Abstract
The safety and quality of cereal grain supplies are adversely impacted by microbiological contamination, with novel interventions required to maximise whole grains safety and stability. The microbiological contaminants of wheat grains and the efficacy of Atmospheric Cold Plasma (ACP) for potential to control these risks were investigated. The evaluations were performed using a contained reactor dielectric barrier discharge (DBD) system; samples were treated for 0–20 min using direct and indirect plasma exposure. Amplicon-based metagenomic analysis using bacterial 16S rRNA gene and fungal 18S rRNA gene with internal transcribed spacer (ITS) region was performed to characterize the change in microbial community composition in response to ACP treatment. The antimicrobial efficacy of ACP against a range of bacterial and fungal contaminants of wheat, was assessed to include individual isolates from grains as challenge pathogens. ACP influenced wheat microbiome composition, with a higher microbial diversity as well as abundance found on the untreated control grain samples. Culture and genomic approaches revealed different trends for mycoflora detection and control. A challenge study demonstrated that using direct mode of plasma exposure with 20 min of treatment significantly reduced the concentration of all pathogens. Overall, reduction levels for B. atrophaeus vegetative cells were higher than for all fungal species tested, whereas B. atrophaeus spores were the most resistant to ACP among all microorganisms tested. Of note, repeating sub-lethal plasma treatment did not induce resistance to ACP in either B. atrophaeus or A. flavus spores. ACP process control could be tailored to address diverse microbiological risks for grain stability and safety.
Highlights
Cereal grains have been a principal component of the human diet for thousands of years and remain the most important contributor to human food supplies globally
Meta-genomic approach was unable to dis tinguish between viable and dead microbial populations within mi crobiome (Cao et al, 2017), the results demonstrated that some bac terial species, for example Acinetobacter, Lysobacter of Gammaproteobacteria, were less abundant or not detected after plasma treatment
A 5-fold repeated Atmospheric Cold Plasma (ACP) treatment did not induce re sistance in either bacterial vegetative cells of B. atrophaeus or fungal spores of A. flavus inoculated on wheat grains
Summary
Cereal grains have been a principal component of the human diet for thousands of years and remain the most important contributor to human food supplies globally. More than 50% of world daily caloric intake comes directly from cereal grain consumption (Awika, 2011; Enghiad et al, 2017). World population is expected to be 50% larger than at present by 2050 and global grain demand is projected to double (Tilman et al, 2002). Fulfilling the food demand of an increasing population is a major global concern, especially due to the fact that more than one-third of food is lost or wasted in postharvest operations. Up to 50%–60% of cereal grains can be lost during processing caused mainly by presence of microorganisms and insects (Kumar and Kalita, 2017), rendering the cereals unsuitable for human or animal consumption
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