Germination and extrusion as combined processes for reducing phytates and increasing phenolics content and antioxidant capacity of Oryza sativa L. whole grain flours.

Whole rice (WR) products with low phytic acid (PA) content and enhanced bio-functional components were obtained by the combination of germination and extrusion processes. Germination conditions (24 h - 35 °C), with a previous soaking process (24 h - 20 °C), were chosen according to the remnant PA content and germination rate. Specific mechanical energy consumption, expansion, sensorial and mechanical hardness, specific volume, solubility, water absorption, free phenolic content (FPC) and antioxidant capacity were evaluated. Results indicated that 175 °C and 14 g 100 g(-1) of moisture were the most appropriate conditions to obtain expanded products and precooked flours based on germinated WR. Selected extruded product presented less PA content (821.6 9 ± 10.3 versus 695.2 0 ± 1.6 mg 100 g(-1)) and higher Fe bio-accessibility, FPC (45.2 9 ± 1.61 versus 66.3 5 ± 3.35 mg GAE g(-1)) and antioxidant capacity compared with WR (34.9 5 ± 0.8 versus 54.6 3 ± 1.6 µmol trolox g(-1)). Combining germination-extrusion processes could be a strategy to obtain expanded products or precooked flours based on WR with enhanced health benefits.

Mycotoxins inactivation by extrusion cooking of corn flour.

AIMS: To evaluate the effects of the extrusion cooking process on the inactivation of mycotoxins in corn flour. METHODS AND RESULTS: Samples of corn flour experimentally contaminated with aflatoxin B1 (AFB1) (50 ppb) and deoxynivalenol (DON) (5 ppm) were extruded. The effects of three extrusion variables (flour moisture, extrusion temperature and sodium metabisulphite addition) were analysed according to a two-level factorial design. The process was effective for the reduction of DON content (higher than 95%) under all the conditions assessed, but was only partially successful (10-25%) for the decontamination of AFB1. CONCLUSION: Extrusion cooking is effective for the inactivation of DON but is of limited value for AFB1, even if metabisulphite is added. More severe extrusion conditions are needed for the detoxification of AFB1. SIGNIFICANCE AND IMPACT OF THE STUDY: As contamination with DON occurs mainly in the field prior to harvesting and that of AFB1 is normally produced during grain storage, maize is often contaminated with DON but not with AFB1. Under these conditions, the described extrusion process can be used for the detoxification of DON. The addition of sodium metabisulphite did not significantly affect the inactivation of AFB1. Extrusion cooking is therefore an appropriate treatment for vomitoxin-contaminated maize in countries where, because of the prevailing conditions, these are the only toxins present.

[Effects of some extrusion variables on corn flour]. / Efectos de algunas variables de extrusión sobre la harina de maíz.

Grits and flour extrusion is a relatively simple operation. Nevertheless, understanding the transport mechanism and property modifications which occur during the operation, is quite complex. Analysis of the effects produced on the material properties, through those methods that better describe the transformations produced, and the correlation of these "indicators" or responses with the process variables, would allow a better interpretation of the process as well as the selection of operation conditions to keep in mind so as to obtain the desirable characteristics in the product. In the present study, the effect of feed moisture, extrusion temperature and screw speed as well as compression ratio on corn flour properties, was evaluated through the following parameters or responses: feed rate, specific consumption of mechanical energy, specific volume, expansion, water solubility and amylogram. According to the results, feed moisture is the most relevant in modifying the properties, whereas the relative importance of temperature and compression ratio depend on the property being analyzed. Thus, for example, for specific consumption of mechanical energy, compression ratio is more important, while for expansion and specific volume, temperature is the most important. On the other hand, solubility appears to be the property that best describes changes involved during processing of the sample, while specific volume and specific consumption of mechanical energy--although being less efficient--also turn out to be very useful responses.