Josip Simunovic

Overview of RFID technology and its applications in the food industry.

Radio frequency identification (RFID) is an alternative technology with a potential to replace traditional universal product code (UPC) barcodes. RFID enables identification of an object from a distance without requiring a line of sight. RFID tags can also incorporate additional data such as details of product and manufacturer and can transmit measured environmental factors such as temperature and relative humidity. This article presents key concepts and terminology related to RFID technology and its applications in the food industry. Components and working principles of an RFID system are described. Numerous applications of RFID technology in the food industry (supply chain management, temperature monitoring of foods, and ensuring food safety) are discussed. Challenges in implementation of RFID technology are also discussed in terms of read range, read accuracy, nonuniform standards, cost, recycling issues, privacy, and security concerns.

Continuous flow microwave-assisted processing and aseptic packaging of purple-fleshed sweetpotato purees.

Pumpable purees from purple-flesh sweetpotatoes (PFSP) were subjected to microwave heating using a 60 kW, 915 MHz continuous flow system, followed by aseptic packaging in flexible containers to obtain a shelf-stable product. Initial test runs were conducted using a 5 kW 915 MHz microwave system to measure dielectric in-line properties and examine the puree temperature profiles. The results demonstrated uniformity in heating of the puree at sterilization temperatures (>121 degrees C), and the dielectric constants and loss factors were within the range of published values for orange-fleshed sweetpotato purees. The pilot-scale test runs in a 60 kW microwave unit produced shelf-stable puree packages stable at room temperature. Polyphenolic content of the PFSP purees were evaluated and the results showed that while total phenolics increased (5.9%) and total monomeric anthocyanins slightly decreased (14.5%) with microwave application, antioxidant activity determined by 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging activity and oxygen radical absorbance capacity (ORAC) assays did not significantly change as a result of microwave processing. Color values showed that microwave-processed samples differed from fresh puree in saturation and hue angle, but not in overall color change. PFSP purees increased in gel strength when microwave processed, packaged, and stored, but the gel could be easily disrupted into flowable purees. Overall, high-quality retention can be obtained by microwave processing and aseptic packaging of PFSP purees so that they can be used as functional food ingredients.

Dielectric Properties of Sweet Potato Purees at 915 MHz as Affected by Temperature and Chemical Composition

A process for rapid sterilization and aseptic packaging of sweet potato puree using a continuous flow microwave system operating at 915 MHz has been successfully developed. In microwave processing, dielectric properties have a major role in determining the interaction between purees and the electromagnetic energy. The objective of this research was to determine how dielectric properties are affected by temperature and chemical composition of purees derived from thirteen sweet potato cultivars with varying flesh colors. Results indicated that temperature, moisture, sugar and starch content had a pronounced effect (p < 0.001) on dielectric properties measured from 15°C to 145°C at 915 MHz. Dielectric constant decreased with increasing temperature, while dielectric loss factor increased quadratically. Power penetration depth of all cultivars decreased with increasing temperature. Predictive equations were developed for dielectric constant (R2 = 0.82) and dielectric loss factor (R2 = 0.90) as a function of temperature, moisture, sugar, and starch. The predictive equations would be useful in determining the dielectric properties of sweet potato purees for the microwave processing technology.

Dielectric Properties of Pumpable Food Materials at 915 MHz

Dielectric properties of pumpable food materials having a potential to be processed using a continuous flow microwave heating system were measured at 915 MHz and in the temperature range of 10–90°C. The products considered in this study were milk and dairy products (ϵ′: 70.0 to 50.8 and ϵ″: 14.7 to 41.3), ready to eat puddings (ϵ′: 69.4 to 52.1 and ϵ″: 17.2 to 23.8), soy beverages (ϵ′: 75.4 to 60.8 and ϵ″: 9.0 to 19.8), and avocado products (ϵ′: 51.6 to 39.0 and ϵ″: 17.7 to 67.5). The results showed that the dielectric constant decreased with an increase in temperature and the dielectric loss factor increased with an increase in temperature. Polynomial correlations for the dependence of dielectric properties on temperature were developed. The dielectric properties measured in this study are important parameters for designing a continuous flow microwave heating system for processing pumpable food materials.

Thermophysical and Dielectric Properties of Salsa Con Queso and its Vegetable Ingredients at Sterilization Temperatures

Aseptic processing of a low-acid multiphase food product using continuous flow microwave heating system can combine the advantages of an aseptic process along with those of microwave heating. The objective of this study was to determine the thermophysical and dielectric properties of salsa con queso and its vegetable ingredients (tomatoes, bell peppers, jalapeno peppers, and onions) at a temperature range of 20 to 130°C to design a safe process for aseptic processing of salsa con queso using a continuous flow microwave system. The influence of temperature on apparent viscosity of salsa con queso was described by an Arrhenius-type relationship. Second order polynomial correlations for the dependence of thermophysical and dielectric properties (at 915 MHz) of salsa con queso and its vegetable ingredients on temperature were developed. The results showed that the dielectric constant decreased with an increase in temperature and the dielectric loss factor increased with an increase in temperature.

Effects of Acid, Salt, and Soaking Time on the Dielectric Properties of Acidified Vegetables

In order to design a continuous microwave process for pasteurization of acidified vegetables, equilibration phenomena in acid and salt solutions must be examined with regards to changes in dielectric properties. The objective of this study was to examine the effects of acid and salt concentration on the dielectric properties of acidified vegetables. Broccoli florets and sweet potato cubes (1.2 cm) were blanched to facilitate acid and salt equilibration by heating for 15 s in boiling de-ionized water. Red bell pepper cubes were not blanched. The vegetable samples were then acidified in solutions of 1–2% sodium chloride with 0.5–2% citric acid. Dielectric properties were measured at 915 MHz from 25 to 100°C after 0-, 4-, and 24-h soaking periods in the solutions using an open-ended coaxial probe connected to a network analyzer. Equilibration occurred within 4 h of salting and acidification. Acid and salt concentration had no significant effect on the dielectric constant (ϵ′). However, ϵ′ was significantly different among vegetables (p < 0.05). Dielectric loss factor (ϵ″) was not affected by acid, but significantly increased with salt concentration. These results provide necessary dielectric property information to apply microwave heating technology in processing of acidified vegetables.

Mitochondrial DNA Fragmentation as a Molecular Tool to Monitor Thermal Processing of Plant‐Derived, Low‐Acid Foods, and Biomaterials

Cycle threshold (Ct) increase, quantifying plant-derived DNA fragmentation, was evaluated for its utility as a time-temperature integrator. This novel approach to monitoring thermal processing of fresh, plant-based foods represents a paradigm shift. Instead of using quantitative polymerase chain reaction (qPCR) to detect pathogens, identify adulterants, or authenticate ingredients, this rapid technique was used to quantify the fragmentation of an intrinsic plant mitochondrial DNA (mtDNA) gene over time-temperature treatments. Universal primers were developed which amplified a mitochondrial gene common to plants (atp1). These consensus primers produced a robust qPCR signal in 10 vegetables, 6 fruits, 3 types of nuts, and a biofuel precursor. Using sweet potato (Ipomoea batatas) puree as a model low-acid product and simple linear regression, Ct value was highly correlated to time-temperature treatment (R(2) = 0.87); the logarithmic reduction (log CFU/mL) of the spore-forming Clostridium botulinum surrogate, Geobacillus stearothermophilus (R(2) = 0.87); and cumulative F-value (min) in a canned retort process (R(2) = 0.88), all comparisons conducted at 121 °C. D121 and z-values were determined for G. stearothermophilus ATCC 7953 and were 2.71 min and 11.0 °C, respectively. D121 and z-values for a 174-bp universal plant amplicon were 11.3 min and 9.17 °C, respectively, for mtDNA from sweet potato puree. We present these data as proof-of-concept for a molecular tool that can be used as a rapid, presumptive method for monitoring thermal processing in low-acid plant products.

Design of conservative simulated particles for validation of a multiphase aseptic process.

Simulated food particles with conservative (fast moving and slow heating) properties are required for validation of multiphase aseptic processing for production of shelf-stable low-acid foods. The validation process requires simulated particles to contain residence time tags, thermosensitive implants, and/or bioloads for temperature detection, time-temperature integration, and bactericidal efficacy confirmation. Conservative particle design (CPD) software was used to determine the wall thickness required for conservative behavior of such particles made with polypropylene (PP) and polymethylpentene (PMP) of wall thickness 1 mm (0.0393 inches) and 2 mm (0.0787 inches) containing tube inserts. Thermocouples were inserted in the simulated and real food particles and the particles were heated up to 127 degrees C under pressurized (24 psi) conditions. Based on the heating rates of the real and simulated particles, an appropriate simulated particle was identified for each type of real food particle. This would allow a food processor to use these designed particles with an appropriate tube insert (diameter) to validate an aseptic process for a multiphase food containing any or all the above tested food materials.

Mitochondrial DNA Fragmentation to Monitor Processing Parameters in High Acid, Plant-Derived Foods

Mitochondrial DNA (mtDNA) fragmentation was assessed in acidified foods. Using quantitative polymerase chain reaction, Ct values measured from fresh, fermented, pasteurized, and stored cucumber mtDNA were determined to be significantly different (P > 0.05) based on processing and shelf-life. This indicated that the combination of lower temperature thermal processes (hot-fill at 75 °C for 15 min) and acidified conditions (pH = 3.8) was sufficient to cause mtDNA fragmentation. In studies modeling high acid juices, pasteurization (96 °C, 0 to 24 min) of tomato serum produced Ct values which had high correlation to time-temperature treatment. Primers producing longer amplicons (approximately 1 kb) targeting the same mitochondrial gene gave greater sensitivity in correlating time-temperature treatments to Ct values. Lab-scale pasteurization studies using Ct values derived from the longer amplicon differentiated between heat treatments of tomato serum (95 °C for <2 min). MtDNA fragmentation was shown to be a potential new tool to characterize low temperature (<100 °C) high acid processes (pH < 4.6), nonthermal processes such as vegetable fermentation and holding times of acidified, plant-derived products.