋白、多肽和氨基酸、还原糖浓度为指标,考察亚临界水温度、时间与pH对降解芝麻饼粕中蛋白与糖的影响。电泳结果显示亚临界水可以有效将因高温变性形成的高分子蛋白降解成低分子蛋白;亚临界水温度、加热时间与pH是芝麻蛋白和糖类水解的显著影响因素;选择适宜的亚临界水条件可以将原上清液中(0.08±0.01)mg/mL、(6.40±0.08)mg/mL、(1.2±0.1)μmol/L、(0.36±0.01)mg/mL的蛋白、多肽、氨基酸与还原糖浓度增加到(5.29±0.08)mg/mL、(22.28±0.05)mg/mL、(185.5±2.7)μmol/L和(4.28±0.12)mg/mL。     

Polysaccharides of Winged Beans (Psophocarpus tetragonolobus [L.] DC), Variety TPT-2

Variety TPT-2 contains little or no starch. Hot water extraction of defatted and partially deproteinized flour yielded soluble and insoluble polysaccharide fractions in yields of 11 and 28%, respectively. Fractional precipitation of the soluble polysaccharides yielded a predominant Fraction I and a minor Fraction II. Fraction I contained 96% polysaccharide. Fraction II and the insoluble fraction contained 81 and 72% polysaccharide, respectively, the remainder being protein, ash and lignin. Fraction I polysaccharide is predominantly (76%) galactan, but it also contains 18% uranic acid. The Fraction II polysaccharide appears to be predominantly arabinogalactan, but contains 15% uranic acid. Cellulose (41%), galactan (25%), xylan (14%) and acidic polysaccharides (15%) predominate in the insoluble polysaccharides.     

Effect of heat,rutin and disulfide bond reduction on in vitro pepsin digestibility of Chinese tartary buckwheat protein fractions

Protein fractions (albumin, globulin, prolamin and glutelin) were extracted from defatted tartary buckwheat flour. The in vitro pepsin digestibilities of the four protein fractions were different, and albumin was more susceptible to pepsin hydrolysis. The native structure of the four protein fractions may be destroyed by heat treatment, and the digestibilities were all improved significantly (P < 0.05). Adding rutin to the digestion mixture of the four fractions did not cause a decrease in pepsin digestibility, although it did cause a significant increase in certain instances (P < 0.05). Treatment with β-mercaptoethanol (2-ME) only caused a higher initial proteolysis rate and did not increase the final digestibility distinctly except for prolamin. After pepsin digestion, the remaining proteins of unhydrolyzed albumin, globulin, prolamin and glutelin (untreated) shared some similarities. They also exhibited a minor band at 20,000 Da and a broad band at 10,000–14,000 Da.