Methods for the direct and indirect assessment of the bacterial content of milk

A Technique for Rapid Bacterial-Density Enumeration through Membrane Filtration and Differential Pressure Measurements

In this article, we present a microfluidic technique for the rapid enumeration of bacterial density with a syringe filter to trap bacteria and the quantification of the bacterial density through pressure difference measurement across the membrane. First, we established the baseline differential pressure and hydraulic resistance for a filtration membrane by fully wetting the filter with DI water. Subsequently, when bacteria were infused and trapped at the pores of the membrane, the differential pressure and hydraulic resistance also increased. We characterized the infusion time required for the bacterial sample to achieve a normalized hydraulic resistance of 1.5. An equivalent electric-circuit model and calibration data sets from parametric studies were used to determine the general form of a calibration curve for the prediction of the bacterial density of a bacterial sample. As a proof of concept, we demonstrated through blind tests with Escherichia coli that the device is capable of determining the bacterial density of a sample ranging from 7.3 × 10⁶ to 2.2 × 10⁸ CFU/mL with mean and median accuracies of 87.21% and 91.33%, respectively. The sample-to-result time is 19 min for a sample with lower detection threshold, while for higher-bacterial-density samples the measurement time is further shortened to merely 8 min.

Rapid and concise quantification of mycelial growth by microscopic image intensity model and application to mass cultivation of fungi

The microbial food fermentation industry requires real-time monitoring and accurate quantification of cells. However, filamentous fungi are difficult to quantify as they have complex cell types such as pellet, spores, and dispersed hyphae. In this study, numerous data of microscopic image intensity (MII) were used to develop a simple and accurate quantification method of Cordyceps mycelium. The dry cell weight (DCW) of the sample collected during the fermentation was measured. In addition, the intensity values were obtained through the ImageJ program after converting the microscopic images. The prediction model obtained by analyzing the correlation between MII and DCW was evaluated through a simple linear regression method and found to be statistically significant (R2 = 0.941, p < 0.001). In addition, validation with randomly selected samples showed significant accuracy, thus, this model is expected to be used as a valuable tool for predicting and quantifying fungal growth in various industries.

Enhanced Antibacterial Property of Sulfate-Doped Ag3PO4 Nanoparticles Supported on PAN Electrospun Nanofibers

Heterojunction nanofibers of PAN decorated with sulfate doped Ag₃PO₄ nanoparticles (SO₄²⁻-Ag₃PO₄/PAN electrospun nanofibers) were successfully fabricated by combining simple and versatile electrospinning technique with ion exchange reaction. The novel material possessing good flexibility could exhibit superior antibacterial property over sulfate undoped species (Ag₃PO₄/PAN electrospun nanofibers). FESEM, XRD, FTIR, XPS and DRS were applied to characterize the morphology, phase structure, bonding configuration, elemental composition, and optical properties of the as fabricated samples. FESEM characterization confirmed the successful incorporation of SO₄²⁻-Ag₃PO₄ nanoparticles on PAN electrospun nanofibers. The doping of SO₄²⁻ ions into Ag₃PO₄ crystal lattice by replacing PO₄³⁻ ions can provide sufficient electron-hole separation capability to the SO₄²⁻-Ag₃PO₄/PAN heterojunction to generate reactive oxygen species (ROS) under visible light irradiation and enhances its antibacterial performance. Finally, we hope this work may offer a new paradigm to design and fabricate other types of flexible self-supporting negative-ions-doped heterojunction nanofibers using electrospinning technique for bactericidal applications.

Evaluation of an improved bioluminescence assay for the detection of bacteria in soy milk

Because soy milk is nutrient rich and nearly neutral in pH, it favors the growth of microbial contaminants. To ensure that soy milk meets food-safety standards, it must be pasteurized and have its sterility confirmed. ATP bioluminescence assay has become a widely accepted means of detecting food microorganisms. However, the high background bioluminescence intensity of soy milk has rendered it unsuitable for ATP analysis. Here, we tested the efficacy of an improved pre-treated bioluminescence assay on soy milk. By comparing background bioluminescence intensities obtained by the conventional and improved methods, we demonstrated that our method significantly reduces soy milk background bioluminescence. The dose-response curve of the assay was tested with serial dilutions of Bacillus sp. culture. An extremely strong log-linear relation between the bioluminescence intensity relative light units and colony formation units CFU/ml emerged for the tested strain. The detection limit of the assay was estimated as 5.2×10(3) CFU/ml from the dose-response curve and an imposed signal limit was three times the background level. The results showed that contaminated samples could be easily detected within 24 h using our improved bioluminescence assay.