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•A facile strategy is proposed to develop pH-responsive films of PVA/PAA-AEP.•pH-responsive behavior is associated with protonation/deprotonation of PAA.•Kinetics of swelling of ...matrix and release of AEP are elucidated.•pH decrease changes predominant release from polymer relaxation to Fick diffusion.•Prolonging the shelf-life of pork (TVB-N < 25 mg/100 g) by 4 days at 25 °C.
This study demonstrates a pH-responsive antibacterial film based on polyvinyl alcohol/poly (acrylic acid) incorporated with aminoethyl-phloretin (PVA/PAA-AEP) for intelligent food packaging. The thermal, mechanical, barrier and light transmittance properties of PVA/PAA are enhanced by PAA presence of ≤6%. The interactions between PVA and PAA were hydrogen and ester bonds. The pH-responsive characteristic is dependent on the protonation/deprotonation tendency of the carboxylic groups on PAA in acidic/alkaline environment. The PVA/PAA3 is selected for the incorporation of AEP and its pH-responsive swelling follows Ritger-Peppas and Schott second-order models. The AEP is hydrogen bonded with the matrix of PVA/PAA3 and the release of AEP is pH-responsive and a rate-limiting step following the First-order model. With pH decrease, the predominant release control was gradually changing from polymer relaxation to Fick diffusion. The PVA/PAA3-AEP films demonstrate AEP content dependent antioxidant and antimicrobial activities. Furthermore, the antibacterial efficiency against Listeria monocytogenes and Staphylococcus aureus is significantly better than Escherichia coli. The target film PVA/PAA3-AEP3 can effectively prolong the shelf-life of pork (TVB-N < 25 mg/100 g) by 4 days at 25 °C, suggesting its great potential in intelligent food packaging.
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•The gel strength decreased significantly as olive oil contents increased.•Ultrasound improved the gelation properties of low-oil (≤3 g/100 g) surimi gels.•Ultrasound hardly ...compensated for poor microstructures of high-oil (4–5 g/100 g) surimi gels.•Ultrasound-assisted heating altered protein secondary structure and intensified non-covalent bonds.
This study was conducted to evaluate the effects of extra virgin olive (EVO) oil incorporation on the physicochemical properties and microstructure of surimi gels subjected to ultrasound-assisted water-bath heating. As the oil content was increased from 0 to 5 g/100 g, the breaking force and gel strength of the surimi gels significantly decreased, while the whiteness level exhibited the opposite tendency irrespective of the heating method. Compared with the traditional water-bath heating method, the ultrasonic heating promoted the unfolding of the α-helix structure and intensified the formation of β-sheet content and non-covalent bonds (ionic bonds, hydrogen bonds, and disulfide bonds), especially disulfide bonds, which contributed to the further crosslinking of the proteins and to gelation, thereby improving the gels’ strength. In addition, smaller cavities and compact microstructures were observed in the low-oil (≤3 g/100 g) surimi gels under ultrasonic treatment, which effectively prevented water migration in the gel network and resulted in a high water holding capacity and uniform water distribution. However, the ultrasonic treatment barely remedied the poor microstructures of the high-oil (>3 g/100 g) surimi gels owing to oil coalescence, which weakened the protein–protein interaction. In conclusion, ultrasonic treatment combined with water-bath heating significantly improved the gelation properties of the low-oil surimi gels, although it did not remarkably improve those of the high-oil gels. The choice of a suitable oil concentration could be of great importance for the production and functioning of surimi products via ultrasound-assisted treatments.
•The elasticity of the film was significantly improved by the incorporation of PVA.•WVP and OP were dependent on CS/PVA ratio.•Initial diffusion of Nisin could be well described by the Fickian ...equation.•pH, ionic strength, film composition and temperature affected Nisin diffusion.•Diffusion of Nisin from film was spontaneous and endothermic.
The aim of this study was to evaluate the kinetics and functional effectiveness of Nisin loaded chitosan/poly(vinyl alcohol) (Nisin–CS/PVA) as an antibacterial packaging film. The films were prepared by coating method and Staphylococcus aureus (S. aureus, ATCC6538) was used as test bacterium. The intermolecular hydrogen bonds between CS and PVA molecules were confirmed. The elasticity of films was significantly improved by the incorporation of PVA, and the film could also bear a relative high tensile strength at 26.7MPa for CS/PVA=1/1. As CS/PVA ratio decreased, the water vapor permeability (WVP) decreased and reached its minimum value 0.983×10−10gm−1s−1 at CS/PVA=1/1, meanwhile, oxygen permeability (OP) increased but still lower than 0.91cm3μmm−2d−1kPa−1 for CS/PVA=1/1 as the CS/PVA ratio was above 1:1. The initial diffusion of nisin (Mt/M∞<2/3) from CS/PVA film could be well described by the Fickian diffusion equation. Owing to the positively charged nisin at pH below isoelectric point (pI, 8.8) and its increasing dissolubility in water as the pH reduced, the diffusion of nisin from the films strongly depended on pH and ionic strength besides CS/PVA ratio and temperature. Moreover, the thermodynamic parameters suggested the spontaneous and endothermic diffusion of nisin from the films. The resulting data can provide some valuable information for the design of film in structure and ingredient.
The effect of biodiesel fuel made from rapeseed oil and methanol on the corrosion properties of copper, mild carbon steel, aluminum, and stainless steel was studied and compared with those of ...commercial diesel fuel. The results show that the metals mentioned above corroded with variable degrees as they were immersed in the biodiesel fuel at 43
°C for 60 days. Their corrosion rates were 0.02334, 0.01819, 0.00324, and 0.00087
mm/year, respectively. However, the corrosion rates of the metals immersed in commercial diesel fuel were relatively lower under the same corrosion conditions. The effects of biodiesel on the corrosion of copper and mild carbon steel were more significant than on aluminum and stainless steel. The corrosion process of metal surfaces in the biodiesel was mainly attributed to the chemical corrosion according to the experimental results with the help of SEM/EDS, AAS, and XPS.
► The effects of biodiesel and commercial diesel fuel on the corrosion properties of copper, mild carbon steel, aluminum, and stainless steel were compared. ► The corrosion rates of metals in biodiesel are higher those in commercial diesel fuel. ► The corrosion rates of copper, mild carbon steel, aluminum, and stainless steel in biodiesel were decreased in order. ► The corrosion process of metal surfaces in the biodiesel was mainly attributed to the chemical corrosion.
Saccharomyces cerevisiae generally consumes glucose to produce ethanol accompanied by the main by-products of glycerol, acetic acid, and lactic acid. The minimization of the formation of by-products ...in S. cerevisiae was an effective way to improve the economic viability of the bioethanol industry. In this study, S. cerevisiae GPD2, FPS1, ADH2, and DLD3 genes were knocked out by the Clustered Regularly Interspaced Short Palindromic Repeats Cas9 (CRISPR-Cas9) approach. The mechanism of gene deletion affecting ethanol metabolism was further elucidated based on metabolic flux and transcriptomics approaches. The engineered S. cerevisiae with gene deletion of GPD2, FPS1, ADH2, and DLD3 was constructed by the CRISPR-Cas9 approach. The ethanol content of engineered S. cerevisiae GPD2 Delta FPS1 Delta ADH2 Delta DLD3 Delta increased by 18.58% with the decrease of glycerol, acetic acid, and lactic acid contents by 22.32, 8.87, and 16.82%, respectively. The metabolic flux analysis indicated that the carbon flux r.sub.ethanol in engineered strain increased from 60.969 to 63.379. The sequencing-based RNA-Seq transcriptomics represented 472 differential expression genes (DEGs) were identified in engineered S. cerevisiae, in which 195 and 277 genes were significantly up-regulated and down-regulated, respectively. The enriched pathways of up-regulated genes were mainly involved in the energy metabolism of carbohydrates, while the down-regulated genes were mainly enriched in acid metabolic pathways. The yield of ethanol in engineered S. cerevisiae increased with the decrease of the by-products including glycerol, acetic acid, and lactic acid. The deletion of genes GPD2, FPS1, ADH2, and DLD3 resulted in the redirection of carbon flux.
•The acid-soluble collagen (ACS) was extracted from four different sources.•The extraction yield and efficiency of fish skin collagen were high.•There were slight differences in physicochemical ...properties of four ACSs.•The thermal stability of ASC from land animals was higher than from fish skin.
The acid-soluble collagens (ASC) extracted from the skins of walleye pollock and silver carp were compared with ASCs from skins of duck and pig in physicochemical properties. The dry weight extraction rates of ASCs from walleye pollock and silver carp were 14.10 % and 10.30 %, which were significantly higher than those of pig and duck (4.53 % and 3.14 %). It was found that the ASCs from skins of pig, walleye pollock and silver carp were all type I collagen with intact triple helix structure, while ASC from duck skin was a mixture of type I and type II collagen.The PI of the four ASCs was in the weakly acidic range (5.49–6.84), but ASCs from two fish skins were less thermally stable than that from pig and duck. The dynamic frequency scanning showed that collagen from porcine skin always maintained elastic behavior, while the other three ASCs changed from viscous behavior to elastic behavior with the increasing of frequency. The collagen from two fish skins had a less dense microstructure. The high extraction rate proved that two fish skins were high-quality raw materials for collagen, and the differences in physicochemical properties allowed fish skin collagen to have different applications than terrestrial animal collagen.
The development of lignocellulosic bioethanol plays an important role in the substitution of petrochemical energy and high-value utilization of agricultural wastes. The safe and stable expression of ...cellulase gene
was achieved by applying the clustered regularly interspaced short palindromic repeats-Cas9 approach to the integration of
expression cassette containing
glyceraldehyde-3-phosphate-dehydrogenase gene (
) promoter in the
chromosome. The target insertion site was found to be located in the
hexokinase 2 by designing a gRNA expression vector. The recombinant SESTC protein exhibited a size of approximately 44 kDa in the engineered
. By using orange peel as the fermentation substrate, the filter paper, endo-1,4-β-glucanase, exo-1,4-β-glucanase activities of the transformants were 1.06, 337.42, and 1.36 U/mL, which were 35.3-fold, 23.03-fold, and 17-fold higher than those from wild-type
, respectively. After 6 h treatment, approximately 20 g/L glucose was obtained. Under anaerobic conditions the highest ethanol concentration reached 7.53 g/L after 48 h fermentation and was 37.7-fold higher than that of wild-type
(0.2 g/L). The engineered strains may provide a valuable material for the development of lignocellulosic ethanol.
Properties, crystallization behavior and oxidative stabilities of enzymatically catalyzed interesterified fats were investigated in this study. Interesterified fats were catalyzed by Lipase Lipozyme ...RM IM, through reaction from beef tallow (BT), palm stearin (PS) and camellia oil (CO)under the mass ratio of 7.55: 2.45: 4 (BT: CO: PS) using 3.65% (w/w) of Lipozyme RM IM at 72.6°C for 3.85 h. After reaction, interesterified fats with 36.8°C sliding melting point (SMP) was obtained. Physicochemical properties (fatty acid profile, triacylglycerol profile, solid fat content (SFC), melting and crystallization curve, polymorphic forms) of interesterified fats were characterized. Results proved that interesterified fats blends after interesterification were improved with desirable β’ type crystals and preferable SFC. Triacylglycerol constituent of interesterified fats displayed a decrease in OOO, PSS/SPS, LLL, SSS and increased in PSO/POS/SPO, POO/OPO, POP/PPO, PLO/PLP/PPL by comparison of physical blends without interesterification. Additionally, it is estimated that interesterified fats have a moderate antioxidative stability about 352 days-shelf life at 20°C through the traditional accelerated oxidation test. In conclusion, interesterified fats with desirable properties could be suitable for plastic fats use.
Aflatoxin B
1
(AFB
1
) contaminates rice during harvest or storage and causes a considerable risk to human and animal health. In this study,
Trametes versicolor
AFB
1
–degrading enzyme (TV–AFB
1
D) ...gene recombinantly expressed in engineered
E. coli
BL21 (DE3) and
Saccharomyces cerevisiae
. The TV–AFB
1
D enzymatic characteristics and AFB
1
degradation efficiency in contaminated rice were investigated. Results showed that the size of recombinant TV-AFB
1
D expressing in
E. coli
BL21 (DE3) and
S. cerevisiae
was appropriately 77 KDa. The kinetic equation of TV-AFB
1
D was
y
= 0.01671
x
+ 1.80756 (
R
2
= 0.994,
K
m
= 9.24 mM, and
V
max
= 553.23 mM/min). The
Kcat
and
Kcat
/
K
m
values of TV-AFB
1
D were 0.07392 (s
−1
) and 8 M
−1
s
−1
, respectively. The AFB
1
concentration of contaminated rice decreased from 100 μg/ml to 32.6 μg/ml after treatment at 32°C for 5 h under the catabolism of TV-AFB
1
D.
S. cerevisiae
engineered strains carrying aldehyde oxidase 1 (
AOX1
) and
Cauliflower mosaic virus
35 S (
CaMV
35 S) promoters caused the residual AFB
1
contents, respectively, decreased to 3.4 and 2.9 μg/g from the initial AFB
1
content of 7.4 μg/g after 24 h of fermentation using AFB
1
-contaminated rice as substrate. The AFB
1
degradation rates of
S. cerevisiae
engineered strains carrying
AOX1
and
CaMV
promoters were 54 and 61%, respectively. Engineered
S. cerevisiae
strains integrated with TV-AFB
1
D expression cassettes were developed to simultaneously degrade AFB
1
and produce ethanol using AFB
1
-contaminated rice as substrate. Thus, TV-AFB
1
D has significant application potential in the AFB
1
decomposition from contaminated agricultural products.
Aflatoxins seriously threaten the health of humans and animals due to their potential carcinogenic properties. Enzymatic degradation approach is an effective and environmentally friendly alternative ...that involves changing the structure of aflatoxins. In this study, Trametes versicolor aflatoxin B1-degrading enzyme gene (TV-AFB1D) was integrated into the genome of Pichia pastoris GS115 by homologous recombination approach. The recombinant TV-AFB1D was expressed in engineering P. pastoris with a size of approximately 77 kDa under the induction of methanol. The maximum activity of TV-AFB1D reached 17.5 U/mL after the induction of 0.8% ethanol (v/v) for 84 h at 28 °C. The AFB1 proportion of 75.9% was degraded using AFB1 standard sample after catalysis for 12 h. In addition, the AFB1 proportion was 48.5% using AFB1-contaminated peanuts after the catalysis for 18 h at 34 °C. The recombinant TV-AFB1D would have good practical application value in AFB1 degradation in food crops. This study provides an alternative degrading enzyme for the degradation of AFB1 in aflatoxin-contaminated grain and feed via enzymatic degradation approach.
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