Non-thermal Processing Method Research Articles

An ultrasound-enhanced system for microbial inactivation using supercritical carbon dioxide

Abstract The effect of ultrasound on the SC-CO 2 inactivation kinetics of E. coli at different pressures (100, 225, 290 and 350 bar; 36 °C), temperatures (31 °C, 36 °C and 41 °C; 225 bar) and varying the composition of the medium (LB Broth, apple and orange juice) was studied. Using only SC-CO 2 the inactivation rate in LB Broth increased progressively as the pressure or temperature rose and the average (for the different process conditions) time needed to achieve a reduction of 8 log-cycles was 50 min. When both SC-CO 2 and ultrasound were used in LB Broth, 95% less time was needed, on average, to achieve the same reduction of 8 log-cycles and the effect of pressure and temperature was minimized; this reduction being achieved after only 2 min at 31 °C and 225 bar. Using the ultrasonic system led to a shorter process time regardless of the treatment medium, preventing the inhibitory effect that the solutes from the juices had on the SC-CO 2 inactivation. The technology developed permits both a drastic decrease in SC-CO 2 inactivation times and also the use of mild process conditions, which could lead to an increase in the quality of the product treated under this new technique. Industrial Relevance Supercritical carbon dioxide (SC-CO 2 ) inactivation technology represents a promising nonthermal processing method, although a too long treatment time is required to guarantee food safety. A patented inactivation technique based on Supercritical Fluids incorporating an ultrasonic transducer is presented. A drastic decrease of the inactivation time is found when high power ultrasound is applied to the SC-CO 2 inactivation process coupled with the food industry’s need for short process times. The inactivation process is improved regardless of the pressure, temperature or treatment medium. Therefore, mild process conditions (time, pressure, temperature) can be used, which result in a higher quality treated product.

Improving Mass Transfer to Soften Tissues by Pulsed Electric Fields: Fundamentals and Applications

The mass transfer phenomenon occurs in many operations of the food industry with the purpose of obtaining a given substance of interest, removing water from foods, or introducing a given substance into the food matrix. Pretreatments that modify the permeability of the cell membranes, such as grinding, heating, or enzymatic treatment, enhance the mass transfer. However, these techniques may require a significant amount of energy and can cause losses of valuable food compounds. Pulsed electric field (PEF) technology is a nonthermal processing method that causes permeabilization of cell membranes using low energy requirements and minimizing quality deterioration of the food compounds. Many practical applications of PEF for enhancing mass transfer in the food industry have been investigated. The purpose of this chapter is to give an overview of the state of the art of application of PEF for improving mass transfer in the food industry.

A Pulsed Electric Field (PEF) bench static system to study bacteria inactivation

Pulsed Electric Fields (PEF) technology is a promising non-thermal processing method for inactivation of microorganisms. A small PEF bench system able to treat a 0.4 ml static liquid volume has been built and tested at the laboratories of the Universita del Piemonte Orientale in Alessandria, Italy. The technique used to produce the required fields consists of charging high voltage cables of various lengths and subsequently discharge them on a cylindrical cell. The pulse intensity can be adjusted to reach a maximum electric field in the cell of about 35 kV/cm and the pulse frequency can reach 10 Hz. We describe the PEF system in some detail and, as a benchmark of its performances, we report preliminary results obtained on Escherichia coli (ATCC 25922) at 10 9 Cfu/ml concentration suspended in a McIlvaine buffer (pH 7.2).

The energetic significance of cooking

While cooking has long been argued to improve the diet, the nature of the improvement has not been well defined. As a result, the evolutionary significance of cooking has variously been proposed as being substantial or relatively trivial. In this paper, we evaluate the hypothesis that an important and consistent effect of cooking food is a rise in its net energy value. The pathways by which cooking influences net energy value differ for starch, protein, and lipid, and we therefore consider plant and animal foods separately. Evidence of compromised physiological performance among individuals on raw diets supports the hypothesis that cooked diets tend to provide energy. Mechanisms contributing to energy being gained from cooking include increased digestibility of starch and protein, reduced costs of digestion for cooked versus raw meat, and reduced energetic costs of detoxification and defence against pathogens. If cooking consistently improves the energetic value of foods through such mechanisms, its evolutionary impact depends partly on the relative energetic benefits of non-thermal processing methods used prior to cooking. We suggest that if non-thermal processing methods such as pounding were used by Lower Palaeolithic Homo, they likely provided an important increase in energy gain over unprocessed raw diets. However, cooking has critical effects not easily achievable by non-thermal processing, including the relatively complete gelatinisation of starch, efficient denaturing of proteins, and killing of food borne pathogens. This means that however sophisticated the non-thermal processing methods were, cooking would have conferred incremental energetic benefits. While much remains to be discovered, we conclude that the adoption of cooking would have led to an important rise in energy availability. For this reason, we predict that cooking had substantial evolutionary significance.

Ultrasound effect on physical properties of corn starch

High power ultrasound (HPU) represents a non-thermal processing method that has been rapidly researched and used in the last 10 years. The application of power ultrasound offers the opportunity to modify and improve some technologically important compounds which are often used in food products. One of them is starch. The aim of this research was to examine the effect of the high power ultrasound of 24 kHz frequency on rheological and some physical properties of corn starch. Various ultrasound treatments were used; an ultrasound probe set with different intensities (34, 55, 73 W cm −2) and treatment times (15 and 30 min) and ultrasound bath of 2 W cm −2 intensity and treatment times (15 and 30 min). Rheological parameters, turbidity and swelling power of corn starch suspensions were determined for native and ultrasonically treated corn starch suspensions. Differential scanning calorimetry was used in order to examine the pasting properties of corn starch. The results have shown that the ultrasound treatment of corn starch distorts the crystalline region in starch granules. The results of differential scanning calorimetry measurements have shown a decrease in enthalpy of gelatinization. A significant decrease in consistency coefficient ( k) has also been observed. The consistency coefficient decreases stepwise jointly with the increasing ultrasound power. The increase in the swelling power is associated with water absorption capacity and corn starch granules solubility, respectively.

Critical Issues Pertaining to Application of Pulsed Electric Fields in Microbial Control and Quality of Processed Fruit Juices

Pasteurisation of fruit juices is normally carried out by thermal means. Heat treatment is an efficient technology for pasteurisation, but may also cause impairment of nutritive and sensory attributes. High-voltage pulsed electric field (PEF) treatment is a promising non-thermal processing method for pasteurisation of liquid foods. Sensory quality of fruit juices is important for consumers. PEF lends itself to be employed as an alternative to produce fruit juices of high quality and safe for consumption, and yet its practical application has been really limited. This paper reviews research carried out recently about the potential use of PEF to different fruit juices, aimed at employing the technology at industrial scale in order to search for wider commercialisation.

THE EFFECTS OF THERMAL AND NONTHERMAL PROCESSING METHODS ON APPLE CIDER QUALITY AND CONSUMER ACCEPTABILITY

ABSTRACT Due to increased concern about the safety of fruit, vegetable and juice products, the FDA has mandated that these must undergo a 5‐log reduction in pathogens. The development of various processing methods for juice products has caused the need to determine the effects of these methods on said products. The effect of thermal pasteurization, UV irradiation and ozone treatment on apple cider quality and consumer acceptability was studied over 21 days. Thermally pasteurized samples were different in color and less preferred in all areas of consumer acceptability. UV‐irradiated samples were lower in soluble solids for the first 7 days and showed no significant difference in consumer acceptability. Ozone‐treated cider had greater sedimentation, lower sucrose content and a decrease in soluble solids by day 21. UV irradiation allows for a more cost‐effective method to produce safe apple cider with minimal quality and consumer acceptability differences.

Inactivation of Escherichia coli O157:H7, Listeria monocytogenes, and Lactobacillus leichmannii by Combinations of Ozone and Pulsed Electric Field

Pulsed electric field (PEF) and ozone technologies are nonthermal processing methods with potential applications in the food industry. This research was performed to explore the potential synergy between ozone and PEF treatments against selected foodborne bacteria. Cells of Lactobacillus leichmannii ATCC 4797, Escherichia coli O157:H7 ATCC 35150, and Listeria monocytogenes Scott A were suspended in 0.1% NaCl and treated with ozone, PEF, and ozone plus PEF. Cells were treated with 0.25 to 1.00 μg of ozone per ml of cell suspension, PEF at 10 to 30 kV/cm, and selected combinations of ozone and PEF. Synergy between ozone and PEF varied with the treatment level and the bacterium treated. L. leichmannii treated with PEF (20 kV/cm) after exposure to 0.75 and 1.00 μg/ml of ozone was inactivated by 7.1 and 7.2 log10 CFU/ml, respectively; however, ozone at 0.75 and 1.00 μg/ml and PEF at 20 kV/cm inactivated 2.2, 3.6, and 1.3 log10 CFU/ml, respectively. Similarly, ozone at 0.5 and 0.75 μg/ml inactivated 0.5 and 1.8 log10 CFU/ml of E. coli, PEF at 15 kV/cm inactivated 1.8 log10 CFU/ml, and ozone at 0.5 and 0.75 μg/ml followed by PEF (15 kV/cm) inactivated 2.9 and 3.6 log10 CFU/ml, respectively. Populations of L. monocytogenes decreased 0.1, 0.5, 3.0, 3.9, and 0.8 log10 CFU/ml when treated with 0.25, 0.5, 0.75, and 1.0 μg/ml of ozone and PEF (15 kV/cm), respectively; however, when the bacterium was treated with 15 kV/cm, after exposure to 0.25, 0.5, and 0.75 μg/ml of ozone, 1.7, 2.0, and 3.9 log10 CFU/ml were killed, respectively. In conclusion, exposure of L. leichmannii, E. coli, and L. monocytogenes to ozone followed by the PEF treatment showed a synergistic bactericidal effect. This synergy was most apparent with mild doses of ozone against L. leichmannii.

Processing concepts based on high intensity electric field pulses

Emerging non-thermal food processing techniques are receiving considerable attention. This is because of their potential for quality and safety improvement of our food supply, for the ability to enhance conventional processing operations or to create alternative ones, as well as modify existing or non-conventional raw materials, food constituents or processed foods. High intensity electric field pulse technology is one of the most advanced emerging non-thermal processing methods and is currently undergoing intensive scientific and developmental evaluation. The objectives of this review are to summarize and identify the key advantages of this emerging technology and to convert it into optimum use. Those attempts are a combination of research on a kinetic basis and on a cellular level and the subsequent transfer of the knowledge gained into pilot scale.

Pulsed Electric Field Processing of Foods: A Review

Use of pulsed electric fields (PEFs) for inactivation of microorganisms is one of the more promising nonthermal processing methods. Inactivation of microorganisms exposed to high-voltage PEFs is related to the electromechanical instability of the cell membrane. Electric field strength and treatment time are the two most important factors involved in PEF processing. Encouraging results are reported at the laboratory level, but scaling up to the industrial level escalates the cost of the command charging power supply and of the high-speed electrical switch. In this paper, we critically review the results of earlier experimental studies on PEFs and we suggest the future work that is required in this field. Inactivation tests in viscous foods and in liquid food containing particulates must be conducted. A successful continuous PEF processing system for industrial applications has yet to be designed. The high initial cost of setting up the PEF processing system is the major obstacle confronting those who would encourage the system's industrial application. Innovative developments in high-voltage pulse technology will reduce the cost of pulse generation and will make PEF processing competitive with thermal-processing methods.

Apple Juice Pasteurization Using Ultrafiltration and Pulsed Electric Fields

Apple juice was treated by means of non-thermal processing methods as a way of verifying whether a microbial stable and quality-acceptable product could be obtained. Ultrafiltration and high electric voltage pulsed electric fields were the techniques used. For ultrafiltration, the factors under study were membrane pore (10,000 and 50,000 daltons), trans-membrane pressure (103, 120.5, 138 and 155 kPa) and recovery percentage (0, 25, 50 and 75% for the 10,000 daltons membrane, as well as 0, 10, 20, 30, 40, 50 and 60% for the 50,000 daltons membrane). In terms of the pulsed electric fields experiments, electric field strength (50, 58 and 66 kVcm–1) and number of pulses (2, 4, 8 and 16) were the factors investigated. The responses to these factors were evaluated for microbial determinations, namely: aerobic plate count, yeasts and moulds, aciduric bacteria, and quality attributes such as pH, acidity, soluble solids and colour. Appropriate statistical comparisons were made between types of membrane and techniques. Multiple linear regression models were fisstted by means of a stepwise technique. Both membrane treatments and pulsed electric fields technique showed that microbial inactivation is possible and efficient. Except for colour, quality attributes were kept unaltered. Significant relative colour changes were observed for both techniques such as browning for the ultrafiltered juice and fading for pulsed electric field treatment.

Identification of mechanisms for decomposition of air pollutants by non-thermal plasma processing

Non-thermal plasma processing methods have been shown to be effective for treating dilute concentrations of pollutants in large-volume atmospheric-pressure air streams. This paper presents results from basic experimental and theoretical studies aimed at identifying the main reactions responsible for the decomposition of four representative compounds: carbon tetrachloride, methylene chloride, trichloroethylene and methanol. Each of these compounds is shown to be decomposed by a different plasma species: electrons, nitrogen atoms, oxygen radicals and positive ions, respectively. By understanding what plasma species is responsible for the decomposition of a pollutant molecule, it is possible to establish the electrical power requirements of the plasma reactor and help identify the initial reactions that lead to the subsequent process chemistry. These studies are essential for predicting the scaling of the process to commercial size units.

Pulsed Electric Field Treatment Chamber Design for Liquid Food Pasteurization Using a Finite Element Method

High voltage pulsed electric field (PEF) treatment is a promising nonthermal processing method that may radically change liquid food preservation technology. One of the key components in the PEF pasteurization process is a treatment chamber. In this work, the chamber was designed with the aid of an electric field optimization technique. The finite element method was used in the numerical analysis of electric fields and for optimization of the electrode geometry. Using the optimized electrodes in the coaxial treatment chamber, a prescribed field distribution in foods was achieved without points of electric field enhancement. Two types of treatment chambers, parallel plate and coaxial electrode, were constructed and tested. Microbial inactivation tests were conducted using exponential decaying and square waveforms. Electric field intensity ranged from 20 to 50 kV/cm, while pulse length ranged from 2 to 20 ms. More than seven log cycles of microbial inactivation of Escherichia coli and Saccharomyces cerevisiae were achieved when the food temperature was maintained below 30 C.

Abstracts

Concentration of milk in the dairy industry is typically achieved by thermal evaporation or reverse osmosis (RO). Heat concentration is energy intensive and leads to cooked flavor and color changes in the final product, and RO is affected by fouling, which limits the final achievable concentration of the product. The main objective of this work was to evaluate forward osmosis (FO) as an alternative method for concentrating milk. The effects of fat content and temperature on the process were evaluated, and the physicochemical properties and sensory qualities of the final product were assessed. Commercially pasteurized skim and whole milk samples were concentrated at 4, 15, and 25°C using a benchtop FO unit. The FO process was assessed by monitoring water flux and product concentration. The color of the milk concentrates was also evaluated. A sensory panel compared the FO concentrated and thermally concentrated milks, diluted to single strength, with high temperature, short time pasteurized milk. The FO experimental runs were conducted in triplicate, and data were analyzed by single-factor ANOVA. Water flux during FO decreased with time under all processing conditions. Higher temperatures led to faster concentration and higher concentration factors for both skim and whole milk. After 5.75 h of FO processing, the concentration factors achieved for skim milk were 2.68 ± 0.08 at 25°C, 2.68 ± 0.09 at 15°C, and 2.36 ± 0.08 at 4°C. For whole milk, after 5.75 h of FO processing, concentration factors of 2.32 ± 0.12 at 25°C, 2.12 ± 0.36 at 15°C, and 1.91 ± 0.15 at 4°C were obtained. Overall, maximum concentration levels of 40.15% total solids for skim milk and 40.94% total solids for whole milk were achieved. Additionally, a triangle sensory test showed no significant differences between regular milk and FO concentrated milk diluted to single strength. This work shows that FO is a viable nonthermal processing method for concentrating milk, but some technical challenges need to be overcome to facilitate commercial utilization.

Observations on the Effect of Sunlight on the Horse and Cow

The quality and safety of food products are the two factors that most influence the choices made by today's increasingly demanding consumers. Conventional food sterilization and preservation methods often result in a reduction in the apparent freshness and quality of the final products. High pressure processing is a relatively new non-thermal food processing method that subjects liquid or solid foods, with or without packaging, to pressures between 50 and 1000 MPa. Extensive investigations have revealed the potential benefits of high pressure processing as an alternative to traditional heat treatments. These benefits are apparent in various areas of food processing, such as the inactivation of microorganisms and enzymes, denaturation and alteration of the functionality of proteins, and structural changes to food materials. Moreover, high pressure can be used to enhance several processing operations, such as freezing, thawing and extraction, thus providing new processing options.