Use of a compound modifier to retard the quality deterioration of frozen dough and its steamed bread.

To retard the quality deterioration of the dough during frozen storage, the effects of a compound modifier (CM) comprised of sodium stearoyl lactate, VC, and ß-glucanase on the properties of the frozen dough, as well as the quality of the frozen dough steamed bread were investigated. The results revealed that CM restricted the migration of water in the dough and improved its rheological properties. Furthermore, CM minimized the deterioration of specific volume and textural properties, and prevented starch retrogradation in the frozen dough steamed bread. Moreover, the addition of CM strengthened the secondary structure of gluten protein and formed a more resilient gluten network. The microstructure of the frozen dough steamed bread showed that CM reduced the damage caused by ice crystals on the gluten network. Overall, the use of CM strengthened the gluten network and effectively delayed the quality deterioration of the frozen dough, thus is potential as an improver for frozen dough.

Advances and trends in microbial production of polyhydroxyalkanoates and their building blocks.

With the rapid development of synthetic biology, a variety of biopolymers can be obtained by recombinant microorganisms. Polyhydroxyalkanoates (PHA) is one of the most popular one with promising material properties, such as biodegradability and biocompatibility against the petrol-based plastics. This study reviews the recent studies focusing on the microbial synthesis of PHA, including chassis engineering, pathways engineering for various substrates utilization and PHA monomer synthesis, and PHA synthase modification. In particular, advances in metabolic engineering of dominant workhorses, for example Halomonas, Ralstonia eutropha, Escherichia coli and Pseudomonas, with outstanding PHA accumulation capability, were summarized and discussed, providing a full landscape of diverse PHA biosynthesis. Meanwhile, we also introduced the recent efforts focusing on structural analysis and mutagenesis of PHA synthase, which significantly determines the polymerization activity of varied monomer structures and PHA molecular weight. Besides, perspectives and solutions were thus proposed for achieving scale-up PHA of low cost with customized material property in the coming future.

Improving the Viability of Probiotics under Harsh Conditions by the Formation of Biofilm on Electrospun Nanofiber Mat.

For improving probiotics' survivability under harsh conditions, this study used Lactiplantibacillus plantarum GIM1.648 as a model microorganism to investigate its ability to produce biofilms on electrospun ethyl cellulose nanofiber mats. SEM observations confirmed that biofilm was successfully formed on the nanofibers, with the latter being an excellent scaffold material. The optimal cultivation conditions for biofilm formation were MRS medium without Tween 80, a culture time of 36 h, a temperature of 30 °C, a pH of 6.5, and an inoculum concentration of 1% (v/v). The sessile cells in the biofilm exhibited improved gastrointestinal and thermal tolerance compared to the planktonic cells. Additionally, the RT-qPCR assay indicated that the luxS gene played a crucial role in biofilm formation, with its relative expression level being 8.7-fold higher compared to the planktonic cells. In conclusion, biofilm formation on electrospun nanofiber mat has great potential for improving the viability of probiotic cells under harsh conditions.

Fabrication of Nano/Micro-Structured Electrospun Detection Card for the Detection of Pesticide Residues.

A novel nano/micro-structured pesticide detection card was developed by combining electrospinning and hydrophilic modification, and its feasibility for detecting different pesticides was investigated. Here, the plain and hydrophilic-modified poly(ε-caprolactone) (PCL) fiber mats were used for the absorption of indolyl acetate and acetylcholinesterase (AChE), respectively. By pre-treating the fiber mat with ethanol, its surface wettability was improved, thus, promoting the hydrolysis of the PCL fiber mat. Furthermore, the absorption efficiency of AChE was improved by almost two times due to the increased hydrophilicity of the modified fiber mat. Noteworthily, this self-made detection card showed a 5-fold, 2-fold, and 1.5-fold reduction of the minimum detectable concentration for carbofuran, malathion, and trichlorfon, respectively, compared to the national standard values. Additionally, it also exhibited good stability when stored at 4 °C and room temperature. The food detection test showed that this nano/micro-based detection card had better detectability than the commercial detection card. Therefore, this study offers new insights into the design of pesticide detection cards, which also broadens the application of electrospinning technique.

Fabrication of nanostructured multi-unit vehicle for intestinal-specific delivery and controlled release of peptide.

An oral multi-unit delivery system was developed by incorporating the nanoparticle (NP) into the nanofiber mat and its efficiency for intestinal-specific delivery and controlled release of a peptide (insulin) was investigated. Initially, the influence of deacetylation degree (DD) of chitosan and ionic gelation methods on the properties of NPs was studied. High DD (95%) chitosan was attributed to higher encapsulation efficiency and stability when crosslinked with polyanion tripolyphosphate. Subsequently, the multi-unit system was fabricated using a pH-sensitive polymer (sodium alginate) as the coating layer to further encapsulate the NP. Fiber mat with an average diameter of 481 ± 47 nm could significantly decrease the burst release of insulin in acidic condition and release most amount of insulin (>60%) in the simulated intestinal medium. Furthermore, the encapsulated peptide remained in good integrity. This multi-unit carrier provides the better-designed vehicle for intestinal-specific delivery and controlled release of the peptide.

A Polyhydroxyalkanoates-Based Carrier Platform of Bioactive Substances for Therapeutic Applications.

Bioactive substances (BAS), such as small molecule drugs, proteins, RNA, cells, etc., play a vital role in many therapeutic applications, especially in tissue repair and regeneration. However, the therapeutic effect is still a challenge due to the uncontrollable release and instable physico-chemical properties of bioactive components. To address this, many biodegradable carrier systems of micro-nano structures have been rapidly developed based on different biocompatible polymers including polyhydroxyalkanoates (PHA), the microbial synthesized polyesters, to provide load protection and controlled-release of BAS. We herein highlight the developments of PHA-based carrier systems in recent therapeutic studies, and give an overview of its prospective applications in various disease treatments. Specifically, the biosynthesis and material properties of diverse PHA polymers, designs and fabrication of micro- and nano-structure PHA particles, as well as therapeutic studies based on PHA particles, are summarized to give a comprehensive landscape of PHA-based BAS carriers and applications thereof. Moreover, recent efforts focusing on novel-type BAS nano-carriers, the functionalized self-assembled PHA granules in vivo, was discussed in this review, proposing the underlying innovations of designs and fabrications of PHA-based BAS carriers powered by synthetic biology. This review outlines a promising and applicable BAS carrier platform of novelty based on PHA particles for different medical uses.

Development of a polysaccharide based multi-unit nanofiber mat for colon-targeted sustained release of salmon calcitonin.

Advances in pharmaceutical technology have promoted the development of colon-targeted delivery system for oral administration of bioactive peptides or proteins to enhance their bioavailability. In this study, a multi-unit nanofiber mat was fabricated by coaxial electrospinning and its feasibility as the colon-targeted delivery system for a bioactive peptide, salmon calcitonin (sCT), was investigated. Sodium alginate and sCT-loaded liposome coated with pectin served as the shell layer and core layer, respectively. An in vitro study demonstrated that the encapsulated sCT was released in a sustained and colon-targeted way. Analysis using different mathematical models showed that release followed a complex mechanism. In addition, greater amounts of sCT were released from the core-shell nanofiber mat into simulated colon fluid (SCF) than was released from a uniaxial nanofiber mat (65.2% vs. 47.8%). The use of a core-shell nanofiber mat further alleviated the burst release of sCT into simulated gastric and intestinal fluid (SGF and SIF), demonstrating the superiority of a multi-unit vehicle for colon-targeted delivery of sCT. Furthermore, 88% of the bioactivity of encapsulated sCT was retained. This multi-unit vehicle offers a better-designed vehicle for the colon-targeted sustained release of bioactive peptides or proteins and, thus, should improve oral bioavailability.

Improving the catalytic characteristics of lipase-displaying yeast cells by hydrophobic modification.

Lipase-displaying yeast cells are a promising alternative to the conventional immobilised lipases for organic bioconversions. However, the hydrophilic characteristics of the yeast cell surface may impede efficient immobilisation. Herein, we tested three methods to enhance the hydrophobicity of the surface of Candida antarctica lipase B-displaying Pichia pastoris cells, co-displaying a fungal hydrophobin, coating with ionic liquids, and adding decane as a hydrophobic carbon source during fermentation. Modified cells showed higher surface hydrophobicity and superior esterification of C6-C18 saturated fatty acids in hydrophobic solvents. When used for biodiesel synthesis, modified cells exhibited an improved initial reaction rate and equilibrium fatty acid methyl ester yield. We systematically discuss the influence of cell surface hydrophobicity on the catalytic properties, and the results provide guidance for improving the catalytic efficiency and operational characteristics of lipase-displaying yeast cells for organic bioconversions.

Enzymatic Process Enhances the Flavour Profile and Increases the Proportion of Esters in Citrus Essential Oils.

Citrus essential oils (CEOs) are important flavors in the food and confectionary industries. A lipase process was proposed for enhancing the flavor profiles and increasing the proportions of esters in CEOs. The effects of the enzymatic process were explored by detecting the constituents of the CEOs of American sweet orange oil (ASO) and Brazil mandarin oil (BMO) through GC/MS and sensory evaluation by a trained panel, and positive effects were confirmed by both methods. A further eleven kinds of CEOs were treated via the lipase process and increments of 10 - 1170% were achieved in the proportions of esters, which were mostly ethyl esters. Enhancement in fruity odor, especially the top note, was demonstrated by all CEOs after enzymatic processing. All CEOs were tested for antimicrobial activities, and only ASO displayed fairly ideal antimicrobial activities. Meanwhile, modified ASO showed a certain increase in antimicrobial activities. This methodology might be considered a sustainable route for acquiring 'natural' essential oils with enhanced flavor profiles and simultaneously enhancing the comprehensive utilization of citrus fruits.

Displaying Candida antarctica lipase B on the cell surface of Aspergillus niger as a potential food-grade whole-cell catalyst.

Aspergillus niger is a recognized workhorse used to produce food processing enzymes because of its extraordinarily high protein-producing capacity. We have developed a new cell surface display system de novo in A. niger using expression elements from generally recognized as safe certified microorganisms. Candida antarctica lipase B (CALB), a widely used hydrolase, was fused to an endogenous cell wall mannoprotein, CwpA, and functionally displayed on the cell surface. Localization of CALB was confirmed by enzymatic assay and immunofluorescence analysis using laser scanning confocal microscopy. After induction by maltose for 45 h, the hydrolytic activity and synthesis activity of A. niger mycelium-surface displayed CALB (AN-CALB) reached 400 and 240 U/g dry cell, respectively. AN-CALB was successfully used as a whole-cell catalyst for the enzymatic production of ethyl esters from a series of fatty acids of different chain lengths and ethanol. In a solvent-free system, AN-CALB showed great synthetic activity and afforded high substrate mole conversions, which amounted to 87 % for ethyl hexanoate after 2 h, 89 % for ethyl laurate after 2 h, and 84 % for ethyl stearate after 3 h. These results suggested that CwpA can act as an efficient anchoring motif for displaying enzyme on A. niger, and AN-CALB is a robust, green, and cost-effective alternative food-grade whole-cell catalyst to commercial lipase.

Quantification analysis of yeast-displayed lipase.

We describe a method for quantification of displayed lipase on yeast cell surface. The strategy uses an organophosphonate ester to irreversibly inhibit the active lipase and release a detectable fluorescent group. The amount of displayed lipase can be represented as "g/g cell" or "molecules/cell". The results obtained correlated well with those obtained by existing methods. Therefore, this method is credible and will provide a powerful tool to promote research of lipase yeast surface display.

Quantitative iTRAQ LC-MS/MS proteomics reveals the cellular response to heterologous protein overexpression and the regulation of HAC1 in Pichia pastoris.

The methylotrophic yeast Pichia pastoris is an attractive platform for a plethora of recombinant proteins. There is growing evidence that host cells producing recombinant proteins are exposed to a variety of cellular stresses resulting in the induction of the unfolded protein response (UPR) pathway. At present, there is only limited information about the cellular reactions of the host cells at the level of the proteome, especially with regard to recombinant protein secretion. Here we monitored xylanase A secretion from Bacillus halodurans C-125 (xynA) in P. pastoris, using strains containing different copy numbers of the gene encoding xylanase A and co-overexpressing the gene encoding the UPR-regulating transcription factor HAC1 by applying a quantitative proteomics approach (iTRAQ-LC-MS/MS). Many important cellular processes, including carbon metabolism, stress response and protein folding are affected in the investigated conditions. Notably, the analysis revealed that strong over-expression of xynA can efficiently improve protein production but simultaneously cause an unfolded protein burden with a subsequent induction of the UPR. This limits the further improvement of protein production levels. Remarkably, constitutive expression of the gene encoding HAC1 lessens the unfolded protein burden by attenuating protein synthesis and increasing ER protein folding efficiency which is beneficial for protein secretion. BIOLOGICAL SIGNIFICANCE: Pichia pastoris expression systems have been successfully used for over 20years in basic research and in the biotechnology industry for the production and secretion of a wide range of recombinant proteins. In particular, secretion of recombinant proteins is still one of the main reasons for using P. pastoris. It has become obvious that many protein products can lead to severe stress on the host cell when being over-expressed, thus limiting the potential yield. Detailed understanding of the physiological responses to such stresses gives rise to engineering of host cells that can better cope with the stress factors. Therefore, the regulatory mechanism of heterologous protein secretion by quantitative mass-spectrometry (MS) proteomics is a growing field and an important endeavor in improving protein annotation. Many important cellular processes, including carbon and amino acid metabolism, stress response and protein folding are affected in the over-expression strains. This data represent a first step towards a systems wide approach to assess the response with recombinant protein induced stress in P. pastoris.

Structure-guided modification of Rhizomucor miehei lipase for production of structured lipids.

To improve the performance of yeast surface-displayed Rhizomucor miehei lipase (RML) in the production of human milk fat substitute (HMFS), we mutated amino acids in the lipase substrate-binding pocket based on protein hydrophobicity, to improve esterification activity. Five mutants: Asn87Ile, Asn87Ile/Asp91Val, His108Leu/Lys109Ile, Asp256Ile/His257Leu, and His108Leu/Lys109Ile/Asp256Ile/His257Leu were obtained and their hydrolytic and esterification activities were assayed. Using Discovery Studio 3.1 to build models and calculate the binding energy between lipase and substrates, compared to wild-type, the mutant Asp256Ile/His257Leu was found to have significantly lower energy when oleic acid (3.97 KJ/mol decrease) and tripalmitin (7.55 KJ/mol decrease) were substrates. This result was in accordance with the esterification activity of Asp256Ile/His257Leu (2.37-fold of wild-type). The four mutants were also evaluated for the production of HMFS in organic solvent and in a solvent-free system. Asp256Ile/His257Leu had an oleic acid incorporation of 28.27% for catalyzing tripalmitin and oleic acid, and 53.18% for the reaction of palm oil with oleic acid. The efficiency of Asp256Ile/His257Leu was 1.82-fold and 1.65-fold that of the wild-type enzyme for the two reactions. The oleic acid incorporation of Asp256Ile/His257Leu was similar to commercial Lipozyme RM IM for palm oil acidolysis with oleic acid. Yeast surface-displayed RML mutant Asp256Ile/His257Leu is a potential, economically feasible catalyst for the production of structured lipids.

Bleach boosting effect of xylanase A from Bacillus halodurans C-125 in ECF bleaching of wheat straw pulp.

Past studies have revealed major difficulties in applications of xylanase in the pulp and paper industry as enzymes isolated from many different species could not tolerate high temperatures or highly alkaline conditions. The thermostable xylanase A from Bacillus halodurans C-125 (C-125 xylanase A) was successfully cloned and expressed in Pichia pastoris with a yield as high as 3361 U/mL in a 2 L reactor. Its thermophilic and basophilic properties (optimal activity at 70 °C and pH 9.0), together with the fact it is cellulase-free, render this enzyme attractive for compatible applications in the pulp and paper industry. The pretreatment of wheat straw pulp with C-125 xylanase A at pH 9.0 and 70 °C for 90 min induced the release of both chromophores (Ab(237), Ab(254), Ab(280)) and hydrophobic compounds (Ab(465)) into the filtrate as well as sugar degradation. Moreover, the addition of 10 U xylanase to 1 g wheat straw pulp (dry weight) as pretreatment improved brightness by 5.2% ISO and decreased the kappa number by 5.0% when followed by hydrogen peroxide bleaching. In addition, compared with two commercial enzymes, Pulpzyme HC and AU-PE89, which are normally incorporated in ECF bleaching of wheat straw pulp, C-125 xylanase A proved to be more effective in enhancing brightness as well as preserving paper strength properties. When evaluating the physical properties of pulp samples, such as tensile index, tearing index, bursting index, and post-color (PC) number, the enzymes involved in pretreating pulps exhibited better or the same performances as chemical treatment. Compared with chemical bleaching, chlorine consumption can be significantly reduced by 10% for xylanase-pretreated wheat straw pulp while maintaining the brightness together with the kappa number at the same level. Scanning electron microscopy revealed significant surface modification of enzyme-pretreated pulp fibers with no marked fiber disruptions.

Combined utilization of lipase-displaying Pichia pastoris whole-cell biocatalysts to improve biodiesel production in co-solvent media.

Lipase-displaying whole cells appear to be efficient biocatalysts because of their low preparation costs and simple recycling procedure. The combined utilization of Candida antarctica lipase B (CALB) and Rhizomucor miehei lipase (RML), separately displayed on Pichia pastoris whole cells, to produce biodiesel in co-solvent media was investigated. A response surface methodology incorporating a D-optimal design was employed to obtain the optimum reaction conditions for methyl ester (ME) synthesis. The synergistic effect of the two displayed lipases and the use of tert-butanol and isooctane as the co-solvent media were found to significantly improve the transesterification reaction. Scaled-up reactions using various types of feedstock were carried out in a 0.5-l stirred reactor under optimum conditions, affording ME yields over 90% in 12h. Moreover, the ME yields remained above 85% after 20 repeated batch cycles. In conclusion, this biocatalyst affords a promising route to efficient biodiesel production.

Quantitative evaluation of Candia antarctica lipase B displayed on the cell surface of a Pichia pastoris based on an FS anchor system.

A new approach is described to quantify the number of enzyme molecules, such as Candia antarctica lipase B, that are displayed on the cell surface of Pichia pastoris. Enhanced green fluorescent protein (EGFP) and Candida antarctica lipase B (CALB) were fused and displayed on the surface of P. pastoris by linking to the anchor flocculation functional domain of FLO1p from Saccharomyces cerevisiae. Confocal laser scanning microscopy, flow cytometry, and fluorescence spectrophotometry were used to monitor the fluorescence intensity of fused EGFP. Combined with the corresponding protein concentration detected in the medium, a standard curve describing the relationship between the fusion protein concentration and fluorescence intensity were obtained and could be used to number CALB displayed on the cell surface. The results showed that approx. 10(4) molecules of CALB molecules were immobilized on the single P. pastoris cell wall based on FS anchor system.

Double Candida antarctica lipase B co-display on Pichia pastoris cell surface based on a self-processing foot-and-mouth disease virus 2A peptide.

To develop a high efficiency Candida antarctica lipase B (CALB) yeast display system, we linked two CALB genes fused with Sacchromyces cerevisiae cell wall protein genes, the Sed1 and the 3'-terminal half of Sag1, separately by a 2A peptide of foot-and-mouth disease virus (FMDV) in a single open reading frame. The CALB copy number of recombinant strain KCSe2ACSa that harbored the ORF was identified, and the quantity of CALB displayed on the cell surface and the enzyme activity of the strain were measured. The results showed that the fusion of multiple genes linked by 2A peptide was translated into two independent proteins displayed on the cell surface of stain KCSe2ACSa. Judging from the data of immunolabeling assay, stain KCSe2ACSa displayed 94 % CALB-Sed1p compared with stain KCSe1 that harbored a single copy CALB-Sed1 and 64 % CALB-Sag1p compared with stain KCSa that harbored a single copy CALB-Sag1 on its surface. Besides, strain KCSe2ACSa possessed 170 % hydrolytic activity and 155 % synthetic activity compared with strain KCSe1 as well as 144 % hydrolytic activity and 121 % synthetic activity compared with strain KCSa. Strain KCSe2ACSa even owned 124 % hydrolytic activity compared with strain KCSe2 that harbored two copies CALB-Sed1. The heterogeneous glycosylphosphatidylinositol-anchored proteins co-displaying yeast system mediated by FMDV 2A peptide was shown to be an effective method for improving the efficiency of enzyme-displaying yeast biocatalysts.

High-throughput screening of B factor saturation mutated Rhizomucor miehei lipase thermostability based on synthetic reaction.

Conventional lipase screening methods are mostly based on hydrolytic activity, which may not always be the best method to assess the enzyme activity, especially for evaluating synthetic activity. Here we developed a high throughput and visual method to screen clones with high synthetic activity and used it to assess lipases thermostability. All mutants' lipase synthetic activity were identified through esterification of caprylic acid and ethanol with methyl red as the pH indicator adding in the substrates on according to the color change halo around the colony on culture plates since synthetic reaction was often accompanied with a rise in pH. After two rounds operation with the pH indicator screening method, we obtained a double mutant Asn120Lys/Lys131Phe from the Rhizomucor miehei lipase saturation mutated library based on amino acid residue B factors. The mutant's initial synthetic activity was a little higher than wild type and its thermostability in synthetic reaction was enhanced, which remained 63.1% residual activity after being heated at 70°C for 5h comparing to 51.0% of wild type. The double mutant with the two residue replacements balanced well between stability and activity. Yeast surface display technology and the pH indicator method, combined with colony screening were shown to facilitate high-throughput screening for lipase synthetic activity.

Production of flavor esters catalyzed by CALB-displaying Pichia pastoris whole-cells in a batch reactor.

Candida antarctica lipase B (CALB) has been employed as an efficient catalyst in the preparation of many flavor esters. A CALB-displaying yeast whole-cell biocatalyst could be an attractive alternative to commercial immobilized CALB because of its low-cost preparation and high enzymatic activity. We investigated the potential application of CALB-displaying Pichia pastoris cells for the production of flavor esters. The optimal conditions for flavor esters synthesis by this biocatalyst were determined in 50-ml shake flasks. Under optimized conditions, the synthesis of 12 kinds flavor esters were scaled up in a 5-l batch stirred reactor. Among these, the mole conversions of 10 exceeded 95% after reactions for 4h. In addition, this biocatalyst showed good tolerance for high substrates concentration and excellent operational stability. Repeated use of the cells in 10 batches resulted in an activity loss of less than 10%. Thus, CALB-displaying P. pastoris whole cells are robust biocatalysts with potential commercial application in the large-scale production of flavor esters in non-aqueous media.

Combination of site-directed mutagenesis and yeast surface display enhances Rhizomucor miehei lipase esterification activity in organic solvent.

To increase the activity of Rhizomucor miehei lipase (RML) in organic solvent, multiple sequence alignments and rational site-directed mutagenesis were used to create RML variants. The obtained proteins were surface-displayed on Pichia pastoris by fusion to Flo1p as an anchor protein. The synthetic activity of four variants showed from 1.1- to 5-fold the activity of native lipase in an esterification reaction in heptane with alcohol and caproic acid as substrates. The increase in esterification activity may be attributed to the four mutations changing the flexibility of RML or facilitating the reaction. In conclusion, this method demonstrated that multiple sequence alignments and rational site-directed mutagenesis combined with yeast display technology is a faster and more effective means of obtaining high-efficiency esterification lipase variants compared with previous similar methods.