The Influence of Extrusion Processing on the Gelation Properties of Apple Pomace Dispersions: Involved Cell Wall Components and Their Gelation Kinetics

Abstract

By-products of fruits and vegetables like apple pomace can serve as techno-functional ingredients in foods. Due to their physicochemical properties, e.g., viscosity, water absorption, or oil-binding, food by-products can modify the texture and sensory perception of products like yogurts and baked goods. It is known that, by extrusion processing, the properties of by-products can be altered. For example, by thermo-mechanical treatment, the capacity of food by-products to increase viscosity is improved. However, the mechanism and involved components leading to the viscosity increase are unknown. Therefore, the complex viscosity of apple pomace dispersions and the involved fractions as pectin (a major part of the water-soluble fraction), water-soluble and water-insoluble fraction, were measured. In the investigated range, an increase in the pectin yield and water solubility was observed with increasing thermo-mechanical treatment by extrusion processing. However, pectin and water-soluble cell wall components had only a limited effect on the complex viscosity of apple pomace dispersions. The insoluble fraction (particles) were investigated regarding their swelling behavior and influence on the complex viscosity. An intensification of thermo-mechanical treatment resulted in increasing swelling behavior.

Functionalization of Enzymatically Treated Apple Pomace from Juice Production by Extrusion Processing

“…These results are similar to the WAI results (Figure 7), suggesting that the water absorption and swelling (Figures 8 and 9) due to macromolecular cell wall alterations play an important role in the thickening behavior of the extruded samples. Thus it is all about swelling not the gelling of individual components as assumed [11,35,36].…”

“…Being rich in dietary fiber (Total Dietary Fiber (TDF): 60-90 g/100 g dm) and phytochemicals such as phloridzin, chlorogenic acid, and quercetin glycosides [4,5,[8][9][10], it has the potential to be used as a valuable food ingredient. However, it shows poor technofunctional properties, e.g., low water solubility and adsorption, as well as low or no thickening and gelling properties, limiting its industrial applications in food products [5,8,11,12].…”

Physicochemical Characteristics, Antioxidant Properties and Consumer Acceptance of Greek Yogurt Fortified with Apple Pomace Syrup

“…The content of the polyphenols in AP is higher than that of fresh apples or juiced apples [11]. The functional component in AP varies depending on the extraction and drying process of the AP [12][13][14][15][16][17][18][19]. Currently, some AP is used as feed in livestock farms and organic fertilizer in orchards and greenhouses, but most are discarded [20].…”