Soaking in lactic acid lowers the phytate-phosphorus content and increases the resistant starch in wheat and corn grains

Abstract

The low availability of phytate phosphorus (Phy-P) from cereals for monogastric livestock can be enhanced using feed technological processes. The present objective was to investigate the effect of soaking of grains in lactic acid (LA) on the Phy-P disappearance and chemical composition in wheat and corn grains and whether changes in the nutrient profiles occurred when cereals were dried and stored for four weeks. Wheat, corn and a 50:50 mixture of both grains were soaked in 0, 10 and 25 g/kg LA (LA0, LA10, and LA25) for 0, 6, 12, 24 and 48 h. Thereafter, samples were either directly analyzed for their nutrient content or stored for 4 weeks at 21 °C until analyses. The effect of LA on the nutrient profiles in wheat, corn and, wheat-corn mixture was more evident with increasing LA concentration and soaking time, with the greatest effect with LA25 after 48 h of incubation. Soaking the cereals in LA25 for 48 h decreased (P < 0.05) the total phosphorus content by 9% across grains and decreased the Phy-P content by 24, 30 and 25% in corn, wheat and wheat-corn mix, respectively (P < 0.05), thereby correspondingly increasing the available phosphorus content. Phytase activity in corn grain represented one-tenth of the activity in wheat. End-product inhibition was indicated by the reduced phytase activity in wheat and wheat-corn mix after 48 h of soaking (P < 0.05). Moreover, crude ash and neutral detergent fiber decreased after soaking in LA, with the greatest change observed with LA25 and 48 h of treatment in LA. Although the LA treatment did not markedly affect the total starch content, soaking in LA25 increased the resistant starch content in wheat by 51%, whereas it decreased by 52 and 19% in corn and wheat-corn mixture, respectively (P < 0.05). Drying and storing the samples for four weeks increased the content of dry matter and crude ash, whereas neutral-detergent fiber, acid-detergent fiber, and non-resistant starch were reduced in the LA-treated grains after storage (P < 0.05). Storage also enhanced the Phy-P disappearance in LA-treated wheat and wheat-corn mix, thereby further increasing the available phosphorus fraction. In conclusion, soaking of grains in LA25 for 48 h demonstrated to be an effective strategy to improve the phytate-P availability in wheat and wheat-corn mix. Beneficial changes in the hemicellulose and resistant starch fractions caused by the LA treatment may have implications for the functional abilities of the LA-treated grains.