Effect of Low-Temperature Superfine Grinding on the Physicochemical and Functional Properties of the Pulp Powder of Citrus reticulata ‘Chachi’

The study aimed to explore the rational utilization of Citrus reticulata ‘Chachi’ pulp. Low-temperature superfine grinding (SG) technology was employed to prepare citrus pulp powder, and its physicochemical properties, microstructure and functional properties were examined. A significant reduction in the particle size of citrus pulp powder was observed after SG treatment (P < 0.05). With increasing grinding time, the particle size decreased, the color became lighter progressively, the tap density decreased, the repose angle and slip angle enlarged, the water-holding capacity decreased, and the oil-holding capacity, water solubility index and swelling degree increased. Meanwhile, the particle distribution of the powder became more homogeneous, while no changes in functional groups occurred. It was also found that SG for 10 min resulted in a significant increase (P < 0.05) in total phenol and vitamin C (VC) contents by 12.70% and 17.27%, respectively, compared with ordinary grinding (OG). By high performance liquid chromatography (HPLC), nine flavonoids were identified, the major ones being hesperidin and narirutin, accounting for 78.06% and 8.96% of the total flavonoid content, respectively; five phenolic acids were identified, with the predominant one being ferulic acid, representing 73.85% of the total phenolic acid content, as well as synephrine and limonin. SG treatment greatly promoted the dissolution of bioactive components. Compared with OG, SG for 10 and 30 min increased the ferulic acid content by 190.72% and 109.68%, respectively. Limonin and nomiline contents significantly increased after SG for 30 and 60 minutes (P < 0.05), while ferulic acid, synephrine, hesperidin, narirutin, eriocitrin, and didymin contents significantly decreased after SG for 120 min (P < 0.05). The in vitro antioxidant activity significantly increased after SG for 10 and 30 minutes (P < 0.05). Overall, low-temperature SG can be used to produce pulp powder of Citrus reticulata ‘Chachi’ with smaller particle size, more uniform particle size distribution, improved color, increased dissolution of bioactive components and enhanced antioxidant properties. However, too long SG results in powder agglomeration, and negatively impacts the fluidity of the powder and the dissolution of bioactive components.