Physical processing of clementine pomace: effects on bioactive compounds and cell wall polysaccharides

Clementine pomace, a by-product of juice extraction, is a rich source of dietary fiber, including cellulose, pectin, and other cell wall polysaccharides, and low-molecular bioactive compounds that provide health benefits. Due to consumer demand for clean-label food products, physical treatments help to obtain functional ingredients for the food industry. This study examined the impact of hot air drying, homogenization, freeze drying, and extrusion treatments on the chemical composition of clementine pomace, especially on the structure of cell wall polysaccharides, using spectroscopic and chromatographic methods. Freeze-drying and extrusion-treated pomaces exhibited the highest contents of carotenoids and phenolic compounds, respectively. The homogenization treatment resulted in a notable increase in the total dietary fiber content. Regardless of treatment, the main component of the water-soluble polysaccharides was highly esterified galacturonan. Its contribution and methylation degree decreased in the order of successive extractions with hot water. Heating of clementine pomace during air drying or extrusion helped to produce more esterified pectin in the CWE fraction with a block distribution of the esterified units. The increased glucose content in the water-soluble fractions obtained from extruded pomace indicated partial destruction of cellulose and associated hemicelluloses. The physical treatments applied to clementine pomace modified cell-wall polysaccharides, which could affect the techno-functional properties of this product and improve its potential as a valuable clean-label ingredient for developing healthy foods.