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%).     

Microstructure and model solute transport properties of transglutaminase‐induced soya protein gels: effect of enzyme dosage,protein composition and solute size

The diffusion of poly(ethylene glycol) (PEG) in transglutaminase (TGase) cross‐linked soya protein gels as affected by enzyme dosage and protein composition was investigated. PEG with different molecular weights (M_w) varying from 6000 to 400 000 g mol^?1 was selected. Results of this study revealed that the time‐related release of PEG from gel slices was found to be controlled by Fickian diffusion process. For PEG with M_w 6000 g mol^?1, the diffusion coefficients (D) were independent on the enzyme dosage and protein composition. However, for PEG with M_w ≥ 20 000 g mol^?1, there were strong dependences of diffusion on the solute size and on the gel network microstructure revealed by scanning electron microscopy (SEM), where more density gel network with smaller pores resulted in lower D of PEG. Lower D values of PEG with M_w ≥ 20 000 g mol^?1 were obtained in gels induced by 2 U g^?1 TGase, and the D values increased with increasing 11S ratio in gels. Moreover, data also showed that the diffusion of PEG with larger size was more sensitive to the variation of gel network.     

A study on the preparation and some functional properties of a cross‐linked casein–gelatin composite by a microbial transglutaminase

A microbial transglutaminase (TGase) was used in this work as biocatalyst to prepare a cross‐linked casein–gelatin composite, a modified protein product with 4‐hydroxyproline about 41 mg g^?1 peptides. Some cross‐linking conditions such as total protein content, the ratio of caseinate to gelatin and original pH were fixed at 5% (w/v), 4:1 (w/w) and 7.5, respectively. Other suitable conditions selected by single factor trials were TGase addition of 20 U g^?1 peptides, reaction temperature of 45 °C and reaction time of 4 h. Peptide profiles from SDS‐PAGE analysis showed the composite was peptide polymers. Compared to that of the original caseinate or the cross‐linked caseinate, the dispersion of the composite exhibited a markedly enhanced apparent viscosity, storage modulus and viscous modulus. Meanwhile, the composite also showed a better water holding capacity, unchanged oil binding capacity and lower enzymatic digestibility in vitro, conferring its applicability as a new protein ingredient.     

Gel‐enhancing effect and protein cross‐ linking ability of tilapia sarcoplasmic proteins

BACKGROUND: Tilapia (Oreochromis niloticus) sarcoplasmic proteins contain substantial transglutaminase (TGase) activity. The enzyme catalyzes the protein cross‐linking reaction, resulting in a more elastic gel. The objective was to investigate the gel‐enhancing effect of sarcoplasmic proteins from tilapia as related to TGase activity. RESULTS: Total TGase activity of sarcoplasmic proteins concentrate (SpC) increased about 3.6‐fold after ultrafiltration using 30 kDa membrane, but specific activity remained unchanged, indicating minimal TGase purification by ultrafiltration. Addition of 1 mg mL^?1 SpC containing 40 units TGase activity induced cross‐linking of tilapia actomyosin, and the extent of cross‐linking increased with added level of SpC. Myosin heavy chain (MHC) and troponin were preferably cross‐linked by tilapia SpC, while actin and tropomyosin were not affected. Higher retention of MHC was observed concomitantly with greater content of cross‐linked protein when SpC was added to lizardfish surimi. Lizardfish surimi with 10 g kg^?1 SpC added and pre‐incubated at 37 °C for 1 h exhibited 91.6% and 26.7% increase in breaking force and deformation, respectively, when compared to the control. CONCLUSIONS: Residual TGase activity in SpC played an important role in catalyzing the protein cross‐linking and enhancing actomyosin gelation. SpC could be a potential ingredient for improving textural properties of fish protein gel. Copyright © 2007 Society of Chemical Industry     

Impacts of glucosamine/oligochitosan glycation and cross‐linking by transglutaminase on the structure and in vitro antigenicity of whey proteins

With the fixed and selected conditions, whey protein concentrate (WPC) was glucosamine‐/oligochitosan‐glycated and cross‐linked by transglutaminase, resulting in glucosamine conjugation of 4.18–5.88 g/kg. Electrophoretic analysis showed cross‐linking and glycation of whey proteins, while circular dichroism analysis indicated that the two reactions contributed less ordered secondary structure to the two products. Enzyme‐linked immunosorbent assay results showed that the two products lost 64–95% antigenic responses of WPC, and oligochitosan was more powerful than glucosamine to reduce the responses. Rocket immuno‐electrophoretic analysis also evidenced antigenicity loss. This applied treatment is efficient to modify the structure and to decrease the allergenicity of whey proteins.     

A musty flavour defect in calcium caseinate due to chemical tainting by 2,4,6-tribromophenol and 2,4,6-tribromoanisole

A musty flavour defect in calcium caseinate that was due to tainting by 2,4,6-tribromoanisole (TBA) is described. The concentration of TBA in tainted calcium caseinate was between 2 and 560 μg kg^?1; substantially above the sensory threshold (0.02 μg kg^?1 in a 10% calcium caseinate solution). The TBA was derived from 2,4,6-tribromophenol (TBP) that had contaminated materials that were used in the calcium caseinate supply chain. TBP is readily converted to TBA by environmental fungi. Potential TBP sources identified in this investigation were timber shipping container floors, and slipsheets constructed from recycled plastics that were used for transporting stacks of calcium caseinate. The TBP sources identified were consistent with trends in the increased industrial use of this chemical in wood products and plastics.     

Rheological,thermal and sensory properties of whey protein concentrate/pectin‐fortified mashed potatoes made from dehydrated flakes

The effect of different amounts of whey protein concentrate (50–150 g kg^?1), low and high methoxyl pectin (5–15 g kg^?1) on the rheological, thermal, structural properties and sensory quality of mashed potatoes prepared from dried mashed potatoes flakes was investigated. The response surface technique was used to analyse the effects of whey protein concentrate and pectin simultaneously on the consistency index, flow behaviour index, apparent viscosity and Casson plastic viscosity. Both whey protein concentrate and pectin decreased the consistency of the mashed potatoes weakening its structure in all concentrations assayed. Results suggest that whey protein concentrate interacts with high methoxyl pectin through non‐covalent interactions. Based on the sensory evaluation results, up to 100 g kg^?1 whey protein concentrate with 15 g kg^?1 of low methoxyl pectin and 15 g kg^?1 of high methxyl pectin could be incorporated to dried mashed potatoes flakes without losing significantly the sensory quality of the product.     

Effect of antioxidants in combination of VCO nanoemulsion on gel properties and storage stability of refrigerated sardine surimi gel

Impacts of β-glucan–virgin coconut oil (VCO) nanoemulsion containing epigallocatechin gallate (EGCG) and α-tocopherol at levels of 0–3.0 g kg⁻¹ on properties and storage stability of surimi gel were investigated. Augmented breaking force, deformation and fracture constant were obtained in gels containing 2.0 g kg⁻¹ EGCG or 1.0 g kg⁻¹ α-tocopherol (P < 0.05). Expressible moisture content increased as EGCG levels were more than 2.0 g kg⁻¹. Smoother microstructure was observed in gels containing 2.0 g kg⁻¹ EGCG. Whiter gels were obtained when β-glucan–VCO nanoemulsion was incorporated. No change in protein pattern of gels was observed regardless of antioxidant incorporation. Viscoelastic moduli decreased as β-glucan–VCO nanoemulsion was added; however, incorporation of 2.0 g kg⁻¹ EGCG or 1.0 g kg⁻¹ α-tocopherol lowered the decrease in G'. β-glucan–VCO nanoemulsion containing gels had higher likeness scores than the control (P < 0.05). Gels containing EGCG and α-tocopherol at selected levels had the improved oxidative stability and lowered microbial loads.     

In vitro inhibitory effects of cranberry bean (Phaseolus vulgaris L.) extracts on aldose reductase, α‐glucosidase and α‐amylase

The in vitro inhibitory activities of different seed extracts prepared from cranberry bean mutant SA‐05 and its wild‐type variety Hwachia against aldose reductase, α‐glucosidase and α‐amylase were examined. The results indicated that the polyphenolics‐rich extracts obtained using 800 g kg^?1 methanol and 500 g kg^?1 ethanol demonstrated inhibitory activities against aldose reductase (IC₅₀ of 0.36–0.46 mg mL^?1) and α‐glucosidase (IC₅₀ of 1.32–1.94 mg mL^?1). The 500 g kg^?1 ethanol extracts also showed α‐amylase inhibitory activities (IC₅₀ of 70.11–80.22 μg mL^?1). Subsequent extracts, prepared further with NaCl and H₂O from precipitates of 800 g kg^?1 methanol or 500 g kg^?1 ethanol extracts, exhibited potent α‐amylase inhibitory activities (IC₅₀ of 17.68–38.68 μg mL^?1). A combination of 500 g kg^?1 ethanol extraction plus a subsequent H₂O extraction produced highest polyphenolics and α‐amylase inhibitors. The SA‐05 α‐amylase inhibitor extracts showed greater inhibitory activities than that of Hwachia. Thus, cranberry bean mutant SA‐05 is an advantageous choice for producing anti‐hyperglycaemic compounds.     

Antioxidant and hypoglycaemic effects of tilapia skin collagen peptide in mice

In this study, tilapia collagen peptide (TCP) was prepared by alcalase hydrolysis of tilapia skin, and the antioxidant and hypoglycaemic effects of TCP were investigated. The results showed that TCP possessed DPPH and ABTS+ free radicals‐scavenging activities. In diabetic mice in which diabetes was induced by injection of alloxan (50 mg kg^?1 bw), high‐dose TCP (1.7 g kg^?1 bw) and the drug metformin (1.0 g kg^?1 bw) were found to reduce 31.8% and 30.3% of blood glucose levels in 25 days, respectively. Moreover, in diabetic mice receiving high‐dose TCP, antioxidant enzymes SOD and CAT were increased by 23% and 59.2%, respectively, and MDA was decreased by 39.1%. Comparing the treated high‐dose TCP group with the metformin group, there were similar SOD (61.5 U mg^?1 vs. 60.2 U mg^?1) and MDA (1.4 nmol mg^?1 vs. 1.3 nmol mg^?1), but more (~7%) CAT (359.8 U g^?1 vs. 336.1 U g^?1). Together, the present data, for the first time, demonstrated that TCP possessed hypoglycaemic effects in mice.     

Exploitation of lettuce waste flour to increase bread functionality: effect on physical,nutritional, sensory properties and on consumer response

Phenol and fibre‐rich flour obtained by air‐drying and grinding of lettuce waste was partially substituted (26, 53, 170 and 575 g kg^?1) to wheat flour to produce functional bread. The addition of flour progressively decreased dough leavening capacity while increased bread moisture and firmness. Lettuce waste flour significantly increased the polyphenolic content (up to 3.4 g GAE kg^?1) of bread samples and enhanced their antioxidant activity by 200%. Bread containing 170 and 575 g kg^?1 of lettuce waste flour presented sensory properties and consumer acceptability comparable to those of commercial wholemeal bread with similar rye bran content. Bread containing at least 170 g kg^?1 of lettuce waste flour could be associated to nutritional claims related to its enhanced fibre content (>30 g kg^?1). Data obtained by conjoint analysis demonstrate the possibility of increasing consumer preference for lettuce waste flour bread by proper nutritional (fibre content) and sustainability (lettuce waste valorisation) claims.     

Hydration of casein micelles and caseinates: Implications for casein micelle structure

By studying the hydration of casein micelles using a variety of techniques, a distinction could be made between water that appeared bound by the protein (∼0.5 g g⁻¹ protein), water associated with the κ-casein brush (∼1.0 g g⁻¹ protein) and water entrapped in the casein micelles (∼1.8 g g⁻¹ protein), yielding a total micellar hydration of ∼3.3 g g⁻¹ protein, in line with casein micelle voluminosity derived from intrinsic viscosity measurements. For caseinate particles, however, the main contributor to intrinsic viscosity was not protein hydration but the non-spherical particle shape. These non-spherical particles in caseinate are likely to be naturally present as primary casein particles (PCP) in casein micelles. PCP could be used to build casein micelles by controlled introduction of micellar salts. Based on the findings of this study, casein micelles could be described as a porous network of non-spherical PCP linked by calcium phosphate nanoclusters.     

酶法糖基化修饰对酪蛋白体外消化能力的影响

利用转谷氨酰胺酶（transglutaminase,TGase）催化制备壳寡糖（1 kDa）糖基化酪蛋白;十二烷基硫酸钠-聚丙烯酰氨凝胶电泳和反相-高效液相色谱证实糖基化修饰反应的发生;体外消化实验（胃蛋白酶＋胰蛋白酶）分析糖基化修饰反应对酪蛋白消化性的影响。结果表明：TGase成功催化壳寡糖连接到酪蛋白分子上,所制备的糖基化酪蛋白中氨基葡萄糖的导入量为6.86 g/kg;糖基化酪蛋白经体外模拟消化后,其水解度和三氯乙酸可溶性氮均低于酪蛋白对照物,糖基化酪蛋白消化物中出现了更多大分子质量的肽段,研究表明TGase途径糖基化修饰降低了酪蛋白的体外消化能力。     

Validation of analytical method for α‐dicarbonyl compounds using gas chromatography–nitrogen phosphorous detector and their levels in alcoholic beverages

This study aimed to establish an analytical method for α‐dicarbonyl compounds (α‐DCs) including glyoxal, methylglyoxal and diacetyl, to determine the content of α‐DCs in 101 various alcoholic beverages using gas chromatography–nitrogen phosphorous detector (GC‐NPD) and to perform exposure assessment. The limit of detection and limit of quantification for α‐DCs were 0.05–0.22 and 0.15–0.70 μg g^?1, respectively. The accuracy and precision were validated in five matrices. The raspberry fruit wine had the highest value at 139.74 μg g^?1 total α‐DCs. The lowest α‐DC concentration among the beverages was detected in rice wine (Makgeolli) at 1.59 μg g^?1. The levels of α‐DCs in various samples were detected as follows: 1.59–56.68 μg g^?1 in rice wine (Makgeolli), 2.73–16.77 μg g^?1 in beer, 8.22–139.74 μg g^?1 in fruit wine and 8.17–91.56 μg g^?1 in rice wine (Cheongju). The estimated daily intake of α‐DCs in the intake‐only group and population group was calculated as 4.22–97.94 μg kg^?1 bw day^?1 and 0.28–7.13 μg kg^?1 bw day^?1, respectively.     

Quality and hygiene of beef burgers in relation to the addition of sodium ascorbate,sodium citrate and sodium acetate

We evaluated the effects of two additive mixtures (sodium ascorbate 1 g kg^?1, sodium citrate 1 g kg^?1 and sodium acetate 1.75 or 2.5 g kg^?1) on the microbiological and physical–chemical characteristics of non‐prepacked beef burgers stored in air at 4 °C or 12 °C for 96 h. Total microbial count reached 7 Log CFU g^?1 48 h later in treated samples at 4 °C. The mixture containing the higher acetate concentration led to a smaller increase in Gram‐negatives, in particular Pseudomonas (2 Log of difference towards control samples at 96 h); at 12 °C, a 1.7 Log difference in Enterobacteriaceae was also shown. Total viable basic nitrogen was significantly lower in the treated samples at 12 °C. The addition resulted in pH stabilisation and lower cooking loss and positively influenced the a* index of burgers at 4 °C. Clearly, the use of these mixtures should not be a substitute of good hygienic practices and optimal storage conditions.     

Effect of cross‐linking on some properties of potato (Solanum tuberosum L.) starches

Starches separated from different potato cultivars were modified using two different cross‐linking agents: epichlorohydrin (EPI) and phosphoryl chloride (POCl₃) at different concentrations (1.0 and 2.0 g kg^?1 POCl₃; 2.5, 5.0 and 10 g kg^?1 EPI). Differential scanning calorimetry, rheological and retrogradation measurements were performed to characterise the influence of cross‐linking on the properties of potato starches. Cross‐linking considerably reduced swelling power, solubility, water‐binding capacity and paste clarity. The decrease became greater as the reagent concentration increased. The starches treated with 1.0 g kg^?1 POCl₃ exhibited exceptionally higher swelling power than their counterpart native starches. Neither cross‐linking agent caused any change in morphology of the starch granules. Studies on the phase transitions associated with the gelatinisation showed significantly higher values for the onset temperature (T_o), peak temperature (T_p), conclusion temperature (T_c) and enthalpy of gelatinisation (ΔH_gel) for the cross‐linked starches than the native starches. Starches treated with both the reagents showed lower peak storage modulus (G′) and loss modulus (G″) than their native counterparts. The tendency of the starch pastes towards retrogradation increased considerably with increases in storage duration. However, the starches treated with 1 g kg^?1 POCl₃ exhibited much lower syneresis than the other cross‐linked starches. Copyright © 2006 Society of Chemical Industry     

Use of low‐voltage direct current electricity treatment to increase phenolics content of postharvest okra: effects of some treatment parameters

Low‐voltage direct current electricity was applied to increase phenolics content of postharvest okra (Abelmoschus esculentus L.) at different values of current (0.10–0.50 A) and application time (900–3600 s). Use of different electrolytes, namely tap water as well as 0.10‐ and 0.15‐mol L^?1 brine, was also investigated. Calcium‐dependent protein kinase was quantified to indicate responses of okra to the treatment. Free and bound phenolics contents were measured and the results used to confirm whether the increased phenolics was due to the applied electricity; initial contents of total, bound and free phenolics were noted to be 6.19, 1.73 and 4.46 g kg^?1, respectively. Total phenolics content (8.12–8.38 g kg^?1) significantly increased when using a current of 0.30 A, application time of 900–3600 s, with brine as the electrolytes. Use of current of 0.30 A and 0.10‐mol L^?1 brine for 900 s is suggested as the appropriate treatment condition.     

Development of antipeptide enzyme‐linked immunosorbent assay for determination of gelatin in confectionery products

The gelatin sources have become a controversial issue with regard to religious and health concern. Thus, the aims of this study were to develop and evaluate the efficiency of polyclonal antibodies against peptide immunogen of collagen α2 (I) chain for determination of gelatin sources in confectionery products by competitive indirect enzyme‐linked immunosorbent assay (ELISA). Collagen α2 (I) chain protein showed resistance against heat treatment and detectable in certain commercial products when analysed by sodium dodecyl sulphate–polyacrylamide gel electrophoresis (SDS‐PAGE). The established ELISA exhibited low cross‐reactivity to fish and chicken gelatin. The IC₅₀ value was 0.39 μg mL^?1, and the limit of detection (IC₁₀) was 0.05 μg mL^?1. There were no false‐positive results from forty‐eight commercially processed products. The present method is useful for determination of gelatin in confectionery products.     

Comparison between microwave hydrodiffusion and pressing for plum juice extraction

Microwave (MW) hydrodiffusion and gravity, a process initially developed for extraction of phytonutrients, can be adapted for production of an organoleptically pleasant juice, which is compared here with classically extracted juice.Clear and cloudy juices were produced from plums cv. ‘Najbolia’ by enzymatic treatment and pressing. Juice yield were 550 g kg^?1 for clear juice, from 670 to 684 g kg^?1 for cloudy juice with or without ascorbic acid (AA), and from 344 to 461 g kg^?1 for MW juice.MW juice was richest in procyanidins (334 mg kg^?1) while the cloudy juice and clear juice with AA were richest in anthocyans (80 and 90 mg kg^?1 respectively), and phenolic acids (from 450 to 510 mg kg^?1 respectively).The MW process was clearly more rapid and simpler, though yields were lower. This process could be an alternative to produce fruit juice where professionals of juice are confronted to extraction problem.     

Comparative study on protein cross-linking and gel enhancing effect of microbial transglutaminase on surimi from different fish

BACKGROUND: Microbial transglutaminase (MTGase) has been used to increase the gel strength of surimi. Nevertheless, its effectiveness varies with fish species. The aim of this study was to elucidate the effect of MTGase at different levels on protein cross‐linking and gel property of surimi from threadfin bream, Indian mackerel and sardine in the presence and absence of endogenous transglutaminase. RESULT: Breaking force of all surimi gels increased as MTGase levels (0–0.6 U g^?1) increased except for threadfin bream surimi gel, where the breaking force decreased at 0.6 U g^?1 (P < 0.05). In the presence of EDTA, the gel strengthening effect was lower, suggesting the combined effect of endogenous transglutaminase with MTGase. With the addition of MTGase, the gel with the highest increase in breaking force showed highest decrease in myosin heavy chain. When cross‐linking activity of MTGase on natural actomyosin (NAM) was determined, the highest decreasing rate in ε‐amino group content with the concomitant increased formation of cross‐linked proteins was found in NAM from threadfin bream. The reactivity of muscle proteins toward MTGase‐induced cross‐linking was in agreement with surimi gel strengthening. CONCLUSION: The composition and properties of muscle proteins of varying fish species more likely determined protein cross‐linking induced by MTGase, thereby affecting their gel properties. Copyright © 2011 Society of Chemical Industry