Application Of An Exterior Phytase In Soybean Milk And Two Cereal Foods

The single-stomached animals had no phytase in their bodies. They couldn't digest the mineral element and protein that could be fixed by phytic acid. When phytase was added to the foods, the phytic acid or phytate in foods could be degraded by phytase to liberate inositol and free inorganic phosphorus. The antinutritional properties of phytic acid or phytate would be eliminated therefore. In this work, our study concentrate on the influencing factors of temperature, pH, hydrolysis time, the level of phytase added and metal ions on phytic acid or phytate degradation. The Optimal hydrolysis conditions for an exterior phytase were determined. Hydrolysis of phytic acid or phytate by interior phytase in foods was first evaluated by the hydrolysis ratio of organic phosphate. An exterior phytase preparation was applied in soybean milk, dough and maize to hydrolyze phytic acid then. After measuring the hydrolysis ratio of organic phosphate, diversification of phytic acid content or free calcium content, hydrolysis results of exterior phytase were evaluated thereby.Organic phosphorus in phytic acid or phytate of soybean milk might be hydrolyzed about 28.1% at 24 h by interior phytase. Organic phosphorus in phytic acid or pyhtate of dough without yeast might only be hydrolyzed about 27.9% at 4 h by interior phytase, but elevated to 40.9% when yeast was added. Organic phosphorus in phytic acid or pyhtate of maize paste might be hydrolyzed about 14.2% at 4 h by interior phytase. Therefore it indicated that the interior phytase had limited degradation. It was impossible to degrade phytic acid or phytate completely only by interior phytase.The optimal hydrolysis conditions for soybean milk were at 45℃, pH4.5 for 2 h with an exterior phytase addition about 300 FTU-kg^-1. The optimal hydrolysis conditions for dough were at 45℃ for 4 h with an exterior phytase addition about 500 FTU-kg^-1 and yeast about 0.3%. But for maize paste with a concentration about 20%, it was preferred to hydrolyze at 45℃, pH4.5 for 4 h with an exterior phytase addition about 300 FTU-kg^-1. The experimental data also showed that Cu²⁺, Zn²⁺, Mn²⁺, Fe²⁺ inhibited phytase while Ca²⁺, Mg²⁺activated it.With selected hydrolysis conditions, organic phosphorus in phytic acid or pyhtate of soybean milk might be hydrolyzed about 82.9% with the addition of exterior phytase, accompanying increase in free calcium content about 49.5 mg-kg^-1. This meant that about 66.7% phytic acid or phytate was degraded. For dough, organic phosphorus in phytic acid or pyhtate might be hydrolyzed about 51.8% with increase in free calcium content about 38.7 mg-kg^-1, which meant that 72.4% phytic acid or phytate was degraded. Organic phosphorus in phytic acid or phytate of maize paste was degraded about 72.4% with increase in free calcium content about 30.5 mg-kg^-1. Most ofphytic acid or phytate was hydrolyzed in paste with such treatment. Exterior phytase had good degradation for phytic acid or phytate in three foods studied to elimitate their antinutritional factors and to improve their nutrition.