壳聚糖/乳清蛋白复合可食性膜的物理性能研究

采用不同分子量壳聚糖(50,250,500,1 000kDa)与乳清蛋白成膜,以期获得具有不同功能性复合可食性膜。采用3%(m/V)壳聚糖乙酸溶液与12%(m/V)经过80℃/30min热变性的乳清蛋白溶液等体积混合,再加入2.4%(m/m,基于乳清蛋白质量)搅拌均匀后铺展成膜。通过对壳聚糖/乳清蛋白复合膜的厚度、穿刺强度、透光性和水化性能进行表征。结果表明,壳聚糖的分子量增加显著提高所成复合膜的厚度、降低穿刺强度、透明性以及吸水性,但能够显著提高对光线(特别是紫外光)的拦截;形态学分析以上这些变化主要归结于壳聚糖的分散性。     

Stability of the mechanical properties of edible films based on whey protein isolate during storage at different relative humidity

Formulations for whey protein isolate (WPI)-based films include low molecular weight plasticizers, which implies certain degree of instability of films properties due to plasticizer migration. The aim of this work was to study the effect of storage time on the mechanical properties of WPI films plasticized with two low molecular weight polyols: glycerol (Gly) and sorbitol (Sor). Films were stored inside cabins at 50% or 75% relative humidity (RH) and at room temperature. Mechanical properties and moisture content were measured at regular intervals for 30 weeks. The effect of plasticizer type and content and RH on mechanical properties right after equilibrium (1 week) was also included in this study.     

Water vapour permeability of edible bilayer films of wheat gluten and lipids

Various formulations and methods of fabricating edible bilayer films consisting of wheat gluten as a structural layer and a thin lipid layer as a moisture barrier were investigated and examined for water vapour permeability. Solid lipids such as beeswax or paraffin wax deposited in a molten state onto the base film were the most effective water vapour barriers. A film consisting of wheat gluten, glycerol and diacetyl tartaric ester of monoglyceride as one layer, and beeswax as the other yielded a water vapour permeability of 0.0048 g mm m⁻² mmHg⁻¹ 24h⁻¹, which was less than that obtained with low density polyethylene.     

Features and performance of edible films,obtained from whey protein isolate formulated with antimicrobial compounds

The goal of this research effort was to assess the efficacy of edible films produced from whey protein isolate (WPI) and glycerol, including incorporation of lactic acid (LA) and propionic acid (PRO), chitooligosaccharides with nominal MW of 3 kDa (COS) and natamycin (NA) as antimicrobial agents. Their features were evaluated in vitro via agar diffusion and viable cell counting, against spoilage microflora often found contaminating cheese surfaces. The effect of incorporating the aforementioned compounds upon thickness, moisture content (MC), solubility (S), density (ρ^s), water activity (a_w) and water vapor permeability (WVP), as well as upon tensile and optical properties of those films were also evaluated. Films formulated with LA, PRO or COS exhibited antimicrobial activity against all microorganisms tested, yet the viable cell count assay was more sensitive and reproducible. COS was the most active against Gram-negative bacteria, whereas LA was the most active against Gram-positive ones. NA was not active against bacteria, but displayed the strongest effect against yeasts. Incorporation of said antimicrobial compounds did not significantly (p > 0.05) affect film thickness, yet it significantly (p < 0.05) reduced tensile strength (TS). Incorporation of LA and NA in particular did not significantly (p < 0.05) affect MC, S, ρ^s, WVP, elongation at break (EB) and Young's modulus (YM) values; however, a statistically significant increase (p < 0.05) of MC, S and WVP, together with a statistically significant decrease (p < 0.05) of ρ^s were attained upon incorporation of PRO or COS. Moreover, PRO produced the highest variation (p < 0.05) in EB, TS and YM, whereas COS produced the highest change (p < 0.05) in optical properties.     

Use of edible films based on whey protein isolate to protect foods rich in polyunsaturated fatty acids

Whey protein isolate (WPI) films acting as oxygen barriers can be used to delay lipid oxidation in foods with high content in polyunsaturated fatty acids (PUFA). The aim of this work was to study as to what extent WPI films are capable of delaying lipid oxidation in vegetable oil, as an example of a food rich in PUFA. The effect of plasticizer type (glycerol or sorbitol) and content (30, 40, 50 and 60%), as well as film thickness (60, 100 and 180 μm) and relative humidity (50 or 75%) were analyzed. In order to evaluate the film protective capability, specially designed methacrylate cells and an accelerated test of oxidative rancidity were used. Results obtained showed that WPI films delayed the rancidity in vegetable oil. Films with sorbitol were more effective than films with glycerol, providing a protection as effective as aluminum foil. Both plasticizer content and film thickness affected its protective capacity significantly. The thickest films with the lowest plasticizer content provided the greatest protection against lipid oxidation. Plasticizer content affected film protection much more intensively than thickness. WPI films presented a more effective protection at 50% RH than at 75% RH.     

Influence of calcium on tensile, optical and water vapour permeability properties of sodium caseinate edible films

The influence of calcium on sodium caseinate edible films with and without lipid addition (oleic acid (OA)–beeswax (BW) mixtures) was investigated through the analysis of tensile, optical and water vapour barrier properties. Calcium was added by substitution of sodium caseinate by calcium caseinate. Calcium caseinate films have less transparency and more rigidity but they have lower water vapour permeability values than sodium caseinate films. The effect of substitution was different for films with and without lipids. Calcium caseinate increased tensile strength and decreased elongation of films, depending on the level of substitution and lipid presence. Among control films (without lipid), water vapour permeability was reduced when calcium caseinate was present, reaching values of 3.9 (±0.2) g mm kPa⁻¹ h⁻¹ m⁻². Nevertheless, in the films containing lipids, this reduction was inhibited when the level of sodium caseinate substitution exceeded 50%. Film transparency and gloss was reduced by calcium caseinate and lipid presence, although pure calcium caseinate films were glossier. When taking all the studied variables into account, the films prepared with 2:1 NaCas:CaCas ratio and 70:30 OA:BW ratio showed the most adequate properties.     

Effect of temperature,pH and film thickness on nisin release from antimicrobial whey protein isolate edible films

BACKGROUND: An active packaging film based on whey protein isolate (WPI) was developed by incorporating nisin to promote microbial food safety. The effect of temperature and pH on the release of nisin from edible films of different thickness was investigated. The film mechanical properties and inhibitory effect were also evaluated. RESULTS: Nisin release was significantly favoured by low pH, with the highest release after 24 h (1325 IU), which was not significantly affected by temperature (5 or 10 °C). Thickness significantly affected film elongation, with thicker films showing the highest elongation (54.3 ± 2.7%). Water vapour permeability (0.15 ± 0.4 g mm m^?2 kPa^?1 h^?1) and elastic modulus were not significantly affected by thickness. The highest nisin effective diffusivity (5.88 × 10^?14 m² s^?1) was obtained using a solution at pH 4, 112 µm film thickness and a temperature of 5 °C. More than four log cycles of Brochotrix thermosphacta were reduced from the surface of a ham sample after 8 days of incubation at 4 °C by the active WPI film containing 473 IU cm^?2 nisin. CONCLUSION: Nisin diffusivity from WPI edible films was favoured at lower pH and film thickness. This active packaging film may be used to preserve the quality and safety of meat products. Copyright © 2009 Society of Chemical Industry     

Effect of rice wax on water vapour permeability and sorption properties of edible pullulan films

Edible films were prepared using various ratios of pullulan and rice wax. Freestanding composite films were obtained with up to 46.4% rice wax. Water vapour barrier properties of the pullulan film were improved with increased addition of rice wax. Moisture sorption isotherms were also studied to examine the impact of rice wax on the water sorption characteristics of the film. The Brunauer–Emmet–Teller (BET) and Guggenheim–Anderson–de Boer (GAB) sorption models were tested to fit the experimental data. The models gave a good fit up to the water activity (a_w) of 0.55 for BET and a full range of a_w from 0.12 to 0.95 for GAB (R² ? 0.98). Changes in the sorption parameters, particularly such as the decrease in monolayer moisture content (Mo), reflect the trend of reduced hydration capacity with increased addition of rice wax, providing useful information on water activity conditions to achieve stability for the composite films.     

超声辐射对大豆分离蛋白膜性能的影响

研究了超声辐射在频率为20kHz,功率为800W条件下,不同处理时间对大豆分离蛋白膜性能的影响。结果表明,超声辐射对膜性能有明显的改善作用。经超声辐射处理2min可以显著提高膜的抗拉强度,相对于对照样提高了64.08%(P≤0.05);同时也明显降低了膜的水蒸汽透过系数,相对于对照样降低了25.70%(P≤0.05)。经超声处理后的膜机械强度和阻湿性能均得到了提高,同时具有均匀透明的外观。     

Antimicrobial activity of whey protein isolate edible films with essential oils against food spoilers and foodborne pathogens

The use of antimicrobial edible film is proposed as a means of improving food safety and extending the shelf-life of food systems by controlling the release of antimicrobials on food surfaces. In this work we first selected and studied 8 different essential oils (EOs) from plants, namely, oregano, clove, tea tree, coriander, mastic thyme, laurel, rosemary, and sage as natural antimicrobials against 2 gram-positive bacteria (Listeria innocua and Staphylococcus aureus) and 2 gram-negative bacteria (Salmonella enteritidis and Pseudomona fragi) by using the agar disk diffusion method. EOs from oregano, clove, and tea tree produced the largest surfaces of inhibition against the growth of the 4 bacterial strains tested. Second and following the assessment of compatibility, stable antimicrobial edible films based on whey protein isolate (WPI) with increasing concentrations (0.5% to 9%) of the 8 EOs were developed and tested for antimicrobial activity against the same gram-positive and gram-negative bacteria. WPI-edible films incorporating oregano or clove EO were found to have the most intense inhibitory effect of microbial growth. The bacterial strain gram-negative P. fragi presented the less susceptibility to the effect of those films. Moreover, only the edible films based on these 2 EOs were active against all 4 studied microorganisms. On the other hand, the edible films incorporating tea tree, coriander, mastic thyme, laurel, rosemary, or sage EOs even at high concentrations (7% to 9%) did not cause any antimicrobial effect against the pathogens S. aureus or S. enteritidis. PRACTICAL APPLICATION: Potential applications of this technology can introduce direct benefits to the food industry by improving safety and microbial product quality. The results of this research have direct application in the food industry with potential applications in various foodstuffs, including meat and poultry products where the control of spoilage bacteria such as P. fragi throughout their chilled storage or the improvement of food safety by controlling pathogens such as S. enteritidis are topics of particular interest for the industry.     

Study of the physical properties of whey protein: sericin protein-blended edible films

Effects of the sericin protein on the physical properties of the whey protein isolate film including the mechanical strength, water vapor permeability, light transmission, moisture content, solubility and swelling were investigated in the present work. The mechanical strength of the whey protein film could be reinforced with 0.1% sericin caused by the hydrogen bonding between the sericin and whey protein molecules. Excess addition of the sericin promoted sericin self-aggregation which made the network microstructure of the film heterogeneous and therefore reduced its mechanical strength. The water vapor permeability of the film decreased with the sericin content; in contrast, the other physical properties of the film such as the moisture content, solubility, swelling, light transmission and transparency were not be significantly affected under the present experimental conditions.     

Mechanical, water vapor barrier and thermal properties of gelatin based edible films

Edible films are thin materials based on a biopolymer. The objectives of this work were to determine the water vapor permeability and the mechanical and thermal properties of edible films based on bovine hide and pigskin gelatins. These films were prepared with 1 g of gelatin/100 ml of water; 15–65 g sorbitol/100 g gelatin; and at natural pH. The samples were conditioned at 58% relative humidity and 22°C for 4 days before testing. The mechanical properties were determined by the puncture test and the water vapor permeability by gravimetric method at 22°C. For DSC analysis, samples were conditioned over silica gel for 3 weeks. Samples (10 mg) were heated at 5°C/min, between −150 and 150°C in a DSC TA 2010. A second scan was run after cell cooling with liquid nitrogen. As expected, the puncture force decreased and the puncture deformation and water vapor permeability increased with the sorbitol content. The origin of gelatin was important only above 25 g sorbitol/100 g gelatin. The DSC traces obtained in the first scan of samples with 15–35 g sorbitol/100 g gelatin, showed a well visible glass transition followed by a sol–gel transition. However, with the increase of sorbitol concentration, the glass transition became broader, typical of the system presenting a phase separation. The model of Couchman and Karazs for ternary system, was used to predict the Tg values as a function of sorbitol concentration.     

热处理和碱处理对可食性大豆分离蛋白膜性能的影响

研究了热处理和碱处理对可食性大豆分离蛋白(SPI)膜性能的影响。对成膜液进行适当的加热和调节pH可以提高SPI膜的抗拉强度(TS)和伸长率(E),降低水蒸气透过系数(WVP)。调节成膜液的pH到9,在70℃加热20min,所得到的膜机械性能和阻湿性能最好。     

Mechanical and water vapour barrier properties of edible gellan films

Edible films based on gellan were developed. Of the plasticizers tested, glycerol was found to be the most suitable with respect to mechanical properties and transparency. The mechanical properties (tensile and puncture), water vapour permeability (WVP) and glass transition temperature (T_g) were examined for gellan films as a function of glycerol concentration. The lowest effective glycerol concentration was ∼60% (film dry weight basis); below this concentration, the films tended to be brittle and difficult to handle, whereas films with more than ∼75% glycerol tended to be sticky. Addition of glycerol to gellan films increased extensibility (tensile elongation and puncture deformation) moderately, but decreased tensile strength, elastic modulus and T_g, and increased WVP of the films. Increasing the a_w caused marked decreases in tensile strength and elastic modulus, but decreased tensile elongation only slightly. In general, tensile strength and elastic modulus appeared to be more sensitive to changes in glycerol content and a_w than puncture strength.     

Antimicrobial activity of whey protein based edible films incorporated with oregano,rosemary and garlic essential oils

The use of edible films to release antimicrobial constituents in food packaging is a form of active packaging. Antimicrobial properties of spice extracts are well known, however their application to edible films is limited. In this study, antimicrobial properties of whey protein isolate (WPI) films containing 1.0–4.0% (wt/vol) ratios of oregano, rosemary and garlic essential oils were tested against Escherichia coli O157:H7 (ATCC 35218), Staphylococcus aureus (ATCC 43300), Salmonella enteritidis (ATCC 13076), Listeria monocytogenes (NCTC 2167) and Lactobacillus plantarum (DSM 20174). Ten millilitres of molten hard agar was inoculated by 200 μl of bacterial cultures (colony count of 1 × 10⁸ CFU/ml) grown overnight in appropriate medium. Circular discs of WPI films containing spice extracts, prepared by casting method, were placed on a bacterial lawn. Zones of inhibition were measured after an incubation period. The film containing oregano essential oil was the most effective against these bacteria at 2% level than those containing garlic and rosemary extracts (P < 0.05). The use of rosemary essential oil incorporated into WPI films did not exhibit any antimicrobial activity whereas inhibitory effect of WPI film containing garlic essential oil was observed only at 3% and 4% level (P < 0.05). The results of this study suggested that the antimicrobial activity of some spice extracts were expressed in a WPI based edible film.     

SPI/MC关混可食膜的性能研究

研究了甲基纤维素(MC)对以甘油为增塑剂的大豆分离蛋白(SPI)膜物理性质的影响.结果表明:SPI膜的抗拉强度和表面疏水性随着MC添加量的增加而显著提高(P≤0.05),在添加量为20.0%(w/w,SPI)时相对于对照样分别提高了66.32%和25.39%;断裂伸长率随着MC添加量的增加而先增大后降低,在添加量为10.0%时最大;膜的透光率、水分含量、可溶性干物质总量和水蒸气透过系数随着MC添加量的增加而降低(P≤0.05),在添加量为20.0%时相对于对照样分别降低了41.58%、14.02%、26.55%和20.86%.     

Starch-gelatin edible films: Water vapor permeability and mechanical properties as affected by plasticizers

Physical and mechanical properties of edible films based on blends of sago starch and fish gelatin plasticized with glycerol or sorbitol (25%, w/w) were investigated. Film forming solutions of different ratios of sago starch to fish gelatin (1:0, 2:1, 3:1, 4:1, and 5:1) were used and cast at room temperature. Amylose content of sago starch was between 32 and 34% and the protein content of the fish gelatin was found to be 81.3%. The findings of this study showed that the addition of fish gelatin in starch solutions has a significant effect (p < 0.05), resulting in films with lower tensile strength (TS) and higher water vapor permeability (WVP). On the other hand, increasing protein content (from 10.9% to 21.6%) in film samples plasticized with sorbitol showed significantly lower (p < 0.05) TS but no trend was observed in % elongation-at-break (EAB) and no differences in WVP. However, TS decreased with higher protein content in the samples when either plasticizers were used in general, but no significance differences was observed among the samples (p < 0.05) with glycerol with exception to film with high protein content (21.6%) only and no trend was observed in % EAB among samples as well. Significant difference (p < 0.05) was observed in TS and viscosity between different formulations with sorbitol. The morphology study of the sago starch/fish gelatin films showed smoother surfaces with decreasing protein in the samples with either plasticizer. DSC scans showed that plasticizers and protein content incorporated with sago starch films reduced the glass transition temperature (T_g) and melting temperature (T_m) and the melting enthalpy (ΔH_m). In this study, observation of a single T_g is an indication of the compatibility of the sago starch and fish gelatin polymers to form films at the concentration levels used.