V.M. Balasubramaniam

Opportunities and Challenges in High Pressure Processing of Foods

Consumers increasingly demand convenience foods of the highest quality in terms of natural flavor and taste, and which are free from additives and preservatives. This demand has triggered the need for the development of a number of nonthermal approaches to food processing, of which high-pressure technology has proven to be very valuable. A number of recent publications have demonstrated novel and diverse uses of this technology. Its novel features, which include destruction of microorganisms at room temperature or lower, have made the technology commercially attractive. Enzymes and even spore forming bacteria can be inactivated by the application of pressure-thermal combinations, This review aims to identify the opportunities and challenges associated with this technology. In addition to discussing the effects of high pressure on food components, this review covers the combined effects of high pressure processing with: gamma irradiation, alternating current, ultrasound, and carbon dioxide or anti-microbial treatment. Further, the applications of this technology in various sectors—fruits and vegetables, dairy, and meat processing—have been dealt with extensively. The integration of high-pressure with other matured processing operations such as blanching, dehydration, osmotic dehydration, rehydration, frying, freezing / thawing and solid-liquid extraction has been shown to open up new processing options. The key challenges identified include: heat transfer problems and resulting non-uniformity in processing, obtaining reliable and reproducible data for process validation, lack of detailed knowledge about the interaction between high pressure, and a number of food constituents, packaging and statutory issues.

Combined Pressure-Thermal Inactivation Kinetics of Bacillus amyloliquefaciens Spores in Egg Patty Mince†

Bacillus amyloliquefaciens is a potential surrogate for Clostridium botulinum in validation studies involving bacterial spore inactivation by pressure-assisted thermal processing. Spores of B. amyloliquefaciens Fad 82 were inoculated into egg patty mince (approximately 1.4 x 10(8) spores per g), and the product was treated with combinations of pressure (0.1 to 700 MPa) and heat (95 to 121 degrees C) in a custom-made high-pressure kinetic tester. The values for the inactivation kinetic parameter (D), temperature coefficient (zT), and pressure coefficient (zP) were determined with a linear model. Inactivation parameters from the nonlinear Weibull model also were estimated. An increase in process pressure decreased the D-value at 95, 105, and 110 degrees C; however, at 121 degrees C the contribution of pressure to spore lethality was less pronounced. The zP-value increased from 170 MPa at 95 degrees C to 332 MPa at 121 degrees C, suggesting that B. amyloliquefaciens spores became less sensitive to pressure changes at higher temperatures. Similarly, the zT-value increased from 8.2 degrees C at 0.1 MPa to 26.8 degrees C at 700 MPa, indicating that at elevated pressures, the spores were less sensitive to changes in temperature. The nonlinear Weibull model parameter b increased with increasing pressure or temperature and was inversely related to the D-value. Pressure-assisted thermal processing is a potential alternative to thermal processing for producing shelf-stable egg products.

High-pressure Food Processing

High pressure processing (HPP) of foods offers a commercially viable and practical alternative to heat processing by allowing food processors to pasteurize foods at or near room temperature. Pressure in combination with moderate temperature also seems to be a promising approach for producing shelf-stable foods. This paper outlines research needs for further advancement of high pressure processing technology. Kinetic models are needed for describing bacterial inactivation under combined pressure-thermal conditions and for microbial process evaluation. Further, identification of suitable surrogate organisms are needed for use as indicator organisms and for process validation studies. More research is needed to evaluate process uniformity at elevated pressure-thermal conditions to facilitate successful introduction of low-acid shelf-stable foods. Combinations of non-thermal technologies with high pressure could reduce the severity of the process pressure requirement. Likewise, processing equipment requires improvements in reliability and line-speed to compete with heat pasteurization lines. More studies are also needed to document the changes in animal and vegetable tissue and nutrient content during pressure processing, from types of packaging, and from storage.

Compression heating influence of pressure transmitting fluids on bacteria inactivation during high pressure processing

Abstract Compression heating characteristics of different pressure transmitting fluids [three different concentrations (75:25, 50:50, 25:75) of water–glycol mix and sodium benzoate (2%) solutions] and their influence on inactivation of spores of Bacillus subtilis in phosphate buffer (0.067 M, pH 7.0) during high pressure processing (HPP) were studied. Experiments were conducted using a pilot scale food processor. Pressure transmitting fluids containing highest percentage of glycol (25:75 water–glycol mix) showed highest temperature increase while 2% sodium benzoate solution showed least temperature increase during high pressure processing. The target pressure, holding time, compressibility, initial temperature, and the rate of heat loss to the surroundings primarily influenced the apparent temperature increase of pressure transmitting fluid in a vessel during HPP. The temperature change was further influenced by the fluid properties such as viscosity, specific heat and thermal conductivity. Use of sodium benzoate solution as pressure-transmitting fluid resulted in highest inactivation of B. subtilis spores. Change in pressure transmitting fluid temperature as a result of compression heating and subsequent heat transfer should be considered in inactivation of bacterial spores by HPP.

Combined pressure-temperature effects on carotenoid retention and bioaccessibility in tomato juice.

This study highlights the changes in lycopene and β-carotene retention in tomato juice subjected to combined pressure-temperature (P-T) treatments ((high-pressure processing (HPP; 500-700 MPa, 30 °C), pressure-assisted thermal processing (PATP; 500-700 MPa, 100 °C), and thermal processing (TP; 0.1 MPa, 100 °C)) for up to 10 min. Processing treatments utilized raw (untreated) and hot break (∼93 °C, 60 s) tomato juice as controls. Changes in bioaccessibility of these carotenoids as a result of processing were also studied. Microscopy was applied to better understand processing-induced microscopic changes. TP did not alter the lycopene content of the tomato juice. HPP and PATP treatments resulted in up to 12% increases in lycopene extractability. all-trans-β-Carotene showed significant degradation (p < 0.05) as a function of pressure, temperature, and time. Its retention in processed samples varied between 60 and 95% of levels originally present in the control. Regardless of the processing conditions used, <0.5% lycopene appeared in the form of micelles (<0.5% bioaccessibility). Electron microscopy images showed more prominent lycopene crystals in HPP and PATP processed juice than in thermally processed juice. However, lycopene crystals did appear to be enveloped regardless of the processing conditions used. The processed juice (HPP, PATP, TP) showed significantly higher (p < 0.05) all-trans-β-carotene micellarization as compared to the raw unprocessed juice (control). Interestingly, hot break juice subjected to combined P-T treatments showed 15-30% more all-trans-β-carotene micellarization than the raw juice subjected to combined P-T treatments. This study demonstrates that combined pressure-heat treatments increase lycopene extractability. However, the in vitro bioaccessibility of carotenoids was not significantly different among the treatments (TP, PATP, HPP) investigated.

Storage Stability of Lycopene in Tomato Juice Subjected to Combined Pressure−Heat Treatments

A study was conducted to characterize the storage stability of lycopene in hot-break tomato juice prepared from two different cultivars and processed by various pressure-heat combinations. Samples were subjected to pressure assisted thermal processing (PATP; 600 MPa, 100 degrees C, 10 min), high pressure processing (HPP; 700 MPa, 45 degrees C, 10 min), and thermal processing (TP; 0.1 MPa, 100 degrees C, 35 min). Processed samples were stored at 4, 25, and 37 degrees C for upto 52 weeks. HPP and PATP treatments significantly improved the extractability of lycopene over TP and control. All-trans lycopene was found to be fairly stable to isomerization during processing, and the cis isomer content of the control and processed juice did not differ significantly. During storage, lycopene degradation varied as a function of the cultivar, processing method, storage temperature, and time. This study shows that combined pressure-temperature treatments could be an attractive alternative to thermal sterilization for preserving tomato juice quality.

Influence of pressurization rate and pressure pulsing on the inactivation of Bacillus amyloliquefaciens spores during pressure-assisted thermal processing.

Pressure-assisted thermal processing (PATP) is an emerging sterilization technology in which a combination of pressure (500 to 700 MPa) and temperature (90 to 120 degrees C) are used to inactivate bacterial spores. The objective of this study was to examine the role of pressurization rate and pressure pulsing in enhancing PATP lethality to the bacterial spore. Bacillus amyloliquefaciens TMW 2.479 spore suspensions were prepared in deionized water at three inoculum levels (1.1 x 10(9), 1.4 x 10(8), and 1.3 x 10(6) CFU/ml), treated at two pressurization rates (18.06 and 3.75 MPa/s), and held at 600 MPa and 105 degrees C for 0, 0.5, 1, 2, 3, and 5 min. Experiments were carried out using custom-fabricated, high-pressure microbial kinetic testing equipment. Single and double pulses with equivalent pressure-holding times (1 to 3 min) were investigated by using the spore suspension containing 1.4 x 10(8) CFU/ml. Spore survivors were enumerated by pour plating, using Trypticase soy agar after incubation at 32 degrees C for 2 days. During short pressure-holding times (< or = 2 min), PATP treatment with the slow pressurization rate provided enhanced spore reduction over that of the fast pressurization rate. However, these differences diminished with extended pressure-holding times. After a 5-min pressure-holding time, B. amyloliquefaciens population decreased about 6 log CFU/ml, regardless of pressurization rate and inoculum level. Double-pulse treatment enhanced PATP spore lethality by approximately 2.4 to 4 log CFU/ml, in comparison to single pulse for a given pressure-holding time. In conclusion, pressure pulsing considerably increases the efficacy of PATP treatment against bacterial spores. Contribution of pressurization rate to PATP spore lethality varies with duration of pressure holding.

Liquid-to-particle convective heat transfer in non-Newtonian carrier medium during continuous tube flow

Abstract Liquid-to-particle convective heat transfer coefficients (hfp) were determined in non-Newtonian carriers during continuous flow using three different experimental techniques. Process parameters such as carrier viscosity, flow rate, particle size, and radial location were found to influence hfp values. Minimum and maximum values of hfp were found to be 363 W/m2 °C and 2010 W/m2 °C respectively over a fluid Reynolds number range of 14·5 to 798. Significant fluid-particle relative velocities (0·02 to 0·19 m/s) were measured during visualization studies of fluid flow around a moving particle. The relative velocity and consequently hfp values were influenced by particle radial location and the local flow field about the particle.

Energy Requirements for Alternative Food Processing Technologies—Principles, Assumptions, and Evaluation of Efficiency

Alternative food preservation technologies include substitutes to heating methods that may have benefits that include reduction of energy consumption. High-pressure processing (HPP), membrane filtration (MF), pulsed electric fields (PEF), and ultraviolet radiation (UV) are examples of alternative preservation technologies of growing commercial interest. As unit operations these technologies operate in 4 modes of energy transfer: momentum, heat, electromagnetic, or photon transfer. The objectives of this review were: (1) to examine the fundamentals of energy requirements of 4 alternative food processing technologies such as HPP, MF, PEF, UV, and conventional high-temperature short-time (HTST) processing, (2) to establish a basis for comparison of energy consumption between or within technologies, and (3) to evaluate specific energy requirements for the 5 technologies to achieve required safety performance in apple juice. Three levels of energy evaluation for each technology including internal energy, applied energy, and consumed energy were reviewed. The comparison of the specific energy for the 5 technologies was based on information published in scientific papers where the inactivation of Escherichia coli in apple juice was explored. Based on the analysis of energy consumption of these technologies it was concluded that MF and UV have the potential to consume less specific energy than HTST, PEF, and HPP. Differences in energy consumption within each group of technologies were also observed and these could be attributed to differences in the systems. The differences in energy consumption within each group of technologies illustrate that there is potential of improvement in most technologies.

Kinetics of Bacillus cereus spore inactivation in cooked rice by combined pressure-heat treatment.

The efficacy of pressure-heat treatment was evaluated for the inactivation of Bacillus cereus spores in cooked rice. The spores of B. cereus ATCC 9818 were inoculated (1.1 × 10(8) CFU/g) in a parboiled rice product (pH 6.0, water activity of 0.95) and inactivated to an undetectable level (<10 CFU/g) by treatment of 600 MPa and process temperatures of 60 to 85 °C or 0.1 MPa and 85 °C. Kinetic inactivation parameters were estimated with linear and nonlinear models. The potential recovery of injured bacteria was also evaluated during storage of the treated product for 4 weeks at 4 and 25 °C. Depending on the process temperature, a 600-MPa treatment inactivated spores by 2.2 to 3.4 log during the 30-s pressure come-up time, and to below the detection limit after 4- to 8-min pressure-holding times. In contrast, a 180-min treatment time was required to inactivate the spores to an undetectable level at 0.1 MPa and 85 °C. The decimal reduction time of spores inactivated by combined pressure-heat treatment ranged from 1.08 to 2.36 min, while it was 34.6 min at 85 °C under atmospheric conditions. The nonlinear Weibull model scale factor increased, and was inversely related to the decimal reduction time, and the shape factor decreased with increasing pressure or temperature. The recovery of injured spores was influenced by the extent of pressure-holding time and process temperature. This study suggests that combined pressure-heat treatment could be used as a viable alternative to inactivate B. cereus spores in cooked rice and extend the shelf life of the product.