EXTRUSION PROCESSING OF UPCYCLED ALMOND INGREDIENTS: UTILIZATION OF ALMOND PROTEIN CONCENTRATE AND SKINS IN DIRECT EXPANDED PRODUCTS

Preston Watanabe

doi:10.7273/000007497

Direct expanded products are considered a major segment of extruded products made and consist of a large portion of the snack food market, both in the U.S. and internationally. The utilization of starch-rich matrices remains a crucial factor in determining the expansion potential, pasting characteristics, and overall quality of direct expanded products. Yet, continual use of primarily starch-based products also overlooks key nutritional benefits from other biopolymers and macronutrients, such as fiber and protein. As a result, ongoing research in finding compatible alternative ingredients for substitution or fortification continues to persist for better value addition of expanded products. Many alternative ingredients have been utilized in literature with varying results, being primarily dependent on the nutritional and functional properties of the ingredients. Thus, this research explores the utilization of byproduct almond ingredients, rich in protein and fiber, in direct expanded extruded products. The first study focused on the extrusion of pearled, short-grain white rice, utilizing a defatted almond protein concentrate flour with ~60% protein content (w/w). This protein flour is the result of upcycled almond press-cakes that were dried and further defatted, forming a stable flour. A Box-Behnken design was used to model the extrusion factors likely to impact extrudate qualities: inclusion level of the protein flour (5, 15, and 25% w/w), moisture content of the flour blend (18, 20, and 22% w.b.), and the screw speed of the extruder (300, 400, and 500 rpm). Modeled responses, with high R2 values, showed strong correlations between extrudate qualities (expansion ratio, water absorption and solubility, and extrudate color) and extrusion factors of influence. Higher % of almond protein inclusions showed higher potential for radial expansions, however also forming large non-uniform, and irregular extrudates. Higher inclusions of protein content also lowered the water absorption capacity of extrudates, while showing no influence on extrudate water solubility. The color of extrudates was influenced by all factors, showing the potential for Maillard browning interactions, dependent heavily on higher protein contents, low moisture, and high screw speeds. Overall, several interactions were observed with the inclusion of almond protein, resulting in varying expanded products of different qualities. Moisture content and screw speed were shown to be significant influences on product quality and may be able to balance negative attributes associated with an increase in protein content. The second study utilized a high-fat (~20% w/w) almond skin flour within a cornstarch base. These almond skins were a result of blanched almond byproducts, further dried and milled to a small particle size (median particle size D(50) = 424.20 ± 24.20μm). Keeping moisture content at a constant 16% w.b., which was shown to be ideal in the almond protein study, almond skin inclusion (5, 10, 15, and 20% w/w) and screw speed (150, 250, 350, 450 rpm) were chosen as main factors of influence. Almond skins were shown to have a significant influence (p>0.05) on radial expansion, water interactions, extrudate color, pasting characteristics, and energy applied to the extrusion system (SME). Overall, almond skins were shown to behave similarly to other non-soluble fibers, leading to reduced expansion and darkening of the extrudates with the increase in the inclusion levels. A low inclusion (5 – 10% w/w) however may be advantageous in expanding cornstarch extrudates, and at low screw speeds were shown to have larger radial expansions than the control (100% cornstarch). The use of these almond ingredients in extrusion may have similar characteristics in their disruption of the starch matrices, but present two different products. Depending on the final product vision, it is possible to at least utilize lower percentages of both ingredients (5-10%) for value addition without compromising overall extrudate quality.

EXTRUSION PROCESSING OF UPCYCLED ALMOND INGREDIENTS: UTILIZATION OF ALMOND PROTEIN CONCENTRATE AND SKINS IN DIRECT EXPANDED PRODUCTS

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