Biomedical subjects

P D Sanz

Publications and source records attributed to P D Sanz.

6 recordsLinked to original sources

PubMed2002

Anisakis simplex larva killed by high-hydrostatic-pressure processing.

Anisakis simplex is a common nematode parasite present in many marine fish, including finfish and squid. It can pose a public health problem if it is not destroyed during food processing. Anisakis larvae were isolated from fish tissue, and their survival of high-pressure treatments in distilled water and physiological isotonic solution was assayed. Treatment at a pressure of 200 MPa for 10 min at a temperature between 0 and 15 degrees C kills all Anisakis larvae, with a lack of motility being used as an indicator of larval death. Lower pressures can be successfully employed down to 140 MPa, but with lower pressures, the treatment time must be increased by up to I h to kill all larvae. Meanwhile, most larvae treated for >10 min at pressures of >120 MPa were dead, with the autofluorescence method being used to determine death. Cycles of compression and decompression increase the destruction of larvae compared with a single pressure treatment for a similar treatment time. Our results indicate that high-pressure treatment is an alternative nonthermal method for killing this nematode. The possible mechanism of death and damage by pressure is discussed, and uses for this treatment in food processing are suggested.

Animals↗

PubMed1999

High pressure response of fruit jams contaminated with Listeria monocytogenes.

High pressure is an alternative to thermal processing and is used to preserve food. Listeria monocytogenes is a bacterium which grows at low temperature, is able to multiply under vacuum, and is responsible for food poisoning. Pressures of 100, 200, 300 and 400 MPa were used for 5, 10 and 15 min at 20 degrees C on pure culture, and on apple and plum jam baby food artificially contaminated with Listeria. Pure culture was also to test pressures of 200, 300, 350 and 400 MPa at 5 degrees C for 30 min. The results were analysed statistically and showed that there were no significant differences between pressures of 100 and 200 MPa at 5, 10 and 15 min. However, at 300 MPa, there were significant differences at 15 min. When the pressure treatment was 400 MPa, significant differences were observed at pressure times of 5, 10 and 15 min. The results were fitted to a linear curve. In pure culture, no viable cells were detected after high pressure treatment of 350 MPa for 30 min at 5 degrees C. The use of low temperature helps to maintain the sensory properties of the product.

Colony Count, Microbial↗

PubMed1999

Response to high-pressure, low-temperature treatment in vegetables: determination of survival rates of microbial populations using flow cytometry and detection of peroxidase activity using confocal microscopy.

Application of high hydrostatic pressure (200, 300, 350 and 400 MPa) at 5 degrees C for 30 min to different micro-organisms, including Gram-positive and Gram-negative bacteria, moulds and yeasts, proved to be more effective in inactivating these organisms than treatments at 20 degrees C for 10 min and at 10 degrees C for 20 min. Moulds, yeasts, Gram-negative bacteria and Listeria monocytogenes were most sensitive, and their populations were completely inactivated at pressures between 300 and 350 MPa. The same conditions of pressure, temperature, and time were applied to different vegetables (lettuce, tomato, asparagus, spinach, cauliflower and onion), achieving reductions of from 2-4 log units in both viable mesophiles and moulds and yeasts at pressures of between 300 and 400 MPa. Sensory characteristics were unaltered, especially in asparagus, onion, tomato and cauliflower, though slight browning was observed in cauliflower at 350 MPa. Flow cytometry was applied to certain of the microbial populations used in the above experiment before and after the pressurization treatment. The results were indicative of differing percentage survival rates depending on micro-organism type, with higher survival rates for Gram-positive bacteria, except L. monocytogenes, than in the other test micro-organisms. Growth of survivors was undetectable using the plate count method, suggesting that micro-organisms suffering from pressure stress were metabolically inactive though alive. The pressurization treatments did not inactivate the peroxidase responsible for browning in vegetables. Confocal microscopic examination of epidermal tissue from onion showed that the enzyme had been displaced to the cell interior. Use of low temperatures and moderately long pressurization times yielded improved inactivation of micro-organisms and better sensorial characteristics of the vegetables, and should lower industrial costs.

Aerobiosis↗

PubMed1997

Effect of high pressure on the reduction of microbial populations in vegetables.

Resistance of micro-organisms to high pressure is variable and directly related to extrinsic and intrinsic factors. Pressures of 100, 200, 300, 350 and 400 MPa were applied at 20 degrees C for 10 min and at 10 degrees C for 20 min using strains of Gram-positive and Gram-negative bacteria, moulds and yeasts, as well as spores of Gram-positive bacteria. The results showed that at pressures of 100 and 200 MPa, decreases in microbial populations were not significant, whereas the populations of all the micro-organisms tested decreased considerably at a pressure of 300 MPa. A pressure of 300 MPa at 10 degrees C for 20 min was required to completely reduce the population of Saccharomyces cerevisiae, and a pressure of 350 MPa was needed to reduce most of the Gram-negative bacteria and moulds. The Gram-positive bacteria were more resistant, and pressures of 400 MPa were unable to completely reduce their populations. The different pressures employed had little effect on the initial numbers of spores. The initial populations of viable aerobic mesophiles and moulds and yeasts in vegetables (lettuce and tomatoes) decreased 1 log unit at pressures of 300 MPa and above under both sets of experimental treatment conditions. However, treatment at that pressure also resulted in alterations in the organoleptic properties of the samples. In the tomatoes, the skin loosened and peeled away, though the flesh remained firm, and colour and flavour were unchanged. The lettuce remained firm but underwent browning; flavour was unaffected. In vegetables use of moderate pressures in combination with other treatment conditions would appear to be required to reduce the populations of contaminating micro-organisms while avoiding the undesirable alterations in organoleptic properties that take place at 300 MPa.

Food Microbiology↗

PubMedDate not supplied

High-presssure shift freezing. Part 2. Modeling of freezing times for a finite cylindrical model.

A comprehensive vision of the heat transfer process involved in high-pressure shift freezing (HPSF) is shown in comparison to the process at atmospheric pressure. In addition, a mathematical model to predict the freezing times is presented. This model takes into consideration the dependence of the thermophysical properties relating to temperature and pressure and the supercooling reached by liquid water at atmospheric pressure after adiabatic expansion in the HPSF process. Experimental and theoretical data appear to agree.

Freezing↗

PubMedDate not supplied

High-pressure shift freezing. Part 1. Amount of ice instantaneously formed in the process.

A mathematical model to calculate the amount of ice formed instantaneously after a rapid expansion in high-pressure shift processes (HPSF) was developed. It considers that when water is expanded it does not extend over its melting curve but reaches a metastable state (supercooled water), which also occurs in practice. Theoretical results appear to agree with experimental data.

Freezing↗