2.3. Preparation of the samples for examination using SEM
Passion fruit powder and the pectin samples were observed using scanning electron microscopy (S-3400N,
Hitachi, Japan). The SEM was used to elucidate morphological changes of samples which were extracted by acidic
extraction method. Dry pectin sample was dried using microwave and wet pectin sample was the crude pectin. The
morphological of wet pectin sample and dry pectin sample were analyzed to obtain the microwave heating effect on
pectin structure. The preparation of pectin samples for SEM include mounting the pectin samples on the aluminum
studs, pectin samples coating with gold in vacuum and observing the pectin samples by SEM.
2.4. Design of experiment
The experiment started with selected pH of 3.3 based on literatures of Tang et al. (2011), Lucia et al. (2012) and
a series of preliminary tests. At each pH level, including a lower and higher pH of 2.0 and 4.5, the optimum
extraction time based on experiment result which gave the highest yield was determined. Each treatment was
conducted in duplicates and completely randomized design (CRD) was used in this study.
3. Results and discussion
3.1. Image study on fruit peel powder and extracted pectin
Fig. 1 shows the photograph and Fig. 2 the micrograph of passion fruit powder and extracted pectin. The
micrograph of passion fruit peel powder (Fig. 2(a)) shows that the peel was compact and flaky in shape. The
extracted wet pectin (Fig. 2(b)) has a nano-structure which was smooth and compact with a little wrinkle on the
surface. The extracted pectin dried using oven (Fig. 2(c)) indicated that drying has some destructive and swelling
effects on pectin structure with mound-shaped pellets formed on smooth pectin surface. A similar image of wet
pectin was obtained by Xu et al. (2014) who extracted pectin from grapefruit peel pectin using ultrasound heating
method and similar image of dry pectin was obtained by Luo et al. (2014) and Minjares-Fuentes et al. (2014) who
extracted pectin from Catharanthus roseus leaves and grape pomace.