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1.
The effect of limited hydrolysis was investigated on the physico‐chemical properties of soy protein isolate–maltodextrin (SPI‐Md) conjugate. The hydrolysates at a degree of hydrolysis (DH) of 1.8% showed much higher surface hydrophobicity (H0; 71.39 ± 3.60) than that of the SPI control (42.09 ± 2.17) and SPI‐Md conjugates (53.46 ± 2.74). Intrinsic fluorescence analysis demonstrated the unfolding of protein molecule and exposure of hydrophobic groups of SPI‐Md conjugate hydrolysates. As evidenced by far‐UV circular dichroism (CD) spectroscopy, the limited hydrolysis increased the unordered secondary structures of SPI‐Md conjugates. The denaturation temperature (Td) of SPI‐Md conjugate was significantly increased by subsequent limited hydrolysis from 102.53 ± 0.60 °C to 108.11 ± 0.61 °C at DH 1.8%. In particular, the emulsifying activity index (EAI) was improved notably after limited hydrolysis of DH 1.8% (147.76 ± 4.39 m2 g?1) compared with that of native SPI (88.90 ± 1.44 m2 g?1) and SPI‐Md conjugate (108.97 ± 1.45 m2 g?1).  相似文献   

2.
The effects of glycerol, sorbitol, xylitol and fructose plasticisers on water sorption, mechanical properties, water vapour permeability (WVP) and microstructure of pullulan–alginate–carboxymethycellulose (PAC) blend films were investigated. At low plasticiser concentrations (below 7% w/w dry basis), antiplasticisation effect was observed, causing an increase in tensile strength (TS) but a decrease in the equilibrium moisture content. As glycerol concentration increased from 0% to 7%, TS increased from 68.1 to 69.6 MPa, whereas equilibrium moisture contents at 0.84 aw decreased from 0.37 to 0.3 g H2O g?1 dry basis. At higher plasticiser concentrations (14–25% w/w), an opposite trend was observed on the PAC films, resulting in the reduction of TS and elevation of moisture content. Among the four plasticisers tested, the fructose‐plasticised films were the most brittle, showing the highest TS, but had the lowest elongation at break (EAB), WVP and equilibrium moisture content values than films plasticised with other polyols. On the other hand, glycerol resulted in the most flexible film structure, exhibiting opposite materials' properties as compared with the fructose‐plasticised films. For instance, at 25% (w/w) plasticiser concentration, EAB and WVP values of fructose‐plasticised films were 33.5% and 3.48 × 10?6 g m Pa?1 h?1 m?2, which were significantly lower than that of glycerol‐plasticised films (58.6% and 4.86 × 10?6 g m Pa?1 h?1 m?2, respectively). Scanning electron microscopy showed that the plasticised PCA films were less homogeneous and more porous than the unplasticised counterparts, indicating that plasticisers had an effect on the microstructural morphology of the film matrix.  相似文献   

3.
Active packaging film was developed by incorporating Lycium barbarum fruit extract (LFE) into chitosan. The effects of LFE on physicochemical properties of the chitosan/LFE films were evaluated. When the weight ratio of LFE to chitosan was increased from 0:1 to 1:1, DPPH (2,2‐diphenyl‐1‐picrylhydrazyl) free radical scavenging activity of the chitosan/LFE films increased near ten‐folds and reached up to 35.8%; water vapour permeability of the chitosan/LFE films decreased 43.0% from 5.67 g m mm?2 day?1 kPa?1, and water solubility decreased from 100% to 24.52% because of interactions between LFE and hydrophilic groups of chitosan confirmed by FTIR. However, the chitosan/LFE films became darker after LFE was incorporated. The pure chitosan film showed better tensile strength (23.19 MPa) and elongation at break (22.29%) than the chitosan/LFE films (15.52 MPa and 9.58% for the one with weight ratio of LFE to chitosan of 0.6:1).  相似文献   

4.
Pure zein films are known to be very hydrophobic, but are inappropriate for edible coating applications because of their brittle nature. In an attempt to improve the flexibility of these coatings, the influence of low concentrations of oleic acid (OA) as a plasticiser on mechanical, topographical and wetting properties of zein thin films was evaluated. Films were first obtained by casting from aqueous ethanol solutions with 4.0% in mass of zein and additions of 0%; 0.25%; 0.50%; and 1.0% (w/w) of OA. The results indicate an improvement in mechanical properties with increasing plasticiser leading to a reduction in the elastic modulus. An increase in the elongation at break has been observed, but with minor influence on tensile strength. All plasticised zein films have similar initial contact angle (approximately 69°) with a time‐dependent receding drop behaviour. An increase in plasticiser concentration increases film’s affinity towards water. As measured by atomic force microscopy, a consistent linear relation (R2 = 0.991) was estimated between film composition and surface adhesion and consequently on the hydrophilicity. Surface topography also varied with plasticiser addition, becoming smoother as the OA concentration increases. When tested as an edible coating on pears (Pyrus communis L.), a formulation with 0.25% wt of plasticiser achieved the best results in preserving the pear mass as measured during the evaluated storage time (12 days) at room temperature. A 0.5% concentration of plasticiser had no influence and higher amounts resulted in a reduction in fruit protection.  相似文献   

5.
The effect of inoculum level of Bifidobacterium animalis ssp. lactis BB‐12 probiotic strain and ripening period on the quality of dry‐cured neck was studied. The microbiological parameters (Enterobacteriaceae, LAB and TVC) and physicochemical attributes (pH value, aw, TBARS index, colour) were determined directly after fermentation at 15 °C for 3 weeks, after 6 and 12 months of ripening at 4 °C. The highest LAB count and a lower pH value were found in the meat inoculated with probiotic strain at 6.6 log cfu g?1 (B2) followed by inoculation with probiotic strain at 6.3 log cfu g?1 (B1). Level of inoculation had not had an influence on water activity, TBARS index and total colour parameters. Changes of fat oxidation during half‐year of ripening were limited in probiotic meat samples compared to naturally fermented control meat (C). Based on the results, it can be concluded that the most favourable physicochemical and microbiological parameters of the dry‐cured neck were obtained after 6 months of ripening. At that time, the Bifidobacterium BB‐12 at both levels is a good potential starter for meat fermentation.  相似文献   

6.
Sesame seed meal protein (SSMP)/nano‐clay composite films were prepared, and the physical properties of the films were determined. The SSMP film was prepared with 5 g of SSMP and 2 g of glycerol in 100 mL of film‐forming solution, and the tensile strength (TS), elongation (E) and water vapour permeability (WVP) of the SSMP film were 2.51 MP, 21.84% and 3.23 × 10?9 g m m?2s?1 Pa?1, respectively. Two types of nano‐clays were incorporated to enhance the physical properties of the SSMP film. The TSs of the SSMP film with 5% Cloisite Na+ and 7% Cloisite 10A were 6.32 and 5.76 MPa, respectively, and the WVPs of the SSMP nanocomposite films were 2.04 × 10?9 g m m?2s?1 Pa?1 compared with the SSMP film without nano‐clay, which was 3.23 × 10?9 g m m?2s?1 Pa?1. Therefore, these results indicate that the SSMP nanocomposite film can be applied in food packaging.  相似文献   

7.
Exopolysaccharides (EPS) excreted by lactic acid bacteria used in the dairy environment are either liberated into the medium (free EPS) or remain attached to the cells (capsular EPS). After batch fermentation of Streptococcus thermophilus ST‐143 at pH 6.0, three EPS fractions were isolated and purified: free EPS (EPSf), capsular‐derived EPS (EPScd) and the entire total EPS (EPStotal). EPSf and EPScd were uncharged, consisted of rhamnose, galactose, glucose and N‐glucosamine in different amounts and showed a molecular mass of 2.6 × 106 Da (EPSf) and, in case of EPScd, 7.4 × 103 Da and 1.4 × 105 Da in a ratio of 9: 1. Intrinsic viscosity of the polymers was 1.14 mL mg?1 (EPSf), 0.06 mL mg?1 (EPScd) but 1.23 mL mg?1 for EPStotal. The higher functionality of the entire EPS that was also observed in shear rheology measurements indicates that the presence of small capsular‐derived EPS facilitates the entanglement of the larger polymeric carbohydrates of the EPSf fraction.  相似文献   

8.
The extracellular α‐l ‐rhamnosidase has been purified by growing a new fungal strain Aspergillus awamori MTCC‐2879 in the liquid culture growth medium containing orange peel. The purification procedure involved ultrafiltration using PM‐10 membrane and anion‐exchange chromatography on diethyl amino ethyl cellulose. The purified enzyme gave single protein band in SDS‐PAGE analysis corresponding to molecular mass 75.0 kDa. The native PAGE analysis of the purified enzyme also gave a single protein band, confirming the purity of the enzyme. The Km and Vmax values of the enzyme for p‐nitrophenyl‐α‐l ‐rhamnopyranoside were 0.62 mm and 27.06 μmole min?1 mg?1, respectively, yielding kcat and kcat/km values 39.90 s?1 and 54.70 mm ?1 s?1, respectively. The enzyme had an optimum pH of 7.0 and optimum temperature of 60 °C. The activation energy for the thermal denaturation of the enzyme was 35.65 kJ?1 mol?1 K?1. The purified enzyme can be used for specifically cleaving terminal α‐l ‐rhamnose from the natural glycosides, thereby contributing to the preparation of pharmaceutically important compounds like prunin and l ‐rhamnose.  相似文献   

9.
Polyphenolic‐rich fraction obtained from locally produced dry ginger powder in Brahmaputra valley, India, and commercially available dry ginger (Zingiber officinale) rhizome powder consisted of [6]‐gingerol (41.9%), [6]‐shogaol (24.3%), 1‐dehydro‐6‐gingerdione (8.6%), [8]‐gingerol (7.2%), [10]‐gingerol (5.1%), [6]‐paradol (5.9%) and [4]‐gingerol (3.6%). Traces of methyl‐[6]‐gingerol and methyl‐[8]‐gingerol (both at 1.8%) were also detected. The fraction exhibited high antioxidant capacity [total phenolics (TP), ferric reducing antioxidant power (FRAP), oxygen radical absorbance capacity (ORAC) and cellular antioxidant activity (CAA assay)], effectively inhibited isolated digestive enzymes (α‐glucosidase, pancreatic lipase and angiotensin converting enzyme) and inhibited the proliferation of colon (HT29; IC50 of 1.06 ± 0.02 mg mL?1) and gastric (AGS IC50 of 1.29 ± 0.03 mg mL?1) adenocarcinoma cells, without affecting the proliferation of their nontransformed counterparts (IC50 > 2.0 mg mL?1). This case study demonstrates that locally produced and commercially available dry ginger powder from Brahmaputra valley, India, retains numerous food components that may enhance human health.  相似文献   

10.
This study was undertaken to evaluate physicochemical (colour, protein content, ash content and zeta potential), structural (size exclusion chromatography and thermal properties) and film‐forming properties of kidney bean, field pea and amaranth protein isolates (KBPI, FPPI and AMPI, respectively). Protein content, ash content, zeta potential and denaturation temperature of the isolates ranged from 83.9 to 91.4%, 2.9 to 4.5%, ?37.3 to ?44.2 mV and 85.5 to 96.2 °C, respectively. Size exclusion chromatography revealed that globulins were prominent proteins in KBPI and FPPI, while AMPI contained both globulins and albumins as major fractions. FPPI showed the highest L* value (88.1), surface charge (zeta potential = –44.2 mV) and protein solubility (80.0–94.2%). Films were prepared from heated (90 °C for 20 min) and unheated protein dispersions of pH 7.0, 8.0 and 9.0 and evaluated for colour, opacity, tensile strength (TS), water‐solubilised matter (WSM) and water vapour permeability (WVP). FPPI films showed the most desirable properties in terms of the highest L* (87.5–90.5), TS (12.6–37.2 MPa) and the lowest opacity (7.1–8.4 A600/mm). FT‐IR spectroscopic analysis of the films revealed that alkaline pH and heat treatment unfolded protein molecules. Alkaline pH reduced opacity, while heat treatment improved TS and water resistance (decreased WSM and WVP) of protein films, which varied with the protein isolates.  相似文献   

11.
Fibre‐rich fractions were obtained from nodes of lotus root and micronised by nine different ball‐milling treatments. The optimum milling conditions were screened out by comparing its effects on physicochemical and hydration properties of micro‐sized particles of lotus node powder fraction (LNPF). The micronisation by ball‐milling treatments was carried out at different speeds (200–400 r min?1) and time (4–12 h). Ball‐milling treatments could effectively (< 0.05) pulverise the LNPF particles to different micro‐sizes. As particle size decreased, a redistribution of fibre components from insoluble to soluble fractions was observed. Furthermore, micronisation treatments, especially 12 h at 300 r min?1, could significantly (< 0.05) increase the hydration characteristics, as well as impart lightness in colour to different extents. Our findings suggested that micronisation can improve physicochemical and hydration characteristics of the fibre components, which provide an opportunity to improve the utilisation and application of lotus node dietary fibre.  相似文献   

12.
The interactions of digestive enzymes (pepsin, pancreatin) and milk proteins (β‐casein, β‐lactoglobulin (β‐Lg)) with (?)‐epigallocatechin gallate (EGCG), (?)‐epigallocatechin (EGC) and (?)‐epicatechin (EC) at gastric and intestinal pH were investigated by fluorescence spectroscopy. The results indicated that in the gastric environment, all three tea catechins showed binding affinities in descending order of strength with β‐casein first, followed by β‐Lg and then pepsin. The highest affinity was observed for EGCG–β‐casein, with a binding constant (KA) of 2.502(±0.201) × 105 m ?1. In the intestinal environment, the binding strengths of the proteins with EGCG and EGC were in the order β‐Lg > pancreatin > β‐casein; for binding with EC, the strength order was β‐casein > β‐Lg > pancreatin. The combination EGCG–β‐Lg had the strongest binding affinity, with a KA of 14.300(±0.997) × 105 m ?1. Thermodynamic analysis revealed that tea catechins complexed with milk proteins and digestive enzymes via different hydrophilic and hydrophobic interactions depending on the different digestion environments and types of catechins, proteins and enzymes.  相似文献   

13.
The effect of X‐ray irradiation on the quality of fresh‐cut, refrigerated purple‐fleshed sweet potato (PFSP) cubes was investigated. Packaged sweet potato cubes were treated with 0, 250, 500, 750 or 1000 Gy X‐ray irradiation and stored at 4 ± 1 °C for 14 days. After 14 days, total aerobic bacteria counts were 4.1 and 3.2 log10 CFU g?1, and mould–yeast counts were 3.3 and 3.0 log10 CFU g?1 in 750 and 1000 Gy treated samples, respectively. Doses up to 1000 Gy did not affect the firmness, moisture content and anthocyanin content of PFSP cubes throughout storage. PFSP cubes' flesh colour did not change during the first week of storage, but lightness (L*) increased after 14 days. Also, irradiation doses at 750 and 1000 Gy decreased saturation (C*) significantly, producing duller flesh colour than controls. Results indicate that X‐ray irradiation treatment at doses up to 1000 Gy can reduce microbial populations while maintaining the physical quality and anthocyanin content of PFSP cubes up to 14 days of storage.  相似文献   

14.
Isothermal unfolding studies for beta‐lactoglobulin (β‐Lg) usually apply a denaturation model suitable for a single submit protein. A method is described for correcting such results in retrospect. This leads to accurate estimates for the Gibbsfree energy of stabilization of native β‐Lg aimer. The denaturation of β‐Lg aimer is described by a dissociation coupled unfolding (DCU) process; Dimer → monomer → unfolded state. The Gibbs free energy change for DCU (ΔG°DCU) was 80 kJ mol?1 at pH 7 and 97 kJ mol?1 for β‐Lg at pH 2.6. With the addition of a range of salts (pH 6.85) then ΔG°DCU increased to 105 kJ mol?1. The literature is replete with denaturation studies employing β‐Lg as the principal protein. In many instances, it would be prudent to reevaluate stability data for β‐Lg in line with techniques outlined here.  相似文献   

15.
This study investigates the effects of fermentation conditions on the production of angiotensin‐converting enzyme inhibitory (ACE‐I) peptides in yogurt by Lactobacillus helveticus 881315 (L. helveticus) in the presence or absence of Flavourzyme®, which is derived from a mould, Aspergillus oryzae and used for protein hydrolysis in various industrial applications. Optimal conditions for peptides with the highest ACE‐I activity were 4% (v/w) inoculum size for 8 h without Flavourzyme® supplementation, and 1% inoculum size for 12 h when combined with Flavourzyme®. The yogurt fermented by L. helveticus resulted in IC50 values (concentration of inhibitor required to inhibit 50% of ACE activity under the assayed conditions) of 1.47 ± 0.04 and 16.91 ± 0.25 mg mL?1 with and without Flavourzyme® respectively. Seven fractions of ACE‐I peptides from the yogurt incorporated with L. helveticus and Flavourzyme® were separated using the preparative high‐performance liquid chromatography. Fraction (F3) showed the highest ACE‐I activity with an IC50 of 35.75 ± 5.48 μg mL?1. This study indicates that yogurt may be a valuable source of ACE‐I peptides, which may explain the outcomes observed in the experimental and clinical studies and foresee the application of fermented milk proteins into functional foods or dietary supplements.  相似文献   

16.
Abstract: Agar‐based nanocomposite films with different types of nanoclays, such as Cloisite Na+, Cloisite 30B, and Cloisite 20A, were prepared using a solvent casting method, and their tensile, water vapor barrier, and antimicrobial properties were tested. Tensile strength (TS), elongation at break (E), and water vapor permeability (WVP) of control agar film were 29.7 ± 1.7 MPa, 45.3 ± 9.6%, and (2.22 ± 0.19) × 10?9 g·m/m2·s·Pa, respectively. All the film properties tested, including transmittance, tensile properties, WVP, and X‐ray diffraction patterns, indicated that Cloisite Na+ was the most compatible with agar matrix. TS of the nanocomposite films prepared with 5% Cloisite Na+ increased by 18%, while WVP of the nanocomposite films decreased by 24% through nanoclay compounding. Among the agar/clay nanocomposite films tested, only agar/Cloisite 30B nanocomposite film showed a bacteriostatic function against Listeria monocytogenes.  相似文献   

17.
In this study, the physical properties of “wet” alginate films gelled with various divalent cations (Ba2+, Ca2+, Mg2+, Sr2+, and Zn2+) were explored. Additionally, the effect of adding NaCl to the alginate film‐forming solution prior to gelling was evaluated. Aside from Mg2+, all of the divalent cations were able to produce workable “wet” alginate films. Films gelled with BaCl2 (without added NaCl) had the highest (P < 0.05) tensile strength and Young's modulus while films gelled with CaCl2 (alone) had the highest puncture strength. The Zn‐alginate and Sr‐alginate films had the highest elongation at break values. Adding NaCl to the alginate film‐forming solution increased the viscosity of the solution. Films with added NaCl were less transparent and had lower tensile strength, elongation, and puncture strength than films formed without NaCl in the film‐forming solution. ATR‐FTIR results showed a slight shift in the asymmetric COO? vibrational peak of the alginate when the “wet” alginate films were gelled with Zn2+.  相似文献   

18.
The current study was aimed to study the shelf life of beef meat at refrigeration storage using novel chitosan derivative (Ch‐D). Chitosan was modified with antimicrobial monomethyl fumaric acid (MFA). The chemical structure of the resulting material was characterized by FT‐IR and HR‐XRD. The results confirmed the successful synthesis of conjugate sample. For the shelf life study, following lots were used: control (distilled water), chitosan 0.5%, Ch‐D 0.5%. The samples were kept at 4 °C for 16 days and analyzed at 4‐day intervals. Ch‐D treatment significantly reduced the total viable counts, enterobacteriaceae, lactic acid bacteria, psychrotrophic bacteria, and yeasts–moulds when compared with the chitosan and control during refrigeration storage. The peroxide value (PV) for Ch‐D was 0.19 ± 0.04 meq O2 kg?1 fat and chitosan was 0.21 ± 0.07 meq O2 kg?1 fat and showed no significant difference (< 0.05) at the end of the storage. Thiobarbituric acid reactive substance (TBARs) value for Ch‐D was 0.48 ± 0.02 mg MDA kg?1 and chitosan was 0.57 ± 0.09 mg MDA kg?1, while the carbonyl contents for Ch‐D was 3.16 ± 0.23 nm  mg?1 protein and chitosan was 3.11 ± 0.16 nm  mg?1 protein at 16 days of storage. Values for Ch‐D and chitosan treatments were significantly lower (< 0.05) for all the quality attributes as compared with the control throughout storage. At the end of storage, Ch‐D treatment showed a significant increase (< 0.05) in lightness (L* = 41.54 ± 0.09) and yellowness (b* = 2.23 ± 0.04). The redness for control was high (a* = 6.12 ± 0.09) as compared with the treated samples. Based primarily on microbial counts, Ch‐D treatment extended the shelf life of beef meat by about 8 days, maintaining acceptable quality attributes.  相似文献   

19.
The effects of combination treatment with aqueous chlorine dioxide (ClO2) and ultraviolet‐C (UV‐C) on the quality of yams were examined. Yam samples were treated with distilled water, 50 ppm aqueous ClO2, 5 kJ m?2 UV‐C or a combination of 50 ppm aqueous ClO2 and 5 kJ m?2 UV‐C. The microbiological analysis of the yams after aqueous ClO2 treatment, UV‐C irradiation or combination treatment indicated significant reductions in the populations of pre‐existing microorganisms. In particular, the combination treatment reduced the populations of total aerobic bacteria, yeast and mould, and coliform bacteria in the yams by 3.2, 3.4 and 3.8 log CFU g?1, respectively. The combination treatment also maintained the colour of the yams during storage. Sensory evaluation results indicated that the qualities of the yams treated with the combination of aqueous ClO2 and UV‐C were better than those of the other treatments. These results clearly indicate that combination treatment with aqueous ClO2 and UV‐C could be useful in improving the microbial safety and extending the shelf life of the yams.  相似文献   

20.
This study mainly evaluated the physical properties of kafirin‐quercetin (KQ) edible films and their application on the quality of cod fillets during cold storage. The results showed that the addition of quercetin significantly increased mechanical properties of KQ films, while decreased water vapor permeability, water solubility, and transparency. As quercetin was 0.4% (wt/vol), the film had the highest tensile strength (4.96 ± 1.23 MPa), the lowest water vapor permeability (1.08 ± 0.09 g·mm·m?2·h·KPa?1) and water solubility (22.02 ± 0.45%). Moreover, compared with the pure kafirin and polythylene films, KQ films could effectively inhibit the cod meat deterioration by restraining the growth of microorganisms and decreasing TVB‐N and TBARs. The KQ0.4% film was the best to prolong the shelf life of cod fillets during cold storage. Therefore, KQ edible films could be used as a potential food packaging material to protect and retain the quality of aquatic products.  相似文献   

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