Effect of cleaning by whirlpool washing machine on heavy metal content and external contamination in commercially grown edible red seaweed, Gracilaria fisheri

Abstract

The agarophytic seaweed, Gracilaria fisheri is used as food and also for agar extraction. This study investigated the use of a novel cleaning method to improve the quality of seaweed products. Dried seaweed was sampled from seaweed farms in Pattani province, southern Thailand during the dry and wet seasons and from seaweed sold in souvenir shops in the area, to determine the level of contamination and its quality and appearance before and after the cleaning process. A whirlpool washing machine was used for cleaning. The concentrations of the heavy metals, Mn, Fe, Cr, Cd, Zn, Ni, Cu, and Pb were investigated in the seaweed, and in the seawater and sediment in which it was grown. The sensory and external qualities were evaluated by 30 testers. The results showed that the concentrations of heavy metals in the seaweed were similar to those in the seawater and that most of the external contamination in the seaweed during the dry and wet seasons, as well as in the purchased samples was from mollusks and epiphytes. Nine cycles of cleaning in the washing machine produced the lowest heavy metal concentrations and external contamination in the dried G. fisheri. The sensory evaluation showed that the color, smell, texture, and extent of contamination were superior in the seaweed subjected to nine washing cycles. The cleaning method adopted in this study for G. fisheri was able to effectively reduce both the heavy metal concentrations by scraping off the cell wall, and cleaning the seaweed using a washing machine is therefore recommended prior to preparing the product for sale.

Keywords

• gracilaria fisheri
• edible seaweed
• heavy metal
• contamination
• post-harvest