Physical properties, microstructure and proximate chemical composition of Roselle (Hibiscus sabdariffa)‎ seeds and kernels

Abstract EN

The objective of the present study was to identify the physical properties (seed index “SI”, specific weight “SP.W”, seed dimensions” length (L), width (W), and thickness (T), sphiresity “Sp” hydration coefficient “HC” structure “% hull, % kernel” and colour), microstructure by Scanning Electron Microscope “SEM” and proximate chemical composition of one variety of Roselle seeds “RS” (var.

Sabahia “17”).

Also, the effects of preconditioning “soaking process in water for 10 hrs- 15 min at temp.

ranging from 25 to 75°C for complete hull removing to obtain Roselle kernel “RK” on the most of the aforementioned characteristics were studied.

The results indicated that, RS have small size (35.2 SI, 5.2 L, 4.3 W, 2.7 T mm and 75.12 Sp).

The “HC ranged between” 5.32, 156.5% according to water temp.

Its colour is dark brown (5R, 5Y, 3B) and have 30% hull and 70% kernel “cotyledon”.

The SEM indicated that the hull was thick, composed of several layers of irregular collapsed cells and mostly were adherent to the kernel.

The kernel consisted of endosperm “End” and aleuron layers.

The End represented the main part that composed of cytoplasm network including fat bodies, protein bodies and starch granules.

The RS contain 8.15% moisture, 25.87% crude protein ”CP”, 21.05 crude ether extract “CEE”, 18.95% crude fiber “CF”, 5.66% ash and 28.47% nitrogen free extract “NFE”.

Complete removing of hull improved general appearance without differences in values of kernel colour produced from different soaking treatments.

The SEM of treated samples showed that soaking treatments altered the hull structure and thus facilitated the hull removing, without any effects on the cotyledon structure.

On the other hand, this treatment led to a pronounced increase in CP, CEE and ash.

These increases ranged between 43.18 and 46.77, 73.78 and 78.6% and 21.2 to 27.3%, respectively.

In contrast, CF and NFE were decreased.

These decreases were about 93% and 39.27%, respectively according to the soaking water temp.

(25–75°C) and time (10 hrs – 15 min).

The statistical analysis showed that there are significant differences between the proximate composition of RS and RK, while no significant difference between the treatment of soaking at temp.

ranging (45–75°C) for different time (2 hrs – 15 min), could be traced.