High Pressure Processing Applications in Plant Foods.

High pressure processing (HPP) is a cold pasteurization technology by which products, prepacked in their final package, are introduced to a vessel and subjected to a high level of isostatic pressure (300-600 MPa). High-pressure treatment of fruit, vegetable and fresh herb homogenate products offers us nearly fresh products in regard to sensorial and nutritional quality of original raw materials, representing relatively stable and safe source of nutrients, vitamins, minerals and health effective components. Such components can play an important role as a preventive tool against the start of illnesses, namely in the elderly. An overview of several food HPP products, namely of fruit and vegetable origin, marketed successfully around the world is presented. Effects of HPP and HPP plus heat on key spoilage and pathogenic microorganisms, including the resistant spore form and fruit/vegetable endogenous enzymes are reviewed, including the effect on the product quality. Part of the paper is devoted to the industrial equipment available for factories manufacturing HPP treated products.

Assessing the pressure resistance of Escherichia coli O157:H7, Listeria monocytogenes and Salmonella enterica to high pressure processing (HPP) in citric acid model solutions for process validation.

Despite the commercial success of high pressure processing (HPP) in the juice industry, some regulatory agencies still require process validation. However, there is a lack of consensus on various aspects regarding validation protocols, including the selection of representative strains to be used in challenge tests. This study characterized the variable response of Escherichia coli O157:H7 (34 strains), Listeria monocytogenes (44 strains) and Salmonella enterica (45 strains) to HPP, and identified potential candidates to use in process validation. Stationary phase cells were submitted to 500 MPa for 1 min at 10 °C in model solutions consisting of tryptic soy broth + 0.6% yeast extract (TSBYE) adjusted to pH 4.5 and 6.0 with citric acid. At pH 6.0, pressure resistance widely varied between species and within strains of the same species. E. coli O157:H7 and L. monocytogenes were the most pressure resistant and showed high variability at strain level, as the total count range given by minimum and maximum counts spread between 2.0 and 6.5 log10 CFU/ml. S. enterica was the least resistant pathogen with more than 82% of the isolates displaying non-detectable counts after HPP. Recovery through storage at 12 °C was also variable for all pathogens, but eventually most strains recovered with median counts on day 14 between 8.3 and 8.9 log10 CFU/ml. For pH 4.5 solutions, 26 E. coli O157:H7 strains displayed survivors after HPP but did not adapt, registering non-detectable counts in the next sampling dates. None of the L. monocytogenes and S. enterica strains survived HPP or incubation at pH 4.5 (<2.0 log10 CFU/ml), suggesting that citric acid at 4.16 g/l is a safe barrier for pathogen control under moderate HPP conditions. Principal component and cluster analyses served to propose strain cocktails for each species based on their pressure resistant and adaptation phenotypes. Additionally, S. enterica was identified as less pressure resistant and less prone to recover following HPP than E. coli O157:H7 and L. monocytogenes, so its relevance in process validation for juices should be questioned. Future work will validate the proposed strain cocktails on real food systems.

Evaluation of factors influencing the growth of non-toxigenic Clostridium botulinum type E and Clostridium sp. in high-pressure processed and conditioned tender coconut water from Thailand.

Bacterial spores survive high pressure processing (HPP). Group II Clostridium botulinum is an obligate anaerobe spore-forming pathogen that can produce the botulinum neurotoxin under refrigeration. This study assessed nontoxigenic type E C. botulinum and Group II Clostridium sp. growth in raw and HPP (550 MPa, 3 min, 10 °C) Thai coconut water (CCW; pH 5.2). No spore germination or growth occurred in HPP CCW inoculated with 105 CFU/ml after 61 days regardless of oxygen concentration (<0.5 - 11 mg/l) or storage temperature (4 and 20 °C). Spore concentration decreased by 3.0 ± 0.1 log CFU/ml in a worst-case scenario consisting of non-HPP filter-sterilized CCW (pH 7.0) under anoxic incubation at 30 °C during 61 days, suggesting spore germination followed by cellular death. Supplementing filter-sterilized CCW (pH 7.0) with selected germinants and free amino acids did not support spore development, but the addition of nutrient-rich laboratory media (TPGY broth) at low concentrations (6.25%) promoted growth, suggesting that a lack of nutrients prevents C. botulinum development in CCW. Further risk assessment will require evaluating other CCW varieties and toxin production.

High-Pressure Biotechnology in Medicine and Pharmaceutical Science.

High-pressure (HP) biotechnology is an emerging technique initially applied for food processing and more recently in pharmaceutical and medical sciences. Pressure can stabilize enzymes and modulate both their activity and specificity. HP engineering of proteins may be used for enzyme-catalyzed synthesis of fine chemicals, pharmaceuticals, and production of modified proteins of medical or pharmaceutical interest. HP inactivation of biological agents is expected to be applicable to sterilization of fragile biopharmaceuticals, or medical compounds. The enhanced immunogenicity of some pressure-killed bacteria and viruses could be applied for making new vaccines. Finally, storage at subzero temperatures without freezing is another potential application of HP for cells, animal tissues, blood cells, organs for transplant, and so forth.