Influence Of Non-Thermal Pretreatment On Pulsed Vacuum Drying Of Apple Slices:Kinetics Modelling,Bioactive Compounds And Phytochemical Degradation

Drying is one the most common form of food processing and helps to extend shelf life of agricultural products.However,conventional forms of drying face many challenges which include long drying time,loss of quality attributes and degradation of phytochemicals.Hence it has become imperative to research into novel drying methods and pretreatment techniques capable of reducing drying times as well as preserving product and nutritional quality.Non-thermal pretreatment of apple fruits prior to drying with novel drying technique,pulsed vacuum drying(PVD),provides a headway in innovative pretreatment and drying approach over contemporary conventional drying with much more improvements like drying time reduction,retention of bioactive compounds and nutritional components as well as conserving energy.This research study was to ascertain the effects of Nonthermal Pretreatment on Vacuum Pulse Drying of Apples:Kinetic Models,Bioactive Compounds and Phytochemical Degradation.The first study entailed the effect of ultrasound-ethanol(US-E)pretreatment duration(10,20 and 30 min)and varied drying temperatures(60,70 and 80°C)on the drying kinetics of apple slices during PVD.The findings revealed that 30 min US-E significantly shortened the drying time with a 26.66,30.77,and 22.22%drying time reduction at 60,70,and 80°C respectively.Effective moisture diffusivity(D_eff)and activation energy(E_a)were in the range of 1.98-4.08×10^-8m²/s and 12.58–23.43k J/mol respectively.Color and textural properties were affected by pretreatment duration and temperature.Furthermore,outcomes from the Fourier transform infrared spectroscopy(FTIR)and the total free amino acid(TFAA)profile revealed that these parameters were preserved by longer pretreatment duration and lower drying temperature.The second research study ascertained the influence of ultrasound and/or ethanolic pretreatment at varied drying temperature(60,70 and 80°C)on the drying kinetics,bioactive compounds,antioxidant properties and microstructure of apple slices under pulsed vacuum dryer.The findings revealed that US+E pretreatment shortened drying time but resulted in the formation of several microchannels which was more prominent in US+E pretreatment with noticeable larger pores and several microchannels on the cell surface as seen in the micrograph evaluation.The Hii model depicted the highest(R²),and lowest root mean square error(RMSE),and?²indicating that Hii model could better predict the drying behavior of apple slices compared to the other models.E_a and D_eff were 17.60–29.86 k J/mol and1.52-3.60×10^-8 m²/s respectively.US+E pretreatment retained Total phenolic content(64.89-75.75 mg/100 g GAE dw),Total flavanol content(45.96-56.25 mg/100 g ER dw),DPPH⁺(66.85-3.34%)and ABTS⁺(62.58-71.17%)than Ethanol,US+W,and control and was further corroborated by the observed peaks as revealed by the FTIR spectroscopy.Color parameters(L*,a*,b*,whiteness)were better retained by Ethanol and US+E pretreatments.In the third study,the influence of acoustically-aided osmo-dehydration on the drying kinetics modelling,thermodynamics,weight reduction,color and vitamin C degradation kinetics of dried apple slices was evaluated.The findings showed that Ultrasound-assisted osmotic dehydration(UOD)pretreatment significantly improved drying time and increased weight reduction comparative to osmotic dehydration(OD),Ultrasound(US),and the control sample.Drying kinetics modelling revealed that the Hii model better described the drying kinetic behavior of the apple slices than the other 9 mathematical models based on R²,lowest RMSE and?².Second-order kinetics could accurately predict the degradation kinetics of vitamin C compared to first-order.Vitamin C degradation kinetics showed lower k-value,higher D-value(time required for 90%degradation),and half-life indicating a higher retention of vitamin C content for UOD pretreatment compared to OD and US during drying.Chromatographic determination and quantification by HPLC-UV/Vis showed different concentration of compounds for the different pretreatment conditions.The relative peak height/position of the various FTIR spectra relates/describes the vitamin C content present in each of the pretreatments after drying.Lastly,a research study of the effect of simultaneous dual frequency ultrasound-assisted osmo-dehydration on the drying characteristics,energy consumption and quality attributes of apple slices under pulsed vacuum dryer was conducted.Results revealed that of the different pretreatments(UOD,US,and OD),the UOD pretreatment significantly decreased drying time,preserved bioactive compounds and antioxidant properties and vitamin C content of dried apple slices than US and OD pretreatments.Also,the results showed that UOD better retained color parameters.