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

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

Despite having high polyphenolic phytochemicals and functional components, apple pomace (AP) is often discarded in landfills, leading to pollution. The study aimed to find a sustainable application for AP in Greek yogurt fortified with AP syrup (APS). Physicochemical characteristics and antioxidant properties were analyzed for APS (APS0.00, APS1.25, APS2.50, APS3.75, APS5.00). As the AP content in the syrup increased, moisture content, titratable acidity, and viscosity significantly increased (p < 0.05). The total polyphenols and flavonoid content of APS increased with increasing AP content. In Greek yogurt fortified with APS (APY), reducing sugar content (0.55 mg/mL to 0.71 mg/mL) significantly increased with fermentation time and AP content, whereas pH level (6.85 to 4.28) decreased. The antioxidant activities by DPPH radical scavenging activity, ABTS radical scavenging activity, ferric reducing antioxidant power, and reducing power were also significantly increased with the AP content and fermentation time. In the consumer acceptance test of APY, APY1.25 had significantly high scores in overall acceptance, taste acceptance, and aftertaste acceptance with purchase intent (p < 0.05). The Greek yogurt fortified with APS as functional food had improved antioxidant properties and consumer acceptance, suggesting the possibility of developing sustainable AP products.

Thermo-mechanical processing of fibre-rich blackcurrant pomace to modify techno-functional properties

Exploring the use of seedless blackcurrant pomace, a fibre-rich by-product of juice pressing, in foods is favourable due to its nutritional profile but also for economic and sustainability aspects. Current applications are limited to products in which rapid fibre swelling, high water solubility or low sedimentation is not essential. In this study, functional properties of seedless blackcurrant pomace were modified by thermo-mechanical treatments using extrusion cooking or micronization in a planetary ball mill. A full factorial design showed that low pomace moisture (11 g/100 g) had the highest impact on swelling capacity (+ 20.6%) and water solubility index (+ 23.2%), whereas variation in extrusion temperature exhibited only minor effects. After milling for 4 h, the median particle size was reduced by 98% to 4 µm and the specific surface area increased from 0.1 to 2.5 m2/mL. Swelling capacity was highest after this time with 7.6 mL/g pomace and, although the amount of extractable sugars was reduced, water solubility increased to 7.6 g/100 g. In contrast to extruded samples, the red colour of the pomace was intensified after milling. Both treatments appear as promising to extend the applicability of fruit by-products in foods, as micronized pomace may counteract sedimentation in liquids, whereas increased swelling capacity after extrusion may have stabilizing effects on yoghurt-like systems.

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

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.