"Natto" fermented soybeans, considered by many as a healthy source of protein, is just one of many food items missing from supermarkets nationwide amid the disaster triggered by the March 11 quake and tsunami.

Ibaraki Prefecture, home to the largest number of natto manufacturers, was among the prefectures affected by the quake. Initial power outages triggered by the crippled Fukushima No. 1 nuclear power plant and a shortage of packaging materials are making it difficult to make natto, according to the Japan Natto Cooperative Society Federation.

Only 36 percent of the usual amount is being marketed in the Kanto region, the federation said.

"The ceiling (of a factory) fell in and a boiler collapsed because of the quake," said Masami Takano, president of natto maker Daruma Foods Co. in Mito, Ibaraki Prefecture. The company, however, managed to resume operations March 23 and sales resumed two days later, he said.

The federation said plastic packages used for natto are made of ingredients including polypropylene, which are made from petroleum.

But because petrochemical complexes in the quake-hit Tohoku region were damaged, the supply needed to make natto containers has not been sufficient.

"We've received 10 times more orders than usual, but we can only operate at 80 percent due to lack of plastic film covering the packages," Takano said.

The threat of power outages is also making output difficult, manufacturers say.

This is because soybeans must be fermented for about 20 hours at stable temperatures of between 42 and 45 degrees.

Other manufacturers of fermented products, including yogurt and miso, are likely having difficulties as well.

But now that Ibaraki appears to be exempt from further power outages because of the need to recover from the disaster, Takanofoods Co., the largest natto maker, known for its Okame Natto brand, was able to resume production.