An Assessment of the Effects of Different Soaking Pretreatments and Microwave Drying Conditions on Selected Phytochemical Properties of Tiger-nut (Cyperus esculentus)

Abstract

The effects of soaking pretreatments and microwave drying conditions on the phytochemical properties of Tiger-nut were assessed. A two factor, four level factorial designs in a completely randomized design was adopted for the study and the Design Expert 13 software was used to establish the experimental matrix for the study. Tiger-nut samples were soaked for 24 hr, 48 hr and 72 hr at room temperature and dried at 100 W, 140 W, 200 W and 280 W microwave powers until constant weight was attained. The resulting samples were reduced and phytochemical contents analyses were carried out on them using standard laboratory protocols. From the results it was observed that the pretreatments and drying conditions caused reduction in moisture content of Tiger-nut to safe storage levels and variation in the drying characteristics (drying rates, drying time, and equilibrium moisture. The drying rates and drying time increased with increase in microwave power. The highest drying rates obtained at 100W microwave power were 0.161 gH₂O/min for the 24hr soaked sample, 0.232 gH₂O/min for the sample soaked for 48 hr and 0.158 gH₂O/min for the sample soaked for 72 hr. The peak drying rates observed at 140 W microwave power were 0.325 gH₂O/min for 24 hr soaking pretreatment, 0.365 gH₂O/min for 48 hr soaking pretreatment and 0.449 gH₂O/min for the 72 hr soaking pretreatment. The peak drying rates obtained at 200 W microwave power were 0.443 gH₂O/min for samples soaked for 24hr, 0.323 gH₂O/min for sample soaked for 48 hr, and 0.323 gH₂O/min for sample soaked for 72 hr. The peak drying rates gotten at 280 W microwave power were 1.018 gH₂O/min for sample soaked for 24hr, 0.938 gH₂O/min for sample soaked for 48 hr, and 0.938 gH₂O/min for sample soaked for 72 hr. The mean drying duration at which EMC was attained for 100 W, 140 W, 200 W and 280 W microwave power dried Tiger-nut was 580 min, 330 min, 310 min and 130 min respectively. The ANOVA of the phytochemical contents showed that at P 0.05, soaking pretreatments and microwave drying conditions caused significant alterations on the phytochemical properties of the Tiger-nut samples. There was a decrease in the flavonoids, alkaloids, tannin, and oxalate contents and a slight increase in the cardiac glycoside and phenol contents of the pretreated and dried samples when compared with the result obtained for the untreated sample (control).