Modelling Drying Kinetics And Ameliorative Effects Of Controlled Relative Humidity Against Browning Pigmentation And Phytochemicals Degradation

To understand the drying kinetics and determine the ameliorative mechanism in phytochemical degradation and browning pigmentation in drying technology through the use of relative humidity?RH?,this project was conducted.This was made possible by drying selected agriculture products with new designed RH-controlled convective-hot air dryer under varied RH conditions.In the first study,drying kinetics of banana under RH?10% 20% 30% and 40%?at 70 ° C and 2.0 m/s air velocity was predicted using 8 mathematical models.The goodness of fit of the models was examined using primary parameters such as coefficient of correlation?R²?,root mean square error?RMSE?and reduced chi-square??²?.The results show that Midilli–Kucuk model could satisfactorily describe RH-convective drying of banana slices with R²,RMSE and ?² in the ranges of 0.99947-0.99986,0.00002-0.00008,and 0.0142-0.01618 respectively.The electric energy analysis showed that a range of 17.9-41.0% increase in energy consumption was observed at every 10% increase in RH,thus establishing a direct relation among them.Results from the thermogram revealed by differential scanning calorimetry demonstrated that the composition,particle size,and dispersion in a matrix of dried banana were affected by RH variation such that alteration in solid transition was noted.This again,affected the crystallinity of banana making lower RH dried sample more brittle when compared with higher RH sample.To understand the role of RH in some quality index such as Maillard reaction which results in browning pigmentation in dried product,the second study was conducted.In this study,ameliorative mechanism for 2-furoylmethyl-amino acid?2-FM-AA?formation?a measurable indicator of Amadori compounds?was studied in RH drying condition.This was achieved by drying banana under RH?10% 20% and 30%?at 2.0 m/s and 60,70 and 80 °C.The results revealed that at every 10% increase in RH,a reduction between 13.4-29.4% of the 2-FM-AA was achieved.Based on statistical parameters such as R²?0.9013–0.9990?,RMSE?0.0121– 0.3085?and ?²(1.5×10^-4–0.1310),the first order model could satisfactorily predict 2-FM-AA formation.Furthermore,rate constants revealed the dependence of 2-FM-AA formation on RH and also demonstrated the critical role played by RH in reducing 2-FM-AA formation.The results also show that,higher temperatures were mainly responsible for 2-FM-AA formation and functional groups deformation;however,this can be mitigated when drying is conducted under higher RH.To ascertain the enzyme inactivation of RH in synergy with ultrasound?US?as a means of measuring the effect of RH on enzymatic browning,the third study was conducted.To achieve this,banana slices were dried under 10% 20% and 30% RH condition with three temperatures?60,70 and 80 °C?at 2.0 m/s.The results showed that first order and secondorder polynomial kinetic model fitted well for enzyme inactivation and browning indexes respectively.Both enzymes inactivation kinetics and enzymatic browning index?EBI?declined significantly?p < 0.05?with increasing drying time in all drying conditions and rate of decrease intensified in longer US-pretreatment duration and lower RH conditions.However,shorter US-pretreatment duration and higher RH conditions reduced the nonenzymatic browning index?NBI?significantly.Again,longer US-pretreatment duration and lower RH shortened the drying time but adversely created more microspores from the micrograph study.Longer US pretreatment and lower RH decrease significantly?p < 0.05?the L* and b* values whereas the a* values was increased.In sum,drying with higher RH with a US pretreated samples were effective enough to reduce enzymatic browning thus enhancing the color of final product.To address the energy consumption of RH drying condition,drying of banana with ultrasound?US?and ethyl oleate?ETHYL?pretreatment was carried out in the fourth study.The results revealed that the synergy of US and ethyl oleate significantly decreased the energy consumption of dried banana slices by 29.1% when compared with the untreated sample.This was collaborated by the lowest moisture effective diffusion value(2.36×10^-6)observed in US + ETHYL pretreated banana slices.Again,the US + ETHYL pretreatment was also effective in controlling enzymes activities and browning pigmentation which is another major problem associated with dried products.For color parameters,US + ETHYL pretreatment recorded the lowest color change?29.70?and highest Chroma?18.49?and Hue angle?80.44?value confirming with the assertion of US and ethyl oleate inactivation and browning prevention capabilities.In effect,the US + ETHYL pretreatment in banana could reduce the energy consumption of dried products whilst maintaining the quality of the products.In the fifth study,the degradation and thermodynamic study of bioactive and antioxidant compounds under RH drying condition were evaluated and also predicted using models.First-order model could satisfactorily describe degradation bioactive and antioxidant compounds of drying of banana slices with highest R²,and lowest RMSE and 2.The results reveal that a range of 4.5-10.7% of these compounds in dried banana slices were retained by 10% increase in RH.From D-value and rate constant values,the thermal degradative level of the compounds in RH drying condition follows the order: Total flavanol content > Total phenolic content > antioxidant?FRAP?.Also,the results suggest that higher drying temperatures can be applied to achieve higher retention of phytochemicals when higher RH?30%?drying conditions are considered in the food industry.In the sixth study,another critical quality parameter such as ?-carotenes and color retention in carrot were evaluated using RH drying condition.In the case of drying prediction,the Wang and Singh model could satisfactorily described RH-convective drying of carrot slices with R²,RMSE and 2 in the ranges of 0.996-0.999,5.4×10^-4-9.4×10^-4 and 0.0150-0.03353 respectively.The study shows that between 41.91-62.05% of total ?-carotenes were retained in dried carrot under the RH condition and a direct correlation was established between ?-carotenes retention and RH.In the case of color change??E?,the ?E obtained ranges between 18.84-23.26 which was also in range to blanched and dried carrot as found in literature.In summary,higher temperatures were mainly responsible for color and ?-carotenes reduction however this was mitigated under higher RH of 30%.In the final study,ameliorative mechanisms for mitigating phytochemical,phenolic compounds and functional groups in pineapple slices was investigated under RH drying condition.The results revealed that higher RH was able to retain significantly?p <0.05?the phytochemical,phenolic and antioxidant concentrations in dried pineapple under same drying temperature.This was also established by the closer proximity between the phytochemical,antioxidant and phenolic compounds and higher RH in correspondence analysis.This was further collaborated by the Fourier transform infrared?FT-IR?spectrum as high temperature and lower RH deformed most functional groups.The result also revealed that concentrations of these compounds may differ as a result of disparities in the chemical composition which may be worsening by hash drying conditions such as high temperature and lower RH.These researches find ameliorative option for mitigating against the loss of phytochemicals and browning pigmentation by exploring the use of RH in drying technology.From the study,higher RH played a critical role in dehydration of agricultural products.The result shows that RH??30%?could savage the intensity of loss of phytochemicals and also reduce browning pigmentation and functional groups deformation in dehydration of agricultural products and therefore must be given attention in the drying industry.