According to the present invention, a low-calorie healthy food product rich in dietary fiber can be provided by using denatured glucomannan in producing food products, or by using denatured glucomannan to form a heat irreversible gelatinized food product, under a wide range of alkaline or acidic conditions. The present invention is a denatured glucomannan formed by isolating and the acetyl group of konjac-glucomannan by an alkali process to suppress swelling, whereupon the denatured glucomannan may then adjusted to be gelled or heated and gelled after being swollen by removing the swelling suppression using a high pH ingredient. Both the denatured glucomannan in addition to any gelatinized product or other food product formed from the denatured glucomannan may be dehydrated, frozen, or dried.
