Dielectric properties of chili powder in the development of radio frequency and microwave pasteurisation

Evaluation of Pilot-Scale Radio Frequency Heating Uniformity for Beef Sausage Pasteurization Process

Radio frequency (RF) heating has the advantages of a much faster heating rate as well as the great potential for sterilization of food compared to traditional thermal sterilization. A new kettle was designed for sterilization experiments applying RF energy (27.12 MHz, 6 kW). In this research, beef sausages were pasteurized by RF heating alone, the dielectric properties (DPs) of which were determined, and heating uniformity and heating rate were evaluated under different conditions. The results indicate that the DPs of samples were significantly influenced (p < 0.01) by the temperature and frequency. The electrode gap, sample height and NaCl content had significant effects (p < 0.01) on the heating uniformity when using RF energy alone. The best heating uniformity was obtained under an electrode gap of 180 mm, a sample height of 80 mm and NaCl content of 3%. The cold points and hot spots were located at the edge of the upper section and geometric center of the sample, respectively. This study reveals the great potential in solid food for pasteurization using RF energy alone. Future studies should focus on sterilization applying RF energy and SW simultaneously using the newly designed kettle.

Effects of Radio Frequency Tempering on the Temperature Distribution and Physiochemical Properties of Salmon (Salmo salar)

Salmon (Salmo salar) is a precious fish with high nutritional value, which is perishable when subjected to improper tempering processes before consumption. In traditional air and water tempering, the medium temperature of 10 °C is commonly used to guarantee a reasonable tempering time and product quality. Radio frequency tempering (RT) is a dielectric heating method, which has the advantage of uniform heating to ensure meat quality. The effects of radio frequency tempering (RT, 40.68 MHz, 400 W), water tempering (WT + 10 °C, 10 ± 0.5 °C), and air tempering (AT + 10 °C, 10 ± 1 °C) on the physiochemical properties of salmon fillets were investigated in this study. The quality of salmon fillets was evaluated in terms of drip loss, cooking loss, color, water migration and texture properties. Results showed that all tempering methods affected salmon fillet quality. The tempering times of WT + 10 °C and AT + 10 °C were 3.0 and 12.8 times longer than that of RT, respectively. AT + 10 °C produced the most uniform temperature distribution, followed by WT + 10 °C and RT. The amount of immobile water shifting to free water after WT + 10 °C was higher than that of RT and AT + 10 °C, which was in consistent with the drip and cooking loss. The spaces between the intercellular fibers increased significantly after WT + 10 °C compared to those of RT and AT + 10 °C. The results demonstrated that RT was an alternative novel salmon tempering method, which was fast and relatively uniform with a high quality retention rate. It could be applied to frozen salmon fillets after receiving from overseas catches, which need temperature elevation for further cutting or consumption.

Effective pretreatment technologies for fresh foods aimed for use in central kitchen processing

The central kitchen concept is a new trend in the food industry, where centralized preparation and processing of fresh foods and the distribution of finished or semi-finished products to catering chains or related units take place. Fresh foods processed by a central kitchen mainly include fruit and vegetables, meat, aquatic products, and edible fungi; these foods have high water activities and thermal sensitivities and must be processed with care. Appropriate pretreatments are generally required for these food materials; typical pretreatment processes include cleaning, enzyme inactivation, and disinfection, as well as packaging and coating. To improve the working efficiency of a central kitchen, novel efficient pretreatment technologies are needed. This article systematically reviews various high-efficiency pretreatment technologies for fresh foods. These include ultrasonic cleaning technologies, physical-field enzyme inactivation technologies, non-thermal disinfection technologies, and modified-atmosphere packagings and coatings. Mechanisms, applications, influencing factors, and advantages and disadvantages of these technologies, which can be used in a central kitchen, are outlined and discussed. Possible solutions to problems related to central-kitchen food processing are addressed, including low cleaning efficiency and automation feasibility, high nutrition loss, high energy consumption, and short shelf life of products. These should lead us to the next step of fresh food processing for a highly demanding modern society. © 2020 Society of Chemical Industry.

Dielectric properties of Mexican sauces for microwave-assisted pasteurization process

The dielectric properties and specifically the complex relative permittivity of foods are key elements for the design of pasteurization processes with high frequency electromagnetic waves. Mexican sauces are recognized worldwide for their flavor and nutritional properties. In this work, the complex permittivity of four of the most representative sauces of Mexican cuisine (chipotle chili, habanero chili, red and green sauce) is presented. The permittivity was measured with the open coaxial probe method at temperatures of 25, 40, 55, 70, 85 °C and in the frequency range of 500 MHz to 6 GHz. Additionally, moisture content, specific heat, viscosity, water activity, density and electrical conductivity are reported, these last three at 25 °C. Dielectric properties were affected by the sauce formulation. The loss factor of each sauce sample at any temperature presents significant changes in relation to the frequency. At 915 and 2,450 MHz, d ε ' ' d T > 0 , which would cause a thermal runaway effect or the uncontrolled rise in temperature in the sauces during the microwave pasteurization. At 5,800 MHz, d ε ' ' d T < 0 , which would give better control for microwave heating than at 915 and 2,450 MHz. At 915 MHz, the loss factor of all sauces is higher than at 2,450 and 5,800 MHz, therefore, more rapid heating can be produced. Moreover, at 915 MHz, microwaves exhibit higher penetration depth than at 2,450 and 5,800 MHz; therefore, at 915 MHz, the greatest uniform microwave dielectric heating would be achieved. Thus, 915 MHz is the frequency recommended for the studied sauces pasteurization. PRACTICAL APPLICATION: This work provides the dielectric properties of Mexican sauces at different temperatures and their penetration depths in the microwave range, which are key information for further microwave-assisted pasteurization process and for getting safer sauces for consumers. Moreover, this research supplies suggestions about what frequency for ISM (Industrial, Scientific and Medical) applications is the best for microwave-assisted pasteurization according to the penetration depth of the electromagnetic wave in the sauces and microwave dielectric heating speed of the sauces.