Jianwei Zhou

Stropharia rugosoannulata is a valuable medicinal and food fungus with high nutritive value. Freeze-drying addresses the storage and transportation challenges of fresh Stropharia rugosoannulata, expanding its market while preserving its flavor and quality more effectively than other drying methods. This study optimizes the vacuum freeze-drying process for Stropharia rugosoannulata using an orthogonal experiment method. The process parameters were optimized to determine their effects on the quality of the vacuum freeze-dried product, including pre-freezing temperature, pre-freezing time, and freeze-drying time. The optimal conditions were identified as a pre-freezing time of 60 h, a pre-freezing temperature of −80 °C, and a freeze-drying time of 72 h. The optimal product exhibited a bright color close to its natural state, with minimal browning and its natural white color maintained post-drying. During the drying process, the internal structure of the raw materials remained intact. After drying, the finished product retained its natural form, making it suitable for sale on the market. The soluble protein content of the vacuum freeze-dried Stropharia rugosoannulata reached 68 mg/g. Optimizing the freeze-drying process can better preserve the tissue structure and bioactive substances of Stropharia rugosoannulata, providing a reference for high-quality food processing and showing potential for sustainable development.

Resistant starch (RS) has the advantage of reshaping gut microbiota for human metabolism and health, like glycemic control, weight loss, etc. Among them, RS3 prepared from pure starch is green and safe, but it is hard to achieve structural control. Here, we regulate the crystal structure of starch with different chain-length distributions (CLDs) via extrusion at low/high shearing levels. The change in CLDs in extruded starch was obtained, and their effects on the fine structure (Dm, d_Bragg, d_Lorentz, degree of order and double helix, degree of crystal) of RS and its physicochemical properties were investigated by SAXS, FTIR, XRD and ¹³C NMR analyses. The results showed that the RS content under a 250 r/min extrusion condition was the highest at 61.52%. Furthermore, the crystalline system induced by high amylopectin (amylose ≤ 4.78%) and a small amount of amylose (amylose ≥ 27.97%) was favorable for obtaining a high content of RS3-modified products under the extruding environment. The control of the moderate proportion of the A chains (DP 6–12) in the starch matrix was beneficial to the formation of RS.

Starch nanoparticles (SNPs) are generally defined as starch grains smaller than 600–1000 nm produced from a series of physical, chemical, or biologically modified starches. Many studies have reported the preparation and modification of SNPs, which are mostly based on the traditional “top-down” strategy. The preparation process generally has problems with process complexity, long reaction periods, low yield, high energy consumption, poor repeatability, etc. A “bottom-up” strategy, such as an anti-solvent method, is proven to be suitable for the preparation of SNPs, and they are synthesized with small particle size, good repeatability, a low requirement on equipment, simple operation, and great development potential. The surface of raw starch contains a large amount of hydroxyl and has a high degree of hydrophilicity, while SNP is a potential emulsifier for food and non-food applications.