Effect Of Different Non-thermal Pretreatment Techniques And Drying Methods On Bioactive Phytochemicals,Quality Attributes,Drying Kinetics And Physicochemical Properties Of Ginger(Zingiber Officinale Roscoe)

Ginger(Zingiber officinale Roscoe)remains among the most notable medicinal spicesworldwide.It is used as a raw material by the pharmaceutical,beverage,cosmetics and the food industries.However,its high moisture content(85-95%)and subsequent high perishability limit its long-term storage.The high amount of water in ginger makes it highly susceptible to wilting and loss of fresh appearance and difficult to handle during storage,processing,and transportation leading to high deterioration and substantial postharvest losses.Drying constitutes an integral part of most food processing techniques that ultimately aim to conserve the quality of the finished product as well as extend its shelf-life.However,conventional drying has been established to negatively impact on the quality of the finished products.It is also expensive to operate and involves a long drying time.Long-term storage of ginger is one of the paramount importance.Hence any effective pretreatment method that reduce moisture content,lessen drying time,reduce processing costs,improve energy consumption and efficiency,enhance the mass transfer and preserve the physical and nutritional properties of the dried product as well as the quality of the finished product is ideal.The general objective of this study was to assess the effect of different non-thermal pretreatment techniques and drying methods on the drying kinetics and physicochemical properties of ginger.The study in its entirety is subdivided into two parts.The first aspect had the following underlying objectives:(1)To optimize the processing parameters for osmosonication pretreatment of ginger using response surface methodology.(2)To investigate the effects of ultrasound,osmotic dehydration,and osmosonication pretreatments on the bioactive compounds,chemical integrity,enzyme inactivation,color,and antioxidant activity of dried ginger slices.(3)To investigate the influence of different non-thermal pretreatments on the drying kinetics and quality properties of dried ginger slices.(4)To determine the effects of various non-thermal pretreatments on the physicochemical properties of dried ginger slices from two geographical locations.The second part of the work aimed;(1)To investigate the influence of different drying techniques on the chromatic properties,sensory attributes,anti-inflammatory,antioxidant,and cytotoxic effects of ginger.(2)To study of the effects of different drying techniques on the quality attributes,enzyme inactivation,volatile compounds,energy consumption and drying kinetics of ginger.(3)To determine the effect of the best pretreatment method and drying technique on the quality of ginger from different African countries.To optimize the conditions for osmosonication pretreatment of ginger,we assessed the effect of sonication frequency(UF)33–68 kHz,sucrose concentration(SC)20–60%w/v and pretreatment time(PT)10–30 min for maximizing 1,1?diphenyl?2?picrylhydrazyl(DPPH),cupric ion reducing capacity(CUPRAC),ferric reducing antioxidant power capacity(FRAP),total phenolic content(TPC),weight reduction(WR),water loss(WL),rehydration ratio(RR)and minimizing polyphenol oxidase,(PPO)and solid gain(SG)of ginger by using response surface methodology(RSM).The results revealed that osmosonication pretreatment had a significant impact on the outcome of the various tests conducted,i.e.,DPPH,FRAP,CUPRAC,TPC,WL WR,RR,SG and PPO.The optimal operating conditions to attain the best results for DPPH,CUPRAC,FRAP,TPC,WL,WR,RR,PPO and SG tests were UF(50 kHz),SC(30%w/v)and PT(30 min).Based on the aforementioned conditions,the final outcome was as follows:WL(62.97%),SG(9.06%),WR(53.98%),RR(3.09),DPPH(65.69 mgTE/g dw),FRAP(50.93mgTE/g dw),CUPRAC(55.32 mgTE/g dw),TPC(23.96 mgGAE/g dw)and PPO(13.21%).These were consistent with predicted values and the overall desirability was 0.758.The RSM plots also revealed that the independent variables significantly enhanced the physicochemical properties of osmosonication-pretreated ginger samples.The outcome of this work suggests the applicability of the optimized osmosonication pretreatment conditions in the food and beverage industries as an alternative pre-dehydration method for ginger.Further comparative studies with other pretreatment methods were therefore recommended.The effects of ultrasound(US),osmotic dehydration(OD)and osmosonication(OS)pretreatments on the total phenolic content(TPC),total flavonoids content(TFC),phytochemical constituents(gingerol derivatives and diarylheptanoids),polyphenol oxidase(PPO),peroxidase,(POD),antioxidant activities and colour of ginger slices dried under relative humidity convective dryer were investigated.OS pretreatment improved the preservation of TPC(13.80-34.79 mg GAE/g d.w),TFC(26.46-62.16 mg CE/g d.w),ABTS(30.37-86.10%),CUPRAC(36.89-73.97mg/g),DPPH(50.57-92.60%),FRAP(26.44-83mg/g)and phytochemical constituents than US and OD.The OS-pretreated sample was more effective in inactivating both PPO(12.09-35.93%)and POD(16.21-39.58%)enzymes compared to US-and OD-treated samples.However,US pretreatment retained the colour quality of the dried ginger slices than the OS and OD pretreatments.OS pretreatment also increased the total colour change(5.43)of the dried ginger samples compared to US(2.81)and OD(4.60).The effects of non-thermal pretreatments on the drying kinetics and quality properties of ginger were investigated.Herein,we sought to investigate the effects of US,OD and OS pretreatments on the microstructure,weight loss,texture,mass transfer,chromatic properties and drying kinetics of ginger slices under relative humidity convective drying.The results revealed that OS pretreatment yielded higher weight loss(16.5%)and lower firmness(12.11 N)than US(9.8%,20.33 N)and OD(6.5%,15.30 N).Microstructural analysis showed that all three pretreatments altered the cell structural integrity of the ginger slices resulting in its collapse and the formation of several micro channels.Mass transfer data showed that the OS pretreatment led to a higher solid gain(3.2%)and water loss(5.1%)than US(2.36%,4.2%)and OD(1.7%,2.53%)pretreatments.The chromatic property analysis revealed that the chroma value and hue angle was higher for the OS-pretreated samples(29.74,88.77 ~o)compared to the US-(26.95,85.76 ~o)and OD(22.96,82.24~o)pretreated samples.Among the three pretreatment methods,OS was found to enhance the drying kinetics compared to the US and OD pretreatments.Weibull model best described and fitted the experimental results(R~2>0.99).Further experiment were conducted on the effect of these non-thermal pretreatment methods(i.e.OS,OD,US)on the physical and chemical properties of China-and Ghana-sourced ginger samples under relative humidity convective drying.The chemical properties of pretreated dried ginger slices were assessed for antioxidant properties(ABTS and DPPH),total phenolic content(TPC),total flavonoids content(TFC),4-,6-,8-,10-gingerol and 6-shogaol levels.The physical properties compared were weight loss,rehydration ratio(RR),texture,and drying kinetics.The outcome of this investigation revealed that OS pretreatment led to a higher preservation of the chemical properties with the Ghana-sourced ginger exhibiting the highest values.The OS-pretreated samples obtained the highest weight losses and rehydration ratios,but the rehydration ratio was higher in the Chinese ginger.OS pretreatment also gave the lowest textural value with the China-sourced samples exhibiting the lowest firmness.Weibull model best fitted the experimental results(R~2>0.99).These findings taken together present OS as the best pretreatment method for drying ginger regardless of its geographical origin.The influence of different drying techniques on the quality attributes,anti-inflammatory,antioxidant,and cytotoxic effects of Ghanaian ginger were investigated.This choice was based on the outcome of previous studies,which found the collected ginger of Ghanaian origin to be better in quality than Chinese ginger.Slices of ginger rhizomes were subjected to freeze drying(FD),relative humidity convective drying(RHCD),infrared drying(FD),microwave drying(MC)and pulsed vacuum drying(PVD).The quality characteristics of the dried slices were assessed and compared on the basis of the chemical composition of their essential oils and selected gingerol derivatives,moisture content,sensory attributes,chromatic properties,antioxidant activities,total phenolic and flavonoid content.Finally,the cytotoxic and anti-inflammatory effects of extracts of the various dried ginger samples were evaluated using RAW 264.7 cells.Holistically,the samples from FD and RHCD gave the best outcomes for all the parameters compared.These two techniques are therefore recommended for large-scale application since they enhance the quality of ginger by maintaining the chemical integrity of both the essential oil and oleoresin components.Ginger slices were again dried with the FD,RHCD,IR and MD at a temperature of 60?.The influence of these drying techniques on the TPC,TFC,antioxidant activities(i.e.ABTS,DPPH,FRAP,CUPRAC),RR,colour,enzyme inactivation(polyphenol oxidase,PPO and peroxidase,POD),energy consumption rate,microstructure,volatile compounds(aroma profile)and drying kinetics were assessed.The results showed that FD-ginger slices retained the highest antioxidant properties;ABTS(51.88 mgTE/g db),CUPRAC(95.51 mgTE/g db),DPPH(132.95 mgTE/g db)and FRAP(95.32 mgTE/g db),bioactive compounds,TPC(118.70 mg GAE/g db)and TFC(98.94mg CE/g db),preserved microstructure and higher volatile compounds compared RHCD,IR and MD.The RHCD-ginger slices attained the highest RR(3.6),lowest energy consumption rate(7.88kWh/kg),lowest PPO(17%)and POD(22%)residual activity with preserved colour properties than FD,IR and MD.RHCD also enhanced the drying kinetics and lessened the drying time compared to FD,IR and MD.Page model best fitted the experimental results of drying kinetics(R~2>0.99).Finally,from the above studies the OS-pretreatment technique and relative humidity convective drying method were observed to be the best techniques for processing of ginger,therefore the quality of OS-pretreated and relative humidity convective dried ginger slices from four African countries were compared for differences in terms of their metabolomes,TPC,TFC,antioxidant activities,sensory characteristics and volatile compounds composition(via electronic-nose determination).The outcome of our study showed marked source-dependent differences in the metabolomes of the samples as captured by the metabolomics approach.Based on the findings of the metabolomics study,6-gingerol content was quantified and found to be higher in the samples of West African origin.In general,the samples from West Africa had higher amounts of secondary metabolites,TPC,TFC,volatile compounds,antioxidant activities and gave better sensory attributes.By country and for all parameters assessed,the following trend was observed:Ghana>Nigeria>Uganda>Kenya.Taken together,our findings at least in part,point to the influence of geographical regions of cultivation on the quality of plant products.With the results of this second aspect of the work considered holistically,it can be concluded that freeze drying and relative humidity convective drying are the best drying techniques for ginger.