Date of this Version
Interest in resistant starch (RS) as a prebiotic is increasing due to its putative impacts on the gastrointestinal microbiome and thus colon health. Application of RS as a food ingredient is also increasing because of its unique functionality. However, a major obstacle when correlating RS containing food systems to the potential health benefits is the discrepancy in the analytical tests applied and the limitations of those methods used throughout the literature. Therefore, the Megazyme resistant starch assay was adapted and developed to monitor RS present in different types of products commonly consumed in the United States, including an extruded ready-to-eat breakfast cereal, a cookie, a muffin, a sport drink, and a nutritional bar. The linearity of the calibration curve based on glucose standards (0.1-1.0 mg/mL) from the validation of the Megazyme RS assay was Y= 0.9918x + 0.0057 with a correlation coefficient of R2 = 0.9995. The low detection (0.0013%) and quantitation limits (0.0048%) of blank samples were needed to assay the final food products. Each processed food required minimal optimization, with the exception of the sports drink, that included increasing the centrifuge time (cookie), to changing the entire formulation (extruded cereal), to removing the moisture and fat prior to analysis (granola, muffin). As a result, % recoveries of 1% spiked samples ranged from 66-100% and the detection limit was lower than 1% for all the processed foods except for muffin and cookie. Application of the validated method to 1% supplemented processed foods showed processing effects, especially for the extruded cereal. RS was also significantly affected when the sports drink was reformulated (sweetener composition and pH) but only non-significant trends resulted when changing the extrusion parameters (barrel temperatures and screw speeds) for the cereal. In summary, application of a more robust and reliable RS assay is important in determining the chemical fate of RS under different processing treatment in processed food supplemented with RS.