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.

Physicochemical Properties of Milk Protein Concentrate Extrudates Generated Using Supercritical Carbon Dioxide

“…Sucrose, lecithin, and Dimodan were added as plasticizers, and the formula was chosen based on previous studies. 18,19 The formulation was extruded using a corotating twinscrew extruder (Wenger TX-52 Magnum, Sabetha KS, USA) coupled with a supercritical carbon dioxide (SC−CO 2 ) injection system. The extruder with an L/D (length/diameter) ratio of 28.5:1 is configured for SC−CO 2 injection into the barrel at an L/D ratio of 24 (Figure 1).…”

“…The ingredients according to formulation (84% MPC80 + 14% sucrose + 1% lecithin + 1% Dimodan) were blended in a ribbon blender (Day, Cincinnati, OH, USA) for 20 min (clockwise and counterclockwise for 10 min each) and stored at room temperature until extrusion. Sucrose, lecithin, and Dimodan were added as plasticizers, and the formula was chosen based on previous studies. , The formulation was extruded using a corotating twin-screw extruder (Wenger TX-52 Magnum, Sabetha KS, USA) coupled with a supercritical carbon dioxide (SC–CO 2 ) injection system. The extruder with an L/D (length/diameter) ratio of 28.5:1 is configured for SC–CO 2 injection into the barrel at an L/D ratio of 24 (Figure ).…”

“…For SX samples, the product temperature was raised to 115 °C, and no CO 2 injection was done during extrusion. These operating conditions and the feed formulation for the extrusion were selected based on previously reported studies. , The prepared MPC extrudates were collected on trays and dried in a hot air convection oven at 80 °C for approximately 2–3 h to achieve a final moisture content of less than 5% (db). The dried extrudates were stored in airtight bags.…”

Principles and Guidelines for In-Line Viscometry in Cereal Extrusion

“…To measure the rheological properties using an SDV, different shear rates must be generated within the slit channel. These different shear rates can be achieved by either varying the rotation speed or frequency [15,[46][47][48][49][50][51][52][53] or by varying the feed rate [54][55][56][57][58][59][60][61][62][63]. However, both approaches interfere with the process, making the molten material subject to different thermomechanical treatments, which can in turn highly affect the rheological properties of the melt [14][15][16].…”