Protein extraction optimisation,characterisation, and functionalities of protein isolate from bitter melon (Momordica charantia) seed

Bitter melon seeds are a rich source of protein. Optimum conditions for protein extraction from the seeds, determined using a response surface design, were at a pH 9.0 and 1.3 M NaCl. Soy protein isolate (SPI) was included for comparison. Surface hydrophobicity of bitter melon seed protein isolate (BMSPI) (690) was significantly higher than that of SPI (399). Electrophoretograms of BMSPI showed bands at 40 and 55 kDa, and at 22, 25, and 35 kDa in non-reducing and reducing buffers, respectively. BMSPI had most of the essential amino acids and hence could be considered as a high quality protein. BMSPI had a single denaturation temperature (113.1 °C) while SPI had two denaturation temperatures (78.0 and 94.8 °C). The proteins exhibited U-shaped curves with solubilities ranging from 62.0% to 67.5% for BMSPI and 86.7% to 90.1% for SPI at pH ? 7.0. BMSPI had lower emulsifying activity (0.36 vs. 0.73), foaming capacity (39.6 vs. 61.0 ml), and foaming stability (21.5 vs. 25.5 min) than had SPI.     

Effect of Maillard‐based conjugation with dextran on the functional properties of lysozyme and casein

The purpose of this research was to find the best experimental conditions for glycosylation of lysozyme and casein with dextran, and to investigate the effect of glycosylation on the functional properties of these proteins. Glycosylation was performed by allowing proteins to react with dextran under Maillard reaction conditions. The extent of glycosylation was determined by sugar analysis, SDS‐PAGE, gel filtration and cation‐exchange chromatography. Glycosylation of lysozyme with a 1:5 weight ratio of protein to dextran, held at 60 °C for one week under a relative humidity of 79% resulted in coupling of 3.0 mole dextran to one mole lysozyme. In the case of casein, at 60 °C, 48 h and 79% relative humidity, 0.1 and 0.13 mole dextran was attached to one mole of casein when a weight ratio of protein to dextran of 1:5 and 1:7.5 was used, respectively. A decrease in the degree of glycosylation occurred when samples were incubated for 72 h. Enzymatic activity of glycosylated lysozyme was reduced by 20% compared with unmodified lysozyme (P < 0.05). Both proteins exhibited improved solubility at different pH values (3, 7 and 9), different temperatures (25, 40 and 60 °C) and increased heat stability, with a better emulsion activity and emulsion stability than with un‐modified proteins (P < 0.05). These changes might increase the applicability of lysozyme as a natural antimicrobial and casein as a protein ingredient in different food systems. Copyright © 2005 Society of Chemical Industry     

Trypsin Inhibitory Activity and Gel‐Enhancing Effect of Sarcoplasmic Proteins from Common Carp

Abstract: Proteinase inhibitory activity of sarcoplasmic protein (SP) extracted from common carp (Cyprinus carpio) muscle and its gel‐improving ability were investigated. SPs displayed 89% and 54% inhibitory activity toward trypsin at 40 and 65 °C, respectively. Protein bands with molecular mass of 69, 50, 44, 41, and 35 kDa appeared on trypsin inhibitory activity staining under nonreducing condition when incubated at 40 °C, while 2 protein bands at 54 and 35 kDa were observed at 65 °C. Addition of SP at 0.18 g protein/100 g increased textural properties of threadfin bream surimi gel. However, when SP was added in combination with various CaCl₂ concentrations (0.1% to 0.5%) it did not further improve textural properties as compared to the addition of SP alone. Retention of myosin heavy chain of threadfin bream surimi was greater with the addition of SP. These results indicated that the gel‐enhancing effect of common carp SP was due to the inhibitory activity toward endogenous trypsin‐like proteinases in threadfin bream surimi. Practical Application: Sarcoplasmic protein from common carp muscle could be used as a functional protein ingredient that minimizes muscle proteolysis and improves textural properties of surimi containing trypsin‐like endogenous proteinases.     

Ready-to-drink protein beverages: Effects of milk protein concentration and type on flavor

This study evaluated the role of protein concentration and milk protein ingredient [serum protein isolate (SPI), micellar casein concentrate (MCC), or milk protein concentrate (MPC)] on sensory properties of vanilla ready-to-drink (RTD) protein beverages. The RTD beverages were manufactured from 5 different liquid milk protein blends: 100% MCC, 100% MPC, 18:82 SPI:MCC, 50:50 SPI:MCC, and 50:50 SPI:MPC, at 2 different protein concentrations: 6.3% and 10.5% (wt/wt) protein (15 or 25 g of protein per 237 mL) with 0.5% (wt/wt) fat and 0.7% (wt/wt) lactose. Dipotassium phosphate, carrageenan, cellulose gum, sucralose, and vanilla flavor were included. Blended beverages were preheated to 60°C, homogenized (20.7 MPa), and cooled to 8°C. The beverages were then preheated to 90°C and ultrapasteurized (141°C, 3 s) by direct steam injection followed by vacuum cooling to 86°C and homogenized again (17.2 MPa first stage, 3.5 MPa second stage). Beverages were cooled to 8°C, filled into sanitized bottles, and stored at 4°C. Initial testing of RTD beverages included proximate analyses and aerobic plate count and coliform count. Volatile sulfur compounds and sensory properties were evaluated through 8-wk storage at 4°C. Astringency and sensory viscosity were higher and vanillin flavor was lower in beverages containing 10.5% protein compared with 6.3% protein, and sulfur/eggy flavor, astringency, and viscosity were higher, and sweet aromatic/vanillin flavor was lower in beverages with higher serum protein as a percentage of true protein within each protein content. Volatile compound analysis of headspace vanillin and sulfur compounds was consistent with sensory results: beverages with 50% serum protein as a percentage of true protein and 10.5% protein had the highest concentrations of sulfur volatiles and lower vanillin compared with other beverages. Sulfur volatiles and vanillin, as well as sulfur/eggy and sweet aromatic/vanillin flavors, decreased in all beverages with storage time. These results will enable manufacturers to select or optimize protein blends to better formulate RTD beverages to provide consumers with a protein beverage with high protein content and desired flavor and functional properties.     

Foaming Characteristics of Commercial Soy Protein Isolate as Influenced by Heat-Induced Aggregation

The foaming properties of commercial soy protein isolate subjected to different temperatures (20–90°C) were assessed. The results revealed that the solubility and surface hydrophobicity of a 5% (w/v) commercial soy protein isolate suspension increased with increasing temperature, which increased foaming capacity and reduced foaming stability. Commercial soy protein isolate supernatant (i.e., soluble fraction) had higher foaming capacity at low temperatures (20–50°C). A high content of commercial soy protein isolate soluble fraction increased foaming capacity but decreased foaming stability. The SDS-PAGE patterns and molecular weight distribution of commercial soy protein isolate revealed that there were soluble, large molecular weight aggregates (>400 kDa) formed mainly from A and B-11S polypeptides of commercial soy protein isolate via disulfide bonds. Additionally, some aggregates also dissociated into small polypeptides and subunits after heat treatment. Commercial soy protein isolate precipitate (i.e., insoluble fraction) had a high content of proline and cysteine, which probably contributed to the foaming stability of commercial soy protein isolate.     

Thermal transitions of melon seed proteins

The heat of denaturation of the protein in melon seed products was studied by differential scanning calorimetry. At a heating rate of 10°C/min, the protein in the raw seed, oil meal and flour showed endothermic transitions with the maximum heat input occurring at 160, 89 and 93°C, respectively. Comparison with isolated melon seed protein fractions indicated that these transitions corresponded to the denaturation of the reserve globulin. The enthalpies of denaturation were 11·3 ± 1·3, 10·5 ± 0·8 and 12·1 ± 0·8 J/g for the raw seed, oil meal and flour, respectively. The water-soluble protein and the glutelin fractions did not show any observable transitions. Milling and defatting processes did not appear to denature the glubulin. However, pH and salts in the suspending medium affected its thermal stability. The heat-induced aggregation of melon seed protein was also studied. Aggregation of the water-soluble protein began at 60°C and the globulin at 81°C. The hot paste viscosity of a 10% w/v dispersion of melon seed flour reached a maximum of 80 Brabender units at 83°C.     

A non-invasive method for the characterisation of milk protein foams by image analysis

An apparatus for the investigation of milk protein foams was introduced based on three jacket columns and exclusively image analysis. The method had a repetition coefficient <10%, and offered a high sample throughput and an expandable design. Sodium caseinate, micellar casein concentrate, whey protein isolate and whey protein concentrate foams were analysed as an application. Foaming properties depended on the protein, the composition of the preparations and the foaming conditions, e.g., stable foams at 20 °C were observed for micellar casein, while sodium caseinate showed a half-life of 22 min. At 50 °C, the stability of sodium caseinate decreased by about 70%. Additionally, a direct link between the foaming properties of sodium caseinate and its degree of enzymatic hydrolysis was found. No changes in foaming properties using Alcalase^® 2.5L occurred up to a degree of hydrolysis of about 3%, while higher degrees of hydrolysis led to decreased foaming properties.     

Effects of Preparative Processes on the Composition and Functional Properties of Protein Preparations from Candida utilis

Protein preparations were made from continuously grown Candida utilis cells using processes which included cell disruption, aqueous protein extraction, nucleic acid reduction, protein precipitation and freeze- or spray-drying. The composition of the preparations was in the range 48–57% crude protein and 2–11% RNA, depending on the procedures used for concentrating protein and reducing nucleic acid. Functional properties examined included water-binding capacity, emulsifying properties, nitrogen and protein solubility, fat absorption, foaming properties, and bulk density. No single yeast preparation was superior to the others in all properties tested. Although heating processes, and in particular heat shocking of cells at 68°C with subsequent incubation at 50–55°C, were generally detrimental to functional properties, no processing procedure always affected all functional properties in the same way. The functional properties of some of the yeast preparations were found to compare favorably with those of the standard reference proteins, soy protein isolate, and sodium caseinate.     

The preparation of an oligochitosan‐glycosylated and cross‐linked caseinate obtained by a microbial transglutaminase and its functional properties

A glycosylated and cross‐linked caseinate (GCC) with glucosamine amount of 4.74 g/kg protein was generated from caseinate and oligochitosan by a microbial transglutaminase. The applied temperature, pH and molar ratio of acyl donor/acceptor were 37 °C, 7.5 and 1:3, respectively; while caseinate concentration, transglutaminase addition and reaction time selected from single‐factor trials were 50 g/L, 10 kU/kg protein and 3 h, respectively. Electrophoretic analysis revealed the cross‐linking and glycosylation of caseinate. Compared with caseinate, GCC showed improved solubility in pH 4–11, higher digestibility in vitro and water binding capacity, about 3‐fold, but lower surface hydrophobicity and oil binding capacity (34%).     

鱼贝肌肉分离蛋白糖基化功能改性的研究与比较

分别对栉孔扇贝闭壳肌分离蛋白及鲤鱼肌肉分离蛋白进行基于糖基化的改性处理,以此探索分离鱼蛋白的功能改性机制,并比较无脊椎类与脊椎类不同蛋白源之间的差异。用碱溶出法制备分离蛋白,将分离蛋白的改性处理分为直接糖基化和间接糖基化。直接糖基化是将分离蛋白与葡萄糖混合后进行干法糖基化;间接糖基化则是将分离蛋白预先经过胰凝乳蛋白酶修饰,再与葡萄糖混合后的糖基化。二者糖基化反应条件一致,其中蛋白与糖质量比为1∶5,温度为60℃,相对湿度为65%,时间为6 h。以赖氨酸、果糖胺及吸光度为糖基化指标,同时结合十二烷基硫酸钠-聚丙烯酰胺凝胶电泳分析来检测糖基化效果;将乳化性和热稳定性作为糖基化产物功能特性的分析指标。研究发现,鲤鱼和扇贝分离蛋白6 h直接糖基化处理均显示了糖基化效果,赖氨酸分别下降59.89%和30.94%,果糖胺浓度分别为3.04 mmol/L和2.99 mmol/L,吸光度分别为0.000和0.084;肌球蛋白重链和肌动蛋白的电泳条带均发生上移;二者功能特性指标中的乳化性分别为14.08 m~2/g和16.44 m~2/g;与对照组26%和50%的下降率相比,糖基化处理组的热稳定性有改善,分别下降14%和28%。扇贝分离蛋白的直接糖基化和间接糖基化处理结果发现,胰凝乳蛋白酶的修饰明显促进糖基化效果,未修饰与修饰的分离蛋白比较,赖氨酸分别下降30.94%和67.64%,果糖胺浓度分别为2.99 mmol/L和5.72 mmol/L,吸光度分别增加265%和500%;蛋白各个组分条带均发生上移;二者功能特性指标中的乳化性分别增加33.11%和37.38%;热稳定性分别下降28%和3%。结果表明,相同条件下鱼类与贝类分离蛋白具有相似的糖基化特性;胰凝乳蛋白酶的修饰能够显著提高分离蛋白的糖基化效果。     

Effect of conjugation with glucosamine on the functional properties of lysozyme and casein

BACKGROUND: Modification with carbohydrates usually changes the functional properties of proteins. Such modification might make non‐conventional food proteins (such as plant and microbial proteins) more applicable for human consumption. The purpose of this research was to conjugate glucosamine to lysozyme and casein using a water‐soluble carbodiimide and to investigate the effect of conjugation on the functional properties of these proteins. RESULTS: Glycosylation with glucosamine converted casein to high‐molecular‐weight species which appeared as diffuse bands in sodium dodecyl sulfate polyacrylamide gel electrophoresis. Approximately 2 and 0.11 mol of glucosamine was attached to 1 mol of casein and lysozyme respectively. Both conjugated proteins exhibited improved solubility at different pHs (3 and 6) and different temperatures (25, 45 and 60 °C), increased heat stability and better emulsifying activity, emulsion stability and foaming capacity compared with the unmodified proteins (P < 0.05). CONCLUSION: These changes might increase the applicability of lysozyme as a natural antimicrobial and casein as a protein ingredient in different food systems. Copyright © 2008 Society of Chemical Industry     

β-葡聚糖糖基化对裸燕麦蛋白功能性质及抗氧化活性的影响

使用β-葡聚糖对裸燕麦蛋白进行糖基化处理,测定裸燕麦蛋白糖基化反应前后的功能性指标,观察糖基化改性过程中复合物的生成情况,分析糖基化改性作用机理,进行体外抗氧化实验。结果表明:在pH5、7、9、11环境中,糖基化反应后的裸燕麦蛋白溶解性均得到改善,pH5环境下提高了3.06倍,pH3~11范围内糖基化裸燕麦蛋白的起泡性提高明显,pH5环境下提高了5倍,在pH5环境下,糖基化裸燕麦蛋白的乳化性及乳化稳定性分别提高了2.48及2.59倍;SDS-PAGE凝胶电泳发现,糖基化改性后有大分子物质生成,内源荧光光谱分析表明糖基化反应过程中体系环境转向亲水性,红外光谱分析反映了蛋白与糖分子之间的共价结合,在圆二色谱中观察到糖基化反应改变了蛋白的二级结构;浓度为10 mg/mL时,糖基化裸燕麦蛋白DPPH·清除率是原蛋白的2.13倍,浓度为2.5 mg/mL时,糖基化裸燕麦蛋白ABTS+·清除率是原蛋白的2.09倍。裸燕麦蛋白与β-葡聚糖的糖基化反应改变了蛋白质的结构,复合物转向亲水性,功能性得到改善,且抗氧化活性也强于原裸燕麦蛋白。     

Thermal Gel Degradation (Modori) in Sardine Surimi Gels

Sardine (Sardina pilchardus) surimi gels set (50°C or 60°C), or set and cooked (50°C or 60°C + 90°C) for different times were studied in order to evaluate modori (thermal gel degradation). The texture data of the set gels were similar to data obtained previously in gels set at lower temperature that produced good kamaboko gels. However, in gels set at 50°C and 60°C modori occurred upon cooking. Microscopically the set gels exhibited globular aggregated structures that became more compact when modori occurred. Results suggested that at modori temperature protein-protein bonding caused massive protein coagulation preventing the formation of a fibrillar matrix upon cooking.     

Characterisation of wines and distilled spirits from melon (Cucumis melo L.)

Melon fermentation and distillation was studied with a view to produce melon spirits. Three different substrates were obtained from melon (Cucumis melo L.). Sugar concentration was around 60–70 g L^?1 and the pH between 4.6 and 5.2. The substrates were clarified and then fermented at one of two pH levels at 20 °C. A commercial Saccharomyces cerevisiae starter culture was used to obtain melon wines with an alcohol concentration of 3.8–5.8% (v/v). The melon wines were distilled in a distillation column to yield distillates with an alcohol content of 33–60% (v/v). The major volatiles in the melon wines and in the distillates were analysed by gas chromatography (GC). The results demonstrated that melon could be a good substrate of fermentation and distillation but also yielded significant differences in the volatiles analysed in the different melon wines and distillates obtained from the different substrates in the different conditions of the experiment. Fermentation pH greatly affected the methanol, acetaldehyde, and butanol contents and thus the final quality of the spirits produced.     

Lipid oxidation and colour in pressure‐ and heat‐treated minced chicken thighs

Lipid oxidation and colour in pressurised and heated chicken samples were evaluated. In a preliminary test, raw and overcooked (100 °C/60 min) minced chicken thighs were pressurised (500 MPa/50 °C/30 min). Samples were stored at 4 °C in contact with air. Thiobarbituric acid reactive substances (TBARS) were quantified at 1, 6 and 9 days. Pressure induced oxidation in chicken, but overcooking generated many more secondary oxidation compounds. In a second experiment, raw minced chicken thighs were pressurised (500 MPa/?10, 5, 20 and 50 °C/30 and 60 min) or cooked (90 °C/15 min). Samples were vacuum stored at 4 °C. TBARS were measured at 1 and 9 days, whereas colour parameters (L, a, b and ΔE) were determined at 1 day. No differences in TBARS values were observed between untreated and pressurised samples, whereas cooked samples presented the highest values. Pressurisation for 30 and 60 min generated similar TBARS contents. At 9 days, oxidation values did not increase. Pressurisation and cooking induced marked colour changes. Pressurised samples were lighter and less red than untreated ones. Samples pressurised at 50 °C were the palest and, together with cooked samples, presented the lowest a values. Therefore pressurised chicken thigh cannot be marketed as a fresh product but can be incorporated as an ingredient in ready‐to‐eat meals. Copyright © 2004 Society of Chemical Industry     

Rheological,gelling and emulsifying properties of a glycosylated and cross‐linked caseinate generated by transglutaminase

The impacts of oligochitosan glycosylation and cross‐linking on some properties of a commercial caseinate were investigated in this study. The glycosylated and cross‐linked caseinate with glucosamine content of 4.74 g kg^?1 protein was generated by transglutaminase (TGase) and oligochitosan at pH 7.5 and 37 °C, with fixed substrate molar ratio of 1:3 (acyl donor to glucosamine acceptor), caseinate content of 50 g L^?1, TGase of 10 kU kg^?1 protein and reaction time of 3 h, respectively. In comparison with the caseinate, the glycosylated and cross‐linked caseinate had decreased reactable amino groups (0.58 vs. 0.51 mol kg^?1 protein), higher apparent viscosity, decreased emulsifying activity index (about 14.5%) and statistically unchanged emulsion stability index (92.6 vs. 90.5%). Based on the mechanical spectra of the acid‐induced gels, the glycosylated and cross‐linked caseinate showed shorter gelation time (95 vs. 200 or 220 min) than the caseinate or cross‐linked caseinate. The gels prepared from the glycosylated and cross‐linked caseinate also had enhanced hardness, springiness and cohesiveness. The results indicated that TGase‐mediated oligochitosan glycosylation and cross‐linking has the potential to obtain new protein ingredients.     

Effect of Heat Processing of Dried Egg White on In Vitro Iron Bioavailability

Egg white (EW) was desugared, adjusted to either pH 7 or pH 9, and freeze-dried. Portions were held at 25°, 50°, 60°, 70° or 80°C for 1 wk. In vitro iron bioavailability (IVIB) was estimated by the method of Kane and Miller (1984) and no differences in IVIB were observed due to EW pH. IVIB of EW held at 50°, 60°, or 70°C was not different (P>0.05) than that of EW held at 25°C [9.87% dialyzable iron (DI)]; only the 80°C treatment led to IVIB lower (6.76% DI, P<0.05) than the 25°C control. Differential scanning calorimetry and nondissociating electrophoresis showed that native protein structure, including that of the iron-binding protein ovotransferrin, was maintained after the 70°C treatment but not after the 80°C treatment.     

PARTIAL PURIFICATION AND CHARACTERIZATION OF PEACH PECTINESTERASE

Pectinesterase (EC 3.1.1.11) was extracted from peaches (Prunus persica) and partially purified by preparative free solution isoelectric focusing. On SDS-PAGE gels, protein bands at 36.3 and 33.9 kilodaltons represented the major bands; minor bands were observed at 108.4, 40.7, and 17.0 kilodaltons. The pH optimum for pectinesterase activity in the partially purified extract was 8.0. The enzyme was stable at 30°C for 30 min between pH values of 5 and 8. Peach pectinesterase is stable when heated at 55°C for 5 min in 0.1 M NaCl, 50 mM sodium phosphate, pH 7, buffer. However, residual activity decreased to 23% of 65°C for 5 min and was inactivated at 70°C for 5 min. The energy of activation of peach pectinesterase was determined to be 34, 600 J/mol °K. The Q₁₀ between 30°C and 60°C was estimated to be 1.5–1.6.     

Canavalia ensiformis Tailing Starch: A Functional Source of Dietary Fiber

Physicochemical and functional characteristics of the tailing starch isolated from the legume Canavalia ensiformis were determined. Proximal composition was 2.86% protein, 4.05% fiber, 0.37% fat, 1.51% ash and 91.33% carbohydrates as nitrogen‐free extract. Total dietary fiber content was 21.3%, soluble fiber was 2.2%, and insoluble fiber was 19.1% as determined by the Prosky method. Amylose content as quantified by differential scanning calorimetry (DSC) was 39.35%. Gelatinization temperature range as determined by DSC was from 77.9 °C to 88.1 °C, with 81.6 °C being the peak temperature. Transition enthalpy was 10.1 J/g. Swelling power ranged from 4.36 g water/g starch at 60 °C to 11.87 g water/g starch at 90 °C. Water solubility, analyzed within the same temperature interval, ranged from 3.29% to 16.93%. Water absorption capacity was 4.22 g water/g starch at 60 °C and 10.33 g water/g starch at 90 °C. Syneresis in a 6% gel stored at 4 °C for 24 h was 25.66 mL water/50 mL gel. Clarity, expressed as transmittance, was 10.46%. Initial pasting temperature was 93 °C, breakdown was —22 Brabender Units (BU), consistency was ‐5 BU, and setback was 17 BU.     

Influence of Oven-Drying Temperature on Physicochemical and Functional Properties of Date Fibre Concentrates

Agri-food by-products rich in dietary fibres may be used as feeds and health foods. Owing to its high fibre content, date flesh could be useful in human nutrition. It is interesting to study the influence of oven-drying temperatures of date fibre concentrates (DFC) on their physicochemical and functional properties for possible use as a potential fibre source in the enrichment of food. DFC from 11 Tunisian date cultivars were dried at different temperatures (40, 50 and 60 °C) and analysed regarding proximate composition (moisture, ash, protein and lipids), physicochemical (water activity (a _w), pH) and functional properties (water holding capacity (WHC), swelling capacity (SC), oil holding capacity (OHC) and emulsifying capacity (EC)). DFC dried at different temperatures showed interesting functional characteristics such as hydration properties, high OHC (2.73–4.60 g oil/g dry fibre) and EC (5.93–12.87%) values. Although drying temperatures promoted little modifications affecting the physicochemical properties of DFC, significant decreases in WHC, SC and EC of DFC were noticed at the highest temperature (60 °C) for most of the date varieties. The observed influence of drying temperature on functional DFC properties calls for the use of low temperature in order to obtain DFC as suitable food ingredient.