The largest share of studies deal with this crop. Wheat is an important, tradable commodity. Its use is versatile, from direct feeding to animals, through the production of flour, to the production of ethanol. Microbiological protection of wheat grain is important both in the field and in grain processing.
Thomas-Popo et al. 
reported the inactivation of both artificial and natural contamination of wheat grains. For artificial contamination by E. coli
and Salmonella enterica
, the total cfu decreased for the initial cca 7 log10
by 3–4 log10
after 20 min of plasma treatment. For natural contamination, the decrease in total cfu of mesophiles, psychrotrophs and Enterobacteriaceae
after 20 min of treatment was almost 1, more than 2 and 1.4 log10
, respectively. On the contrary, the yeast and molds were completely destroyed after only 10 min.
The following two related works 
reported the inactivation of bacterial endospores of Bacillus amyloliquefaciens
and Geobacillus stearothermophilus
in wheat grains. While in the first case, the total cfu of B. amyloliquefaciens
was reduced by 2 log10
from initial 106
cfu/g after 30 s, using the other source of NTP in the second case led to the 0.8 log10
and 3 log10
after 5 min and 60 min, respectively.
According to Zahoranova et al. 
, the concentration of epiphytic bacteria decreased from the initial cca 5 × 104
cfu/g by more than 1 log10
after 600 s. Epiphytic yeast was not detected and filamentous fungi were completely inactivated from the initial 600 cfu after 120 s of treatment. For artificial contaminations, the less resistant Fusarium nivale
and F. culmorum
were completely inhibited after 90 s, Trichothecium roseum
after 180 s and Aspergillus flavus
after 240 s; however, the most resistant, A. clavatus
, was not totally inhibited after 300 s.
Selcuk et al. 
used Aspergillus paraciticus
spp. isolated from foods for artificial contamination in 5 × 106
cfu/g of grains and reported a reduction of more than 2 log10
after 30 min of treatment.
Hoppanova et al. 
treated the grains inoculated with Fusarium culmorum
spores in a concentration of 105
with plasma or in combination with 10% of Vitavax2000 fungicide. Complete inactivation occurred after 180 s and 60 s of plasma exposure alone and plasma exposure with fungicide, respectively.
Filatova et al. 
used artificial contamination with Fusarium culmorum
and natural contamination with Alternaria
spp.; the infection levels decreased from 40% to 7% and from 4% to 2%, respectively. Inactivation of these fungi led to better germination, growth and grain yield.
, the authors did not report the inactivation of fungal spores, but the resistant behavior of the treated samples to fungus attack, which decreased from 40% to 20% after 2 or 4 min of treatment.
In the work of Los et al. 
, the authors inactivated the natural microflora of mesophilic bacteria, yeasts and molds of 104
cfu/g. Maximal reductions of 1.5 log10
CFU/g for bacteria and 2.5 log10
CFU/g for fungi were achieved after 20 min of treatment. The following study 
demonstrated that direct plasma exposure for 20 min significantly reduced the concentration of all pathogens. The reduction levels for the vegetative cells of Bacillus atrophaeus
were higher than for all the fungal species tested, while the spores of B. atrophaeus
were the most resistant. Repeating sublethal plasma treatment did not induce resistance to ACP in either B. atrophaeus
or A. flavus
Kordas et al., 2015 
, reported the decrease in fungal contamination on grains from an initial cca 250 cfu per 100 grains to cca 25 cfu per 100 grains after 10 s of treatment.
Works related to wheat are the most numerous and show the possible applications of plasma in the widest range; as for the inactivation of the microorganism, so for increasing the resistance of crops. So far, all works are on a more or less laboratory scale.
Insects may also cause serious problems. The following four papers described the possible inactivation of Tribolium and other species in wheat by NTP.
Shahrzad et al. 
reported the killing of Tribolium confusum
and Ephestia kuehniella
larvae in wheat from cca 300 to 0 in 20 s. Ratish Ramanan et al. 
achieved the total elimination of eggs, larvae and adults of T. castaneum
in wheat flour containing 10 eggs, 5 larvae or 5 adults in 15 min. In 
, 25 insects of T. castaneum
and T. confusum
per 30 g of wheat showed 100% mortality after 15 min of exposure. On the other hand, a very low mortality of T. castaneum
of approximately 5% in wheat grains was reported in an otherwise chaotic paper 
Rice grains are often attacked by various microbiological pathogens 
. Rice, as one of the most consumed cereals in the world, was the focus of the several following papers.
The first attempts were reported by Kang et al. 
, who treated with NTP rice grains infected by Fusarium fujikuroi
mold spores that cause bakanae disease. They sprayed the spore suspension of 106
cfu/mL on rice plants. The harvested grains were then exposed to NTP, which caused the number of infected grains to decrease from 100% of the control set to 20% in grains exposed for 30 min.
The follow-up study 
reported the successful effect of NTP on the control of two rice seed-borne diseases. It also examines the bakanae disease caused by Fusarium fujikuroi
mold and the blight disease caused by Burkholderia plantarii
bacteria. The bakanae disease severity index and the percentage of plants with symptoms were reduced to 18% and 8% after 10 min of exposure. The index of blight disease was reduced to 39%.
Natural rice contamination was also studied in the following two papers. Park et al. 
reported the decontamination of natural contamination of brown rice grains by bacteria, yeasts and molds and reported a reduction of more than 1.5 log10
after 10 min of exposure. In 
, complete inactivation of natural contaminants (pathogenic fungi and other microorganisms) in a rice grain husk after 1 min of exposure was reported.
Inactivation of artificial contamination by Aspergillus oryzae
, Penicillium digitatum
spores and E. coli
(initial concentrations of contaminants are not given) was reported in 
. The surface of rice and lemons was sterilized after 20 min of irradiation with a combination of plasma and UV light.
Finally, an attempt to industrial application was reported in 
, where the development of a large-scale NTP generator followed by a UV-C treatment was described. To evaluate the efficacy of rice natural microorganisms decontamination, the number of natural bacteria was reduced from initial 5.6 log10
to 1 log10
cfu/g; for yeasts and molds, the reduction was from 3.7 log10
to 2 log10
cfu/g after 7 min of treatment.
Works related to rice present similar results as those for wheat; however, the attempt to industrially up-scale gives hope for further development and usage.
Maize is currently grown all over the world, with the United States being one of the world’s largest producers. Several papers devoted to corn decontamination start with Selcuk et al. 
, who used the Aspergillus parasiticus
spp. food isolated for artificial contamination of 5 × 106
cfu/g of grains. They reported an approximate 70% reduction after 30 min of treatment. The paper 
focused mainly on grain germination but also reported that, after 4 min of grain treatment, the inhibition of artificial contamination of grains by Fusarium verticillioides
and F. graminearum
was achieved so that all grains, contrary to the control, germinated without visible mold growth occurrence.
, the authors used artificial contamination of Fusarium culmorum
and natural contamination of Alternaria
spp. The infection level decreased slightly from 76% to 66% and from 30% to 10%, respectively. This inactivation of fungi caused by grain treatment led to better germination, growth and grain yield.
, the authors investigated the inhibition of the native microbiota and potentially dangerous pathogens (Aspergillus flavus
, Alternaria alternata
and Fusarium culmorum
) in grains. Complete devitalization of the native microbiota was observed after 60 s of treatment for bacteria and 180 s for filamentous fungi. For artificial contaminations, total elimination from the initial 3–4 log10
(CFU/g) was observed after 60 s for F. culmorum
and after 300 s for A. flavus
and A. alternata
, the decrease in artificial infection with A. flavus
and A. parasiticus
from the initial 107
cfu/g by 5 log10
in 5 min was reported. The natural contamination of the fungi of the initial almost 104
cfu/g and of the aerobic mesophilic bacteria of the initial 103
cfu/g was totally inactivated after 3 min. Much lower inhibition was reported in 
, where the initial number of more than 200 fungi per 100 grains was reduced to 30% after 20 min of treatment.
Although all cited works are devoted to the fungi only, it can be assumed that, for other microorganisms, the decontamination efficiency will be comparable to previous crops.
It is one of the oldest cereals in the world and is geographically widespread. Today, most barley grown, especially winter barley, is used for feed purposes. Barley is an important feed grain for many countries, especially for those that are not suitable for maize production. Barley also received attention for NTP decontamination.
, the concentration of artificial contamination with Aspergillus niger
and Penicillium verrucosum
in the total mold count of more than 5 log spores/g grains was reduced by 2.5–3 log. Furthermore, the use of air plasma also resulted in a decrease in ochratoxin A concentration from 56 (untreated) to 20 ng/g after 3 min.
The two previously mentioned works also deal with barley. Selcuk et al. 
used Aspergillus parasiticus
spp. isolated from foods for artificial contamination at 5.006 cfu/g of grains and reported a reduction of more than 1 log10
after 30 min of treatment. Hoppanová et al. 
treated grains inoculated with Fusarium culmorum
spores in a concentration of 105
with plasma or in combination with 10% Vitavax2000 fungicide. Complete inactivation occurred after 120 s and 60 s of plasma exposure alone and plasma exposure with fungicide, respectively.
The paper 
is focused mainly on the germination of grains. They reported inhibition of artificial contamination of grains by Fusarium verticillioides
and F. graminearum
after 4 min of treatment, insomuch as all grains germinated without visible mold growth as opposed to the control. In the work 
, the authors inactivated both native microflora and artificial contamination. For the natural microflora of mesophilic bacteria, yeasts and molds of 104
cfu/g, maximum reductions of 1.5 log10
CFU/g for bacteria and 2.5 log10
CFU/g for fungi were achieved after 20 min of treatment. For artificial contamination, a total reduction of more than 3 log10
was observed after 20 min of exposure for E. coli
, Bacillus atrophaeus
vegetative cells and Penicillium verrucosum
spores, while the reduction for the endospores of B. atrophaeus
reached only 2.4 log10
Much weaker inhibition was reported in 
, where the initial number of more than 200 fungi per 100 grains was reduced by up to 20% after 20 min of treatment.
In the work 
, unusual plasma-processed air (PPA) was used for inactivation of B. atrophaeus
(DSM 675) endospores on barley grains, where gas flows from the active plasma to the incubation bottles. The number of spores was reduced from the initial concentration of ~106
CFU/per 10 g by 3.00 ± 0.33 log10
after 3 min of exposure.
Obtained results are again comparable with other crops, but the last cited work suggests the possibility of using PPA, which could markedly simplify the whole operating process and the transformation to real processing.