Safety and quality assessment of cheeses with mold Dolganova, S G; Budaeva, A B; Khundanova, T L ...
IOP conference series. Earth and environmental science,
08/2020, Letnik:
548, Številka:
8
Journal Article
Recenzirano
Odprti dostop
In many Russian regions, increased cheese production has allowed to satisfy the population needs. Cheeses made with the participation of mold fungi are very popular. In violation of technological ...regimes, sanitary - hygienic conditions of production, storage, various types of cheese defects arise. The aim of this work is to assess the quality and safety of cheeses with mold according to physicochemical and microbiological indicators. Six samples of mold cheese from various manufacturers were examined according to standard methods. The mass fraction of moisture and active acidity in the investigated samples of cheese with mold were within the specified values in the regulatory documentation. Mass fraction of fat in terms of dry substance in two samples below the stated. In terms of quality and safety, among the six samples of cheese with mold, been sold in the Irkutsk distribution network, were detected Escherichia coli Bacteria and Listeria groups, therefore all do not correspond the requirements. We believe that it is necessary to include in-state standard 32263-2013 requirements for organoleptic and physicochemical indicators for cheeses with the development of molds. The pH limits for such cheeses are set from 4.0 to 7.0, since this indicator, in general, is involved in the formation of the quality and safety of this product.
Abstract
Terahertz (THz) technology offers a variety of applications in label-free medical diagnosis and therapy, majority of which rely on the effective medium theory that assumes biological tissues ...to be optically isotropic and homogeneous at the scale posed by the THz wavelengths. Meanwhile, most recent research discovered mesoscale (
$$\sim \lambda $$
∼
λ
) heterogeneities of tissues;
$$\lambda $$
λ
is a wavelength. This posed a problem of studying the related scattering and polarization effects of THz-wave–tissue interactions, while there is still a lack of appropriate tools and instruments for such studies. To address this challenge, in this paper, quantitative polarization-sensitive reflection-mode THz solid immersion (SI) microscope is developed, that comprises a silicon hemisphere-based SI lens, metal-wire-grid polarizer and analyzer, a continuous-wave 0.6 THz (
$$\lambda = 500$$
λ
=
500
µm) backward-wave oscillator (BWO), and a Golay detector. It makes possible the study of local polarization-dependent THz response of mesoscale tissue elements with the resolution as high as
$$0.15 \lambda $$
0.15
λ
. It is applied to retrieve the refractive index distributions over the freshly-excised rat brain for the two orthogonal linear polarizations of the THz beam, aimed at uncovering the THz birefringence (structural optical anisotropy) of tissues. The most pronounced birefringence is observed for the Corpus callosum, formed by well-oriented and densely-packed axons bridging the cerebral hemispheres. The observed results are verified by the THz pulsed spectroscopy of the porcine brain, which confirms higher refractive index of the Corpus callosum when the THz beam is polarized along axons. Our findings highlight a potential of the quantitative polarization THz microscopy in biophotonics and medical imaging.
Terahertz (THz) solid immersion microscopy is a novel promising THz imaging modality that overcomes the Abbe diffraction limit. In our prior work, an original reflection-mode THz solid immersion ...microscope system with the resolution of 0.15λ (in free space) was demonstrated and used for imaging of soft biological tissues. In this paper, a numerical analysis, using the finite-difference time-domain technique, and an experimental study, using a set of objects with distinct refractive indexes, were performed in order to uncover, for the first time, the object-dependent spatial resolution of the THz solid immersion microscopy. Our findings revealed that the system resolution remains strongly sub-wavelength 0.15-0.4λ for the wide range of sample refractive indices n = 1.0-5.0 and absorption coefficients α = 0-400 cm
(by power). Considering these findings, two distinct regimes of the THz solid immersion microscopy were identified. First is the total internal reflection regime that takes place when the sample refractive index is relatively low, while the sub-wavelength resolution is enabled by both the evanescent and ordinary reflected waves at the interface between a high-refractive-index material and an imaged object. Second is the ordinary reflection regime that occurs when the sample refractive index is high enough, so that there is no more total internal reflection at the interface, while only the ordinary reflected waves inside a high-refractive-index material are responsible for the sub-wavelength resolution. The resultant conclusions are general and can be applied for analysis of solid immersion lenses operating in other spectral ranges, such as visible and infrared, given linear nature of the Maxwell's equations.
A continuously-tunable terahertz (THz) bandpass filter based on the resonant electromagnetic-wave transmission through a metal-hole array featuring a gradually changing period was developed and ...fabricated on a silicon substrate using optical lithography. A gradient geometry of the metal-hole array yields a wide tunability of the filter transmission, when operating with a focussed THz beam. The filter was studied numerically, using the finite element method, and experimentally, using the THz pulsed spectroscopy. We find that the central wavelength of the filter transmission band can be tuned in the wide range of
λ
c
= 400–800
μ
m with the relative bandwidth of Δ
λ
/
λ
c
≃ ~0.4. Finally, Kapton-based anti-reflection coating was applied to the filter flat side, in order to suppress an interference pattern in the filter transmission spectrum. We believe that the developed filter holds strong potential for multispectral THz imaging and sensing due to its conceptual simplicity and case of operation. Moreover, the presented filter concept can be translated to other spectral ranges, where appropriate technologies are available for the fabrication of gradient sub-wavelength metal-hole arrays.
PDF
