Giovanna Ferrentino

E: Food Engineering & Physical Properties

The objective of the present study was the evaluation of the effectiveness of supercritical carbon dioxide (SC-CO(2)) as a nonthermal technology for the pasteurization of fresh-cut coconut, as an example of ready-to-eat and minimally processed food. First, the inactivation kinetics of microbiota on coconut were determined using SC-CO(2) treatments (pressures at 8 and 12 MPa, temperatures from 24 to 45 °C, treatment times from 5 to 60 min). Second, the effects of SC-CO(2) on the hardness and microstructure of fresh-cut coconut processed at the optimal conditions for microbial reduction were investigated. SC-CO(2) treatment of 15 min at 45 °C and 12 MPa induced 4 log CFU/g reductions of mesophilic microorganisms, lactic acid bacteria, total coliforms, and yeasts and molds. The hardness of coconut was not affected by the treatment but the samples developed an irregular and disorderly microstructure. Results suggested the potential of SC-CO(2) in preserving fresh-cut fruits and ready-to-eat products.

Optimization of supercritical carbon dioxide treatment for the inactivation of the natural microbial flora in cubed cooked ham

This study aims to investigate the effects of supercritical carbon dioxide (SC-CO₂) treatment on the inactivation of the natural microbial flora in cubed cooked ham. Response surface methodology with a central composite design was applied to determine the optimal process conditions and investigate the effect of three independent variables (pressure, temperature and treatment time). Additionally, analyses of texture, pH and color together with a storage study of the product were performed to determine its microbial and qualitative stability. Response surface analysis revealed that 12 MPa, 50 °C, 5 min were the optimal conditions to obtain about 3.0, 1.6, and 2.5 Log(CFU/g) reductions of mesophilic aerobic bacteria, psychrophilic bacteria and lactic acid bacteria respectively. Inactivation to undetectable levels of yeasts and molds and coliforms was also obtained. A storage study of 30 days at 4 °C was carried out on the treated product (12 MPa, 50 °C, 5 min) monitoring microbial growth, pH, texture, and color parameters (L*, a*, b* and ΔE). Microbial loads slightly increased and after 30 days of storage reached the same levels detected in the fresh product. Color parameters (L*, a*, b*) showed slight variations while pH and texture did not change significantly. On the basis of the results obtained, SC-CO₂ can be considered a promising technique to microbiologically stabilize cubed cooked ham and, in general, cut/sliced meat products without affecting its quality attributes.

Comparison of quantitative PCR and flow cytometry as cellular viability methods to study bacterial membrane permeabilization following supercritical CO2 treatment.

Foodborne illness due to bacterial pathogens is increasing worldwide as a consequence of the higher consumption of fresh and minimally processed food products, which are more easily cross-contaminated. The efficiency of food pasteurization methods is usually measured by c.f.u. plate counts, a method discriminating viable from dead cells on the basis of the ability of cells to replicate and form colonies on standard growth media, thus ignoring viable but not cultivable cells. Supercritical CO2 (SC-CO2) has recently emerged as one of the most promising fresh food pasteurization techniques, as an alternative to traditional, heat-based methods. In the present work, using three SC-CO2-treated foodborne bacteria (Listeria monocytogenes, Salmonella enterica and Escherichia coli) we tested and compared the performance of alternative viability test methods based on membrane permeability: propidium monoazide quantitative PCR (PMA-qPCR) and flow cytometry (FCM). Results were compared based on plate counts and fluorescent microscopy measurements, which showed that the former dramatically reduced the number of cultivable cells by more than 5 log units. Conversely, FCM provided a much more detailed picture of the process, as it directly quantifies the number of total cells and distinguishes among three categories, including intact, partially permeabilized and permeabilized cells. A comparison of both PMA-qPCR and FCM with plate count data indicated that only a fraction of intact cells maintained the ability to replicate in vitro. Following SC-CO2 treatment, FCM analysis revealed a markedly higher level of bacterial membrane permeabilization of L. monocytogenes with respect to E. coli and S. enterica. Furthermore, an intermediate permeabilization state in which the cellular surface was altered and biovolume increased up to 1.5-fold was observed in L. monocytogenes, but not in E. coli or S. enterica. FCM thus compared favourably with other methods and should be considered as an accurate analytical tool for applications in which monitoring bacterial viability status is of importance, such as microbiological risk assessment in the food chain or in the environment.

Ethylene-Producing Bacteria That Ripen Fruit

Ethylene is a plant hormone widely used to ripen fruit. However, the synthesis, handling, and storage of ethylene are environmentally harmful and dangerous. We engineered E. coli to produce ethylene through the activity of the ethylene-forming enzyme (EFE) from Pseudomonas syringae. EFE converts a citric acid cycle intermediate, 2-oxoglutarate, to ethylene in a single step. The production of ethylene was placed under the control of arabinose and blue light responsive regulatory systems. The resulting bacteria were capable of accelerating the ripening of tomatoes, kiwifruit, and apples.

Accurate flow cytometric monitoring of Escherichia coli subpopulations on solid food treated with high pressure carbon dioxide

Evaluation of flow cytometry coupled with viability markers to monitor the inactivation of Escherichia coli cells spiked on solid food following High Pressure Carbon Dioxide (HPCD), a mild processing technology.

Dense phase carbon dioxide: food and pharmaceutical applications.

Dense phase carbon dioxide (DPCD) is a non-thermal method for food and pharmaceutical processing that can ensure safe products with minimal nutrient loss and better preserved quality attributes. Its application is quite different than, for example, supercritical extraction with CO 2 where the typical solubility of materials in CO 2 is in the order of 1% and therefore requires large volumes of CO 2. In contrast, processing with DPCD requires much less CO 2 (between 5 to 8% CO 2 by weight) and the pressures used are at least one order of magnitude less than those typically used in ultra high pressure (UHP) processing. There is no noticeable temperature increase due to pressurization, and typical process temperatures are around 40°C.

Effects of Pasteurization on Volatile Compounds and Sensory Properties of Coconut (Cocos nucifera L.) Water: Thermal vs. High-Pressure Carbon Dioxide Pasteurization

Coconut water is a tropical beverage with a distinctive odor and flavor that has until now not been adequately characterized. In the present paper, the volatile compound composition of coconut water was investigated using head space solid-phase microextraction-gas chromatography-mass spectrometry (HS-SPME-GC-MS). Analyses were made of fresh untreated (FU) samples and samples pasteurized using two different technologies: conventional thermal treatment (thermal pasteurization (TP)) and high-pressure carbon dioxide (HPCD) pasteurization, which has recently attracted great interest as an innovative nonthermal preservation treatment. Seventy-three volatile compounds were identified; 27 of them reported for the first time in coconut water. The results showed that HPCD treatment depletes short- and medium-chain alcohols, while TP treatment triggers an increase in aldehydes, ketones, and 2-acetyl-1-pyrroline, an aroma compound active at low odor thresholds and characterized by “popcorn” and “toasted” odor descriptors. Sensory discrimination analysis (triangle test) showed there to be no significant differences between HPCD and FU samples, while TP and FU samples were perceived significantly differently. Descriptive sensory analyses evidenced more intense “cooked,” “toasted bread,” and “hazelnut” characteristics in TP-treated coconut water, consistent with HS-SPME-GC-MS data. In conclusion, instrumentally measurable changes in volatile compounds were more moderate with HPCD than with TP treatment and were not sensorially perceivable compared with the FU product.

Quality Attributes of Fresh-Cut Coconut after Supercritical Carbon Dioxide Pasteurization

pH (13%), fat content (24%), total phenol content (29%), flavonoid compounds (49%), antioxidant capacity (30%) and an increase of dry matter (11%) and titratable acidity (51.1%) were observed while polyphenol oxidase (PPO) exhibited 35% and 98.5% inactivation. Peroxidase enzyme activity increased by 77.8% and 30.4% at 12 MPa, 40 ∘ C, 30 min and 12 MPa, 45 ∘ C, 15 min, respectively. Sensory evaluations revealed no significant differences in appearance, texture, taste, and aroma of treated fresh-cut coconut compared to the untreated. The study confirms the feasibility of SC-CO 2 process for the pasteurization of fresh fruits with a firm structure and opens the door to the possibility of exploiting such a technology at industrial level.

Dense-Phase Carbon Dioxide Processing of Fluid Foods

Publisher Summary The need for a food preservation method that is safe and inexpensive and that preserves heat-sensitive compounds resulted in the use of pressurized carbon dioxide (CO2) as a food preservation method. Dense-phase carbon dioxide (DPCD) treatment has attracted great interest in the nonthermal treatment of liquid foods or liquid model solutions. DPCD has been shown to inactivate microorganisms as well as conventional heat pasteurization without the loss of nutrients or quality changes that may occur due to thermal effects. Pressure and temperature are the main control parameters for DPCD. They significantly affect microbial inactivation, and they influence the CO2 physical state (i.e., liquid, gas, or supercritical) and its properties such as viscosity and diffusivity. Most of the DPCD inactivation studies currently available in the scientific literature have been performed in inoculated or spoiled foods or in inoculated simple model systems and liquid substrates, such as physiological saline solution or culture media. In recent years, the number of published studies in which natural microorganisms in real foods are targeted and inactivated by DPCD has increased. DPCD has progressed, both in terms of theoretical and predictive capabilities and in the accumulation of experience in its applications to many juices and beverages. However, the lack of the first commercially successful DPCD operation is making new entries into the field difficult. Another issue is the use of CO2, which is a greenhouse gas. Therefore, this technology can only be used in some niche areas, which calls for further research and investigation studies.