For the enhancement of protein’s bioavailability, a specific delivery system was developed by coaxial electrospinning. Bovine serum albumin (BSA) was used as protein model, and the core–sheath fiber mat was fabricated using sodium alginate as shell layer and the BSA-loaded chitosan nanoparticle that was prepared previously as core layer. By optimizing electrospinning parameters, uniform fibers with diameters ranging from 200–600 nm were obtained, and transmission electron microscopy and confocal laser scanning microscopy revealed their core–sheath structures. Fourier transform infrared spectroscopy (FTIR) analysis demonstrated that there existed molecular interaction between components, which enhanced the mat’s thermal stability and mechanic property. It was found that the predominant release mechanism of BSA from fiber mat was erosion, and little change occurred in the secondary structure of encapsulated BSA indicated by FTIR and circular dichroism analysis. The study shows that the obtained fiber mat is a potential delivery system for protein.Keywords: coaxial electrospinning; core−sheath fiber; protein; release kinetics; stability;

•Overview of electrospinning techniqueand its advantages.•Applications of electrospun biopolymer fibers in encapsulation of small molecules.•Applications of electrospunbiopolymer fibers in encapsulation of macromolecules.BackgroundBioactive compounds have gained increasing attention for their health benefits. However, the instability of bioactive compounds during food processing and storage, and low bioavailability or chemical instability when exposed to upper gastrointestinal tract conditions significantly compromised the envisioned benefits, thus limiting their applications. Electrospinning has been recognized as a promising method to encapsulate bioactive compounds since it does not involve any severe conditions of temperature, pressure, or harsh chemicals. Therefore, the nanofibers produced by electrospinning have attracted particular attention in food industry due to the potential as vehicle for the encapsulation and controlled delivery or release of bioactive compounds.Scope and approachElectrospinning is a novel delivery approach for bioactive compounds, it opens a new horizon in food technology with the possibility of commercialization in the near future. This paper presents a brief summary of electrospinning, and its application in encapsulation different types of bioactive compounds by biopolymer matrixes are also highlighted. Further, the existing limitations and scope for future research are discussed.Key findingsRecently, considerable studies have been carried out in encapsulation of bioactive compounds using electrospinning. The obtained nanofilm could enhance stability, encapsulation efficiency and oral bioavailability of bioactive compounds, as well as achieve targeted delivery and controlled release, thus facilitating the development of functional foods.

Essential oils (EOs) are effective antimicrobial agents against a variety of foodborne pathogens; however, their peculiar flavor limits their applications in food preservation. Smaller amounts of EOs in the packaging material are preferable, and a combination of EOs with other antimicrobial compounds can decrease the required dose of EOs while maintaining the appropriate antimicrobial activity. In this study, a novel antimicrobial electrospun nanofilm, namely polyvinyl alcohol/β-cyclodextrin/cinnamon essential oil/lysozyme (PVA/β-CD/CEO/LYS), was fabricated by the combination of CEO and LYS as an antimicrobial agent. The suitable CEO and LYS concentration were determined as 2% (w/w) and 0.25% (w/w), respectively. Attenuated total reflectance-Fourier transform infrared spectroscopy (ATR-FTIR) and thermogravimetric analysis (TGA) indicated the existence of a molecular interaction among PVA, β-CD, CEO, and LYS, which improved the thermal stability of CEO and LYS. Compared to the PVA/LYS and PVA/β-CD/CEO nanofilm with an individual antimicrobial agent, PVA/β-CD/CEO/LYS nanofilm exhibited stronger antibacterial activity against Listeria monocytogenes and Salmonella enteritidis. In addition, it exhibited an excellent antifungal activity against Aspergillus niger and Penicillium. Its minimum inhibition concentration (MIC) against L. monocytogenes and S. enteritidis was approximately 0.8–1 mg mL−1 (corresponding CEO concentration 7.6–9.5 μg mL−1 and LYS concentration 36–45 U mL−1) and minimum bactericidal concentration (MBC) was approximately 6–7 mg mL−1 (corresponding CEO concentration 57–66.5 μg mL−1 and LYS concentration 270–315 U mL−1). Therefore, the antimicrobial PVA/β-CD/CEO/LYS electrospun nanofilm has a potential for application in active food packaging.

In order to obtain good quality special fats for fast frozen food, blends of palm stearin (PS) and soybean oil (SO) (5 : 5, 6 : 4 and 7 : 3, PS : SO) were subjected to enzymatic interesterification in a fluidized bed reactor. The slip melting point of the interesterified blends thus obtained was 45 °C when the flow rates were 2.24, 1.57 and 0.40 mL min−1, respectively. After interesterification, the contents of SSS- and UUU-type TAGs decreased, whereas the contents of SUU-type TAGs increased. In addition, the β form crystal reduced and β′ form crystal increased due to the change in the type of TAGs. The solid fat content of the interesterified blends was 5–40% at 10–45 °C. The results of sensory evaluation indicated that the special fats prepared from the interesterified blends had better quality when they were applied in the preparation of fast frozen dumplings. Hence, enzymatic interesterification is promising in preparing high-quality special fat for fast frozen food.

•Crude glycerol was efficiently transformed into microbial oil by Lipomyces starkeyi.•L. starkeyi was tolerance to high level of methanol present in the crude glycerol.•Addition of surfactant can enhance the microbial oil production by L. starkeyi.•Kinetic model for lipid production by L. starkeyi in a 5 L fermentor was built.The capability of using crude glycerol as the sole carbon source for microbial oil production by Lipomyces starkeyi AS 2.1560 was investigated. The optimal crude glycerol concentration, nitrogen source, C/N ratio, inoculum concentration, culture temperature, and pH for lipid production were 70 g/L, yeast extract + peptone, 60, 10.0%, 30 °C, and 6.0, respectively. Under the optimal condition, the maximum biomass, lipid content, lipid yield, and lipid coefficient were 21.1 g/L, 35.7%, 7.5 g/L, and 17.3%, respectively. Methanol present in the crude glycerol had minor inhibition on the lipid production. Addition of 0.05 g/L PEG-200, 0.1 g/L potassium oleate or sodium stearate into the medium enhanced the lipid production by 6.4%, 7.7% and 10.4%, respectively. Lipid fermentation was further performed in a 5 L fermentor and the biomass, lipid content, and lipid yield after 10 days’ fermentation were 29.2 g/L, 42.9%, and 12.5 g/L, respectively. The corresponding kinetic models for the cell growth, lipid synthesis, and glycerol consumption were built. The maximum specific growth rate and the correlation coefficient of lipid synthesis to cell growth were 0.40 and 0.56, respectively. This study shows that L. starkeyi AS 2.1560 is a promising strain for lipid production on crude glycerol.Download high-res image (164KB)Download full-size image

•Zein fibers containing fish oil and ferulic acid was fabricated by electrospinning.•Ferulic acid significantly improved the oxidative stability of encapsulated fish oil.•Addition of ferulic acid didn't change the release behavior of encapsulated fish oil.A composite zein nanofibrous mat containing fish oil and ferulic acid was successfully fabricated by electrospinning. The process became more fluent and continuous by adding 30 g/L glycerol into the polymer solutions and using modified coaxial electrospinning. The average diameter of nanofibers was 440 nm. The loading capacity and encapsulation efficiency of fish oil were 20% and 94%, respectively. FTIR data demonstrated that fish oil and ferulic acid were successfully embedded into the nanofibers and there were interactions among the molecules of zein, fish oil and ferulic acid. Addition of ferulic acid into the nanofibers significantly improved the oxidative stability of encapsulated fish oil; moreover, it did not change the release behavior of fish oil. The release of encapsulated fish oil was controlled by a combination of diffusion and macromolecular chain relaxation. This composite nanofibrous mat with favorable oxidation stability and release property is potential in application as nutrition additive.Download high-res image (283KB)Download full-size image

•The core-shell structured nanofilm was fabricated by coaxial electrospinning.•The nanofilm exhibited a good colon-specific and controlled release property.•The release of BSA from nanofilm in SCF was dominant by erosion mechanism.A novel core-shell structured nanofilm for the delivery of protein to the colon was developed by coaxial electrospinning using bovine serum albumin (BSA) as protein model. Firstly, the BSA-loaded chitosan nanoparticle was prepared by ionic gelation, and then the coaxial nanofilm was fabricated using alginate as shell layer and the BSA-loaded chitosan nanoparticle as core layer. Scanning electron microscopy analysis showed that the obtained nanofilm exhibited a smooth surface, and the core-shell structure was evidenced by the aid of transmission electron microscopy. There was little change in the secondary structure of encapsulated BSA and around 75% of BSA was released in the simulated colonic fluid. The corresponding kinetics models of BSA release in different simulated digestive fluids were built and the results revealed that the release of BSA in colon followed a complex mechanism. This study shows that electrospun nanofilm is a promising colon-specific delivery system for bioactive protein.The core-shell structured electrospun nanofilm is a promising colon-specific delivery system for bioactive protein.Download high-res image (124KB)Download full-size image

Coaxial electrospinning was firstly developed to encapsulate fish oil in composite nanofibers to improve its oxidative stability. TEM analysis revealed that a clear core–shell structure was formed in the obtained coaxial nanofibers, the average diameter of which was 560 nm. The loading capacity and encapsulation efficiency of fish oil were 14.5% and 96.9%, respectively. FTIR data demonstrated that fish oil was successfully entrapped into the coaxial electrospun nanofibers. The oxidative stability of encapsulated fish oil in the coaxial nanofibers was significantly enhanced compared to that in single nanofibers. Meanwhile, most of the encapsulated fish oil can be efficiently released from the coaxial electrospun nanofibers and the release was controlled by a combination of diffusion and macromolecular chain relaxation. This coaxial electrospun nanofibrous mat with favourable oxidative stability and release properties has potential for an application as a nutritional additive.

Ionic liquid (IL) pretreatment has emerged as a promising technique that enables complete utilization of lignocellulosic biomass for biofuel production. However, imidazolium IL has recently been shown to exhibit inhibitory effect on cell growth and product formation of industrial microbes, such as oleaginous microorganisms. To date, the mechanism of this inhibition remains largely unknown.In this study, the feasibility of [Bmim][OAc]-pretreated rice straw hydrolysate as a substrate for microbial lipid production by Geotrichum fermentans, also known as Trichosporon fermentans, was evaluated. The residual [Bmim][OAc] present in the hydrolysate caused a reduction in biomass and lipid content (43.6 and 28.1%, respectively) of G. fermentans, compared with those of the control (7.8 g/L and 52.6%, respectively). Seven imidazolium ILs, [Emim][DEP], [Emim]Cl, [Amim]Cl, [Bmim]Cl, [Bzmim]Cl, [Emim][OAc], and [Bmim][OAc], capable of efficient pretreatment of lignocellulosic biomass were tested for their effects on the cell growth and lipid accumulation of G. fermentans to better understand the impact of imidazolium IL on the lipid production. All the ILs tested inhibited the cell growth and lipid accumulation. In addition, both the cation and the anion of IL contributed to IL toxicity. The side chain of IL cations showed a clear impact on toxicity. On examining IL anions, [OAc]− was found to be more toxic than those of [DEP]− and Cl−. IL exhibited its toxicity by inhibiting sugar consumption and key enzyme (malic enzyme and ATP-citrate lyase) activities of G. fermentans. Cell membrane permeability was also altered to different extents in the presence of various ILs. Scanning electron microscopy revealed that IL induces fibrous structure on the surface of G. fermentans cell, which might represent an adaptive mechanism of the yeast to IL.This work gives some mechanistic insights into the impact of imidazolium IL on the cell growth and lipid accumulation of oleaginous yeast, which is important for IL integration in lignocellulosic biofuel production, especially for microbial lipid production.

To give an insight into the kinetics of microbial oil fermentation with lignocellulosic hydrolysate as substrate, lipid production by Trichosporon fermentans in rice straw hydrolysate was investigated in a 5 L fermentor. For comparison, fermentation in its simulated medium was also performed to evaluate the effect of inhibitors present in the rice straw hydrolysate on the cell growth and lipid accumulation of T. fermentans. The optimum fermentation time, maximum biomass, and lipid content of T. fermentans in the rice straw hydrolysate were 10.5 days, 28.6 g/L, and 43.9%, respectively, while the corresponding values in the simulated medium were 8.5 days, 27.0 g/L, and 65.0%, respectively, indicating that the inhibitors in the rice straw hydrolysate did show some inhibition on the cell growth and lipid accumulation of T. fermentans. Kinetic models of lipid fermentation with T. fermentans showed the maximum specific growth rate and the correlation coefficient of lipid synthesis to cell growth in the rice straw hydrolysate were 0.40 and 0.51, respectively, which are much lower than those in the simulated medium (0.58 and 0.73). To better understand the influential mechanism of inhibitors in the rice straw hydrolysate on the growth and lipid accumulation of T. fermentans, the physiological and biochemical changes of cells in the fermentation were further investigated. The reduced activities of adenosine triphosphate (ATP) citrate lyase, malic enzyme, and xylose reductase, and the elongation of cells at the beginning of fermentation, partly account for the inhibitory effect of inhibitors in the rice straw hydrolysate.

The effects of five representative aldehydes in lignocellulosic hydrolysates on the growth and the lipid accumulation of oleaginous yeast Trichosporon fermentans were investigated for the first time. There was no relationship between the hydrophobicity and the toxicity of aldehyde, and 5-hydroxymethylfurfural was less toxic than aromatic aldehydes and furfural. Binary combination of aromatic aldehydes caused a synergistic inhibitory effect, but combination of furan and aromatic aldehydes reduced the inhibition instead. A longer lag phase was found due to the presence of aldehydes and the decrease of sugar consumption rate, but more xylose was utilized by T. fermentans in the presence of aldehydes, especially at their low concentrations. The variation of malic enzyme activity was not related to the delay of lipid accumulation. Furthermore, the inhibition of aldehydes on cell growth was more dependent on inoculum size, temperature, and initial pH than that on lipid content.

Oleaginous yeast Trichosporon fermentans was proved to be able to use sulphuric acid-treated sugar cane bagasse hydrolysate as substrate to grow and accumulate lipid. Activated charcoal was shown as effective as the more expensive resin Amberlite XAD-4 for removing the inhibitors from the hydrolysate. To further improve the lipid production, response surface methodology (RSM) was used and a 3-level 4-factor Box–Behnken design was adopted to evaluate the effects of C/N ratio, inoculum concentration, initial pH and fermentation time on the cell growth and lipid accumulation of T. fermentans. Under the optimum conditions (C/N ratio 165, inoculum concentration 11%, initial pH 7.6 and fermentation time 9 days), a lipid concentration of 15.8 g/L, which is quite close to the predicted value of 15.6 g/L, could be achieved after cultivation of T. fermentans at 25 °C on the pretreated bagasse hydrolysate and the corresponding lipid coefficient (lipid yield per mass of sugar, %) was 14.2. These represent a 32.8% improvement in the lipid concentration and a 21.4% increase in the lipid coefficient compared with the original values before optimization (11.9 g/L and 11.7). This work further demonstrates that T. fermentans is a promising strain for lipid production and thus biodiesel preparation from abundant and inexpensive lignocellulosic materials.