STUDIES ON EXTRUSION PROCESSING OF INSTANT PORRIDGE FLOURS FOR AFRICAN PROCESSOR OPTIMIZATION, ACCEPTANCE, MARKETABILITY FOR CONSUMERS, AND IMPROVEMENT IN IN VITRO FECAL FIBER FERMENTATION
The Food Processing and Postharvest Handling Innovation Lab (FPIL) project seeks to reduce food loss and link up consumers with food-to-food fortified instant products that are enriched with micronutrient sources that target vitamin A, zinc, and iron deficiencies. These are mostly maize-based products, but may be combined with other cereals, such as sorghum, and pseudocereals, such as amaranth. The general goal of this thesis study was to facilitate the adoption of extrusion technology to process instant flours, assess the acceptance and willingness to pay (WTP) for these products, and to assess the health impacts of the products on gut health. A low-cost, single-screw extruder was used that was developed at Purdue, and has been placed in different locations in Africa country study sites. The first study aimed to optimize process conditions of a low-cost single-screw extruder, currently done at 35% feed moisture, for African small- to medium-scale entrepreneurs to produce good quality and low-cost pregelatinized instant pearl millet porridge flours and other whole grains by relating feed moisture (27, 29, 31, 33, and 35%) to extrusion energy, drying time and physicochemical properties. We found that we could lower the feed moisture to 27% and still attain good pasting profiles of the porridges, reduce drying time, have better expansion of the extrudates, obtain increased L* color values of the flours, and with a higher extrusion energy but lower drying time. In conclusion, the single screw extruder can be efficiently operated at 27% feed moisture compared to the currently used 35% feed moisture and obtain instant flours with desired quality. It is not known whether higher extrudate energy consumption may be offset by the lower drying time representing lower drying energy. In the second study, we investigated extrusion enhance in vitro fecal fermentation of maize bran, which has been characterized by a poor gut microbiota fermentation property due to its highly crosslinked and densely branched arabinoxylan chemical structure, making it poorly available to the gut microbiota. We hypothesized that this dense cell wall matrix can be opened for better fermentation by applying extrusion. Test conditions of a twin-screw extruder at Purdue were low (200 RPM) and high (400 RPM) shear rates applied to a maize meal and bran mixture (60:40) at different feed moisture conditions (20, 25, 30%). In vitro fermentation of test materials was conducted on stool samples from three donors. Extrusion increased total short chain fatty acids and produced individualized donor effects on the gut microbiota. Some extruder test condition effects were observed on certain bacteria. For example, extrusion at 30% feed moisture and 400 RPM tended to increase genera of Subdoligranulum and Eubacterium hallii and Ruminococcus torques groups in Donor 1 compared to non-extruded bran. There was also a trend of increase in Subdoligranulum and Blautia in extruded compared to non-extruded bran in Donor 2. In Donor 3, Lachnospiraceae NK4A136 group was increased at 20 and 25% feed moistures at 200 RPM and 30% feed moisture at 400 RPM compared to non-extruded bran. In the final study, we investigated the acceptance and WTP for instant fortified flours using the Becker-DeGroot-Marschak mechanism when consumers are incrementally given nutrition information and demonstration how to reconstitute instant flours. This study was conducted in Eldoret, Kenya. Participants preferred the fortified thick porridge higher in maize content than fortified thin porridge prepared from the same blend. Contrarily, thin porridge made from fortified flour with higher sorghum content was ranked more highly than for the corresponding thick porridge. Participants were willing to pay more for instant fortified products higher in sorghum when given product name and nutrient composition, even without a practical demonstration of how to reconstitute the flours. For the instant product higher in maize, consumers needed demonstration of how to reconstitute the instant flour for them pay a higher premium. These findings suggest that food-to-food fortified instant porridge flours have the potential to be adopted and can be used as a vehicle to deliver micronutrients to these populations and that extrusion somewhat enhances fermentation of whole grain fibers by the gut microbiome.