| In recent years,cold plasma technology has received considerable attention as a novel,environmentally friendly,highly efficient and sustainable approach for food processing.Its applications have been well-established for microbial decontamination in foods and biological materials,as well as in other industrial processes.A more recent area for the application of cold plasma is the effect of cold plasma treatment on the protein molecules in food systems and the corresponding outcomes on the techno-functional and/or physico-chemical properties as well as allergenicity response.These variations are caused by modification in the protein conformation and structure by the different active species contained in a plasma gas.In protein manipulation with plasma,a number of process variables like treatment time,power or voltage,and type of feed gas,as well as the nature of the sample and the treatment environment influences the outcome of protein's characteristic function in food systems and the human body.A typical example of an important food item that contain an abundance of amino acids/proteins which exhibit both techno-functionality in food systems and are able to elicit allergenic sensitivity in the human body are crustaceans such as king prawn(Litopenaeus vannamei).Thus,it becomes imperative to understand in detail plasma-induced interactions with various muscle proteins from king prawn.In the first part of this work,myofibrillar proteins were extracted and purified from the meat portions of king prawn followed by exposure to time dependent(0,2,4,6,8 and 10 min)treatments by an atmospheric pressure plasma jet(APPJ)device which employs air as the feed gas.The specific species observed in the air plasma includes RNS and ROS such as N2(UV-A),N2+(UV-B),NO,OH radicals and atomic oxygen while the production of nitric acid(HNO3)and nitrous acid(HNO2)respectively recognized for their acidifying and oxidizing effects occurred in the liquid medium.The results showed a decrease in p H as a result of reactive oxygen and nitrogen species(ROS and RNS,respectively)formed during plasma application.Exposure of the samples to APPJ treatment led to reduced protein solubility as well as increase in particle size,turbidity and foaming capacity caused by modification of both secondary and tertiary structure of the proteins.These results confirm the hypothesis that APPJ generated in air contains significant portions of oxidizing and reactive species that are able to cause unfolding of MPs and at longer duration can result in almost complete degradation of the protein secondary structure proteins from prawn using air-plasma jet systems.The main protein component of animal muscles especially after slaughter is natural actomyosin(NAM).It is also a vital factor used to determine the meat processing suitability due to its physicochemical and techno-functional properties.In the second part of this dissertation,APPJ system was also employed against NAM from king prawn,for treatment times 0,1,2,3,4 and 5 min.But the emission spectrum mainly comprised of the emission lines of argon in its different excited states as well the presence of strong atomic oxygen emissions since a different gas composition(98% Argon + 2% oxygen)was employed.The findings suggest that the emulsifying activity index and foaming properties of NAM was significantly(P < 0.05)improved compared to control after 5 min treatment duration.Whilst the solubility of NAM solutions showed no significant changes as treatment progressed from 1 to 4 min only except at 5 min and the absorbance at 350 nm which portrays turbidity was noticed to increase gradually with increasing plasma exposure time,due to the association of protein monomers or aggregates.These changes were as a result of protein–protein interactions which spur changes in secondary and tertiary structures of the protein molecules that affect protein functionality in food systems.In the third part,the main objective of the investigations conducted was to assess the effect of APPJ on the molecular structure and allergenic response of prawn tropomyosin(TM),the major allergenic protein found in crustaceans.The findings revealed that for Ig E reactivity of TM,nearly about 17.6% significant reduction in Ig E-binding capacity was observed while for Ig G binding,approximately 26.87% reduction occurred due to the fragmentation of conformational epitopes.By applying CAPJ treatment from 3 to 9 min,only slight changes in TM antigenicity are obtainable.At longer treatment times,surface hydrophobicity and total SH contents are altered considerably accompanied by changes in the content of secondary structures evident by a decline and increase in ?-helix and ?-sheets structures respectively.These modifications in secondary and tertiary structures may have collectively influence the antibody-binding capacity of TM.The reduction in Ig G & Ig E binding potential may be due to the modification of conformational structure and release of hydrophobic or hydrophilic residues which permit re-orientation of antigenic epitopes.In last part,the impact of ultrasonication combined with non-thermal plasma generated using dielectric barrier discharge,on the allergenicity,digestibility and conformational integrity of TM was examined.According to the results of this study,applying plasma as a pretreatment for 5 min prior to sonication(4-20 min)on TM from prawn exhibited higher reduction in the allergenicity as demonstrated by western blot and enzyme-linked immunosorbent assay(ELISA)analysis.Up to 79% reduction in Ig E recognition potential was recorded for PU treatment as against a maximum of 47% and 23% respectively for the individual application of cold plasma and ultrasound respectively.In addition,this hurdle approach significantly enhanced the gastrointestinal-digestibility of TM.PU treatment affected the proportions of secondary structures,total SH contents and hydrophobicity,indicating unfolding of the protein.Precisely,TM had a more loosened structure which allowed oxidation of amino acid residues and cleavage of peptide bonds,thereby permitting disorientation or destruction of binding sites for the antibodies.In summary,key information that ought to be taken into consideration when formulating new seafood products processed by cold plasma technology is the potential effect of plasmainduced interactions on the techno-functional properties and allergenicity response when applied in real food systems or consumed by humans,respectively.In our study,for the first time,we provided a scientific basis showing that the targeted use of plasma-assisted modification of prawn muscle proteins can enhance some aspects of their functionality and can,therefore,promote resourceful production of protein ingredients for improving existing products and developing new products.In addition,we established that cold plasma is a promising approach for attenuating the Ig G/Ig E binding capacities of tropomyosin,the major allergenic protein present in prawns,leading to the possibility of deriving hypoallergenic products.This finding is potentially beneficial for individuals who develop abnormal immune response upon contact or ingestion of prawns.In addition,a detailed investigation of the plasma-induced effects was also elucidated using a top-down method through suitable analytical techniques that provide an outlook into the conceivable mechanical pathways,from a macroscopic to molecular level.Consequently,the feedback on non-thermal atmospheric plasma as an excellent tool for protein manipulation will foster incorporating plasma processes into existing unit operations in established product-specific process lines employed in the seafood industry. |
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