Hypobaric hydrogen sulfide; a novel means to prevent food spoilage
Lead Research Organisation:
King's College London
Department Name: Pharmaceutical Sciences
Abstract
Hypobaric hydrogen sulfide
According to Boyles law, gas pressure (P) is inversely proportional to volume (V) thus decompressing a sealed chamber containing foods to induce hypobaric conditions will increase the gas volume and drive the conversion of a liquid H2S donor into a gas. If foods were exposed to H2S under hypobaric conditions the gas exposure could be tightly controlled and thus provide a suitable approach to expose food to H2S gas on an industrial scale. Preliminary data gathered by the applicants thus far has suggested that that H2S is indeed very potentent, i.e., it has a single figure ng/ml minimum inhibitory concentrations (MIC) for fungal species in sealed hypobaric vessels. In addition, researchers at King's have designed and produced, using a 3D printer, hypobaric cells that could be used to test the concept in the laboratory. Researchers at Edingburgh Napier have industrial scale sealed vesles to scale this process up. Together these two research teams plan to work with Natures Way Foods in a collaborative project that has the aim of determining how the type of H2S donor and delivery conditions influence the antifungal and antibacterial action of H2S. It is anticipated that fulfilling this aim will provide the basis for a new industrial process to control fungal and microbial growth on foods, thus slow down food spoilage and preventing food wastage.
Program and Methodology
Phase 1 - Understanding food H2S exposure using gas donors at atmospheric and hypobaric conditions (Lead - Dr S A Jones, King's College London)
The work will use three H2S donors, NaHS, hydroxybenzothioamide, GYY4137 selected based on their commercial availability, differential rates of H2S release and different physicochemical properties.
Study 1a - H2S release from the H2S donor - A method established in Kartha et al., (Analytical Biochemistry 423 (2012) 102-108) will be used to determine gas release kinetics of the three H2S donors at atmospheric and hypobaric conditions.
Study 1b - H2S food residues - The penetration of the H2S into lettuce leaves and spinach (of interest to the commercial partner) will be assed at both atmospheric and hypobaric conditions using the three donors in a diffusion cell assay.
Phase 2 - Understanding the antimicrobial and antifungal effects of sulfide gases under atmospheric and hypobaric conditions in vitro (Lead - Prof Ian Singleton, Edinburgh Napier University)
Study 2a - Assessing the effect of H2S on Food Pathogens in vitro - The MICs of atmospheric and hypobaric gas exposure will be tested using different strains of E. coli K12, L. innocua (important species in leafy foods), A. niger and P. expansum.
Study 2b - Test the involvement of Reactive Oxygen Species (ROS) - ROS scavengers (e.g. ascorbic acid) will be added to the growth medium and H2S toxicity to the species detailed in Study 2a will be reassessed. The dye 2',7' dichloro-dihydrofluorescein diacetate (H2DCFDA) will be used to directly observe ROS. The expression and function of catalase and super oxide dismutase (SOD) will be monitored pre and post exposure using RT-PCR and enzyme assays.
Phase 3 - Using sulphide gases to prevent food spoilage (Lead - Dr S A Jones, King's College London)
The optimised gas exposure protocol will be used to delay/prevent the growth of microbial and fungal species isolated during the industrial placement and spiked onto fresh foods (ranging from leaves, common vegetables and fruits). The gas application protocol will be manipulated to ensure food quality is not lost. A pilot scale exposure chamber will be used for the studies.
According to Boyles law, gas pressure (P) is inversely proportional to volume (V) thus decompressing a sealed chamber containing foods to induce hypobaric conditions will increase the gas volume and drive the conversion of a liquid H2S donor into a gas. If foods were exposed to H2S under hypobaric conditions the gas exposure could be tightly controlled and thus provide a suitable approach to expose food to H2S gas on an industrial scale. Preliminary data gathered by the applicants thus far has suggested that that H2S is indeed very potentent, i.e., it has a single figure ng/ml minimum inhibitory concentrations (MIC) for fungal species in sealed hypobaric vessels. In addition, researchers at King's have designed and produced, using a 3D printer, hypobaric cells that could be used to test the concept in the laboratory. Researchers at Edingburgh Napier have industrial scale sealed vesles to scale this process up. Together these two research teams plan to work with Natures Way Foods in a collaborative project that has the aim of determining how the type of H2S donor and delivery conditions influence the antifungal and antibacterial action of H2S. It is anticipated that fulfilling this aim will provide the basis for a new industrial process to control fungal and microbial growth on foods, thus slow down food spoilage and preventing food wastage.
Program and Methodology
Phase 1 - Understanding food H2S exposure using gas donors at atmospheric and hypobaric conditions (Lead - Dr S A Jones, King's College London)
The work will use three H2S donors, NaHS, hydroxybenzothioamide, GYY4137 selected based on their commercial availability, differential rates of H2S release and different physicochemical properties.
Study 1a - H2S release from the H2S donor - A method established in Kartha et al., (Analytical Biochemistry 423 (2012) 102-108) will be used to determine gas release kinetics of the three H2S donors at atmospheric and hypobaric conditions.
Study 1b - H2S food residues - The penetration of the H2S into lettuce leaves and spinach (of interest to the commercial partner) will be assed at both atmospheric and hypobaric conditions using the three donors in a diffusion cell assay.
Phase 2 - Understanding the antimicrobial and antifungal effects of sulfide gases under atmospheric and hypobaric conditions in vitro (Lead - Prof Ian Singleton, Edinburgh Napier University)
Study 2a - Assessing the effect of H2S on Food Pathogens in vitro - The MICs of atmospheric and hypobaric gas exposure will be tested using different strains of E. coli K12, L. innocua (important species in leafy foods), A. niger and P. expansum.
Study 2b - Test the involvement of Reactive Oxygen Species (ROS) - ROS scavengers (e.g. ascorbic acid) will be added to the growth medium and H2S toxicity to the species detailed in Study 2a will be reassessed. The dye 2',7' dichloro-dihydrofluorescein diacetate (H2DCFDA) will be used to directly observe ROS. The expression and function of catalase and super oxide dismutase (SOD) will be monitored pre and post exposure using RT-PCR and enzyme assays.
Phase 3 - Using sulphide gases to prevent food spoilage (Lead - Dr S A Jones, King's College London)
The optimised gas exposure protocol will be used to delay/prevent the growth of microbial and fungal species isolated during the industrial placement and spiked onto fresh foods (ranging from leaves, common vegetables and fruits). The gas application protocol will be manipulated to ensure food quality is not lost. A pilot scale exposure chamber will be used for the studies.