In‐process flow behavior and structure formation during supercritical fluid extrusion of milk protein concentrate

Abstract

The in-line flow behavior of milk protein concentrate (MPC) and MPC-sucrose (MPC-S) blends with and without added supercritical CO2 (SC-CO2) during extrusion was quantified using a slit die rheometer and related to the expansion characteristics of extrudates. The apparent viscosity of the melt was in order: MPC > MPC + SC-CO2 > MPC-S > MPC-S + SC-CO2. A lower viscosity reduction factor due to SC-CO2 incorporation was observed for MPC-S (1.3–1.1) compared to MPC (1.5–1.2) owing to decreased volume fraction of protein in MPC-S. Increase in the apparent viscosity increased the expansion ratio for both MPC and MPC-S extrudates from 2.2 to 4.3 and 1.9 to 4 and decreased the average cell size from 924 to 392 and 936 to 354 µm, respectively. Thus, expansion and cellular architecture of MPC-based extrudates can be improved by controlling the melt viscosity. The findings of this study could have significant utility in designing novel milk protein-based products. Practical applications Milk protein concentrates are highly valuable and nutritionally attractive products and their conversion into expanded and texturally designed foods will be a valuable addition to the market. The cellular architecture of such foods is one of the primary indicators of the consumer-acceptable quality and depends upon the melt rheology, which in turn is related to the feed composition and processing conditions within the extruder. Relating the in-line rheological properties to extrudate characteristics can provide better decision-making ability for the selection of feed ingredients, diluents, and inert ingredients for the development of expanded milk protein puffs of commercial utility.