Starch retrogradation, driven by reassociation and recrystallization of gelatinized amylose and amylopectin chains, induces undesirable firming, syneresis, and sensory deterioration, ultimately shortening the shelf-life of starch-based foods. Enzymatic modification has emerged as a promising route to retard retrogradation, but its efficacy critically depends on the structural features targeted by the enzyme, the susceptibility of the starch substrate, and the accessibility of catalytic sites. This review systematically interprets the structure-dependent mechanisms underlying enzymatic retrogradation regulation, covering the differential regulatory patterns of various enzyme systems. This review further clarifies the essential distinction between substrate structural susceptibility and enzyme catalytic accessibility, and summarizes advanced modification strategies based on porous starch construction and controlled starch swelling to optimize enzyme-substrate interfacial contact efficiency. In addition, mainstream detection techniques are compared based on the different levels of the studied starch structure. Finally, the practical applicability of enzymatic anti-retrogradation technologies in diverse staple and processed starch-based food systems are also summarized. We propose that the key design principle is controlled structural remodeling enabled by enzyme action within a defined processing window, rather than indiscriminate starch degradation. This work provides systematic theoretical insights and practical guidance for the quality stabilization and shelf-life extension of starch-based food products.
Grid-forming converters have gradually become critical equipment for supporting modern power systems. With the rapid development of distributed generation, single-phase grid-forming converters (SGFMCs) have attracted extensive attention. However, SGFMCs face the challenge of impedance modeling, which affects the stability analysis and controller design. This paper investigates the impedance modeling, interaction mechanisms, and sub-synchronous resonance (SSR) mitigation methods. Regarding the impedance modeling, SGFMCs have more complex internal relationships than three-phase grid-forming converters owning to their orthogonal signal generation unit. Existing impedance models for double-power loops SGFMCs rarely account for the mirror frequency effect (MFE), resulting in inaccurate impedance characterization. To fill this research gap, this paper adopts the harmonic linearization method to derive two single-input single-output impedance models that fully capture the MFE for two typical SGFMCs. Furthermore, the interaction mechanism between SGFMCs and grid is explicitly elucidated. Analytical results demonstrate that both SGFMCs are susceptible to SSR under strong grid conditions. To improve the system stability, an impedance shaping method is proposed to mitigate SSR for SGFMCs under strong grid conditions. Finally, experimental results verify the correctness of the theoretical analysis.
n-Octadecane is considered a promising organic phase change material (PCM) for medium and low temperature latent heat storage systems, but its inherently low thermal conductivity limits practical applications. Combining nanoparticles with metal matrix structures to construct a macro-micro dual-scale conductive network is an advanced enhancement strategy for improving the latent heat storage efficiency of PCMs. This strategy has attracted considerable attention in engineering thermophysics. However, the cross-scale synergistic heat transfer mechanism between the two enhancement levels still requires more systematic and in-depth investigation. In this study, a metal matrix-nanoparticle multilevel-enhanced PCM (MNePCM) was developed to preserve natural convection as much as possible at the macroscale while improving the intrinsic thermal conductivity of the PCM through microscopic nanoparticles. Subsequently, melting-based heat storage experiments were sequentially conducted on PCMs under three enhancement strategies to identify the effects of nanoparticles and the metal matrix on the melting-based heat storage characteristics of PCMs. A coupled fluid-thermal-solid numerical model was established to elucidate the effects of the metal matrix and nanoparticles on heat conduction and natural convection during melting and to quantify their cross-scale synergistic enhancement. The accuracy of the numerical model was validated against the experimental results. The results show that the 2 × 2–6 × 6 metal matrix increased the heat storage rate by 224.66%-158.98%. At the same porosity, higher-order cofignurations accelerated initial melting through larger metal-PCM interfacial areas and shorter local PCM conduction distances, while transient spatial matching between the metal walls and the evolving solid and liquid interface produced configuration-dependent local melting rate enhancement, termed the structure-interface synchronization effect. As melting progressed, lower-order matrices achieved better overall performance because their wider liquid-flow channels and thicker continuous metal walls favored natural convection and long-range heat conduction. Nanoparticle addition further improved thermal diffusivity, with stronger enhancement at higher concentrations. Under synergistic enhancement, the 2 × 2 MNePCM containing 5 wt% nanoparticles increased the heat storage rate by 260.62%, although the energy storage density decreased by 18.93%. A multilevel enhancement factor (MLEF) was proposed to evaluate this trade-off. Under equal weighting, the 5 wt%-2 × 2 MNePCM exhibited the best overall performance. This study provides theoretical guidance for optimizing high-performance composite PCMs and thermal energy storage units for medium and low temperature latent heat storage systems.
Alternaria alternata is a common contaminant of crops, fruit, and cereals, presenting serious risks to food safety, human health, and resulting in considerable economic losses. Therefore, green, safe, and environmentally friendly antifungal agents are urgently needed to control this pathogen. In this study, the antifungal effects of carvone and a lipopeptide crude extract from Bacillus velezensis JZ against A. alternata were evaluated. Inhibitory activities on mycelial growth and pathogenicity in postharvest strawberries were investigated, along with the underlying mechanisms. In vitro assays revealed that both carvone and the lipopeptide crude extract markedly inhibited mycelial growth. The minimum inhibitory concentration (MIC) of carvone was 0.30 μL/mL, while that of the lipopeptide crude extract was 2%. In vivo experiments showed that both treatments effectively suppressed A. alternata mycelium growth on postharvest strawberry. To elucidate their distinct antifungal mechanisms, transcriptomic analysis was performed, revealing divergent transcriptional patterns. Combined physiological-biochemical and transcriptomic analyses revealed that carvone and lipopeptide crude extract suppressed A. alternata growth by jointly disrupting ergosterol synthesis, cell wall remodeling, DNA repair, ROS homeostasis and mitochondrial metabolism. Carvone triggered more severe damage to cell membranes, DNA and energy metabolism, with differential regulation of ergosterol content, energy metabolism, ion transport and DNA replication-related genes; while the lipopeptide crude extract mainly induced marked cell wall destruction and excessive ROS accumulation, and inhibited cell wall synthesis, CoQ2 and ion transport genes without affecting DNA replication. Both treatments down-regulated Cyp51, DNA repair and CatB genes but up-regulated autophagy-related genes. These findings delineate both divergent and common transcriptional regulatory patterns induced by carvone and the lipopeptide crude extract in A. alternata, providing a theoretical basis for understanding their antifungal mechanisms and supporting the development of novel antifungal agents against this pathogen.
The seismic response simulation of cross-fault tunnels requires a rational representation of the strong ground motion − fault dislocation coupling effect. Paired fling-step ground motion records from both sides of a fault, referred to as across-fault ground motions, can directly capture this coupling effect but remain scarce. Therefore, this study proposes a multi-parameter permanent displacement (MPPD) model for synthesizing fling-step ground motions. By introducing the maximum displacement (Dmax), minimum displacement (Dmin), permanent displacement (Dsite), and period of fling-step pulse (Tf), the model can flexibly characterize fling-step displacement. The MPPD model is first used to simulate and replace the permanent displacement components of typical fling-step records, and the synthesized motions are compared with the original records to verify its effectiveness. It is then applied to near-fault PEER records without permanent displacement to reconstruct their fling-step characteristics, demonstrating its broader applicability. Finally, based on the C0028EW strong earthquake record from the 2022 Menyuan earthquake, across-fault ground motions on both sides of the F5 fault are synthesized and input into a surrounding rock-fault-tunnel numerical model to simulate the seismic damage of the Daliang Tunnel. The results show that severe damage is mainly concentrated in the fault-crossing section and gradually decreases away from the fault plane. The simulated deformation characteristics and failure mode agree well with the observed seismic damage. These findings indicate that the MPPD-based across-fault ground motions can reasonably reflect the strong ground motion − fault dislocation coupling effect, providing an effective input method for seismic damage analysis and design of tunnels crossing active faults.
