Effect of blanching on the physicochemical characteristics and microstructure of canistel seed flour (Pouteria Campechiana (Kunth) Baehni)

Abstract

Canistel seeds are part of the residues of Canistel fruit which can be used as functional foods, such as flour to be processed into various foods. This research was aimed at determining the physicochemical properties of canistel seed flour. Canistel seed was made into flour with two treatments; they were Blanched Canistel Seed Flour (BCSF) (at 80oC for 10 minutes) and Unblanched Canistel Seed Flour (UCSF). The flour process involves sorting, washing, treatment, stripping the shell and epidermis, washing again, drying, flaking and sieving. Physical analysis carried out included yield (by difference method), white degree of spectrophotometric reflectance method (Chromatometer), starch gelatinization profile using Rapid Visco Analyzer (RVA), the morphology of starch granules using polarization microscopy and Scanning Electron Microscope (SEM). Chemical analysis conducted on the BCSF and UCSF samples included proximate, amylose, amylopectin and starch content. Blanching at 80°C for 10 minutes had a significant effect on the physical properties of Canistel seed flour; yields were higher (41.6%) and chromatometric (colour) levels were lower (80.61). Pasting properties profile showed that UCSF had higher peak viscosity, breakdown viscosity but lower setback viscosity compared with the BCSF. Scanning Electron Microscope (SEM) and polarized light microscope showed starch granule structure changed due to the blanching. The appearance of starch granules on UCSF shows a tight starch granule. The appearance of starch granules on BCSF shows blanching treatment has changed the shape of the starch granules to be broken or damaged. The unblanched canistel seed flour (UCSF) showed that the starch granule still had birefringence appearance. This shows that the granule structures of the UCSF remained undamaged. Observation of the morphology of starch granules using polarization microscopy on BCSF showed the starch granule was not visible and there was no appearance of birefringence. The loss of birefringence indicates that the starch granules had been damaged due to heating or hydrolysis. Chemical analyses on the samples showed significantly higher amylose content (24.79) but lower amylopectin content (31.39) in BCSF than UCSF. Starch, fat and carbohydrates contents were not significantly different (p>0.05) between BCSF and UCSF. Ash and protein content were significantly higher (p>0.05) in UCSF compared to the BCSF. Blanching of canistel seed flour reduces the swelling power of starch granules, increases retrogradation, accelerates thickening, decreases nutrition content, and changes microstructure of Canistel seed flour.