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

Abstract

Food by-products can be used as natural and sustainable food ingredients. However, a modification is needed to improve the technofunctional properties according to the specific needs of designated applications. A lab-scale twin-screw extruder was used to process enzymatically treated apple pomace from commercial fruit juice production. To vary the range of the thermomechanical treatment, various screw speeds (200, 600, 1000 min−1), and screw configurations were applied to the raw material. Detailed chemical and functional analyses were performed to develop a comprehensive understanding of the impact of the extrusion processing on apple pomace composition and technofunctional properties as well as structures of individual polymers. Extrusion at moderate thermomechanical conditions increased the water absorption, swelling, and viscosity of the material. An increase in thermomechanical stress resulted in a higher water solubility index, but negatively affected the water absorption index, viscosity, and swelling. Scanning electron microscopy showed an extrusion-processing-related disruption of the cell wall. Dietary fiber analysis revealed an increase of soluble dietary fiber from 12.6 to 17.2 g/100 g dry matter at maximum thermo-mechanical treatment. Dietary fiber polysaccharide analysis demonstrated compositional changes, mainly in the insoluble dietary fiber fraction. In short, pectin polysaccharides seem to be susceptible to thermo-mechanical stress, especially arabinans as neutral side chains of rhamnogalacturonan I.

Defined shear and heat treatment of apple pomace: impact on dietary fiber structures and functional properties

“…A distinct decrease in galactose contents was only found for the sample that was treated at 160 °C and 40% water content. These results are consistent with previous studies stating that arabinose and galacturonic acid portions in IDF of apple pomace decrease under thermomechanical stress [3,17]. Also, studies on chokeberry pomace that was treated by using a CCR showed that under various thermal effects arabinose and galacturonic acid containing pectic polymers are most prone to degradation [22].…”

“…The largest amount of LMW-SDF was formed at a treatment temperature of 160 °C and a water content of 40% (F). These results support the findings that dietary fiber from apple pomace is susceptible to thermomechanical stress [3,17]. However, a detailed chemical interpretation of the changes of IDF, SDF, and LMW-SDF contents is difficult because these changes are most likely the result of a complex interaction: cleavage of glycosidic linkages, degradation of carbohydrate units, and the formation of high-molecular weight Maillard reaction products that are captured as dietary fiber.…”

“…3). The correlation between disruption of the cell wall, water absorption, and viscosity of the dispersions was previously reported for extruded apple pomace [3,17].…”

“…The molecular weight distribution of SDF polymers was determined by dissolving SDF in 50 mM sodium nitrate for 24 h at 40 °C, followed by centrifugation and separation of the supernatant according to hydrodynamic volume using two size exclusion columns in series (TosohTSK-gel G6000PWxl 300 mm × 7.8 mm, particle size 13 µM; TSKgel G4000PWxl 300 mm × 7.8 mm, particle size 10 µM) and a guard column (TosohTSK-gel PWxl 40 mm × 6.0 mm, particle size 12 µM). Sodium nitrate was used as eluent (flow rate: 0.5 mL min −1 , 50 °C), detection was carried out by HPLC-RI (Hitachi, Merck, Darmstadt, Germany) [17].…”

Chemical composition and technofunctional properties of carrot (Daucus carota L.) pomace and potato (Solanum tuberosum L.) pulp as affected by thermomechanical treatment

“…As a result, syneresis in food products such as deserts and sausages can be decreased or the texture of bread be improved [10]. We recently demonstrated that the functional properties of, for example, apple and chokeberry pomace are strongly affected by extrusion [10,[12][13][14]. On a polysaccharide structural level, extrusion of these food by-products mainly degraded arabinans as neutral side chains of rhamnogalacturonan I [12,13].…”