Development of a pasteurization method based on radio frequency heating to ensure microbiological safety of liquid egg

The combined effect of cold plasma and radio frequency on the preservation of cooked crayfish during refrigerated storage

To improve the shelf life of crayfish, the preservation effects of cold plasma (CP) and radio frequency (RF) treatments were investigated in this study. The crayfish samples were treated by CP (130 kV, 3 min), RF (3.5 kW, 15 min) or their combinations and stored at 4 °C. Afterward, the quality attributes (microbial stability, physicochemical parameters, water distribution and protein structures) of the treated crayfish tails were measured during 12 days. According to the total viable count (TVC) and total volatile basic nitrogen (TVB-N) values, the CK samples became unacceptable during 3-6 days, while the RF + CP treatment extended the shelf-life to 9-12 days. Besides, the thiobarbituric acid reactive substances (TBARS) values for all the investigated crayfish samples were maintained within 11 mg/100 g throughout the whole storage period. Low-field nuclear magnetic resonance (LF-NMR) analysis indicated that the samples after RF treatments exhibited less free water contents than those without RF treatments, implying that RF treatments might restrict the water migration. Moreover, Fourier transform infrared (FTIR) spectroscopy analysis revealed that RF + CP treatments slightly reduced the α-helix contents and increased the contents of β-sheet and random coil in crayfish proteins, while these structural changes were not obvious at the later stage of storage. In addition, the RF + CP treatment effectively delayed the color and textural deterioration of crayfish during storage. Overall, this study showed that the combined treatments of RF and CP effectively extended the shelf life of crayfish and improved the storage quality.

Increasing the pasteurization temperature of liquid egg white by phosphorylation modification: Exploring the mechanism and application

Pasteurization is an effective sterilization technique for the treatment of liquid egg white (LEW), but the pasteurization temperature is generally limited because increased temperature can lead to aggregation of the proteins and affect their processing properties. In this study, phosphorylation modification was used to increase the thermal stability and pasteurization temperature of LEW, aiming to enhance the pasteurization sterilizing effect. The FT-IR results showed that the phosphate groups were successfully grafted into protein molecules, improving the order degree of protein molecules. In this case, the pasteurization temperature of LEW increased from 58 °C to 61 °C, without accompanying thermal aggregation. The molecular structural results suggested that the enhanced thermal stability was attributed to the decreased average particle size and the increased electrostatic repulsion between protein molecules, which largely reduced the turbidity of LEW during pasteurization treatment. Meanwhile, this process was dominated by noncovalent interactions (hydrophobic interactions and hydrogen bonding). Furthermore, the phosphorylation modification can synchronously improve emulsifying and foaming properties of LEW. Therefore, this work suggested that phosphorylation has great potential to improve thermal stability and pasteurization temperature of LEW, which can be utilized to extend its sterilizing effect and shelf life.

Phenotypic, genotypic, and resistome of mesophilic spore-forming bacteria isolated from pasteurized liquid whole egg

The production of whole-liquid eggs is of significant economic and nutritional importance. This study aimed to assess the phenotypic and genotypic diversity of mesophilic aerobic spore-forming bacteria (n = 200) isolated from pasteurized whole liquid egg and liquid egg yolk. The majority of the isolates were identified as belonging to the genera Bacillus (86 %), followed by Brevibacillus (10 %) and Lysinibacillus (4 %). For the phenotypic characterization, isolates were subjected to various heat shocks, with the most significant reductions observed at 80 °C/30 min and 90 °C/10 min for isolates recovered from raw materials. On the other hand, the decrease was similar for isolates recovered from raw material and final product at 100 °C/5 min and 110 °C/5 min. Genotypic genes related to heat resistance (cdnL, spoVAD, dacB, clpC, dnaK, and yitF/Tn1546) were examined for genotypic characterization. The dnaK gene showed a positive correlation with the highest thermal condition tested (110 °C/5 min), while 100 °C/5 min had the highest number of positively correlated genes (clpC, cdnL, yitF/Tn1546, and spoVAD). Whole Genome Sequencing of four strains revealed genes related to sporulation, structure formation, initiation and regulation, stress response, and DNA repair in vegetative cells. The findings of this study indicate that these mesophilic aerobic spore-forming bacteria may adopt several strategies to persist through the process and reach the final product. As the inactivation of these microorganisms during egg processing is challenging, preventing raw materials contamination and their establishment in processing premises must be reinforced.

Tolerance to heated egg in egg allergy: Explanations and implications for prevention and treatment

Hen's egg allergy is the second most frequent food allergy found in children. Allergic symptoms can be caused by raw or heated egg, but a majority of egg-allergic children can tolerate hard-boiled or baked egg. Understanding the reasons for the tolerance towards heated egg provides clues about the molecular mechanisms involved in egg allergy, and the differential allergenicity of heated and baked egg might be exploited to prevent or treat egg allergy. In this review, we therefore discuss (i) why some patients are able to tolerate heated egg; by highlighting the structural changes of egg white (EW) proteins upon heating and their impact on immunoreactivity, as well as patient characteristics, and (ii) to what extent heated or baked EW might be useful for primary prevention strategies or oral immunotherapy. We describe that the level of immunoreactivity towards EW helps to discriminate patients tolerant or reactive to heated or baked egg. Furthermore, the use of heated or baked egg seems effective in primary prevention strategies and might limit adverse reactions. Oral immunotherapy is a promising treatment strategy, but it can sometimes cause significant adverse events. The use of heated or baked egg might limit these, but current literature is insufficient to conclude about its efficacy.

Radio Frequency Treatment of Food: A Review on Pasteurization and Disinfestation

Radio frequency (RF) is a novel technology with several food processing and preservation applications. It is based on the volumetric heating generated from the product's dielectric properties. The dielectric properties of each material are unique and a function of several factors (i.e., temperature, moisture content). This review presents a list of dielectric properties of several foods and describes the use of RF as an innovative technology for the food industry. This paper includes several examples of pasteurization, fungi inactivation, and disinfestation in selected food products. The aim of this review is to present the potential applications of RF in pasteurization and disinfestation and research needs that should be addressed. RF has been successfully applied in the inactivation of pathogens such as Salmonella spp., Listeria monocytogenes, and Escherichia coli in low- and high-moisture food. The disinfestation of crops is possible using RF because of selective heating. This process inactivates the insects first because of the different dielectric properties between the pests and the food. The products' final quality can be considerably better than conventional thermal processes. The processing time is reduced compared to traditional heating, and thermal damage to the food is minimized. The main drawback of the technology is the lack of uniform heating, mainly when the product is surrounded by a packaging material with different dielectric properties from the food.

Validation of Pasteurisation Temperatures for a Tomato-Oil Homogenate (salmorejo) Processed by Radiofrequency or Conventional Continuous Heating

Salmorejo is a viscous homogenate based on tomato, olive oil and breadcrumbs commercialised as a "fresh-like" pasteurised-chilled purée. Due to its penetration, dielectric heating by radiofrequency (RF) might improve pasteurisation results of conventional heating (CH). The objective was to validate the pasteurisation temperature (70-100 °C, at 5 °C intervals) for salmorejo processed by RF (operating at 27.12 MHz for 9.08 s) or conventional (for 10.9 s) continuous heating. The main heat-induced changes include: orangeness, flavour homogenisation, loss of freshness, thickening, loss of vitamin C and lipid oxidation. Both CH and RF equivalent treatments allowed a strong reduction of total and sporulated mesophilic microorganisms and an adequate inhibition of the pectin methylesterase, peroxidase and, to a lesser extent, polyphenol oxidase but did not inhibit the polygalacturonase enzyme. Pasteurisation at 80 °C provided a good equilibrium in levels of microbiological and enzymatic inhibition and thermal damage to the product. Increasing this temperature does not improve enzyme inactivation levels and salmorejo may become overheated. A "fresh-like" good-quality salmorejo can be obtained using either conventional or radiofrequency pasteurisers.

A review on egg pasteurization and disinfection: Traditional and novel processing technologies

Salmonella Enteritidis is a pathogen related to many foodborne outbreaks involving eggs and egg products. Regulations about whether eggs should be pasteurized are very different and inconsistent worldwide. In the United States, eggs are not required to be pasteurized. Hence, less than 3% of the eggs in the country are pasteurized. The standard pasteurization method (57°C, 57.5 min) uses a long thermal process that increases the cost of the product and affects its quality. Foodborne outbreaks can be reduced if eggs are properly pasteurized to inactivate Salmonella spp. However, the technology to pasteurize eggs needs to offer a faster and more reliable method that can be scaled up to industry settings at a low cost and without affecting product quality. Several novel technologies have been tested for eggshell disinfection and egg pasteurization. Some thermal technologies have been evaluated for the pasteurization of eggs. Microwave has limited penetration depth and is a technical challenge for egg pasteurization. However, radio frequency can penetrate eggshells effectively to inactivate Salmonella, considerably reduce processing time, and maintain the quality of the product. Nonthermal technologies such as ultraviolet, pulsed light, cold plasma, ozone, pressure carbon dioxide, electrolyzed water, and natural antimicrobials have been explored for surface cleaning of the intact egg as alternatives without affecting the internal quality. This review presents some of these novel technologies and the current challenges. It discusses the possible combination of factors to achieve the egg's internal pasteurization and the eggshell's disinfection without affecting the quality at a low cost for the consumer.

Effect of Load Spatial Configuration on the Heating of Chicken Meat Assisted by Radio Frequency at 40.68 MHz

Food heating assisted by radio frequencies has been industrially applied to post-harvest treatment of grains, legumes and various kind of nuts, to tempering and thawing of meat and fish products and to post-baking of biscuits. The design of food processes based on the application of radiofrequencies was often based on rules of thumb, so much so that their intensification could lead significant improvements. One of the subjects under consideration is the shape of the food items that may influence their heating assisted by radiofrequency. In this work, a joint experimental and numerical study on the effects of the spatial configuration of a food sample (chicken meat shaped as a parallelepiped) on the heating pattern in a custom RF oven (40.68 MHz, 50 Ohm, 10 cm electrodes gap, 300 W) is presented. Minced chicken breast samples were shaped as cubes (4 × 4 × 4 cm3) to be organized in different loads and spatial configurations (horizontal or vertical arrays of 2 to 16 cubes). The samples were heated at two radiofrequency operative power levels (225 W and 300 W). Heating rate, temperature uniformity and heating efficiency were determined during each run. A digital twin of the experimental system and process was developed by building and numerically solving a 3D transient mathematical model, taking into account electromagnetic field distribution in air and samples and heat transfer in the food samples. Once validated, the digital tool was used to analyze the heating behavior of the samples, focusing on the most efficient configurations. Both experiments and simulations showed that, given a fixed gap between the electrodes (10 cm), the vertically oriented samples exhibited a larger heating efficiency with respect to the horizontally oriented ones, pointing out that the gap between the top electrode and the samples plays a major role in the heating efficiency. The efficiency was larger (double or even more; >40% vs. 10−15%) in thicker samples (built with two layers of cubes), closer to the top electrode, independently from nominal power. Nevertheless, temperature uniformity in vertical configurations was poorer (6−7 °C) than in horizontal ones (3 °C).

Upscaling via a Prospective LCA: A Case Study on Tomato Homogenate Using a Near-to-Market Pasteurisation Technology

Thanks to food technology, the production of cold tomato soups such as salmorejo, a traditional Spanish dish, has become industrialised. Thermal treatments play an important role in ready-to-eat meals, prolonging their shelf-life. Radiofrequency (RF) heating is less energy-intensive than conventional heat exchangers and has been successfully used to pasteurise food; novel applications, however, provide results at laboratory or pilot scale, so conclusions might not be translatable to industry. In this study, a prospective Life-Cycle Assessment of salmorejo pasteurised using RF was performed to highlight the relevance of upscaling and to compare its environmental impacts with those of conventional pasteurisation. “Gate-to-gate” results show that the pilot has greater environmental impacts due to its greater energy consumption, as thermal energy is not recovered. The packing and landfill of organic waste exhibit the highest impacts at industrial scale. RF technology does not imply significant environmental improvements versus conventional pasteurisation. Potential changes in the energy background of future scenarios have relevant consequences in the environmental impacts. “Farm-to-factory-gate” analysis highlights ingredients and tomato valorisation as the most impacting stages. The prospective LCA of scaled up scenarios constitutes a tool for environmental screening in food ecodesign, contributing to Sustainable Development Goal 12.