Recent developments in off-odor formation mechanism and the potential regulation by starter cultures in dry-cured ham.

Foul-smelling odors are main quality defects of dry-cured ham, which are connected with the excessive degradation of the structural proteins and excessive oxidation of lipids caused by the abnormal growth of spoilage microorganisms, threatening the development of dry-cured ham industry. Characterizing the key microorganisms and metabolites resulted in the spoilage of dry-cured ham, and discussing the relationship between spoilage microorganisms and metabolites are the key aspects to deeply understand the formation mechanism of off-odor in dry-cured ham. Until now, there is no detailed discussion or critical review on the role of spoilage microorganisms in developing the off-odor of dry-cured ham, and the regulation of off-odor and spoilage microorganisms by starter cultures has been not discussed. This review shows the recent achievement in the off-odor formation mechanism of dry-cured ham, and outlines the potential regulation of off-odor defects in dry-cured ham by starter cultures. Results from current research show that the abnormal growth of Lactic acid bacteria, Micrococcaceae, Enterobacteriaceae, Yeasts and Molds plays a key role in developing the off-odor defects of dry-cured ham, while the key spoilage microorganisms of different type hams are discrepant. High profile of aldehydes, acids, sulfur compounds and biogenic amines are responsible for off-odor development in spoiled dry-cured ham. Several starter cultures derived from these species of Staphylococcus, Penicillium, Debaryomyces, Pediococcus and Lactobacillus show a great potential to prevent microbiological hazards and improve flavor quality of dry-cured ham, whereas, the ecology, function and compatibility of these starter cultures with the processing parameters of dry-cured ham need to be further evaluated in the future.

Ultrasound-assisted phosphorylation of goose myofibrillar proteins: improving protein structure and functional properties.

BACKGROUND: Goose meat is rough and embedded with dense connective tissue, impairing protein solubility. Therefore, to improve the functional properties of goose myofibrillar protein (GMP), ultrasound was used to assist the phosphorylation of GMP. RESULTS: The fact that GMP attached covalently with the phosphate group of sodium tripolyphosphate (GMP-STP) was disclosed directly by Fourier transform infrared spectroscopy. Furthermore, ultrasound significantly improved the hydrophobicity and solubility of GMP-STP, which could be attributed to the conversion of α-helix to ß-sheet, ß-turns, and random coils by sonication. The spatial stabilization of the protein phosphorylation process was boosted by ultrasound, making the droplets more dispersed, and thus an improvement in the functional properties of GMP-STP was observed. Water-holding capacity, oil-binding capacity, and emulsifying and foaming properties were best at an ultrasound power of 400 W. CONCLUSION: Ultrasound-assisted phosphorylation has great potential to modulate the structure-function relationship of proteins. © 2023 Society of Chemical Industry.

The combination of high-throughput sequencing and LC-MS/MS reveals the mechanism of Staphylococcus inoculation on bacterial community succession and taste development during the processing of dry-cured bacon.

BACKGROUND: To understand the mechanism of co-inoculation of Staphylococcus vitulinus and Staphylococcus xylosus (SX&SV) on taste quality of dry-cured bacon, physicochemical parameters, microbial community, metabolite compositions and taste attributes were investigated during the processing of dry-cured bacon with Staphylococcus inoculation. The potential correlation between core bacteria and metabolites was evaluated, and the metabolic pathway of key metabolites was further explored. RESULTS: The values of pH, water activity and adhesiveness were significantly lower in SX&SV, and more than 2.56- and 2.15-fold higher values in richness and overall acceptance were found in SX&SV bacon than in CK bacon. The overwhelming advantage of Staphylococcus was confirmed in SX&SV by high-throughput sequencing. Sixty-six metabolites were identified by liquid chromatography-tandem mass spectrometry, and oligopeptides, amino acid derivatives and organic acids were the key components. Pearson correlation demonstrated that the accumulation of oligopeptides, amino acid derivatives and organic acids were positively correlated with high abundance of Staphylococcus. The pathways of purine metabolism, glutathione metabolism and glutamate metabolism were mainly involved in developing the taste quality of SX&SV. CONCLUSION: The co-inoculation of Staphylococcus vitulinus and Staphylococcus xylosus enhanced the taste attributes of dry-cured bacon. The present study provides the theoretical reference with respect to regulating the taste quality of fermented meat products by starter cultures of Staphylococcus during manufacture. © 2023 Society of Chemical Industry.

Effect of lentinan on gelling properties and structural changes of goose myofibrillar protein under oxidative stress.

BACKGROUND: The reduction of protein oxidation is important for maintaining the product quality of reconstituted meat. In this study, the dose-dependent effects of lentinan (LNT) on gelling properties and chemical changes in oxidatively stressed goose myofibrillar protein were investigated. RESULTS: Myofibrillar protein (MP) with 200 µmol g-1 protein LNT increased gel strength by 87.90 ± 9.26% in comparison with LNT-free myofibrillar protein after oxidation. Scanning electron microscopy analysis revealed that the gel network containing LNT was compact, with small pores and uniform distribution. The absolute value of the zeta potential reduced significantly following oxidation of LNT with 200 µmol g-1 protein at 4 °C for 12 h compared with the zeta potential without LNT, according to the laser particle size analyzer. The incorporation of LNT increased protein solubility and -SH content, inhibited carbonyl formation, enhanced α-helix content and tryptophan intrinsic fluorescence intensity, and reduced exposure of hydrophobic groups and protein aggregation. CONCLUSION: The results indicated that adding LNT to myofibrillar protein could improve gel. This is related to its protective effect on conformational changes in the oxidation system. Lentinan is therefore recommended for oxidatively stressed goose meat processing to enhance the MP gelling potential. © 2023 Society of Chemical Industry.

Contribution of process-induced molten-globule state formation in duck liver protein to the enhanced binding ability of (E,E)-2,4-heptadienal.

BACKGROUND: Extracted proteins of alternative animal origin tend to present strong off-flavor perception due to physicochemical interactions of coextracted off-flavor compounds with proteins. To investigate the relationship between absorption behaviors of volatile aromas and the processes-induced variations in protein microstructures and molecular conformations, duck liver protein isolate (DLp) was subjected to heating (65/100 °C, 15 min) and ultra-high pressure (UHP, 100-500 MPa/10 min, 28 °C) treatments to obtain differential unfolded protein states. RESULTS: Heat and UHP treatments induced the unfolding of DLp to varied degrees, as revealed by fluorescence spectroscopy, ultraviolet-visible absorption, circular dichroism spectra and surface hydrophobicity measurements. Two types of heating-denatured states with varied unfolding degrees were obtained, while UHP at both levels of 100/500 MPa caused partial unfolding of DLp and the presence of a molten-globule state, which significantly enhanced the binding affinity between DLp and (E,E)-2,4-heptadienal. In particular, significantly modified secondary structures of DLp were observed in heating-denatured samples. Excessive denaturing and unfolding degrees resulted in no significant changes in the absorption behavior of the volatile ligand, as characterized by observations of fluorescence quenching and analysis of headspace concentrations. CONCLUSION: Defining process-induced conformational transition behavior of matrix proteins could be a promising strategy to regulate food flavor attributes and, particularly, to produce DLp coextracted with limited off-flavor components by modifying their interaction during extraction processes. © 2023 Society of Chemical Industry.

Cleavable molecular beacon-based loop-mediated isothermal amplification assay for the detection of adulterated chicken in meat.

A simple, sensitive, specific and fast method based on the loop-mediated isothermal amplification (LAMP) technique and cleavable molecular beacon (CMB) was developed for chicken authentication detection. LAMP and CMB were used for DNA amplification and amplicon analysis, respectively. Targeting the mitochondrial cytochrome b gene of chickens, five primers and one CMB probe were designed, and their specificity was validated against nine other animal species. The structure of CMB and concentrations of dNTPs, MgSO4, betaine, RNase H2, primers and CMB were optimized. The CMB-LAMP assay was completed within 17 min, and its limit of detection for chicken DNA was 1.5 pg µL-1. Chicken adulteration as low as 0.5% was detected in beef, and no cross-reactivity was observed. Finally, this assay was successfully applied to 20 commercial meat products. When combined with our developed DNA extraction method (the extraction time was 1 min: lysis for 10 s, washing for 20 s and elution for 30 s), the entire process (from DNA extraction to results analysis) was able to be completed within 20 min, which is at least 10 min shorter than other LAMP-based methods. Our method showed great potential for the on-site detection of chicken adulteration in meat.

Rapid solid phase microextraction of DNA using mesoporous metal-organic framework coating for PCR-based identification of meat adulteration.

A rapid, convenient, low-cost, and selective DNA isolation method was developed for identifying meat adulteration. A mesoporous metal organic framework (Meso-UIO-66)-coated solid phase microextraction system was employed as an isolation device to simplify DNA isolation into three steps (lysis, washing, and elution). Meso-UIO-66 was utilized as the adsorbent because of its positively charged surface, high chemical stability, and mesoporous structure. Meso-UIO-66 was characterized by scanning electron microscopy, transmission electron microscopy, powder X-ray diffraction, Fourier transform infrared spectroscopy, ultraviolet‒visible spectroscopy, X-ray photoelectron spectroscopy, and nitrogen adsorption-desorption tests. Parameters that affected DNA isolation were optimized. This method can be used to isolate and purify DNA from meat in 60 s, and the DNA concentration and purity are comparable to those of samples isolated with a commercial kit. Multiple DNA detection was achieved by coupling this method with the multiplex polymerase chain reaction technique, and the detection limit was lower than 1% (w/w).

Research progress in the screening and evaluation of umami peptides.

Umami is an important element affecting food taste, and the development of umami peptides is a topic of interest in food-flavoring research. The existing technology used for traditional screening of umami peptides is time-consuming and labor-intensive, making it difficult to meet the requirements of high-throughput screening, which limits the rapid development of umami peptides. The difficulty in performing a standard measurement of umami intensity is another problem that restricts the development of umami peptides. The existing methods are not sensitive and specific, making it difficult to achieve a standard evaluation of umami taste. This review summarizes the umami receptors and umami peptides, focusing on the problems restricting the development of umami peptides, high-throughput screening, and establishment of evaluation standards. The rapid screening of umami peptides was realized based on molecular docking technology and a machine learning method, and the standard evaluation of umami could be realized with a bionic taste sensor. The progress of rapid screening and evaluation methods significantly promotes the study of umami peptides and increases its application in the seasoning industry.

Novel milk casein-derived peptides decrease cholesterol micellar solubility and cholesterol intestinal absorption in Caco-2 cells.

This study sought to assess the cholesterol-lowering activity of peptides obtained from milk casein hydrolyzed with neutrase. The bioactive peptides were separated using a Sephadex G-10 chromatographic column (Amersham Pharmacia Biotech, Uppsala, Sweden) after ultrafiltration using a 1-kDa molecular mass cutoff membrane. Via ultra-performance liquid chromatography-electrospray ionization-tandem mass spectrometry, we determined that peptides Thr-Asp-Val-Glu-Asn [TDVEN; ß-casein f(143-147)], Leu-Gln-Pro-Glu [LQPE; ß-casein f(103-106)], Val-Ala-Pro-Phe-Pro-Glu [VAPFPE; αS1-casein f(40-45)], and Val-Leu-Pro-Val-Pro-Gln [VLPVPQ ß-casein f(185-190)] reduced micellar cholesterol solubility. After Caco-2 cells were treated with LQPE, VLPVPQ, and VAPFPE, the Niemann-Pick C1-Like 1 (NPC1L1) protein levels decreased by (means ± SEM) 19.33 ± 2.47%, 52.1 ± 3.77%, and 23.09 ± 8.52%, respectively, compared with the control group. Treatment with each peptide induced significant upregulation of ATP binding cassette subfamily G member 8 antibody (ABCG8) mRNA expression by 398.1 ± 23.27%, 86.4 ± 27.07%, and 92.8 ± 8.49%. We found that VLPVPQ and LQPE significantly upregulated ATP-binding cassette transporter A1 (ABCA1) transcription by 203.9 ± 8.44% and 220.8 ± 36.42% respectively, whereas VLPVPQ significantly decreased mRNA expression of acetyl-CoA-acetyltransferase 2 (ACAT2) and microsomal triacylglycerols (MTP). The cholesterol-lowering action of milk-derived peptides may be induced by suppression of micellar cholesterol solubility and affects the expression of cholesterol absorption-related proteins and enzymes in intestinal epithelial cells. This research discovers new milk-derived peptides with decreasing cholesterol micellar solubility and provides a theoretical basis of in vitro cholesterol-lowering effects of peptides.

Production and transepithelial transportation of angiotensin-I-converting enzyme (ACE)-inhibitory peptides from whey protein hydrolyzed by immobilized Lactobacillus helveticus proteinase.

Lactobacillus helveticus LB 10 proteinases immobilized with sodium alginate were used to hydrolyze whey protein to produce angiotensin-I-converting enzyme (ACE)-inhibitory peptides. The generated hydrolysates were tested for ACE-inhibitory activity and for their ability to be transported across Caco-2 cell monolayers. Using a response surface method, we determined that a proteinase concentration of 7.55 mg/mL, sodium alginate concentration of 2.03 g/100 mL, and glutaraldehyde concentration of 0.39% were found to be the optimal immobilization conditions. Compared with free proteinase, the immobilized proteinase had significantly higher pH, thermal and storage stability, and reusability. Whey protein hydrolysates were fractionated by gel filtration chromatography and ACE-inhibitory peptide mixtures were transported across Caco-2 cell monolayers in a human intestinal-absorption model. The di- and tripeptides KA, EN, DIS, EVD, LF, AIV, and VFK (half-maximal inhibitory concentrations (mean ± standard deviation) of 1.24 ± 0.01, 1.43 ± 0.04, 1.59 ± 0.27, 1.32 ± 0.05, 1.60 ± 0.39, 2.66 ± 0.02, and 1.76 ± 0.09 mmol/L, respectively) were detected on the basolateral side of the Caco-2 cell monolayer using ultra-performance liquid chromatography-tandem mass spectrometry. These results highlight that ACE-inhibitory peptides are present on the basolateral side of the Caco-2 cell model after transportation of whey protein hydrolysate across the Caco-2 cell membrane.

A novel colorimetric immunosensor based on platinum colloid nanoparticles immobilized on PowerVision as signal probes and Fe3 O4 @ß-cyclodextrin as capture probes for ractopamine detection in pork.

BACKGROUND: A novel colorimetric immunosensor was developed for the simple, sensitive and selective detection of ractopamine (RAC) based on using ß-cyclodextrin-modified Fe3 O4 particles (Fe3 O4 @ß-CD) as capture probes and complex platinum colloid nanoparticles (PtNPs-PV) composed of platinum colloid nanoparticles (PtNPs) and polymerase chelate PowerVision (PV) as signal probes. RESULTS: PtNPs-PV double catalyzed the chromogenic substrate 3,3'-diaminobenzidine (DAB), which induced changes in the color of DAB and chromogenic absorbance. Incubation temperature, pH and incubation time were systematically optimized and, under optimum conditions, the measured absorbance values showed a linear relationship with the RAC concentrations in the range 0.03-8.1 ng mL-1 . The detection limit was 0.01 ng mL-1 . The sensor exhibited high sensitivity and specificity, as demonstrated by testing structurally similar organic compounds such as salbutamol, clenbuterol and dopamine. The practicality of the developed colorimetric immunosensor was supported by the successful detection of RAC in pork samples with recovery ranging from 94.00% to 106.00%. CONCLUSION: We designed a novel sandwich-type noncompetitive colorimetric immunoassay for the detection of trace levels of RAC in pork. The proposed method can also be used for the detection of toxins in food products via PtNPs-PV amplification. © 2018 Society of Chemical Industry.

Change of the structure and the digestibility of myofibrillar proteins in Nanjing dry-cured duck during processing.

BACKGROUND: To investigate the change of bioavailability and structure of myofibrillar proteins during Nanjing dry-cured duck processing, carbonyl content, sulfhydryl (SH) group, disulfide (SS) group, sodium dodecyl sulfate polyacrylamide gel electrophoresis, surface hydrophobicity, secondary structures and in vitro digestibility were determined. RESULTS: During processing, carbonyl content and surface hydrophobicity increased; SH turned into SS group; α-helix turned into ß-sheet and random coil fractions. Protein degradation occurred during dry-curing and drying-ripening stages. The in vitro digestibility of pepsin and pancreatic proteases increased during the salt curing stage and decreased during the drying-ripening stage. CONCLUSION: The increase of digestibility could be attributed to the mild oxidation, degradation and unfolding of proteins while the decrease of digestibility was related to the intensive oxidation and aggregation of proteins. Protein degradation was not a main factor of digestibility during the drying-ripening stage. Results demonstrated that the bioavailability loss of myofibrillar proteins in Nanjing dry-cured duck occurred during the stage of drying-ripening instead of curing. © 2017 Society of Chemical Industry.

Transepithelial transport of milk-derived angiotensin I-converting enzyme inhibitory peptide with the RLSFNP sequence.

BACKGROUND: To exert an antihypertensive effect after oral administration, angiotensin I-converting enzyme (ACE)-inhibitory peptides must remain active after intestinal transport. The purpose of this article is to elucidate the transport permeability and route of ACE-inhibitory peptide Arg-Leu-Ser-Phe-Asn-Pro (RLSFNP) across the intestinal epithelium using Caco-2 cell monolayers. RESULTS: Intact RLSFNP and RLSFNP breakdown fragments F, FNP, SFNP and RLSF were found in RLSFNP transport solution across Caco-2 cell monolayers using ultra-performance liquid chromatography-tandem mass spectrometry. RLSFNP fragments FNP, SFNP and RLSF also contributed to ACE inhibitory effects. Protease inhibitors (bacitracin and leupeptin) and absorption enhancers (sodium glycocholate hydrate, sodium deoxycholate and Na2 EDTA) improved the transport flux of RLSFNP. A transport inhibitor experiment showed that intact RLSFNP may be transported via the paracellular route. CONCLUSION: Intact RLSFNP can be transported across the Caco-2 cell monolayers via the paracellular route. Extensive hydrolysis was the chief reason for the low permeability of RLSFNP. © 2017 Society of Chemical Industry.

Metabonomics profiling of marinated meat in soy sauce during processing.

BACKGROUND: Marinated meat in soy sauce is one of the most popular traditional cured meat products in China. Its taste quality is directly related to primary and secondary metabolites. Herein, the change of metabolite composition of marinated meat in soy sauce during processing was systematically characterised using 1 H NMR and multivariate data analysis. RESULTS: The marinated meat in soy sauce metabonome was dominated by 26 metabolites, including amino acids, sugars, organic acids, nucleic aides and their derivatives. PC1 and PC2 explained a total of 78.6% and 16.6% of variables, respectively. Amino acids, sugars, acetate, succinate, uracil and inosine increased during marinating, while lactate, creatine, inosine-5'-monophosphate (5'-IMP) and anserine decreased (P < 0.05). After marinating, most of the metabolites decreased except for acetate and alanine (P < 0.05). There was a negative effect on the taste of marinated meat in soy sauce during the late stage of dry-ripening. CONCLUSION: These findings indicated that the potential of NMR-based metabonomics is of importance for taste quality of marinated meat in soy sauce, which could contribute to a better understanding of the changes of taste compounds in meat products during processing. Shortening the dry-ripening period could be considered to improve the taste quality. © 2017 Society of Chemical Industry.

The effect of cooking temperature on the aggregation and digestion rate of myofibrillar proteins in Jinhua ham.

BACKGROUND: In order to evaluate the effect of cooking temperature on the nutrition quality of dry-cured hams, 60 biceps femoris samples from 16 Jinhua hams were divided into four groups (control, 70, 100 and 120 °C) and cooked for 30 min. Carbonyl content, sulfhydryl groups, surface hydrophobicity, microstructure, protein aggregation and digestibility of myofibrillar proteins were investigated. RESULTS: Cooking promoted carbonylation and decreased sulfhydryl groups in a temperature-dependent way. Scanning electron microscopy and Nile Red revealed that protein aggregation became a main phenomenon at 120 °C; it coincided with surface hydrophobicity. The increased carbonyl content and decreased sulfhydryl groups contributed to the formation of aggregates. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis profiles showed the initial difference in proteolysis rate among four groups. The in vitro digestibility of pepsin and of trypsin and α-chymotrypsin increased from the control to 100 °C and decreased from 100 to 120 °C. CONCLUSION: The increased digestibility could be attributed to the oxidation of proteins and exposing recognition sites of digestive enzymes, while the decreased digestibility was due to the formation of aggregates. Cooking was a main factor that affected the digestibility of Jinhua ham, and cooking at 100 °C could be an ideal way to gain the highest digestibility of Jinhua ham. © 2018 Society of Chemical Industry.

The Proliferation Mechanism of Lactobacillus plantarum RB1 Stimulated by Stachyose.

The proliferation mechanism of Lactobacillus plantarum RB1 promoted by stachyose was investigated in this work. The hydrolysis of stachyose, the glycometabolism, and the cytoactivity of L. plantarum RB1 were detected after proliferation. The specific activity of α-galactosidase of L. plantarum RB1 in the stachyose group was significantly higher than the control group (without stachyose), which indicated that the stachyose induced L. plantarum RB1 and produced more α-galactosidase to hydrolyze stachyose. The glycometabolism which includes glycolysis and tricarboxylic acid (TCA) cycle was significantly enhanced in the stachyose group compared with the control group. For the glycolysis, the reducing sugar content in the fermentation broth was significantly lower, while the lactic acid content and the specific activity of lactic dehydrogenase (LDH) as the key enzyme in glycolysis were higher than in the control group. For the TCA cycle, the specific activity of pyruvate dehydrogenase (PDH) as a gatekeeping enzyme leads glycolysis to TCA cycle energy-generating pathways was significantly enhanced compared with the control group. Moreover, the cell metabolic activity of L. plantarum RB1 in stachyose was significantly higher than the control group. These results indicated that the stachyose highly promotes proliferation of lactic acid bacteria (LAB) by inducing LAB to produce more α-galactosidase to hydrolyze stachyose, increasing glycometabolism and cytoactivity of LAB, which revealed the mechanisms how the stachyose promotes the proliferation of LAB.

The effect of microwave on the interaction of flavour compounds with G-actin from grass carp (Catenopharyngodon idella).

BACKGROUND: In order to investigate the influence of non-thermal effects of microwaves on the flavour of fish and meat products, the G-actin of grass carp in ice baths was exposed to different microwave powers (0, 100, 300 or 500 W); the surface hydrophobicity, sulfhydryl contents, secondary structures and adsorption capacity of G-actin to ketones were determined. RESULTS: As microwave power increased from 0 to 300 W, the surface hydrophobicity, total and reactive sulfhydryls increased; α-helix, ß-sheet and random coil fractions turned into ß-turn fractions. As microwave power increased from 300 to 500 W, however, hydrophobicity and sulfhydryl contents decreased; ß-turn and random coil fractions turned into α-helix and ß-sheet fractions. The tendencies of adsorbed capacity of ketones were similar to hydrophobicity and sulfhydryl contents. CONCLUSION: The increased adsorbing of ketones could be attributed to the unfolding of secondary structures by revealing new binding sites, including thiol groups and hydrophobic binding sites. The decreased binding capacity was related to the refolding and aggregation of protein. The results suggested that microwave powers had obvious effects on the flavour retention and proteins structures in muscle foods. © 2017 Society of Chemical Industry.

iTRAQ proteomic analysis of N-acetylmuramic acid mediated anti-inflammatory capacity in LPS-induced RAW 264.7 cells.

Lactobacillus acidophilus probiotic bacteria have lasting beneficial health effects in the gastrointestinal tract, including protecting against pathogens, improving immunomodulation, and producing beneficial bacteria-derived molecules. In lipopolysaccharide (LPS) induced RAW 264.7 cells treated with peptidoglycan or N-acetylmuramic acid (NAM) from L. acidophilus, 390 differentially expressed proteins (8.76%) were identified by iTRAQ analysis, 257 (5.77%) of which were upregulated and 133 (2.99%) were downregulated under LPS-induced conditions. Most of these proteins were grouped into the following inflammation-related cellular signaling: lysosome pathway, calcium signaling pathway, and Toll-like receptor (TLR) signaling pathway. Among them, clathrin, SERCA, and interleukin 1 receptor antagonist were differentially expressed to a significant degree in peptidoglycan or NAM pretreated RAW 264.7 cells. Bioinformatics analysis indicated that NAM may mediate an anti-inflammatory process via a Ca(2+) -dependent NF-κB pathway. These observations reveal new insights into the molecular mechanisms involved in the suppression of LPS-induced macrophage inflammation by L. acidophilus.

Highly Sensitive Electrochemical Determination of Alfatoxin B1 Using Quantum Dots-Assembled Amplification Labels.

A competitive electrochemical immunoassay for highly sensitive detection of AFB1 is demonstrated using layer-by-layer (LBL) assembled quantum dots (QDs) as labels. To investigate the effects of the higher sensitivity of square wave voltammetric stripping (SWV) and of the LBL technique on the proposed immunoassays, the proposed assay was compared to electrochemical (EC) and fluorescent immunoassays, which did not use LBL technology. Peanut samples were analyzed using the three immunoassays. The limits of detection (LODs) were 0.018, 0.046 and 0.212 ng/mL, respectively, while the sensitivities were 0.308, 1.011 and 4.594 ng/mL, respectively. The proposed electrochemical immunoassay displayed a significant improvement in sensitivity, thereby providing a simple and sensitive alternative strategy for determining AFB1 levels in peanut samples.

Purification and characterization of α-acetolactate decarboxylase (ALDC) from newly isolated Lactococcus lactis DX.

BACKGROUND: Diacetyl (2,3-butanedione) is a common flavor aroma from fermented dairy products. There is a need to screen new microorganisms that can efficiently produce large amounts of diacetyl. RESULTS: A new lactic acid bacterium that produced high concentrations of diacetyl was identified based on Gram staining, microscopic examination and 16S rDNA sequence analysis as Lactococcus lactis DX. Its α-acetolactate decarboxylase (ALDC) was purified using 0.45 g mL(-1) ammonium sulfate precipitation, Sephacryl S-300 and S-200 HR and native-PAGE. The purified ALDC displayed a monomer structure and had a molecular mass of about 73.1 kDa, which was estimated using SDS-PAGE. IR analysis showed that the ALDC had a typical protein structure. The optimal temperature and pH for ALDC activity were 40 °C and 6.5 respectively. The ALDC of L. lactis DX was activated by Fe(2+) , Zn(2+) , Mg(2+) , Ba(2+) and Ca(2+) , while Cu(2+) significantly inhibited ALDC activity. Leucine, valine and isoleucine activated the ALDC. CONCLUSION: A strain that had high ability to produce diacetyl was identified as L. lactis DX. The difference in diacetyl production may be due to the ALDC, which is different from other ALDCs.