Log Cycle Reduction Research Articles

Protective role of wood hemicelluloses: Enhancing yeast probiotics survival in spray drying and storage

Wood hemicelluloses, specifically galactoglucomannans (GGM) and glucuronoxylans (GX) are investigated for their efficacy in spray-dried microencapsulation of Saccharomyces cerevisiae subsp. boulardii (SB). This study demonstrated that GGM and GX effectively protected SB during spray drying at feed concentrations of 15 and 20 % and inlet air temperatures of 105 and 140 °C, ensuring survival rates over 90 %, comparable to gum Arabic, with all achieving over 108 cfu/g in the microcapsules. However, GGM and GX were unable to sustain SB viability when the microcapsules were stored at 33 and 75 % RH (22 °C), beyond 21 and 7 days, respectively. When stored at 4 °C, GX demonstrated a greater ability to protect SB than GGM, with log-cycle reductions of 3 and 6, respectively, after two months. Microstructure analyses showed almost all SB were entrapped by wall materials, with many microcapsules having a wall thickness of 1 − 2 µm. Overall, GX is effective for stable yeast probiotic powders, enabling the development of new probiotic enhanced formulations with prolonged viability and stability.

Effect of UV LED and Pulsed Light Treatments on Polyphenol Oxidase Activity and Escherichia coli Inactivation in Apple Juice.

Enzymatic browning in fruits and vegetables, driven by polyphenol oxidase (PPO) activity, results in color changes and loss of bioactive compounds. Emerging technologies are being explored to prevent this browning and ensure microbial safety in foods. This study assessed the effectiveness of pulsed light (PL) and ultraviolet light-emitting diodes (UV-LED) in inhibiting PPO and inactivating Escherichia coli ATTC 25922 in fresh apple juice (Malus domestica var. Red Delicious). Both treatments' effects on juice quality, including bioactive compounds, color changes, and microbial inactivation, were examined. At similar doses, PL-treated samples (126 J/cm2) showed higher 2,2- diphenyl-1-picrylhydrazyl inhibition (9.5%) compared to UV-LED-treated samples (132 J/cm2), which showed 1.06%. For microbial inactivation, UV-LED achieved greater E. coli reduction (>3 log cycles) and less ascorbic acid degradation (9.4% ± 0.05) than PL. However, increasing PL doses to 176 J/cm2 resulted in more than 5 log cycles reduction of E. coli, showing a synergistic effect with the final temperature reached (55 °C). The Weibull model analyzed survival curves to evaluate inactivation kinetics. UV-LED was superior in preserving thermosensitive compounds, while PL excelled in deactivating more PPO and achieving maximal microbial inactivation more quickly.

Use of whey protein concentrate to encapsulate hydrophobic natural antimicrobials to improve their incorporation into high moisture foods enhancing their antimicrobial activity

Synthetic antimicrobials have been questioned by consumers; thus, natural antimicrobials have emerged as an alternative. However, their use is limited by their low miscibility in high-moisture foods. The objective of this work was to formulate and characterize microparticles of cinnamaldehyde (E-CIN) and vanillin (E-VA) using whey protein concentrate (WPC), and to assess the effect of the encapsulation on the inactivation of L. innocua in a protein beverage. The concentration of WPC (1:1 or 2:1) in the E-CIN did not affect the droplet size and stability, thus the 1:1 ratio was selected. On the contrary, in E-VA increasing WPC concentration (2:1) reduced the droplet size, increasing stability. E-CIN presented greater antimicrobial activity than the unemulsified CIN. E-CIN (1.0 g/L) showed the greatest antimicrobial activity with 3.5 log cycles reduction of L. innocua. While vanillin encapsulation had an insignificant effect on the antimicrobial activity, reducing 1.0 log cycles of L. innocua. In conclusion, cinnamaldehyde was more effective than vanillin, and the encapsulation with WPC increased its antimicrobial activity. Further research is necessary to improve the stability and the antimicrobial activity of vanillin microparticles. Industrial relevanceThis work proposes an alternative to replace synthetic antimicrobials with natural antimicrobials of plant origin. It is based on solving the problem of the low miscibility of hydrophobic antimicrobials such as cinnamaldehyde (cinnamon oil) and vanillin, to incorporate them into foods with high moisture content. This information could be useful for the beverage and juice industry, as encapsulated natural antimicrobials can be used to obtain high-quality, fresh, clean label products. Additionally, extending the shelf life of the product can be advantageous for commercialization purposes.

Bootstrapping for Estimating the Conservative Kill Ratio of the Surrogate to the Pathogen for Use in Thermal Process Validation at the Industrial Scale

A surrogate is commonly used for process validations. The industry often uses the target log cycle reduction for the test (LCRTest) microorganism (surrogate) to be equal to the desired log cycle reduction for the target (LCRTarget) microorganism (pathogen). When the surrogate is too conservative with far greater resistance than the pathogen, the food may be overprocessed with quality and cost consequences. In aseptic processing, the Institute for Thermal Processing Specialists recommends using relative resistance (DTarget)/(DTest) to calculate LCRTest (product of LCRTarget and relative resistance). This method uses the mean values of DTarget and DTest and does not consider the estimating variability. We defined kill ratio (KR) as the inverse of relative resistance.The industry uses an extremely conservative KR of 1 in the validation of food processes for low-moisture foods, which ensures an adequate reduction of LCRTest, but can result in quality degradation. This study suggests an approach based on bootstrap sampling to determine conservative KR, leading to practical recommendations considering experimental and biological variability in food matrices. Previously collected thermal inactivation kinetics data of Salmonella spp. (target organism) and Enterococcus faecium (test organism) in Non-Fat Dried Milk (NFDM) and Whole Milk Powder (WMP) at 85, 90, and 95°C were used to calculate the mean KR. Bootstrapping was performed on mean inactivation rates to get a distribution of 1000 bootstrap KR values for each of the treatments. Based on minimum temperatures used in the industrial process and acceptable level of risk (e.g., 1, 5, or 10% of samples that would not achieve LCRTest), a conservative KR value can be estimated. Consistently, KR increased with temperature and KR for WMP was higher than NFDM. Food industries may use this framework based on the minimum processing temperature and acceptable level of risk for process validations to minimize quality degradation.

Comparison of sanitization efficacy of sodium hypochlorite and peroxyacetic acid used as disinfectants in poultry food processing plants

This study, we aimed to evaluate the in situ disinfection efficacy of peroxyacetic acid (PAA) and sodium hypochlorite (SH) against pathogens (Escherichia coli, Staphylococcus aureus, Salmonella Typhimurium, and Listeria monocytogenes in suspension, and food contact surfaces of steel and utensil. In the clean and contaminated conditions, as the concentrations of PAA and SH increased (0–200 ppm) for 1 min and 5 min, the viable count of pathogenic bacteria reduced. In particular, more than 7 log cycle reductions in the pathogen population were observed using 200 ppm PAA and 100 ppm SH, except for S. aureus in the latter. Four pathogenic bacteria spiked (5–6 log/mL), each on the surface of the main processing machine (stainless steel, n = 36), displayed over 6 log reduction after treatment with 100 ppm PAA for 5 min, which was more effective than SH treatment at similar conditions. To compare the sterilization effect, swab sampling (n = 27) before and after working with poultry on cutting boards, knives, and worktable was performed. E. coli, coliforms, and total bacteria were considerably reduced using 100 ppm of both PAA and SH. After five different treatment concentrations (0–200 ppm) at 4 °C for seven days, chicken breasts treated with 200 ppm PAA exhibited a significant (P < 0.05) inhibitory effect on the total bacteria (1.29 log10) and coliform group organisms (1.10 log10) populations compared with the control chicken breast. Overall, PAA treatment had an effective antimicrobial activity in fresh poultry samples. The microbiological safety of poultry is an important public health concern worldwide, thus, the use of PAA as a disinfectant will greatly contribute to the improvement of poultry microbial safety.

Influence of matrix pH on batch thermal pasteurization of sweet lime juice: Global kinetic models for Saccharomyces cerevisiae and polyphenol oxidase inactivation and degradation of vitamin C

AbstractA set of experiments were conducted to screen the most thermo‐resistant microorganism and spoilage enzyme in sweet lime juice. Furthermore, the impact of matrix pH on the batch thermal treatment (75–95°C/0–10 min) intensities on Saccharomyces cerevisiae survival, PPO inactivation, and vitamin C retention in the sweet lime juice was evaluated. The influence of cumulative come‐up time (tCUT) and cooling time (tCOOL) was separated from the isothermal holding period (tHOLD). All three responses fitted best to the first‐order kinetics. The rate constants (k) ranged between 0.0053 and 0.471 s−1 (for S. cerevisiae), 0.00114 and 0.00731 s−1 (for PPO), and 0.000017 and 0.000142 s−1 (for vitamin C). The microbial and enzyme inactivation rate increased at a low pH level for a certain temperature, whereas, for vitamin C, an opposite trend was prominent through marginal. A new global kinetic model for k as a function of matrix pH and the temperature was developed in which the sensitivity of k to pH change was introduced as SpH. The optimized thermally pasteurized juice (95°C/298 s of holding time) at pH 3.5 showed &gt;5 log cycle reduction in S. cerevisiae count (t5D, s) and 99% inactivation in PPO activity (t99, s) while retaining 57% vitamin C and 39% loss in total phenolics. The optimally treated pasteurized sample at pH 3.5 was examined for phenolic profiling, microbial cell morphology, and enzyme conformational change. The thermally pasteurized sample had a sensory acceptance of 6.9 out of 9 scales.Practical applicationsThe present study developed a systematic study for designing a thermal pasteurization condition for sweet lime juice. First, the most thermo‐resistant microorganism and spoilage enzymes in sweet lime juice were screened out based on the sensitivity index. Further, a global kinetic model was developed for the most resistant microorganisms, resistant enzymes, and vitamin C. This model can describe the impact of matrix pH and temperature on the treatment time to achieve microbial safety and enzymatic stability. Pasteurization time was estimated for each combination of pH and temperature. Assessing the impact of pH levels in the matrix on the effectiveness of thermal pasteurization would assist the industry in determining optimal harvesting conditions for fruit with the desired pH.

Antibacterial Effect of Melanoidins Derived From Xylose and Phenylalanine Against Bacillus cereus and Clostridium perfringens

Melanoidins produced from the combination of D-xylose and L-phenylalanine have been reported to exhibit strong antibacterial effects. This study investigated the influence of environmental factors, such as temperatures (10, 15, 20, 25, 30, 35, 40, and 45°C), pH (5.5, 6.0, 6.5, 7.0, 7.5, and 8.0), and water activity (aw: 0.99, 0.96, and 0.93), on the antibacterial effect of the melanoidins produced from the combination of D-xylose with L-phenylalanine against Bacillus cereus and Clostridium perfringens in culture media. Furthermore, freeze-dried powdered melanoidin was used to determine the minimum concentration for growth inhibition, to compare the antibacterial effect of the melanoidin with conventional food preservatives. The liquid melanoidins significantly inhibited the growth of B. cereus (up to 4 log CFU/mL at the maximum) and C. perfringens (up to 6.5 log CFU/mL at the maximum) regardless of the incubation temperatures. However, the remarkable difference between the presence and absence of the melanoidins was demonstrated in the range of 20–35°C as 4 log-cycle lower in B. cereus and 2 log-cycle lower in C. perfringens than those without the melanoidins. The antibacterial effect of the melanoidin on B. cereus was not influenced by pH from 5.5 to 7.0, which exhibited 2–3 log-cycle lower viable counts than those without the melanoidin. Only one log-cycle difference between with and without the melanoidin was shown in C. perfringens growth under the pH range of 5.5–7.0. Although there was no significant difference in the growth of B. cereus between three aw conditions, the melanoidin exhibited a significant antibacterial effect at aw 0.99 demonstrating 4 log-cycle lower viable numbers than those without the melanoidin. Minimum inhibitory concentration of the melanoidin powder for B. cereus and C. perfringens was 7 mg/mL and 15 mg/mL, respectively, regardless of the kind of foods. Furthermore, the melanoidin exhibited comparable antibacterial effect on B. cereus and C. perfringens to potassium sorbate and sodium benzoate under the same concentration as the minimum inhibitory concentration of the melanoidin, demonstrating 2 log-cycle reduction during 3 days of incubation period at 25°C. The results presented here suggest that the xylose- and phenylalanine-based melanoidin demonstrates the possibility to be an alternative food preservative.

Non-thermal emerging processing Technologies: Mitigation of microorganisms and mycotoxins, sensory and nutritional properties maintenance in clean label fruit juices

The increase in the fruit juice consumption and the interest in clean label products boosted the development and evaluation of new processing technologies. The impact of some emerging non-thermal technologies in food safety and sensory properties has been evaluated. The main technologies applied in the studies are ultrasound, high pressure, supercritical carbon dioxide, ultraviolet, pulsed electric field, cold plasma, ozone and pulsed light. Since there is no single technique that presents high potential for all the evaluated requirements (food safety, sensory, nutritional and the feasibility of implementation in the industry), the search for new technologies to overcome the limitations is fundamental.The high pressure seems to be the most promising technology regarding all the aspects mentioned. Some of the outstanding results are 5 log reduction of E. coli, Listeria and Salmonella, 98.2% of polyphenol oxidase inactivation and 96% PME reduction. However its cost can be a limitation for industrial implementation. The combination of pulsed light and ultrasound could overcome this limitation and provide higher quality fruit juices. The combination was able to achieve 5.8–6.4 log cycles reduction of S. Cerevisiae, and pulsed light is able to obtain PME inactivation around 90%, 61.0 % more antioxidants, 38.8% more phenolics and 68.2% more vitamin C comparing to conventional processing, and similar sensory scores after 45 days at 4 °C comparing to fresh fruit juice.This review aims to update the information related to the application of non-thermal technologies in the fruit juice processing through systematic and updated data to assist in industrial implementation strategies.

Pomegranate Peel Powder: In Vitro Efficacy and Application to Contaminated Liquid Foods

In this study the recycling of pomegranate peel powder (PPP) was proposed. In particular, the use of powder loaded in a silk fibroin polymeric matrix to create an active pad was tested. For the sake of comparison, the powder alone was also analysed. Both powder and active pad efficacy was assessed in two different food systems, soymilk (rich in proteins), preliminarily contaminated with Pseudomonas spp. and yeasts, and apple juice (rich in carbohydrates), preliminarily contaminated with Alyciclobacillus acidoterrestris. Three different concentrations of powder alone and powder in the pad were tested (5%, 7.5% and 10% w/v) in both types of beverages. To assess a possible dependence of the efficacy on the powder granulometry, different powder sizes were preliminarily analysed on Pseudomonas spp. and yeasts using an in vitro test. PPP was effective on both Pseudomonas spp. and yeasts. No significant differences appeared among the tested granulometries and therefore in the subsequent tests powder with an average diameter of 250 µm was used. Results recorded with soymilk and apple juice were different. When applied to the soymilk, the activity of PPP in the pad was less effective than that recorded when the powder was directly added to the beverage. With the two highest powder concentrations directly added to food, more than four log cycle reductions in Pseudomonas spp. and yeast cells were recorded, compared to soymilk without any powder. Compared to the control sample, all the soymilk samples either with PPP or with the active pad showed a delayed microbial and fungal growth. When applied to apple juice, both powder and pad were effective at completely inhibiting the proliferation of A. acidoterrestris (<102 CFU/g).

Evaluation of a novel water-soluble decanoic acid formulation as a fruit sanitizer

Fruits irrigated with contaminated water can transmit various pathogens. High sugar content in fruits such as black cherry (BC) fruit encourages microbial proliferation. A novel water-soluble decanoic acid (WSDA) was evaluated as a fruit sanitizer and compared with other traditional fruit sanitizers such as ethanol, bleach, or dishwasher surfactants. WSDA sanitizer killed yeasts, molds and bacteria including E. coli microbes effectively as other sanitizers with (4 log cycle reduction) of microbial load. Furthermore, the bacterial sanitization mechanism i.e. bactericidal or bacteriostatic was evaluated for alcohol, bleaching and WASDA solutions. E. coli was selected as the model pathogen used for such comparison. Results indicated that the mechanism of action for the three sanitizer solutions against E. coli was bactericidal. The problem with most used fruit sanitizers is their negative influence on fruit quality in terms of physical, mechanical and taste properties. In addition, some led to toxicological and ecological concerns. Thus, studies were conducted to explore the changes in the exocarp cell structure of BC fruit upon exposure to WSDA and other sanitizers using microscopic investigation. WSDA could have a very mild or gentle effect on the BC fruit cells compared to other sanitizers. Alcohol, bleaching and dishwasher surfactant changed the cellular structures and the intercellular spaces. Sanitizers may also affect fruit swelling. WSDA showed an increase in percent weight gain but it was significantly (p < 0.05) much lower than dishwasher surfactant and bleaching solution. BC Fruit flesh firmness and hardness were investigated upon exposure to different sanitizer solutions. BC fruit treated with WSDA showed the highest firmness values. Some liquid sanitizers could affect fruit quality in terms of fruit taste. Sensory evaluation in terms of the sanitizer's smell, texture and hedonic of BC fruit after soaking in different sanitizers was carried out. All sensory parameters of BC fruit soaked with WSDA were similar with insignificant differences (p > 0.05) compared to BC fruit soaked in tap water. However, the sensory parameters were significantly different (p < 0.05) when compared with alcohol, bleach and dishwasher surfactant. This ensures that WSDA was superior to other evaluated sanitizers in terms of physical, mechanical and fruit quality.

Ultrasound processing of sweet lime juice: Effect of matrix pH on microbial inactivation, enzyme stability, and bioactive retention

AbstractThe effect of pH on microbial, enzyme inactivation, and bioactive retention in ultrasound (US) treated sweet lime (Citrus limetta) juice was studied. The pH of the juice varied at 3.5, 4.0, and 4.5, whereas the US duty cycle (DC) ranged between 75% and 95% (0.07–0.7 W/cm3), and the treatment time varied between 15 and 30 min. More than 5‐log reduction in Saccharomyces cerevisiae and Escherichia coli was achieved at DC 95% (25 min) while Listeria monocytogenes got inactivated at DC 85% (25 min). 95%–99% inactivation of peroxidase and pectin methylesterase was achieved at DC 95% (30 min), while 60% inactivation in polyphenol oxidase (PPO) was observed. The addition of ascorbic acid (1 g/L) as an EI resulted in the complete inactivation of PPO at DC 85% (25 min). A maximum color change (ΔE*) of 2.6 was noticed at the highest US treatment condition (DC 95%, 30 min). Eventually, pH showed a marginal effect (˂5%) on retaining vitamin C and bioactive compounds, but US treatment enhanced them. US treatment at DC 95% (30 min) produced microbially safe (˃5‐log cycle reduction) and enzymatically stable (99% enzyme inactivation) juice. To conclude, optimized US treatment increased total phenolic content (TPC), antioxidant capacity, and vitamin C in sweet lime juice by 16.7%, 10.7%, and 14.1%, respectively.Practical applicationsConsumer demand for superior quality sweet lime juice with minimal processing. This explores the opportunity of applying US technology as one of the nonthermal treatments for such a product. Furthermore, the treated juice should be microbially safe and enzymatically stable with better bioactive preservation. Typically, the pH of the fruit juice is one of the main influencing factors controlling microbiological spoilage. The current study explores the consequence of matrix pH and US conditions on the microbial inactivation, enzyme stability, and bioactive compounds of US‐treated sweet lime juice. The hypothesis is that the ultrasonic power required to achieve microbial safety at a lower pH of sweet lime juice should be lower. This will eventually help the industry choose an optimal harvesting condition to obtain the desired pH during processing.

Microwave decontamination process for hummus: A computational study with experimental validation

There has been an increasing demand for healthy snacks, and hummus is preferred as a plant-based product its rich protein content. Its increased consumption, on the other hand, has raised food safety issues with linkages to Listeria outbreak and a recent Salmonella related recall. These were observed in ready-to-eat hummus and indicated the requirement of further processing. Conventional thermal processes might require longer times with negative impact on the quality due to the high viscosity of hummus with its solid-like rheology. For an efficient process design, microwave (MW) processing might be considered with its volumetric heating feature. Therefore, the objective of this study was to present MW application for a decontamination process for hummus.For this purpose, a computational model was developed to determine the temperature change during the process. This model was validated using the experimentally obtained temperature data from samples processed in polystyrene petri dishes (60 g – 8.5 cm in diameter and 1.2 cm in height) in a lab-scale MW system. Color changes were determined, and changes in its viscosity were used to understand the variation in the rheological attributes. Hummus samples were also inoculated with Salmonella cocktail to ≈7–8 log10 CFU/g prior to the MW process, and 70 W MW processing for 5 min (to average temperature of 95.3 °C) resulted in >4 log cycle reduction. Changes in color and rheological attributes were not significant with rather limited mass losses, and these indicated the possible MW processing for hummus decontamination with the need of designing an industrial scale processing.

Design consideration and modelling studies of ultrasound and ultraviolet combined approach for shelf-life enhancement of pine apple juice

Although both ultraviolet (UV) radiation and ultrasound (US) treatment have their capabilities in microbial inactivation, applying any one method alone may require a high dose for complete inactivation, which may affect the sensory and nutritional properties of pineapple juice. Hence, this study was intended to analyse and optimise the effect of combined US and UV treatments on microbial inactivation without affecting the selected quality parameters of pineapple juice. US treatment (33 kHz) was done at three different time intervals, viz. 10 min, 20 min and 30 min., after which, juice samples were subjected to UV treatment for 10 min at three UV dosage levels, viz. 1 J/cm2, 1.3 J/cm2, and 1.6 J/cm2. The samples were evaluated for total colour difference, pH, total soluble solids (TSS), titrable acidity (TA), and ascorbic acid content; total bacterial count and total yeast count; and the standardization of process parameters was done using Response Surface Methodology and Artificial Neural Network. The results showed that the individual, as well as combined treatments, did not significantly impact the physicochemical properties while retaining the quality characteristics. It was observed that combined treatment resulted in 5 log cycle reduction in bacterial and yeast populations while the individual treatment failed. From the optimization studies, it was found that combined US and UV treatments with 22.95 min and1.577 J/cm2 ensured a microbiologically safe product while retaining organoleptic quality close to that of fresh juice.

Edible coatings and application of photodynamics in ricotta cheese preservation

The present study evaluated the efficiency of an edible coating of alginate and erythrosine in the preservation of ricotta cheese submitted to the technique of Photodynamic Inactivation of Microorganisms (PDIM). Three treatments were evaluated: samples of cheese coated with alginate solution, with alginate solution and 10 μmol/L erythrosine and with 100 μmol/L erythrosine. Mechanical properties, water vapor sorption, solubility and permeability and the release of erythrosine in aqueous medium were characterized. The antimicrobial effect of the coatings followed by photodynamic application was evaluated during cheese storage for 21 days. The coated cheese samples were physico-chemically analysed during 21 days of storage. Salmonella and S. aureus were not detected in any cheese samples, but a 1 log cycle reduction in the Coliform count was only observed when 100 μmol/L erythrosine was used. The PDMI technique did not induce lipid oxidation in cheese samples. The presence of 100 μmol/L reduced tensile strength by 25% at rupture. The water solubility and water vapor permeability of the roofs were not affected by the addition of erythrosine. The application of edible coatings in combination with PDIM is a good alternative to extend the shelf life of ricotta cheese without compromising sensory attributes and nutritional characteristics.

Application of antimicrobial coating based on carboxymethyl cellulose and natamycin in active packaging of cheese

The effects of carboxymethyl cellulose (CMC)-natamycin (N; 0.05 and 0.5%) coating on the quality of high-moisture mozzarella cheese (HMMC) were examined. The cheeses were immersed in the coating solutions and then kept at 7 °C for 8 days and microbial specifications (i.e., total mesophilic count, total psychrophilic count, lactic acid bacteria, and yeast-mold), pH, weight loss, and sensory properties were examined. The results of the agar spot diffusion assay represented inhibitory effects of CMC-N coating solution on Aspergillus flavus, A. fumigatus, A. niger, Penicillium citrinum, and Candida albicans. In HMMC, the natamycin-free CMC coating caused a significant decrease (p < 0.05) in all microbial groups, while the addition of natamycin to the coating only reduced the count of mold and yeast. As a result, the coating with natamycin at 0.05 and 0.5% represented a 0.6 and 0.9 log cycle reduction in yeast-mold populations, respectively. Based on the total mesophilic count, the control samples reached the 7 log CFU/g on day 4, indicating a 4-day shelf life of HMMC, while in HMMC coated with and without natamycin this limit was achieved on the 8th day of storage, which indicates that the coatings have doubled the HMMC shelf life.

Antibacterial and Antibiofilm Activity of Mercaptophenol Functionalized-Gold Nanorods Against a Clinical Isolate of Methicillin-Resistant Staphylococcus aureus

Gold nanorods (AuNRs) were synthesized by the seed-mediated wet chemical method using a binary surfactant system. AuNRs were stabilized with polyethylene glycol, then functionalized with 4-mercaptophenol (4-MPH) ligand by surface ligand exchange. The surface-functionalized AuNRs (4-MPH-AuNRs) exhibited a typical UV–vis spectrum of AuNRs with a slightly shifted longitudinal peak. Furthermore, 4-MPH-AuNRs demonstrated a similar Fourier-Transformed Infrared spectrum to 4-MPH and a fading of the thiol band, which suggests a successful functionalization through thiol-gold binding. The antibacterial and antibiofilm activities of 4-MPH-AuNRs were evaluated against a clinical isolate of Methicillin-Resistant Staphylococcus aureus (MRSA). The results indicate that 4-MPH-AuNRs exhibit a bactericidal activity with a minimum inhibitory concentration (MIC) of ~ 6.25 upmug/mL against a planktonic suspension of MRSA. Furthermore, 4-MPH-AuNRs resulted in a 1.8–2.9 log-cycle reduction of MRSA biofilm viable count over a concentration range of 100–6.0 upmug/mL. The bacterial uptake of the surface-modified nanorods was investigated by inductively coupled plasma-optical emission spectroscopy (ICP-OES) and scanning electron microscopy (SEM) imaging; the results reveal that the nanorods were internalized into the bacterial cells after 6 h (h) of exposure. SEM imaging revealed a significant accumulation of the nanorods at the bacterial cell wall and a possible cellular internalization. Thus, 4-MPH-AuNRs can be considered a potential antibacterial agent, particularly against MRSA strain biofilms.

Conventional and ohmic heating pasteurization of fresh and thawed sheep milk: Energy consumption and assessment of bacterial microbiota during refrigerated storage

This study aimed to assess the energy consumption of ohmic heating (OH) and conventional heating (CH) for pasteurization of fresh and thawed sheep milk and their impact on bacterial microbiota throughout refrigerated shelf-life (4 °C ± 1, 15 days). OH pasteurization using 8.33 and 5.83 V/cm electric field strength spent 72–73% less energy than CH pasteurization (515 KJ). The cultivation-dependent approach showed that at least 4.2 log cycle reductions were achieved in sheep milk submitted to CH and OH pasteurization, regardless sheep milk was fresh or thawed. Data from amplicon sequencing indicated that Staphylococcus was the most prevalent genus in raw samples at day 1 (F1D1: 58.35%; T1D1: 69.50%), while Pseudomonas became the most abundant after 15 days under cold storage (F1D15: 50.15% and T1D15: 54.50%). The relative abundance of all bacterial genera assessed remained similar on pasteurized samples by CH and OH throughout refrigerated storage. Industrial relevanceOhmic heating (OH) presents as a critical advantage rapid and uniform heating of fluid food material. No studies assessed the use of OH for pasteurization of sheep milk and to evaluate the impact of this technology on sheep milk bacterial microbiota during refrigerated storage. The findings of this study prove the feasibility of sheep milk pasteurization using OH8.33 V/cm. OH also ensured the bacteriological stability of sheep milk during 2 weeks of storage under refrigeration conditions prior to dairy products manufacturing. This approach comprises a cheaper and easier way to store milk when compared to frozen storage, with potential benefits to small farmers and dairy industries.

Ultrasound and heat treatment effects on Staphylococcus aureus cell viability in orange juice

Ultrasounds are being considered an excellent alternative technology in juice preservation. Yet, when combined with heat treatment, the process seems to be further intensified. This work aimed to evaluate and compare the impact of ultrasounds and heat treatments, when applied alone or in combination, on Staphylococcus aureus survival in orange juice. Inoculated commercial pasteurized orange juice was treated at different times at 20, 30, 40, 50 and 60 °C. SEM analyses were applied to identify morphological changes in S. aureus cells appearance. The microbial inactivation data were fitted using two mathematical models, depending on the behaviour observed.Sonication at 20, 30, and 40 °C induced 4.02 ± 0.52, 3.80 ± 0.49 and 4.30 ± 0.74 log cycles reduction of S. aureus after treatments of 90, 60 and 60 min, respectively. The heat treatments at the same temperatures had no impact on S. aureus survival. When 50 and 60 °C were applied, more than 5-log reductions were attained for both thermosonication and heat treatments alone. A synergistic effect was observed between sonication and high temperatures. At 50 °C, the thermosonication reduced the treatment time from 60 to 35 min and the microbial load from 5.14 ± 0.08 to 10.76 ± 0.28 log cycles reduction, compared to heat treatment alone. Results from SEM images showed that cells undergo membrane damage during sonication exposure. This was observed by collapsed cells, cell disruption, and holes in the cell’s membrane.Thermosonication proved to be a viable alternative to thermal pasteurization of orange juice since milder treatments can be safely applied, improving the final product quality.

Response surface optimization and quality prediction of high pressure processed sugarcane juice (Saccharumofficinarum)

High pressure processing (HPP) has been an effective technique for retarding the browning and microbial fermentation in sugarcane juice with minimal effect on its nutrient profile. The present study deals with the optimization of high-pressure processing (HPP) of sugarcane juice. The influence of pressure (300–600 MPa), temperature (30–60 °C) and dwell time (10–25 min) on the inactivation of polyphenol oxidase (PPO), peroxidase (POD), total color difference (TCD), total phenols (TP) and relative antioxidant capacity (AOX) of the sugarcane juice were assessed using the response surface methodology (RSM). The optimized HPP parameters were determined to be 523 MPa/50 °C/11 min with a desirability value of 0.65. The predicted values of PPO inactivation, POD inactivation, TCD, TP and relative AOX under the optimized conditions were 62%, 59%, 2.8, 33 mg GAE/100 mL and 95%, respectively. The developed RSM models were verified and validated by comparing the predicted and experimental values of the responses. At this optimized condition, 5 log cycle reduction in total aerobic mesophiles and yeast and mold count with complete destruction of coliforms was observed ensuring the microbial stability of the juice.

Enhanced fusidic acid transdermal delivery achieved by newly isolated and optimized Bacillus cereus Keratinase

The expanding interest in bioremediation of poorly degradable wastes has led to the discovery of many microbial enzymes capable of degrading recalcitrant substances such as keratinaceous wastes that are produced in vast quantities on daily basis. Such enzymes don’t only work as a bioremediation tool but also have multiple beneficial applications. Hence, environmental samples were collected from sewage water, soils, animal bodies and feces in order to isolate keratinase producing organisms. Keratinolytic isolates were isolated from sewage water; soils; animal bodies; animal feces, and identified both traditionally and molecularly through 16S-rRNA sequencing to be Bacillus cereus strain. Produced keratinase was purified by centrifugation, ammonium sulfate precipitation, and HPLC, then assayed using Azokeratine based analysis. keratinase quantification yielded a 420 ± 1.63 U/mL. Optimum production was obtained at 40 °C, pH 7, 3 days incubation, 0.5 % substrate, 0.4 g/l magnesium ion, 2% v/v inoculum, 0.5 g/l NaCl, 0.4 g/l K2HPO4, and 0.3 g/l KH2PO4. Production was increased by 1.9 fold after acclimatization to reach 809 ± 2.49 U/mL in only 2 days. Thermal and pH stability testing revealed the effectiveness of the isolated keratinase over a wide range of temperatures at neutral pH. Finally, isolated keratinase enhanced fusidic acid topical penetration to treat induced deep skin bacterial infection in mice. A 1.4 fold decrease in treatment period and a 2 log cycle reduction in the viable count of Staphylococcus aureus were noticed in keratinase/fusidic acid treated mice compared to mice treated with fusidic acid alone. This study shed some light on a simple keratinase production optimization technique and suggested a promising medical application of this enzyme as a drug delivery agent.