Effect of citrate ions on the softening of root crops prepared with freeze-thaw impregnation of macerating enzymes.

UNLABELLED: Freeze-thaw impregnation is a technique used for the rapid impregnation of substances into foodstuffs. Freeze-thaw impregnation with macerating enzymes has been applied to soften foodstuffs, while retaining their original shapes and flavors. In this study, we found that co-impregnation with citrate ions and macerating enzymes significantly facilitated the softening of root crops. When burdock roots were processed by the impregnating solution at pH 4.0-5.0, co-impregnated burdock roots exhibited 1/6-1/3 firmness values compared with burdock roots impregnated with only enzymes. The impregnation with citrate ions alone at pH 4.0 to 5.0 did not soften burdock roots. The firmness of burdock roots was positively correlated with the amount of water-insoluble calcium in the samples. The results suggested that the degradation of pectins by pectinolytic activities could promote contact with citrate to bridging-calcium ions interacting with the pectin chains. Therefore, the softening by the synergistic effect of citrate ions and macerating enzymes was related to the amount of pectins contained in root crops. That is, the synergistic effect was significant with burdock roots and carrots (from which 50% of polysaccharides are pectins) unlike with lotus rhizomes and bamboo shoots (from which 30% and 10% of polysaccharides are pectins, respectively). PRACTICAL APPLICATION: Freeze-thaw impregnation with macerating enzymes and citrate ions can be applied for the production of care foods which can be eaten without chewing. The softened products induce the pleasure of eating for consumers because their original shapes and flavors are retained.

Decreased hardness of dietary fiber-rich foods by the enzyme-infusion method.

A novel technique is reported for softening plant tissues while retaining their shape by impregnating them with macerating enzymes under reduced pressure after defrosting the frozen plants. Samples were removed immediately from the enzyme solution after the freeze-infusion treatment, and the hardness was measured. Six enzymes and three enzymes were respectively chosen from 18 commercial enzymes for softening burdock roots and bamboo shoots. The tissue degradation due to impregnation of the tissues with the enzymes and the reaction time were investigated. Burdock roots and bamboo shoots were progressively softened during the reaction: the hardness reached 1.0 x 10(4) N/m(2) or less. The water-soluble dietary fiber contents increased as a result of the freeze-infusion treatment. This softening technique, which retained the food shape, could enhance the production of food products for elderly persons and those under nursing care. Foods produced by this method can replace current minced and liquid dietary components.