Decontamination of chokeberries (Aronia melanocarpa L.) by cold plasma treatment and its effects on biochemical composition and storage quality of their corresponding juices

To improve the microbiological quality of chokeberries, corona discharge plasma jet (CDPJ) was employed as a decontaminating agent. The mean levels of aerobic bacteria and yeast and molds contaminants in chokeberries were 4.78 and 4.87 log CFU/g, respectively; the viable counts were decreased by 2.09 and 1.83 log units following CDPJ treatment for 3 min, respectively. A first-order kinetic model was well-suited for explaining the inactivations. The concentration of total polyphenols of chokeberries was unaffected (up to 3 min treatment), whereas DPPH radical scavenging activity was significantly decreased by CDPJ treatment (2 min and more). CDPJ treatment (all tested times) of chokeberries led to a significant decrease of monomeric anthocyanin content of their corresponding juices, whereas soluble solids content (Brix) and pH were unaffected. After storage at 4 °C for 72 h, juices obtained from CDPJ-treated berries possessed relatively low levels of contaminants with no significant alterations in pH and soluble solids content when compared with controls. In conclusion, CDPJ treatment for 2 min was optimal to improve the microbiological quality of the berries without negatively affecting biochemical qualities of their corresponding juices.     

Inactivation of Listeria monocytogenes on a polyethylene surface modified by layer-by-layer deposition of the antimicrobial N-halamine

Modification of food contact surfaces to be antimicrobial represents an approach to address the problem of cross-contamination in the food industry. The effect of increasing levels of surface modification on low density polyethylene (LDPE) through application of N-halamines on the inactivation kinetics of Listeria monocytogenes Scott A was evaluated. Increasing levels of modification were applied through layer by layer deposition on LDPE surface (1–5 double layers of polyethyleneimine and poly(acrylic acid)). Surface modification was achieved and confirmed through Fourier Transform Infrared Spectroscopy (FTIR). From 1 to 5 double layers, the N-halamine content ranged from 3.42 ± 1.2 to 27.30 ± 3.5 nmol cm⁻². More than four logarithmic cycles (>99.99%) reduction was reached against L. monocytogenes Scott A after different contact times depending on the level of modification, that varied from 50 to 110 min (from 5 to 2 double layers). Inactivation kinetics followed a sigmoidal behavior.     

Inactivation of polyphenol oxidase from Pacific white shrimp by dense phase carbon dioxide

The inactivation of polyphenol oxidase (PPO) from Pacific white shrimp exposed to dense phase carbon dioxide (DPCD) treatment was investigated. PPO activity showed a dramatic loss at 4–25 MPa and 37 °C. At the lower pressure (4–15 MPa), the experimental data of inactivation followed the first-order reaction kinetic model, the pressure sensitivity (Z_P) of the kinetic parameters was 49.02 MPa and the activation volume (△ V^≠) was − 120.88 cm³/mol. At the higher pressure (20 and 25 MPa), the experimental data of inactivation followed the biexponential kinetic model. The kinetic rate constant k_F and k_S of fast and stable fractions were 2.45 and 0.08 min^{− 1}, respectively. The decimal reduction time D_F and D_S were 0.94 and 29.43 min at 25 MPa and 37 °C, respectively. After DPCD treatment, the loss activity of PPO had no restoration storing for 6 days at 4 °C. The results of SDS-PAGE and activity staining also showed that DPCD treatment had the obvious inhibitory effect on PPO from Pacific white shrimp. The PPO activity in vivo was easier to be inactivated than that in crude PPO extracts under the same DPCD treatment conditions.

Industrial relevance

There is a growing interest in non-thermal pasteurization methods, which could retain food's freshlike physical, nutritional, and sensory qualities. Pacific white shrimp accounts for 90% of the global aquaculture shrimp production, they are becoming increasingly popular. However, enzymatic browning of shrimp has been of great concern to food scientists and food processors. Dense phase carbon dioxide (DPCD) may be an adequate tool to obtain high quality since PPO activity could not be inactivated totally by high pressure under 400 MPa yet. The present work deals with the inactivation of PPO from Pacific white shrimp exposed to DPCD treatment in order to explore the feasibility of shrimp by DPCD process.     

Comparison of the inactivation kinetics of pectin methylesterases from carrot and peach by high-pressure carbon dioxide

The inactivation of pectin methylesterases (PMEs) from carrot and peach in buffer by high-pressure carbon dioxide (HPCD) at 55 °C was investigated. The two PMEs were effectively inactivated by HPCD, their residual activity (RA) decreasing with increasing pressures. The RA of the two PMEs exhibited a fast decrease firstly and reached a constant after a prolonged treatment time; their inactivation kinetics was adequately modelled by a fractional-conversion model. The non-zero RA(A_∞)of the two PMEs was 6–7%, with increasing pressures the kinetic rate constant, k, increased and the decimal reduction time, D, decreased for the HPCD-labile fraction of the two PMEs. The labile fraction of carrot PME was more susceptible to HPCD than that of peach PME; the activation volume, V_a, and Z_P (the temperature increase needed for a 90% reduction of D) was −1079.37 cm³/mol and 5.80 MPa for carrot PME, and −130.51 cm³/mol and 48.31 MPa for peach PME.     

Modeling the inactivation of Salmonella typhimurium by dense phase carbon dioxide in carrot juice

The inactivation of Salmonella typhimurium inoculated into acidified carrot juice subjected to dense phase carbon dioxide (DPCD) was investigated. The pressures in the study were 10, 20 and 30 MPa, the temperatures were 32, 37 and 42 °C, and the treatment time was 5–90 min. The inactivation effect of DPCD was enhanced by increasing pressure and temperature. The sigmoid inactivation curves were characterized with the lag phase, exponential inactivation phase, and resistant phase. The inactivation curves were fitted to the modified Gompertz equation and the modified Logistic equation, the modified Gompertz equation was superior since its lowest residual sum of squares (RSS) was lower although there was no significant difference of goodness-of-fit between both models as indicated by F-test. The λ (the duration of the lag phase) and t_4-D (the time necessary to achieve 4-log cycles reduction) decreased with increasing pressure or temperature. The k_dm (the maximum specific value of the inactivation rate, min⁻¹) increased with increasing temperatures, and decreased with increasing pressures. The activation energy (Ea) and the activation volume (Va) necessary for inactivating S. typhimurium by DPCD were 19.06–29.39 kJ mol⁻¹ and 18.89–58.27 cm³ mol⁻¹.     

Effectiveness of chitosan on the inactivation of enteric viral surrogates

Chitosan is known to have bactericidal and antifungal activity. Although human noroviruses are the leading cause of non-bacterial gastroenteritis, information on the efficacy of chitosan against foodborne viruses is very limited. The objective of this work was to determine the effectiveness of different molecular weight chitosans against the cultivable human norovirus and enteric virus surrogates, feline calicivirus, FCV-F9, murine norovirus, MNV-1, and bacteriophages, MS2 and phiX174. Five purified chitosans (53, 222, 307, 421, ∼1150 kDa) were dissolved in water, 1% acetic acid, or aqueous HCl pH = 4.3, sterilized by membrane filtration, and mixed with equal volume of virus to obtain a final concentration of 0.7% chitosan and 5 log₁₀ PFU/ml virus. Virus-chitosan suspensions were incubated for 3 h at 37 °C. Untreated viruses in PBS, in PBS with acetic acid, and in PBS with HCl were tested as controls. Each experiment was run in duplicate and replicated at least twice. Water-soluble chitosan (53 kDa) reduced phiX174, MS2, FCV-F9 and MNV-1 titers by 0.59, 2.44, 3.36, and 0.34 log₁₀ PFU/ml respectively. Chitosans in acetic acid decreased phiX174 by 1.19–1.29, MS2 by 1.88–5.37, FCV-F9 by 2.27–2.94, and MNV-1 by 0.09–0.28 log₁₀ PFU/ml, respectively. Increasing the MW of chitosan corresponded with an increasing antiviral effect on MS2, but did not appear to play a role for the other three tested viral surrogates. Overall, chitosan treatments showed the greatest reduction for FCV-F9, and MS2 followed by phiX174, and with no significant effect on MNV-1.     

不同LET碳离子对V79细胞辐射敏感性的影响

以中国仓鼠肺V79细胞为材料,利用兰州近代物理研究所重离子研究装置（HIRFL）产生的碳离子,研究了不同线性能量传递（LET）的重离子对体外培养细胞的存活效应,并与γ射线的结果作了比较。结果表明,不同LET碳离子引起细胞失活效应由大到小的顺序依次为125、200、700keV/μm。碳离子表现为无肩区的存活曲线,属单靶单击模型,γ射线表现为有肩区的存活曲线,属多靶单击模型。LET值为125、200、700keV/μm时得到的失活截面分别为35、12、8μm^2。当细胞存活比率为0.1和0.37,在LET为125keV/μm时得到相对生物学效应（RBE）值为1.47和2.19。     

Inactivation kinetics of food enzymes during ohmic heating

Ohmic heating of milk and fruit and vegetable juices was carried out at several incubation temperatures to investigate inactivation of alkaline phosphatase, pectin methylesterase and peroxidase. Mechanisms of inactivation of these enzymes and corresponding kinetic models were verified for each food material, using the multitemperature evaluation of inactivation data. Compared to inactivation by conventional indirect heating, kinetic parameters were changed but inactivation mechanisms remained the same. The kinetic parameter changes were relatively minor for pectin methylesterase and alkaline phosphatase. A significant destabilization of the labile isozyme fraction of peroxidase occurred by the effect of ohmic heating when the greatest decrease of stability was obtained for carrot juice.     

Recent Advances in the Use of High Pressure as an Effective Processing Technique in the Food Industry

High pressure processing is a food processing method which has shown great potential in the food industry. Similar to heat treatment, high pressure processing inactivates microorganisms, denatures proteins and extends the shelf life of food products. But in the meantime, unlike heat treatments, high pressure treatment can also maintain the quality of fresh foods, with little effects on flavour and nutritional value. Furthermore, the technique is independent of the size, shape or composition of products. In this paper, many aspects associated with applying high pressure as a processing method in the food industry are reviewed, including operating principles, effects on food quality and safety and most recent commercial and research applications. It is hoped that this review will promote more widespread applications of the technology to the food industry.     

Enzyme inactivation kinetics: Coupled effects of temperature and moisture content

Enzymes are often dried for stability reasons and to facilitate handling. However, they are often susceptible to inactivation during drying. It is generally known that temperature and moisture content influence the enzyme inactivation kinetics. However, the coupled effect of both variables on enzyme inactivation over a broad temperature–moisture content range is still not well understood. Therefore, the inactivation of β-galactosidase in maltodextrin matrix is investigated using a newly developed method. An improved kinetic modelling approach is introduced, to predict the inactivation over a large range of temperature–moisture values. The model assumes a two-step inactivation mechanism involving reversible unfolding and irreversible inactivation. The model is able to describe the inactivation kinetics of β-galactosidase accurately, showing the temperature-dependent kinetic transition from reversible unfolding to irreversible inactivation limited. Application of this approach can provide immediate understanding of the effect of processing on enzyme inactivation and indicates the processes’ critical points, which offers the possibility for optimisation.