Susceptibility of 5-methyltetrahydrofolic acid to heat and microencapsulation to enhance its stability during extrusion processing

摘要

Folic acid is a common form of folate used for food fortification to prevent the incidence of neural birth defects among others. However, 5-methyltetrahydrofolic acid (5-MTHF) is considered, a better alternative to folic acid and is less likely to mask the symptoms of B_(12) deficiency in older populations. Also it is less bioavailable, and present in very low amount in foods. Fortification of foods with 5-MTHF is considered problematic, because it is highly sensitive to normal food processing operations. A comparative study on the thermal stability of folic acid and 5-MTHF in various liquid model food matrices such as milk, soymilk, starch-water and water during boiling and autoclaving at various time intervals was performed. Thermal degradation of 5-MTHF was more severe than folic acid in all food matrices e.g., almost 70% loss of 5-MTHF vs 17% loss of folic acid. Microencapsulation of 5-MTHF is considered to improve the stability of 5-MTHF during processing. A combination of pectin (P) and sodium alginate (A) at three different proportions (P60:A40, P70:A30, P80:A20) were employed for encapsulating 5-MTHF by spray drying. Microcapsules with the highest loading efficiency of 60% of vitamin (from P80:A20) and unencapsulated 5-MTHF powder was incorporated into starch and extruded at six different temperatures (100,110, 120, 130,140, 150 ℃). The 5-MTHF had better stability (84-94.5% retention) compared to the free form (65.3-83.2%) in all extruded products. The effectiveness of encapsulation was more evident at higher extrusion temperatures.