Oral self-disintegrating puffs are quintessential for two major populations: infants and older adults with dysphagia or swallowing issues. Yet the current markets of self-disintegrating puffs are directed only at infant consumers and do not meet the needs of other population groups, specifically the elderly or the 70% of the world population suffering from lactose intolerance. Additionally, the current market of self-disintegrating snack puffs is carbohydrate-based and greatly lacking in ability to provide long term satiety (Kreger, Lee, & Lee, 2012).

The supercritical fluid extrusion system using dense CO2 as the blowing agent can be used to produce puffed products (Rizvi, Mulvaney, & Sokhey, 1995). This allows for processing to be conducted at temperatures below 100 °C, making it ideal for milk protein-based puffs (Chauvet, Sauceau, & Fages, 2017; Johannsen & Brunner, 1997; Paraman, Wagner, & Rizvi, 2012; Rizvi et al., 1995). Previous research from our lab showed that the integrity of milk protein concentrate (MPC) can be maintained near pre-extrusion levels when extruded with supercritical carbon dioxide (SC-CO2) (Arora & Rizvi, 2021).

For the milk protein-rich extrudates to self-disintegrate in the mouth, they need the addition of a calcium chelator (Arora & Rizvi, 2022). Calcium chelators work by binding to the calcium in casein micelles and therefore prevent the calcium bridging that causes casein aggregation during processing (de Kort, Minor, Snoeren, van Hooijdonk, & van der Linden, 2012). Our previous research has also shown the use of sodium hexametaphosphate (SHMP) in extruded MPC based puffs can enhance the oral dissolvability of these products (Rizvi & Arora, 2022), but there has not been any research to date on SC-CO2 extruded puffs that contain either skim milk powder (SMP) or lactose hydrolyzed skim milk powder (LHSMP) in the formulation and in-situ generation of a health promoting prebiotic.

Since galactose is a precursor to the oligosaccharide known as galacto-oligosaccharide (GOS) we hypothesized that with the control of temperature, shear, and the pH with the SC-CO2, the extruder could be used for the in-line polymerization of the galactose in LHSMP with the lactose coming from MPC into GOS. This phenomenon of monomer polymerization in the presence of an acid was first patented by Farber et al. (Farber, 1936). Later the relationship between the amount of glucose used in a concentration in relation to the amount of acid catalyst and the degree of glucose polymerization into gluco-oligosaccharides also called polydextrose were examined by Fetzer, Crosby, Engel, and Kirst (1953). This study showed that the reaction equilibrium rate was dependent on pH and temperature (Fetzer et al., 1953). It has been shown on multiple occasions that one of the easiest ways to form polydextrose is through an acid catalyzed reaction using water as a solvent (Moreau, Belgacem, & Gandini, 2004). More recently, this acid catalyzed glucose polymerization has been attempted in high pressure environments using technologies like extrusion. Hwang et al. (1998) showed that the extruder could be used to polymerize glucose into polydextrose using 2% citric acid as the catalyst. This work was then built upon many years later by Tremaine, Reid, Tyl, and Schoenfuss (2014) who used twin screw extrusion and showed that lactose alone did not polymerize well during extrusion, but the addition of glucose allowed for the polymerization of polylactose with a citric acid catalyst. In contrast to previous work that focused on polymerization of glucose, our work focuses on the polymerization of galactose and lactose into galacto-oligosaccharides (GOS) within a self-disintegrating puff. As a prebiotic, GOS offers many health benefits therefore, the goal of this project was to use supercritical extrusion processing for in-process generation of GOS-enriched, self-disintegrating puffs using either SMP or LHSMP, in combination with milk protein concentrate powder and characterize their properties.