Impact of processing pre-treatments on color and the level of heavy metal reduction of the green alga Ulva sp.: A preliminary study

Ulva sp. is an abundant green alga in Gunungkidul waters, Indonesia, considered a source of nourishing food, sought after by food industries. This green alga could be served as a dish, a seasoning, or an ingredient; hence, the assessment of its safety is important. The present study was conducted to reduce heavy metal residues in Ulva sp. collected from Sepanjang beach, Gunungkidul, Indonesia by using two different processing treatments, i.e., washing with citric acid and blanching at various times and seaweed-to-solution ratios. The number of heavy metal residues (As, Cd, Pb, and Hg) was determined by Inductive Coupled Plasma Mass Spectrometry (ICP-MS) and visual green color loss was measured by a color spectrophotometer. The result showed that the concentration of As and Cd in the unprocessed sample was higher than SNI 2690:2015 specification for raw seaweed as well as the National Food and Drug Agency of the Government of Indonesia (BPOM Indonesia) permissible limits in food. Washing Ulva sp. with citric acid 0.5% for 10 min in a seaweed-to-solution ratio of 1:20 could reduce the level of as up to 42.53%, whereas washing Ulva sp. with citric acid 0.5% for 15 min in a seaweed-to-solution of 1:10 could reduce the level of Cd up to 96.12%. All processing treatments affected the appearance of Ulva sp. which is indicated by the increase in color differences (ΔE) > 2.