and is considered as one of the most promising NTP. Subjecting food to high-pressure intensities of 100 to 600MPa, using liquid pressure transmission medium in an elastic container at ambient or lower temperatures can achieve microbial inactivation. HPP has been used successfully to pasteurise several high-acid foods, extending their shelf lives considerably. As HPP only affects non-covalent bonds, most of low-molecular weight compounds contributing to quality attributes, such as colour, flavour, bioactive activity, are retained well. However, for the foods where quality mainly depends on the structural and functional macromolecules, especially polysaccharides and proteins, their modification induced by HPP may affect the food quality.

The desirable quality changes induced by high temperature for some food products, such as texture, colour, flavour, could not be obtained through HPP. Moreover, the main costs involving HPP are the equipment installation and maintenance, while the energy consumption of HPP is lower compared with thermal processing due to the uniform and instantaneous energy transmission.

Furthermore, HPP is regarded as environmentally- friendly due to its waste-free process. For the microbiological aspects, the inefficiency of microbial inactivation by HPP has been found in past decades. For vegetative microorganisms, the existence of pressure-resistant subpopulations, the revival of sublethal injury (SLI) state cells, and the resuscitation of viable but non-culturable (VBNC) state cells pose challenges for the further development of HPP application.

Hurdle technology

As employment of intense HPP conditions may trigger adverse effects on food quality, as well as high costs of equipment installation and maintenance, mild methods are required for effectively microbial inactivation, in which hurdle technology exhibits as a reasonable alternative. Hurdle technology implies that the hurdles are deliberately combined to improve the microbiological stability and the sensory quality of foods, as well as nutritional and economic properties. Microbial challenges of HPP application are combined with selected hurdles to enhance the microbial inactivation. As for vegetative microorganisms, the pressure-resistant subpopulations, the revival of SLI state cells and the resuscitation of VBNC state cells, they may pose challenges for further HPP development. The combination of HPP and selected hurdles may enhance the microbial inactivation that effectively eliminates the pressure- resistant subpopulations, reduces the population of SLI and VBNC state cells, and inhibits their revival or resuscitation HPP applications. This is based on

Ingredients Insight /

intelligent hurdle technologies that may achieve mild but reliable preservation effects. Over three decades of studies have provided a substantial body of evidence describing the microbial inactivation by HPP in combination with hurdles, such as moderately elevated or low temperature, low pH, natural antimicrobials (NAs). More recently, the combination of HPP with other NTP were also reported. These combinations may achieve the enhancement – additive or synergistic effect – of microbial inactivation without strengthening the treatment intensity, thus reducing the equipment costs, improving the production efficiency, and preserving the food quality. In this way, 1802 HPP enhances microbial inactivation and the pressure- resistant subpopulation is effectively eliminated. The population of SLI or VBNC state cells is reduced, and their revival or resuscitation is inhibited. Several previous reviews have elaborated the current applications and the inactivation mechanisms of single HPP, as well as the combination with NAs. However, the comprehensive applications and inactivation mechanisms of the combinations of HPP and selected hurdles for vegetative microorganisms have not been summarised and elucidated. This review lists the various microbial challenges for HPP application and provides an updated overview of the microbial inactivation of the combination of HPP and selected hurdles over the past decades – finally restructuring their possible inactivation mechanisms. The inactivation of bacterial spores is not reviewed and is therefore different to those observed in vegetative microorganisms.

The future of HPP

Future perspective HPP combined with selected hurdles, such as moderately elevated or low temperature, low pH, NAs, and NTP, could achieve synergistic or additive effect for microbial inactivation, which can effectively eliminate the pressure-resistant subpopulation, reduce the population of SLI or VBNC state cells and inhibit their revival or resuscitation. Further studies should focus on the process of optimisation, and the inactivation mechanism and exploration of new complementary methods aiming to obtain minimal processing and high-quality HPP-processed foods. The molecular mechanisms of pressure resistance of vegetative microorganisms are warranted for further studies. The understanding of the specific expression of genes or proteins responsible for the pressure resistance may help to accurately find out new complementary methods to combine with HPP. Except for the microbiological aspects, there are few descriptions about the effect of HPP alone or combination with hurdles on food qualities lacks, which also requires further consideration. ●


100– 600MPa

The high-pressure intensity that food is subject to uses liquid pressure transmission medium in an elastic container at ambient or lower temperatures can achieve microbial inactivation – HPP has experienced huge growth in food engineering since the 1990s.

Comprehensive Reviews in Food Science and Food Safety

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