Characterization and modeling of thin layer drying of cocoyam slices

Convective hot air drying of cocoyam slices was investigated at different drying temperature (40 to 90) and slice thickness (2, 4, 6 mm) at an air velocity of. The effect of drying temperature and slice thickness on the drying characteristics and drying time were determined to study the effects of heat on processed cocoyam. Mathematical modeling of the thin layer drying process was performed using eight thin layer drying models. The models were tested for validity using coefficient of determination (), chi square () and root mean square error (RMSE). The effect of the drying temperature on the colour of dried cocoyam was also investigated. The colour was measured using CIE L* a* b* method. The results showed that, increasing the drying air temperature and decreasing slice thickness reduces the drying time of cocoyam. The effective moisture diffusivity increased with increase in drying temperature and the biot number () of cocoyam at temperature of 40 to 70 were less than 0.1 while that of 80 to 90 were in the range of 0.1 <  100. The activation energy obtained at 40 to 90 was 37.92 kJ. The Page model was found to be best fit for the drying kinetics of cocoyam. The largest colour difference was observed at 90 compared to the fresh sample. Increase in temperature reduced the brightness and yellowness of cocoyam

Effect of Low-Frequency Ultrasonic-Assisted Enzymolysis on the Physicochemical and Antioxidant Properties of Corn Protein Hydrolysates

The aim of this study was to investigate the effect of low-frequency ultrasound on the enzymolysis of corn protein. A L9 (34) orthogonal design was used to optimize ultrasound pretreatment conditions. Degree hydrolysis (DH), conversion rate of protein (CR), and DPPH IC50 were selected as analytical indicators. Under the optimal ultrasound conditions (5 W/L power, 2 s/2 s on/off time, 50°C temperature, and 25 min time), the DH, CR, and radical (DPPH∙, OH∙) scavenging capacities were significantly increased. Molecular weight distribution and amino acid profile analysis showed that ultrasound pretreatment enhanced the formation of short-chain peptides with molecular weight of 200–3000 Da, especially the peptides containing hydrophobic amino acids. Moreover, 40 potential antioxidant peptides were purified by C18 semipreparative column and identified by UPLC-ESI-MS. The results suggest that the optimal ultrasonic-assisted enzymolysis technology could be useful for preparation of antioxidant peptides from corn

Influence of ultrasound-pretreated convective drying of Roselle (Hibiscus sabdariffa L) leaves on its drying kinetics and nutritional quality

The drying kinetics and the nutritional qualities of Roselle (Hibiscus sabdariffa L) leaves as affected by ultrasound pretreatment during hot air drying were investigated in this work. Ultrasound frequency and power at 20 kHz and 600 W, respectively, were used for the experiment. Roselle leaves were subjected to ultrasound pretreatment in distilled water for 0 min (untreated), 5 min (UD5), 10 min (UD10) and 15 min (UD15) before hot air drying. The result showed that UD15 samples had about 47% reduction in drying time compared with the untreated samples. The effective moisture diffusivity of the treated and untreated samples ranged from 1.21 to 3.29 × 10−1m2/s. The Page and Logarithmic models best described the drying behavior for the untreated and treated samples respectively. The values of the mass transfer Biot number (ratio of internal mass transfer resistance to external mass transfer resistance) for all the samples ranged from 0.9032 to 1.2391. The samples of UD10 and UD5 had the highest amount of carotenoid and vitamin C contents, respectively, amongst the untreated and treated samples. The total color change of the treated samples were significantly lower than the untreated samples after drying. Drying of Roselle leaves is usually done using convective drying method with its attendant's effects such as long drying time, loss of nutrients and high energy usage. But this work showed that application of ultrasound pretreatment during drying of Roselle leaves can significantly reduce the drying time and at the same time retain the nutritional quality of the dried treated samples