Impact of high-hydrostatic pressure pretreatment on conventional and ultrasound-assisted pectin extraction from fresh and dried apple pomace: Structural, rheological, and functional analysis

Apple pomace, a by-product of the apple processing industry, is a valuable source of pectin with applications in food and biodegradable materials. However, conventional extraction (CE) methods can compromise pectin's structural integrity, prompting the need for alternative techniques. This study evaluates the impact of high hydrostatic pressure (HHP) at 200 and 600 MPa, combined with CE and ultrasound-assisted extraction (UAE), on the yield, structure, and rheology of pectin from fresh and dried apple pomace. The highest yield (12.32 %) was obtained from dried pomace treated with HHP at 200 MPa followed by UAE, while UAE alone achieved similar yields to CE with shorter extraction time. Pectin from dried pomace showed higher molecular weight and galacturonic acid content, indicating better polymer integrity. HHP at 200 MPa preserved structural features, while 600 MPa caused degradation, lowering viscosity and shear resistance. All samples were classified as high-methoxyl pectin (degree of esterification 57.44 %–74.02 %). Thermal analysis indicated slightly enhanced stability in HHP-UAE-extracted pectin. Rheological analysis confirmed shear-thinning behavior, with viscosity differences most notable at low shear rates. These results highlight the effectiveness of moderate-pressure HHP (200 MPa) in enhancing pectin extraction while maintaining its structural and functional properties.