Shares of Wei Chuan Foods Corp, the Taiwan food company whose chairman recently resigned amid a tainted lard scandal, plunged for a fourth day on Tuesday in a rout that has seen its market value shrink by one-quarter in less than a week.

Wei Chuan, which produces everything from ice cream to the flavor-enhancer monosodium glutamate, tumbled by the 7 percent daily limit at the close in Taipei trading. The stock capped a four-day, 25 percent decline, the steepest since its listing in 1991. Taiwan's Taiex Index gained 0.7 percent.

The company, which had gotten the tainted edible oil from supplier and fellow Ting Hsin International Group member Cheng I Food, said last month it expects to lose NT$79.4 million ($2.65 million) from product recalls and lost inventory. Its chairman, Wei Yin-chun, resigned last week, as the government started investigations into the safety of its food supply.