Development of Candied Strawberry Products via Neural Network-Optimized Sugar-Infiltration Processes

Conventional thermal processing of candied strawberries causes severe nutrient degradation and impairs the nutritional quality of the final products. To address this problem, high hydrostatic pressure (HHP) and ultrasound (US) were adopted as non-thermal auxiliary techniques for sugar-infiltration treatment in this study. Single-factor experiments were performed, and response surface methodology (RSM) and back-propagation neural networks (BPNN) were applied to optimize the processing parameters, with the sensory score used as the evaluation indicator. The optimization performance of the two models was then compared. Thermally processed candied strawberries served as the control group, and the moisture, total sugar, total acid, total phenolic, and total flavonoid contents of all sample groups were determined. The BPNN produced smaller relative errors than RSM in both HHP-assisted (0.95% vs. 1.15%) and US-assisted (0.47% vs. 0.68%) sugar-infiltration optimization, which confirms its superior predictive capability. The optimal HHP-assisted parameters were an infiltration time of 7.70 min, a treatment pressure of 258.00 MPa, and a sugar-solution concentration of 45.00%. The optimal US-assisted conditions were a treatment time of 50.00 min, an ultrasonic power of 80.00%, and a sugar-solution concentration of 45.00%. No significant differences in moisture content were observed among the three processing groups (thermal processing, 19.45 ± 0.35 g/100 g; US treatment, 19.51 ± 0.26 g/100 g; HHP treatment, 19.88 ± 0.21 g/100 g). The non-thermal treatments markedly enhanced nutrient retention: the total phenolic contents of the US- and HHP-treated samples reached 4.85 mg/g and 4.89 mg/g, respectively, which were 6.8-fold higher than that of the thermally processed samples (0.71 mg/g), and the corresponding total acid contents were 5.93 g/kg and 6.19 g/kg, approximately 9.5-fold higher than that of the thermal group (0.64 g/kg). In contrast, the thermally processed samples showed significantly higher total sugar contents than the non-thermal treatments. Both HHP and US processing effectively suppressed the thermal degradation of phenolic compounds and organic acids and reduced the total sugar content by approximately 24%. These results indicate that non-thermal processing is an effective route for manufacturing low-sugar, high-nutrition candied strawberry products.