Morphology, Functional and Pasting Properties of Ginger Starches Prepared by Four Different Drying Methods

Abstract

Aim: This study aims at providing information on the morphology, physico-chemical and pasting properties of the ginger starches prepared by air drying, oven drying, freeze drying and microwave drying methods with a view to improving their utilization. Place and Duration of Study: Department of Pharmaceutics and Pharmaceutical Technology, Olabisi Onabanjo University, Nigeria and Department of Pharmaceutics, University of Ibadan, Nigeria between March 2013 and February 2014 Methodology: Starch was isolated from the rhizomes of Zingiber officinale and dried by oven, freeze drying, air drying and microwave drying methods. They were studied for their composition, morphological, functional and pasting properties Result: The residual protein content of the four starches was slightly different averaging 5.06%. The residual protein of air dried starch was the lowest and that freeze dried starch was the highest. There was no significant variation in the saponin and tannin contents of the dried samples. The amylose content of the ginger starches ranged between 20.7% and 22.1%.The rank order of the amylose content was microwave dried >freeze dried> air dried>oven dried. Drying methods had a significant effect (P<0.0001) on the solubility index and swelling capacity of the dried samples investigated. The rank order of the swelling capacity of the ginger starches was freeze dried<air dried<oven dried<microwave dried. A higher solubility index was observed among the oven-dried sample and the microwave sample compared to freeze dried and air dried samples. X-ray fluorimetric (XRF) analysis of the different starch powders showed the presence of iron, copper and zinc in trace amounts; and the absence of heavy metals like lead and mercury. All the four dried samples have fairly good flow. Significant differences were observed in individual pasting parameters of the ginger starches especially in peak viscosity, trough viscosity, final viscosity and setback viscosity. Peak viscosity was found to be lowest for freeze dried starch (300.42RVU) and highest for oven dried starch (324.25RVU). The rank order of the final viscosity was oven dried > microwave dried > air dried>freeze dried. Conclusion: This study revealed that the physicochemical as well as the pasting properties of the ginger starches prepared by the four drying methods make them to be considered as excellent resource with possible applications in many food and pharmaceutical processing. The results also showed that difference in drying methods during processing has an effect on composition and pasting properties of ginger starch.