| Nonthermal plasma(NTP)technology is an emerging innovative food processing strategy applied in various food systems.The technique has a unique low temperature that allows the processing of thermolabile food products as well as offers beneficial effects on the modification of food properties.NTP has demonstrated marked antimicrobial efficacies with good retention of important physical,chemical,sensory,and nutritional parameters for an array of food products.NTP reactive species are regarded as the key chemical reactive substances with immense antimicrobial properties against spoilage and pathogenic microorganisms of food safety concerns.These beneficial traits,coupled with the paucity of studies on the application of NTP on important thermolabile food products such as tiger nuts,led to this research work.This study elucidates the application of NTP processing on tiger nut and its milk with their corresponding microbial and quality stability as well as enhancement of their functional characteristics and antioxidant capacities.Along similar lines,the kinetic modeling of NTP preservation of tiger nut milk to ensure microbial safety was conducted.Analyses of plasma-induced effects along with a comparison to conventional thermal treatments were carried out.These analyses comprised of microbial enumeration(total background bacteria,mold and yeast,Bacillus cereus ATCC 14579,and Klebsiella pneumoniae R-70),quality(p H,titratable acidity,color,Brix,and sensory analysis),enzymatic activity(peroxidase),compositional(fat content),functional(phenolic and flavonoid),and antioxidant properties(DPPH,ABTS,and FRAP)of the plasma-treated tiger nuts and its milk.In summary,the main outcome of the study are as follows:1.Sequential and individual application of plasma-activated water and blanching for decontamination of tiger nuts tubersSequential and individual application of plasma-activated water(PAW)and blanching for decontamination of tiger nuts was evaluated.A 15 min PAW washing and blanching at 60°C for 5 min decontaminated K.pneumoniae and total background bacteria by 3.70 and 4.36 log CFU/g,respectively.The phenolic contents,lipid oxidation,and antioxidant capacity of the treated tiger nuts were not significantly altered compared with that of the control sample.In contrast,changes in p H,total color value,and flavonoid contents were observed.The combined treatment did not drastically affect the overall acceptability of the milk prepared from the PAW-treated tiger nuts.The results provide an insight into the application of NTP technology in the preservation and quality retention of thermolabile food products such as tiger nut milk.Reactive oxygen and nitrogen species(22,2-,and2-,)were generated in a time-dependent manner in the PAW,and these immensely contributed to the microbial decontamination.2.Application of nonthermal plasma for inactivation of background microflora in tiger nut milk and ensuing physicochemical changesThe microbial and physicochemical properties of tiger nut milk were studied under different NTP exposure times of 2,4,6,8,and 12 min.The NTP processing resulted in the inactivation of the milk background bacteria,mold,and yeast to undetectable limits.The treatment also decreases the peroxidase activity by more than 4 folds after extending the treatment beyond 4 min.The loss in enzyme activity was linked to the oxidation effect of plasma reactive species,including atomic oxygen,ozone,and hydroxyl radicals,which might have oxidized the amino acid side chain.Likewise,a significant reduction in p H was recorded after 8 and 12 min treatment,whereas heightened titratable acidity and lipid oxidation were noticed in all the treated samples.The findings could be a prelude for the potential application of NTP treatment of tiger nut milk in the food industry.3.Inactivation kinetics of Bacillus cereus in tiger nut milk by nonthermal plasmaNTP inactivation kinetics of B.cereus inoculated in tiger nut milk conducted revealed Weibull model adequately described the inactivation kinetics with log reduction of 5.28 log CFU/m L achieved at input powers of 39 to 46 W.Regarding the quality attributes of the treated milk,the treatment did not cause significant changes in soluble solids and titratable acidity at a low input power of 39 W and short treatment duration.Marked declines in p H,flavonoid contents,and antioxidant activity,and increment in total color values and phenolic concentrations at extended treatment time and higher input powers were noticed.Among the various NTP technologies used in this study(dielectric barrier discharge(DBD)plasma and PAW),the DBD plasma applied to the liquid milk sample exhibited the most potent antimicrobial effect with some changes in quality.In contrast,the PAW employed for washing tiger nuts(solid sample)has shown promise in both microorganisms'inactivation and retention of quality.Therefore,appropriate selection of plasma devices for specific sample matrix,process condition combinations,and approach for plasma exposure of food materials are critical for practical NTP application that can offer an improved sustainable plasma food processing that could reduce losses due to microbial spoilage and quality deterioration.The potential of NTP processing to be adopted in the food industry and the underlying challenges were discussed in this work,thus provided a significant contribution to the utilization of NTP technology in the food industry. |
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