Whole black pepper is a dry product, which is often naturally contaminated with bacterial endospores and sometimes also with human pathogens like Salmonella. Dry pepper itself is a shelf-stable ...product, but if it is incorporated into high moisture minimally processed food, the microorganisms can reduce the shelf-life of the final product and/or can cause foodborne diseases. In this study the antimicrobial effect of two different atmospheric pressure plasma applications for the decontamination of whole black pepper was investigated. Naturally contaminated peppercorns and with Bacillus subtilis spores, Bacillus atrophaeus spores and Salmonella enterica inoculated ones were treated using a plasma jet or a microwave-driven remote plasma. Surface color and the content of essential oils and piperine was measured. S. enterica, B. subtilis spores and B. atrophaeus spores were reduced by 4.1, 2.4 and 2.8 log, respectively, after 30 min remote plasma treatment. Direct plasma jet treatment did not result in equivalent inactivation levels. However, both plasma applications did not considerable affect the quality parameters.
•Two different plasma devices were evaluated regarding their antimicrobial effects.•Remote plasma showed promising results regarding the decontamination of pepper.•Both plasma applications did not considerable affect the pepper quality.•Proper selection of plasma sources is essential to reach the process goal.•Remote plasma offers interesting potential as non-thermal decontamination process.
•Transfer of plasma-induced surface modification to dry bulky food products.•Techno-functional properties of protein and fiber-rich flour fractions were modified.•Plasma treatment decreased protein ...solubility in protein-rich pea flour.•Protein solubility of pea protein isolate was increased.
This study aimed at evaluating the potential of cold atmospheric pressure plasma (CAPP) treatment for the functionalization of dry bulky and powdery food materials. CAPP treatment was capable of modifying protein and techno-functional properties of different flour fractions from grain pea (Pisum sativum ‘Salamanca’). Experiments using a pea protein isolate indicated that the reason for the increase in water and fat binding capacities in protein rich pea flour to 113% and 116%, respectively, is based on plasma-induced modifications of the proteins as their solubility was increased to 191%. This is also supported by detected changes in tryptophan fluorescence spectra. With increasing treatment times the fluorescence emission intensity increased at 328nm and decreased at 355nm indicating structural and/or compositional changes of the proteins. The results indicate that the application of CAPP can be exploited as a means to modulate functionality of dry bulk materials in the food sector.
During post-harvest processing of fresh cut and dried fruits and vegetables, polyphenol oxidase (PPO) and peroxidase (POD) need to be inactivated or inhibited in order to avoid undesirable browning ...reactions and loss of sensorial or nutritional quality. To meet this goal, the application of plasma processed air (PPA) offers a promising “gentle” alternative to traditional methods, such as pasteurization or the addition of anti-browning compounds. Using ambient air as process gas instead of an expensive noble gas, such as argon, exhibits a substantial improvement for the development of large-scale plasmas at ambient pressure and allows the indirect treatment of larger goods within a remote exposure reactor. In this study the ability of PPA to inactivate PPO and POD in complex food matrices and its impact on quality parameters, such as color, texture and cell integrity directly after freshly cutting and during storage of warm air dried and freeze dried produce was evaluated.
The study evidently shows that PPA processing is capable of reducing the activity of PPO and POD in the freshly cut tissue from both apple and potato. Following exposure to PPA for 10min the PPO activity was reduced by about 62% and 77% in fresh cut apple and potato tissue, respectively. POD, as the more temperature-stable enzyme, was even less stable upon PPA treatment for 10min and was reduced by about 65% and 89% in fresh cut apple and potato tissue, respectively. Blackening of the potato tissue could be completely prevented by plasma treatment while a browning different from the habitual nature of enzymatic browning occurred upon exposure of the apple tissue to PPA. In both cases, the pH value on the tissue surface dropped to 1.5 while cell integrity and dry matter content were not significantly affected.
The quality and shelf life of freshly cut and dried fruits and vegetables greatly depend on the activity of naturally occurring enzymes which catalyze browning reactions at cut surfaces. This study shows that the application of PPA, as a promising nonthermal “pasteurization” technology, enables the inactivation of PPO and POD in complex food matrices. It further describes the impact of the PPA treatment on quality parameters of the freshly cut tissue from apple and potato and goes beyond on evaluating color, texture and enzyme activity in warm air dried and freeze dried tissue over a storage time of three weeks. The results contribute to the understanding and product-specificity of PPA-induced effects on quality and shelf life of fresh cut and dried fruit and vegetable produce and could be a basis for a possible industrial implementation.
•PPA treatment of fresh cut produces was investigated.•Plasma treatment inhibited polyphenol oxidase and peroxidase activity in complex food matrices.•The blackening of fresh cut and dried potato tissue was prevented by PPA treatment.•PPA processing offers a promising innovative pretreatment to drying processes.•The novel nonthermal process is amenable to continuous industrial scale processing.
Fresh fruits and vegetables, destined to be eaten raw or minimally processed only, harbor the risk of conveying pathogenic microorganisms. Factors such as weather conditions, which favor survival or ...growth of microorganisms, and improper handling during cultivation or in the postharvest chain, can contribute to outbreaks of food-borne illness. Application of chemical sanitizers or physical treatments often shows a limited efficiency or does not meet consumer acceptance. Availability of gentle and effective techniques for disinfection of fresh produce, therefore, is highly desirable. Non-thermal gas plasma (NTP) treatment is a promising novel technique to reduce the microbial load on fresh fruits and vegetables. However, knowledge on practical applicability of NTP for fresh fruits and vegetables is very limited. In this study, chlorophyll fluorescence imaging (CFI) was used to elucidate suitable process parameters for application of an atmospheric pressure plasma-jet (kINPen 09, INP Greifswald, Germany) on corn salad, a perishable leafy green. Keeping a distance of 17mm to the plasma-jet, corn salad leaves could be treated for up to 60s at a fixed power (8W) and 5Lmin−1 of argon mixed with 0.1% oxygen. Surface temperature on leaves did never exceed 35.2°C. Antibacterial tests were performed on corn salad, cucumber, apple, and tomato and achieved an inactivation of artificially inoculated Escherichia coli DSM 1116 of 4.1±1.2, 4.7±0.4, 4.7±0, and 3.3±0.9logunits, respectively, after 60s treatment time. Additional tests with a dielectric barrier discharge plasma and indirect plasma treatment within a remote exposure reactor, fed by a microwave induced plasma torch, did not result in equivalent levels of quality retention as observed using the plasma-jet.
Development of gentle non-thermal disinfection methods aims to provide the industry with new tools to actively improve the microbial status of fresh produce beyond the preventive benefits of good hygiene practices and the limited efficacy of post-harvest washing. The presented study shows how cold plasma can be applied to heat-sensitive lettuce leaves without detrimental effects to product quality. The additional microbiological tests offer insights into the antibacterial capacity of cold plasma on different produce surfaces. The results contribute to prompt the development of appropriate large-scale plasma sources to establish a new plasma-based sanitation technique for fresh fruits and vegetables, which should also be implementable into running process lines.
•Sufficient distance to ionization zone enables gentle plasma application on leaves.•Quality retention allows for a gentle plasma treatment of up to 1min.•Admixture of 0.1% oxygen to argon does not detrimentally affect quality.•Efficient inactivation of microbes is limited to the initial min of treatment.
Currently used disinfection or sanitation methods for fresh fruits and vegetables lack antimicrobial effectiveness, but are high in costs, water consumption or chemicals. One alternative could be to ...apply nonthermal plasma at atmospheric pressure to the described issue. The experimental set‐up implements microwave plasma, which generates plasma processed air (PPA) containing manifold reactive nitrogen species‐based chemical and antimicrobial compounds. Five different fresh produces were first contaminated with seven different microorganisms e.g., bacteria, yeasts and endospores followed by a treatment with PPA. The plasma was ignited for 7 s only. After a post‐plasma treatment time of maximum 15 min with PPA, reduction factors of microbiological load greater than 6 log were detected. Furthermore, sensory examinations showed only little influences in texture, appearance and odor. The characteristics of plasma and its generated cocktail of chemical compounds leads to a high microbial inactivation on various specimens and offers a wide range of possible applications. PRACTICAL APPLICATIONS: Nonthermal atmospheric pressure plasma is a nonthermal, nontoxic and low‐cost possibility to inactivate microorganisms on fresh produce surfaces. It could be used in dry and wet environments and allows a treatment of fresh food and virtually every conceivable surface in batch or inline processes along the whole value chain of food production, and could be implemented as an alternative to ozone or chlorine dioxide treatment.
•Suitability of indirect plasma is closely linked to the type of fresh produce.•Antimicrobial efficacy varies from minor on cucumbers to high on carrots.•Delayed effects on carotenoid-colored produce ...need to be controlled.•Combined quality retention and microbial improvement were best on apples.•Indirect application enables the use of thermal plasma sources on heat-sensitive produce.
The ubiquitous presence of spoilage microorganisms and sporadic occurrences of human pathogens on heat-sensitive fresh produce are serious economic and health issues. A potential solution for the gentle sanitation of fresh fruit and vegetables is the application of atmospheric pressure plasmas. In this study, a microwave-driven air plasma torch was used for indirect treatment of whole pieces of fruits and vegetables within a remote exposure chamber for up to 10min. The impact of this technique on the external quality of apples, cucumbers, tomatoes and carrots, and its antimicrobial efficacy on indigenous and inoculated microorganisms were examined. After 5min of plasma application, total mesophilic counts were reduced by 3.4±0.4, 1.2±0.5, 5.2±0.5, and 3.3±0.5 log cycles on apples, cucumbers, carrots and tomatoes, respectively. After 10min, counts of artificially inoculated Escherichia coli were reduced by 4.6±2.0 and 6.0±0.8 log cycles on apples and carrots, respectively. Significant effects of plasma treatment were found on color of tomatoes and carrots, and on chlorophyll fluorescence parameters of cucumbers, whereas elasticity remained almost unaffected in all produce. The plasma processed air treatment proved to be suitable for apples as the most stable product. For more susceptible produces such as carrots, however, plasma induced effects on the surface. Hence, in such cases, the application of indirect plasma needs to be specifically adapted to ensure product quality and safety.
Application of plasma is well-established in various industrial processes; its use has also been suggested as an innovative technology in the food sector. Besides the ability to inactivate ...undesirable microorganisms on heat-sensitive foods, cold atmospheric pressure plasma (CAPP) may also modify and intensify the secondary metabolism in agricultural plant produces along the whole value-added chain. This is because CAPP provides a source of reactive oxygen and nitrogen species and specific UV radiation.
The objective of this study was to determine the effects of CAPP treatment on the flavonol glycoside profile of pea seedlings (Pisum sativum ‘Salamanca’), while considering the potential impact on their metabolic activity in different growth stages. Pea seeds, sprouts, and seedlings were exposed to semi-direct CAPP using a dielectric barrier discharge device with air as the process gas. Applying voltages between 6 and 12kVpp at a frequency of 3.0kHz resulted in optical emission spectra dominated by UV-B and UV-C radiation. The specific energy densities were monitored upon varying voltages and treatment times.
Exposing swollen pea seeds to plasma (9kVpp) between 1 and 10min increased germination rate and dry matter content but decreased growth rate. Non-acylated and monoacylated triglycosides of quercetin and kaempferol dominated the flavonol glycoside profile, quercetin-3-O-p-coumaroyl-triglucoside being the main flavonoid glycoside. In 15d-old pea seedlings, the concentration of flavonoid glycosides was dose-dependently decreased after two CAPP treatments compared to none or three treatments. Furthermore, photosynthetic efficiency of treated pea sprouts and seedlings declined potentially indicating a negative effect of CAPP treatment on plant metabolism. The responses of pea tissues greatly depended on time point and duration of CAPP treatments. This study represents a first step towards the implementation of the CAPP technology for a targeted modification of valuable secondary plant metabolites during post-harvest chain of agricultural produces.
•The application of cold plasma during post-harvest processing of pea seeds was tested.•CAPP treatment affected the flavonol glycoside profile dose-dependently.•Plasma affects germination, growth and photosynthesis of pea sprouts and seedlings.•The applied CAPP was proven to be a source of UV-B and UV-C radiation.•An innovative process for the production of functional food is discussed.
Atmospheric plasma provides the advantages of high microbial inactivation that can be performed under ambient conditions. It is consequently regarded as potential alternative to traditional food ...preservation methods.
In this study we systematically tested the influence of argon as plasma carrier gas with admixtures of oxygen (0–0.34vol.%) and nitrogen (0–0.3vol.%) towards its emission intensity of UV-C light, excited OH and N2-species and atomic oxygen. A mixture of argon, 0.135vol.% oxygen and 0.2vol.% nitrogen emitted four fold more UV photons than pure argon. However, sporicidal effects on Bacillus atrophaeus (3.1 log10) and Bacillus subtilis spores (2.4 log10) were found for pure argon plasma, which were similar as compared to the sporicidal effect of the plasma with highest UV-emission. To distinguish lethal effects caused by emitted UV-light and reactive species, UV-sensitive mutant spore strains (PS578 and FB122) were exposed to plasmas with different UV-emission intensities and a significant impact of UV-light on the first phase of spore inactivation was confirmed.
As an efficient method for the inactivation of microorganisms at low temperatures and atmospheric pressure, plasma is already commercially used for the sterilization of medical devices. The results presented in this study could be useful for a process optimization regardless if the plasma is applied for food preservation or surface decontamination. Especially the impact of emitted UV photons from the plasma on the first inactivation phase of endospores attached to surfaces, depicts a high potential of such plasmas for a rapid spore inactivation.
•A systematically testing of argon plasma with admixtures of oxygen and nitrogen was done.•Highest UV-emission for a mixture of argon with 0.135vol.% O2 and 0.2vol.% N2.•Similar sporicidal effects were found for a pure argon plasma compared to the one with highest UV-emission.•UV-sensitive spore strains confirmed the sporicidal effect of emitted UV-photons.•Biphasic spore inactivation was found, with a dominant effect of UV-photons on the first inactivation phase.
Plasma is used as a common technology for the treatment and modification of surfaces in a variety of industrial branches. Decontamination of inorganic materials by plasma is possible with ...deterioration of the materials properties of a few nanometres. The inactivation efficacy of microwave plasma processed air against vegetative bacteria and bacterial endospores was investigated. The gained results provide inactivation rates up to 6 log in total treatment times (15–30 min) comparable to sterilization treatment times of thermo‐sensitive medical devices with ethylene oxide, formaldehyde or H2O2. Additions like O2 or O3 did not promote the antimicrobial efficacy. Moreover, this new method is characterized by advantages like no thermal influence, no toxicity for human and environment and low costs.
The antimicrobial efficacy of a microwave plasma setup (PLexc®) against E. coli, S. aureus, and B. atrophaeus endospores with and without bovine serum albumin (BSA) on glass bottles is investigated. Moreover, the microwave plasma processed air decontaminates the specimen within treatment times comparable to currently common methods like EO, FORM, and H2O2. The decontamination efficiency raised up to 6 log cfu specimen−1 by plasma treatment.
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