A pilot study on PCR-based detection of four foodborne pathogenic microorganisms

To establish PCR-based detection methods for Staphylococcus aureus, Shigella, Pasteurella multocida and Pseudomonas aeruginosa, the nuc, ipah, ptfa and oprl genes were amplified by singleplex PCRs and multiplex PCR using specific primers that were designed according to the DNA sequences retrieved from GenBank. Then the annealing temperature was optimized, accompanied by a study of the specificity and sensitivity of the singleplex PCRs and multiplex PCR. The results showed that DNA fragments of 280, 474, 150 and 331 bp were specifically amplified from the four pathogenic bacteria mentioned above. No target DNA fragments were obtained from other pathogenic bacteria, including Salmonella typhimurium, Campylobacter jejuni, Clostridium perfringens and pathogenic Escherichia coli. The sensitivity of the singleplex PCRs were 100, 1, 1 and 10 pg/μL respectively. The detection limits of the four pathogenic bacteria in the multiplex PCR were 100, 1, 10 and 10 pg/µL respectively. These results showed that singleplex PCRs and multiplex PCR have good specificity and sensitivity. In conclusion, this experiment has laid a foundation for further research on rapid detection methods against these four pathogenic bacteria in food.     

Development of a Simple,Rapid Multiplex PCR Method Using the 16S rRNA Gene to Determine the Country of Origin of Brackish Water Bivalve <Emphasis Type="Italic">Corbicula japonica</Emphasis>

In this study, a multiplex PCR detection method was developed to identify the country of origin of Corbicula japonica (clams), a commercially important bivalve in Asia. Specific primer sets that have a single nucleotide mismatch at the 3′ terminus were designed after sequencing the mitochondrial 16S rRNA gene of clams identified as C. japonica originating from Korea, China, and Japan. Using this method, each origin was clearly identified based on the PCR products: three bands for Korean C. japonica (100, 283, and 384 bp), one band for Chinese C. japonica (384 bp), and two bands for Japanese C. japonica (384 and 100 bp). These results indicate that the 16S rRNA gene, which is usually used to identify species, can distinguish the country of origin within C. japonica. Our multiplex PCR assay should be a useful tool for the fair trade of the species.     

Polymerase chain reaction for the detection of<Emphasis Type="Italic"> Phaseolus vulgaris</Emphasis> beans in chestnut purée

A method based upon polymerase chain reaction (PCR) for the detection of Phaseolus vulgaris beans in chestnut purée was developed. The method involves DNA isolation by the GeneSpin kit and PCR with primers oriented to a sequence of a nuclear gene encoding PvLEA-18, a late embryogenesis-abundant protein of beans. The PCR method was shown to be specific for Ph. vulgaris, producing a 100 bp fragment with six Ph. vulgaris cultivars, and negative results with four non-Ph. vulgaris Phaseolus samples and five non-Phaseolus legumes. When evaluated with model mixtures of Ph. vulgaris beans and the chestnut purée, a detection limit of 1% was determined.     

Rapid Detection of <Emphasis Type="Italic">Vibrio parahaemolyticus</Emphasis> in Shellfish by Real-Time Recombinase Polymerase Amplification

Vibrio parahaemolyticus (V. parahaemolyticus) is a zoonotic pathogen generally found in seafood. To detect the foodborne pathogen rapidly and accurately for food safety measures, we developed a real-time recombinase polymerase amplification (RPA) method. An evaluation of the specificity and sensitivity of the method is discussed here. A set of primers and probe was specially designed to target the tlh gene, which is usually regarded as a marker of total V. parahaemolyticus strains. During the reaction, target DNA was amplified and tagged with specific fluorophore within 10 min and at an incubation temperature of 40 °C. In addition to fast amplification and low temperature, the fluorescence signal was synchronized with the amplification of products for the generation of real-time data. The detection limit of this assay was 0.4 pg/μL of DNA, which is comparable to assays that use the bacterial culture as template, 4?×?10³ cfu/mL. The real-time RPA method had a stable performance when testing the spiking shellfish samples at the same level of contamination by the pathogen in different kinds of shellfish. Thus, the real-time RPA method shows great potential for on-site detection of V. parahaemolyticus, especially in low-resource settings.     

Quantification of <Emphasis Type="Italic">Penicillium nalgiovense</Emphasis> on Dry-Cured Sausage ‘Salchichón’ Using a SYBR Green-Based Real-Time PCR

To evaluate the effective implantation of a specific protective culture of Penicillium nalgiovense, a real-time quantitative PCR (qPCR) using SYBR Green methodology was developed. Two specific primers were designed on the basis of the published partial sequences of the Internal Transcribe Spacer (ITS)1–5.8S-ITS2 region of various strains of P. nalgiovense. Using the developed method, a PCR product of 51 bp with a T _m value 81.34 °C was detected. T _m values of the amplified product allowed specific differentiation between P. nalgiovense and the remaining mould species tested. The developed qPCR method was tested on inoculated slices of dry-cured sausage (‘salchichón’) showing an efficiency of 97.24 %, a R ² value of 0.99 and a detection limit of P. nalgiovense of 1 log colony-forming units (cfu)/cm². The qPCR method demonstrated that the protective strain of P. nalgiovense grew and competed against an ochratoxin A (OTA)-producing Penicillium verrucosum strain on commercial dry-cured sausage. This qPCR method provides a specific, accurate and sensitive detection and quantification of P. nalgiovense on dry-cured sausage salchichón in order to estimate its colonization during their processing. This assay will improve strategies to prevent and control unwanted mould colonization and OTA risk in dry-cured meat commodities.     

Effects of organic acid pretreatment on microstructure,functional and thermal properties of unripe banana flour

Starch availability has been implicated in unripe matured banana (Musa species), which when processed yields flour suitable for application in low gluten and composite wheat formulations. Unripe Musa species: Williams, Luvhele, Mabonde and Muomva-red obtained from fruit bunch were pretreated with ascorbic, citric and lactic acids, processed into 50 g of flour and characterised for their functional and thermal properties. Scanning electron microscope of unripe banana flour (UBF) showed varying micrographs of flour, with polygonal for Luvhele, oval for Mabonde, elongated for Muomva-red and between polygonal and spherical for Williams. The bulk density of UBF samples was within the range of 0.66–0.84 g/mL for all organic acid pretreatment while citric acid pretreated UBF had the least browning index. Significant difference (p < 0.05) was recorded in swelling power with no significant difference in water solubility index except for Mabonde UBF. Thermal properties showed single endothermic transition for all UBF samples at various pretreatment concentration. The onset temperature (To) of UBF ranges from 49.82 to 65.59 °C, peak temperature (Tp) from 60.11 to 76.71 °C, conclusion temperature (Tc) from 70.36 to 94.16 °C and enthalpy of gelatinization (ΔH) from 2.61 to 32.24 J/g. Short amylopectin chains present in starch of UBF was attributed to low To, Tp, Tc and ΔH values recorded for Mabonde cultivar, while the contribution of heat-moisture treatment rather than organic acid pretreatment of UBF samples was attributed to different gelatinization and transition temperatures recorded for all cultivars examined.     

Comparative Study on the Inactivation and Photoreactivation Response of <Emphasis Type="Italic">Listeria monocytogenes</Emphasis> Seafood Isolates and a <Emphasis Type="Italic">Listeria innocua</Emphasis> Surrogate after Pulsed Light Treatment

The inactivation and photoreactivation response of six seafood-isolated Listeria monocytogenes and one Listeria innocua strain after pulsed light (PL) treatment was evaluated. The lower inactivation levels found after exposure of treated samples to daylight during the first 90 min of storage confirmed that both L. innocua and L. monocytogenes have the capability to photorepair PL-induced DNA damage upon appropriate conditions. Photoreactivation levels from 0.2 to 2.1 log CFU cm^?2 were observed depending on treatment intensity (fluence) and Listeria strain. Complete photorepair of PL-caused damage was not found even after treatments inducing low inactivation levels. Photoreactivation increased up to 2.1 log with the applied fluence up to a threshold able to cause between 2.4 and 5.4 log reductions under dark storage. Photorepair was not avoided but lower photoreactivation was observed after higher fluence inducing more than 6 log reductions under dark storage. Both L. innocua and L. monocytogenes serotype 1/2b exhibited the highest photoreactivation levels whereas serotypes 1/2a showed the lowest ones. The overall inactivation and photoreactivation responses of tested Listeria strains were comparable indicating that L. innocua may be a good surrogate for the safe evaluation, optimization and validation of PL technology to control L. monocytogenes in food products and food processing facilities.     

Probe-Based Fluorescence Melting Curve Analysis for Differentiating <Emphasis Type="Italic">Larimichthys polyactis</Emphasis> and <Emphasis Type="Italic">Larimichthys crocea</Emphasis>

Larimichthys polyactis (redlip yellow croaker) and Larimichthys crocea (large yellow croaker) are commercially important fish species in East Asia with high differences in their market values. In Korea, consumers prefer L. polyactis to L. crocea, although it is difficult to distinguish them based on their morphological traits. The objective of this study was to develop an assay for differentiating L. polyactis and L. crocea using fluorescence melting curve analysis (FMCA) with a single locked nucleic acid (LNA) probe. Species-specific regions of the mitochondrial 16S rDNA were selected as LNA probes. The target sequences of L. polyactis and L. crocea had a 2-bp difference, and a single LNA probe was identified using melting temperature (Tm) shift. LNA probe was 100 % complementary to the target sequence of ten L. polyactis samples, giving a significantly higher Tm value (66 °C) than that of five L. crocea samples (42 °C). Overall, the developed LNA-based FMCA system had high efficiency, multiplexity, and simplicity, and could be effectively used for differentiating L. polyactis and L. crocea, and as a food analyzing method based on DNA sequence.     

Effect of Thermosonic Pretreatment and Microwave Vacuum Drying on the Water State and Glass Transition Temperature in <Emphasis Type="Italic">Agaricus bisporus</Emphasis> Slices

This study aimed to understand the micromechanism of thermosonic pretreatment and microwave vacuum drying on Agaricus bisporus. The water state and glass transition temperature (T _g ) of fresh and thermosonically treated Agaricus bisporus slices during microwave vacuum drying were studied using differential scanning calorimetry (DSC), low-field nuclear magnetic resonance (LF-NMR), and magnetic resonance imaging (MRI). Results showed that four population groups were contained in the initial distribution of transverse relaxation time (T ₂) data of fresh A. bisporus slices: T ₂₁ (0.38–7.05 ms), T ₂₂ (9.33–32.75 ms), T ₂₃₁ (37.65–265.61 ms), and T ₂₃₂ (305.39–811.13 ms). Thermosonic pretreatment significantly decreased the initial free water content of A. bisporus sample but was accompanied by a sharp increase in its immobilized water. “Semi-bound water transfer” appeared during microwave vacuum drying (MVD) at moisture contents (X _w ) of 0.70 and 0.60 g/g (wet basis (w.b.)) for untreated and thermosonically treated samples, respectively. MVD caused dramatic changes in the water state and enhanced the T _g by decreasing the content and mobility of immobilized water in A. bisporus tissues. The mobility of semi-bound water for thermosonically and MVD-treated samples was higher than for MVD-untreated samples, resulting in T _g values decreasing by approximately 2–11.5 °C, but the uniformity of water distribution in thermosonic-treated and MVD-treated samples was better at X _w  ≤ 0.52 g/g (w.b.).     

Influence of 10-MeV E-Beam Irradiation and Vacuum Packaging on the Shelf-Life of Grass Carp Surimi

The effects of 10-MeV E-beam (0, 1, 3, 5, and 7 kGy) irradiation and vacuum packaging on extending the shelf-life of grass carp surimi stored at 4 °C were evaluated basing on the total viable counts (TVC), physiochemical 2-thiobarbituric acid reactive substance (TBARS), total base nitrogen (TVB-N), biogenic amines (BAs), texture (TPA) and color, and sensory changes in surimi samples. The results showed that comparing the control samples, the TVC and TVB-N content in surimi were significantly (p?<?0.05) decreased by irradiation with different doses. Irradiation significantly (p?<?0.05) inhibited the increase of putrescine (PUT), cadaverine (CAD), histamine (HIM), and tyramine (TYM) contents during storage. However, these parameters were significantly (p?<?0.05) increased with storage time. After irradiation, the samples generally had higher lightness and lower a ^* and b ^* values and lower hardness and chewiness significantly (p?<?0.05). Based on the sensory analysis, unfavorable ‘metal odor’ or ‘irradiated odor’ was observed in surimi irradiated at 5 and 7 kGy.     

Stabilization of Refrigerated Avocado Pulp: Chemometrics-Assessed Antibrowning Allium and Brassica Extracts as Effective Lipid Oxidation Retardants

The effectiveness of Allium and Brassica extracts to inhibit the evolution of lipids oxidation in avocado pulp under refrigeration (storage at 4 °C) was studied. Onion, garlic, scallion, white cabbage, cauliflower, and Brussels sprouts extract were tested as preserving agents in refrigerated avocado pulp. Allium extracts promoted almost a 60% retention of the intrinsic anti-radical capacity of the pulps. Considering secondary oxidation effects, extinction coefficient at 270 nm shows that all treated pulps (except those with scallion addition) were acceptable at the 30th storage day (K ₂₇₀ < 0.22), but they were all significantly less oxidized than the untreated samples (K ₂₇₀ = 1.8) (P < 0.05). Garlic-treated avocado showed the highest antioxidant effectiveness, based on C=CH cis proportion (I _cis = 108.3), while samples with white cabbage extract presented the highest C=CH trans (I _trans = 5.7) proportion after 30 days. The PCA method was discriminant enough since 83.6% of the variance was explained by the first two principal components, allowing the samples to be grouped according to storage time and extract type. This study confirmed that the addition of garlic, onion, and cauliflower extracts enhanced lipid antioxidant properties in refrigerated avocado pulps.     

Enterohemorrhagic <Emphasis Type="Italic">Escherichia coli</Emphasis> (EHEC) in water from karst springs: detection with real-time PCR and isolation of strains

Within 2 months, two water sources in a karst area in Switzerland were sampled 9 times each, and analyzed by real-time PCR for 6 EHEC O-types, Shiga-like-toxin (stx1 and stx2) and intimin (eae) genes. With the exception of O111, 5 O-types were recorded regularly and at high frequencies (O26: 33.3 %; O157: 33.3 %; O104: 66.6 %; O103: 72.2 %; O145: 94.4 %). Genes for Shiga-like-toxins and intimin were almost omnipresent (stx1: 77.8 %; stx2: 83.3 %; eae: 77.8 %). Strain isolation was undertaken for O-groups 26, 103, 104, 145 and 157. Sample selection for strain isolation was based on Cq-values for the O-groups and stx1, stx2 and eae. From selected samples, frozen enrichment cultures were cultivated on EHLY-agar and 50 typical colonies screened for the O-type and genes encoding for stx1, stx2 and eae. With this approach, only one virulent EHEC-strain could be isolated (Escherichia coli O103, stx1 +; stx2 ?; eae +). We carried out one extensive testing with 800 colonies of O-group O145, and no virulent strain was isolated. Our findings showed that PCR-results are not sufficient to formulate epidemiological conclusions and that the isolation of strains is necessary. However, as the detection procedure of EHEC in foods is cumbersome and expensive, the appropriateness of such an approach in official food control is a matter of debate.     

Development and characterization of reconstituted hydrogel from <Emphasis Type="Italic">Aloe vera</Emphasis> (<Emphasis Type="Italic">Aloe barbadensis</Emphasis> Miller) powder

Structural and rheological characterization of reconstituted hydrogels developed from A. vera non-fibrous alcohol insoluble residue (NFAIR) powder using different methods [viz., shaking (S), heating-shaking (HS), and heating (H)] and concentrations (viz., 0.2–1.6 %, w/v) was carried out. Functional group distribution by FTIR spectroscopy and Congo red (CR) method revealed the presence of acetylated acemannan in A. vera powder. Dynamic oscillation studies of A. vera (NFAIR) fluids at all concentrations of 0.2–1.6 %, w/v, showed gel strength in the order of H > HS > S method. However, in H method, increase in concentration from 0.2 to 1.6 %, w/v showed the conformational transition from semi-diluted solution to weak gel nature. Rheological models described the effect of heating temperatures (HT); 30–90 °C, and times (Ht); 15–60 min on viscoelastic behavior in reconstituted A. vera fluids. The reconstituted A. vera hydrogel prepared with a concentration of 1.6 %, w/v using 50 °C (HT) and 30 min (Ht) condition showed a good agreement with the Power law (storage modulus, G′) and Weak gel model (complex modulus, G*) fitted data (R² > 0.94) resulting higher viscoelastic moduli intercepts; G′₀ (71.5 Pa s ^n′), G″₀ (33.5 Pa s ^n″), lower slopes; n′ (0.22), n″ (0.06), higher network strength (A _F , 121.3 Pa s^1/z ) and number of network (z, 5.3) values. The obtained results suggested that heating at 50 °C/30 min can develop aqueous weak gel networks of A. vera with enhanced gel strength which may be utilized as a novel gelling agent for wide variety of targeted applications in food and pharmaceutical sectors.     

Smart NMR Method of Measurement of Moisture Content of Vegetables During Microwave Vacuum Drying

Microwave drying is usually combined with vacuum environment in conjunction with hot air flow to draw the moisture rapidly. The moisture content of the vegetables undergoing drying is hard to measure online. This research designed a microwave vacuum drying (MVD)-low-field nuclear magnetic resonance (NMR) smart device and investigated the feasibility of NMR method for online measurement of state of moisture during MVD. The relation between the signal amplitude (A ₂) and the true moisture content (M ₁) of six kinds of vegetables (mushroom, carrot, potato, lotus, edamame, vegetable corn) was fitted to estimate if NMR can measure the M ₁ of vegetables directly. Results showed that A ₂ and M ₁ of different fresh vegetables had no single empirical mathematical model to fit. However, for each kind of these vegetables, the A ₂ and corresponding M ₁ in different MVD stages showed a significant linear relationship. The predicted moisture content (M ₂) of mushroom: M ₂ = 5.25351 × 10^?4 A ₂ ? 0.34042, R = 0.996; carrot: M ₂ = 5.78756 × 10^?4 A ₂ ? 0.14108, R = 0.998; potato: M ₂ = 3.10019 × 10^?4 A ₂ ? 0.10612, R = 0.991; lotus: M ₂ = 2.32415 × 10^?4 A ₂ ? 0.01573, R = 0.998; edamame: M ₂ = 3.13310 × 10^?4 A ₂ ? 0.4198, R = 0.996; vegetable corn: M ₂ = 1.69461 × 10^?4 A ₂ ? 0.09063, R = 0.995. The linear models between M ₂ and A ₂ were able to estimate the end point (M ₁ < 8%) of MVD with a high accuracy (P > 0.950).     

Detection of Viable <Emphasis Type="Italic">Vibrio cholerae</Emphasis> Cells in Seafood Using a Real-Time Visual Loop-Mediated Isothermal Amplification Combined with Propidium Monoazide

Vibrio cholerae is an important foodborne pathogen causing severe intestinal infectious diseases that have high incidence and mortality. Almost all of rapid testing methods including immunological and molecular assays for V. cholerae are incapable of distinguishing live cells from dead ones, which may overestimate the number of bacteria and result in many false positive results. To address the problems, live cell-specific dye such as propidium monoazide (PMA) is employed. The loop-mediated isothermal amplification (LAMP) assay is a nucleic acid amplification method that is fast, specific, and sensitive. In this study, we developed a real-time visual LAMP assay using PMA dye to detect thyA gene, thereby identifying viable V. cholerae cells. The results showed that only V. cholarae strains could be detected, and there was no cross-reaction with non-V. cholarae strains. Besides, the sensitivity of the PMA-LAMP assay was 1.1 × 10² CFU/mL and the entire reaction could be accomplished within 1 h. The sensitivity was on par with that of the PMA-qPCR assay. The detection limit in different artificially inoculated samples was 5 CFU/25 g materials for the tested pathogens. In the practical test, the PMA-LAMP assay performed well in comparison with PMA-qPCR and the culture method. Hence, PMA-LAMP assay can provide a highly effective and rapid approach for detecting viable V. cholerae.     

Steaming time effects on the moisture migration and structural properties of Chinese Northern-style steamed bread

The aim of this study was to investigate the steaming time effects on proton transverse relaxation behavior with low field 1H nuclear magnetic resonance and structural properties of Chinese Northern-style steamed bread (CNSB). Three proton populations could be distinguished at the first 4 min: T_2b (0.1–1 ms) corresponded to rigid and exchangeable protons; T₂₂ (9–21 ms) was associated with the water protons in small and large meshes of the dough microstructure; T₂₃ (69–300 ms) was assigned to the water protons on the surface of samples. The starch gelatinization began and the water turned into the integral part of the biopolymer at 6 min, forming T₂₁ (1–3 ms) fraction. The gelatinization effect was strengthened up to 8 min and supplied a more mobile microenvironment, resulting in the increase of T₂₁, A₂₁ and M₂₁. However, the gelatinization process ended at 8 min, bringing about the stabilization of T₂₁, A₂₁ and M₂₁ until 25 min. T₂₂ fraction accounted for the largest proportion during all the steaming process. All variation trends on structural properties of CNSB and T₂ relaxation parameters including T_i, A_i (relative intensity of T_i), and M_i (population abundance of T_i) indicated that 6 and 8 min were the two transitions. The gluten matrix began to be disrupted at 6 min and was quite damaged up to 8 min by scanning electron microscopy. The peaks at 15°, 18°, 20°, and 23° in X-ray diffraction patterns appeared in the first 6 min but were lost up to 8, 10, and 25 min.     

Evaluation of colour properties and chemical quality parameters of cactus juices

The chemical composition and visual appearance of cactus fruits from the genera Opuntia and Hylocereus were investigated. Colour properties were assessed in solutions with pH ranging from 1 to 8 and expressed as chroma, hue and colour shade. Between pH 3 and 7, all samples were stable as indicated by hue and chroma values. The colour shade of the red juice of Opuntia ficus-indica cv. 'Rossa' was in the range of red beet preparations hitherto most commonly used for colouring low-acid food commodities. Hylocereus was characterized by purplish hues, whereas the juice from O. ficus-indica cv. 'Gialla' displayed a yellow tonality. An improved spectrophotometric method for pigment quantification was proposed. Betacyanin contents were 525.3, 73.9 and 1.3 mg/l in juices from Hylocereus polyrhizus, Opuntia ficus-indica cv. 'Rossa' and O. ficus-indica cv. 'Gialla', whereas betaxanthins amounted to 48.3, 36.4 and 5.3 mg/l in O. ficus-indica cv. 'Gialla', O. ficus-indica cv. 'Rossa', and H. polyrhizus, respectively. Although the colourless fruits from O. ficus-indica cv. 'Bianca' and H. undatus could not be considered as a colour source, selected quality parameters were also investigated with respect to their nutritional value. To the best of our knowledge, this is the first report about the chemical quality parameters of H. polyrhizus and H. undatus.     

Steady- and Unsteady-State Determination of the Water Vapor Permeance (<Emphasis Type="Italic">WVP</Emphasis>) of Polyethylene Film to Estimate the Moisture Gain of Packed Dry Mango

The water vapor permeance (WVP; g m^?2 d^?1 Pa^?1) of packaging films quantifying the water vapor transfer rate between foods and its surroundings is usually determined in units operating under steady-state conditions that do not necessarily reflect food handling scenarios. This study evaluated the determination of the WVP of a polyethylene (PE) film by steady-state method ASTM F1249-06 using a permeability cell and unsteady-state method ASTM E96/E96M in which 102 vacuum-sealed PE bags containing silica gel were stored (37.8 °C, 75% relative humidity) and weighed over 25 days. Average steady-state WVP (2.935 ± 0.365 × 10^?3, n = 4) fell within the 95% quantiles of unsteady-state WVP values (1.818–3.183 × 10^?3, n = 2142). Moisture uptake of dehydrated mango stored at 37.8 °C and 75% relative humidity was predicted with WVP values obtained by both methods. Predictions were validated by monitoring over 25 days the weight gain of 100 PE bags with dry mango. Experimental moisture averages during storage fell within one standard deviation of predictions using the unsteady-state WVP (R ² = 0.974). The same was observed only until day 15 for predictions obtained with the steady-state WVP. Calculations for days 20–25 overestimated the moisture uptake by 6.0–7.2%, resulting in registered R ² = 0.924. The unsteady-state WVP determination is low-cost, uses large numbers of film samples, and allowed more accurate predictions of dry mango moisture uptake. Knowledge of the moisture uptake controlled by the film WVP is essential when predicting the safety and quality changes limiting the shelf-life of foods.     

Drying kinetics,colour, total phenolic content and antioxidant capacity properties of kiwi dried by different methods

This study analysed the convective (60, 70 and 80° C), microwave (120 and 350 W) and freeze drying methods in terms of their effects on the drying characteristics, colour, total phenolic content (TPC) and antioxidant capacity of kiwi slices. Nine different mathematical models were applied to experimental data to achieve the most accurate calculation for drying curves. The Midilli et al. and Wang and Singh models proved to be the most suitable at explaining the drying kinetics of kiwi samples as compared to other models according to the statistical tests. Each drying method was significantly affected by colour parameters (L*, a*, b*, C, α and ΔE). The dried samples exhibited respectively 5–49 % and 10–47 % less TPC and antioxidant capacity compared to the fresh sample. According to the correlation analysis conducted between TPC and antioxidant capacity for kiwi slices, there is a positive correlation (R ²  = 0.7796). Microwave dried samples at 120 W particularly had the lowest TPC and antioxidant capacity. Freeze drying method yielded the closest values with respect to colour values, total phenol content and antioxidant capacity to those of fresh samples when compared to the other methods.     

Real-Time Recombinase Polymerase Amplification Assay for the Detection of <Emphasis Type="Italic">Vibrio cholerae</Emphasis> in Seafood

Vibrio cholerae, the most hazardous Vibrio species, is threatening aquacultured animals and even human beings. In recent years, a few genetic markers that target V. cholerae have been reported, but their application was limited by techniques or themselves. The outer membrane lipoprotein gene lolB has been identified as a specific marker by using PCR and quantitative PCR methods. In this study, we developed a real-time recombinase polymerase amplification (RPA) assay targeting lolB gene in an attempt to provide a sensitive, rapid, and reliable detection method of V. cholerae. The sensitivity of RPA assay was determined by amplifying the standard plasmid dilutions. The detection limit down to five copies was achieved within 10 min, which was lower than that of qPCR (ten copies after 25 cycles within 1.5 h). The reproducibility of RPA assay was verified by eight independent experiments, presenting a high R ² value of the standard regression line (0.97). In addition, the specificity was confirmed with DNA extracted from other bacteria, shrimps, clams, and fishes using both methods. Finally, V. cholerae in shrimp samples were quantified using real-time RPA and qPCR with consistent outcomes, while no amplification was obtained from clam and fish samples using both methods. The applicability in the food industry was confirmed by quantitative detection of natural seafood.