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

Abstract

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°C for 10 min and at 10°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°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.

Use of Pressure for Improving Storage Quality of Fresh-Cut Produce

“…through activation of the spore's nutrient receptors (Shigeta et al 2007). In addition to these spoilage microorganisms, E. coli O157 (Gill and Ramaswamy 2008), Salmonella typhimurium (Arroyo et al 1997), L. monocytogenes (Préstamo et al 1999), and Aeromonas hydrophila (Durães-Carvalho et al 2012) were completely inactivated by HP of 350-600 MPa for 3-10 min at room temperature, although the occurrence of pressure-resistant strains has been reported in E. coli O157:H7 (Jordan et al 2001) and L. monocytogenes (Van Boeijen et al 2008).…”

“…The HP treatment also eliminated Escherichia coli (Dogan and Erkmen 2003;Muñoz et al 2007;Lavinas et al 2008), E. coli O157 (Jordan et al 2001;Whitney et al 2008), and Listeria monocytogenes (Jordan et al 2001) inoculated into the fruit juices. However, there are few studies on successful application of HP to fresh vegetables (Arroyo et al 1997;, and little information exists on the effect of HP on the microbiological safety and shelf life of fresh-cut produce.…”

Possibilities of Using of High Pressure in Fruit and Vegetable Industry

“…Jest ona zwykle bardziej odporna na działanie wysokich ciśnień niż sztucznie wprowadzone drobnoustroje [2,30]. Na przykład ciśnienie 350 MPa (20 °C, 10 min) zmniejszyło populację 10 4 komórek/ml drożdży i pleśni naturalnie występujących w pomidorach i sałacie o 3 rzędy wielkości, podczas gdy w tych samych warunkach całkowitej inaktywacji uległy wprowadzone w tej samej liczbie Saccharomyces cerevisiae, Aspergillus niger i Penicillum spp.…”

“…Na przykład ciśnienie 350 MPa (20 °C, 10 min) zmniejszyło populację 10 4 komórek/ml drożdży i pleśni naturalnie występujących w pomidorach i sałacie o 3 rzędy wielkości, podczas gdy w tych samych warunkach całkowitej inaktywacji uległy wprowadzone w tej samej liczbie Saccharomyces cerevisiae, Aspergillus niger i Penicillum spp. [2].Metoda z wykorzystaniem wysokiego ciśnienia może być dobrym sposobem utrwalania kwaśnych produktów owocowych takich, jak: soki owocowe, dżemy, galaretki [10,17]. Podstawową mikroflorę tych produktów stanowią drożdże, pleśnie i bakterie kwasu mlekowego, a więc organizmy stosunkowo wrażliwe na działanie ciśnienia [1,35].…”

Disinfection of Human Tissues in Orthopedic Surgical Oncology by High Hydrostatic Pressure

“…The most efficient methods of inactivation are gamma irradiation and thermal inactivation as well as chemical sterilization methods such as the peracetic acid-ethanol treatment of bone (49). The direct effect of HHP to achieve killing of vegetative bacterial, yeast and mould cells, has been documented as well (50,51), although much higher pressure values of 500 -700 MPa are needed than for the inactivation of viruses (52,53). Interestingly, Gram-positive bacteria are more resistant to HHP than Gram-negative bacteria (54).…”