Effects of soluble soybean polysaccharide and lard on the re-steaming quality of frozen steamed stuffed bun dough

Steamed stuffed buns are fermented wheat flour products. However, they have often suffered from quality deterioration of the dough during freezing, frozen storage, and subsequent re-steaming. The quality defects are also characterized by the texture hardening, reduced elasticity, surface cracking, and sensory acceptance. Mechanical damage caused by ice crystal growth can also weaken the gluten network, leading to the retrogradation of starch. This study aims to systematically investigate the synergistic regulation of soluble soybean polysaccharides (SSPS) and lard (LD) on the quality improvement of frozen and re-steamed stuffed bun dough. Three types of steamed buns were selected as the typical fillings—pork (representing a high-fat and high-protein system), cabbage and mushroom (representing a high-moisture and high-fiber system), as well as red bean paste (representing a high-sugar and high-starch system). The applicability of the additives was evaluated in complex food matrices. A multi-dimensional analytical approach was employed to characterize the physicochemical properties and microstructural evolution of the dough. The textural characteristics were quantified using a Texture Analyzer, while the water mobility and distribution were monitored via Low-Field Nuclear Magnetic Resonance (LF-NMR). Furthermore, the protein secondary structures and starch crystallinity were identified using Fourier Transform Infrared Spectroscopy (FTIR) and X-ray Diffraction (XRD), respectively. The microscopic morphology of the dough was visualized using Scanning Electron Microscopy (SEM). The results demonstrated that the combined addition of SSPS and LD significantly improved the eating quality of the re-steamed stuffed bun dough, compared with the control or single-addition groups. Texture profile analysis indicated that the hardness and chewiness were reduced significantly, whereas the elasticity and resilience were enhanced (p<0.05). LF-NMR analysis revealed that the additives significantly altered the state of water within the dough matrix. Specifically, the bound water content in pork, cabbage, and mushroom, and red bean paste bun doughs increased by 29.14%, 26.23%, and 43.97%, respectively. The synergistic effect of SSPS and LD effectively inhibited water migration to reduce the proportion of free water, thereby mitigating the mechanical damage to the gluten network caused by ice crystallization. At the molecular level, chemical analysis showed that the SSPS-LD treatment promoted the conversion of free sulfhydryl groups (-SH) into disulfide bonds (S-S), significantly increasing the disulfide bond content. The additives facilitated the polymerization of gluten proteins, thus enhancing the stability of the network through covalent cross-linking. FTIR spectra further indicated that the gluten secondary structure was represented by a transition from disordered random coils to ordered structures, specifically an increase in the proportion of β-sheets. XRD patterns confirmed that while the crystal pattern remained unchanged, the crystallinity of the starch was significantly reduced in the SSPS-LD group, indicating an effective inhibition of starch retrogradation. Microstructural observations via SEM verified that the SSPS-LD group possessed a denser, more continuous, and uniform gluten network, with significantly improved pore distribution, compared with the coarse and porous structure of the control group. In conclusion, the SSPS primarily enhanced the water retention to form the strong hydrogen bonding networks with gluten and starch. While the LD functioned as a lubricant to interact with amylose for the lipid-starch complexes, which hindered the starch recrystallization. The synergistic effect of SSPS and LD was realized to stabilize the overall network structure via combined covalent and non-covalent cross-linking. These findings can provide a solid theoretical basis for polysaccharide-lipid interactions to reduce the quality deterioration in functional ingredients and wheat flour products of complex food systems.