In this study, the effects and mechanisms of hot water blanching and steam blanching pretreatments on the texture formation of dried apricot fruits were compared and analyzed from the aspects of macroscopic texture, water distribution, microstructure and cell wall component characteristics. The results showed that the strong thermal penetration effect of steam blanching significantly weakened intercellular adhesion, reduced the hardness of dried fruits and enhanced the ductility. The hardness of the dried fruit prepared by steam pretreatment at 95 ℃ was 502.64 g, and its ductility was significantly higher than that of other groups. Hot water blanching pretreatment remarkably facilitated the the dissolution of sugar molecules, resulting an increase in the hardness of dried fruits, with the highest value (1067.42 g) observed at 95 ℃. Furthermore, steam pretreatment at 75 ℃ significantly reduced the mobility of water molecules, which was accompanied by an increase in the proportion of immobilized water (S₂₂ increased to 97.33%). The surface of the dried fruit with steam pretreatment at 75 ℃ was flat, with enhanced reflectivity and reduced absorbance, which was consistent with improved color. Moreover, steam blanching affected the thermal stability of the cell wall by promoting the exposure of carboxylic acid groups and the cleavage of glycosidic bonds, thereby affecting the texture formation of dried apricot.

The effect of multi-frequency pulsed ultrasound (20 kHz, 20 + 28 kHz, and 20 + 28 + 40 kHz) on characteristics of a peach pulp-κ-carrageenan blend gel system containing erythritol as a cosolute was systematically studied. Rheological analysis showed that the blend gel system was a pseudoplastic fluid. With the increase in pulsed ultrasound frequency, the consistency coefficient increased and the flow index decreased. Dynamic rheological analysis showed that single-frequency and dual-frequency pulsed ultrasound could significantly enhance the elastic modulus (G’) and viscosity modulus (G”), while triple-frequency pulsed ultrasound had the opposite effect. The particle size was significantly reduced by the cavitation effect produced by multi-frequency pulsed ultrasound, the effect being most pronounced with triple-frequency pulsed ultrasound. Compared with the control group, D₅₀, D_[4,3], and D_[3,2] of the samples treated by triple-frequency pulsed ultrasound were decreased by 12.32%, 9.80% and 7.57%, respectively. Additionally, multi-frequency pulsed ultrasound could increase the absolute value of the phase angle and conductivity, and reduce the impedance value. Compared with the control group, the absolute value of the phase angle and the conductivity were increased by 35.82% and 10.15% in the triple-frequency pulsed ultrasound group, respectively; and the impedance value was reduced by 38.52%. As the pulsed ultrasound frequency increased, the association between the blend system and water was enhanced, so that a bound water signal appeared. No new absorption peaks were found in the Fourier transform infrared spectra of ultrasound-treated samples, indicating that ultrasound treatment did not destroy the functional groups, but instead only strengthened hydrogen bonding. The micropores of the blend gel system were enlarged by both single-frequency and dual-frequency pulsed ultrasound treatments, while triple-frequency pulsed ultrasound treatment resulted in denser and more uniform pores. This study can provide a reference for improving the quality of blend gels of κ-carrageenan and developing gel-like peach pulp products.

In this study, changes in the textural properties, dielectric properties, cell wall polysaccharide content and microstructure of yellow peach blocks were investigated after osmotic dehydration (OD) treatment with binary/ternary osmotic solutions containing sucrose and maltitol. Meanwhile, changes in the soluble sugar content were determined by ¹H nuclear magnetic resonance (¹H NMR) spectroscopy. Our aim was to clarify the synergistic effect of maltitol and sucrose on improving the properties of yellow peach blocks during OD treatment. Compared to the control group, The hardness, chewiness and adhesiveness of yellow peach blocks treated with a ternary osmotic solution with a 1:4 ratio of sucrose to maltitol (SM14) were significantly reduced. OD resulted in a significant decrease in the impedance (Z) and effective resistance (R_s) as well as a significant increase in the electrostatic capacity (C_s) of yellow peach blocks, suggesting that OD could affect peach pulp cell properties by acting on cell wall polysaccharides. ¹H NMR results showed that OD with ternary osmotic solutions significantly reduced the sucrose content in peach fruit block tissue; for the SM14 group, the signal intensity of sucrose and maltitol were 19803.9 ± 156.00 and 54934.9 ± 1239.11, respectively. Meanwhile, the contents of water-soluble pectin (WSP) and CDTA-soluble pectin (CSP) in the SM14 group were increased to (26.63 ± 1.80) mg/g and (21.59 ± 0.71) mg/g, respectively, while the content of Na₂CO₃-soluble pectin (NSP) was decreased to (27.24 ± 0.46) mg/g compared to the control group. Microstructure analysis showed that round and relatively intact cells with low degree of collapse and a significant increase in cell wall thickness were observed in the SM14 group, demonstrating sucrose and maltitol synergistically protect peach pulp cells. Therefore, ternary osmotic solutions of sucrose maltitol could effectively ameliorate the quality deterioration of yellow peach blocks caused by binary osmotic solutions, broadening the application of sugar alcohol.