不同干燥方式下调理猪肉干品质变化及其机制

为进一步明确干燥方式对调理猪肉干品质特性的影响及其机制，该研究分别采用热风干燥（Hot Air Drying，HAD）、真空冷冻干燥（Vacuum Freeze Drying，VFD）和对流烤箱干燥（Convection Oven Drying，COD）方式制备调理猪肉干，对干燥特性和剪切力、色泽、水分活度、感官特性、蛋白质体外消化率等品质指标进行测定，并结合水分迁移规律、微观结构、肌肉氧化特性等指标和化学计量学方法，揭示干燥方式对其品质变化的影响。结果表明：干燥方式对调理猪肉干的干燥速率、剪切力、水分活度、色泽、蛋白质体外消化率等均有显著影响（P<0.05），其中COD处理通过不断产生热循环，由内而外加快了样品中水分的迁移和蒸发，使干燥速率提升33%，VFD处理组样品剪切力、水分活度、红度值（29.96 N、0.637和2.49）远低于其他2组，而亮度值、色彩强度值和蛋白质体外消化率较高。此外，低场核磁共振显示结合水是调理猪肉干内部水分的主要组分，而COD样品中结合水的弛豫时间最短，表现为持水力较佳，同时其蛋白质氧化、交联和聚集程度较低，使得体外消化率和感官得分最高，进一步综合偏最小二乘回归（Partial Least Squares Regression，PLSR）结果可知，采用COD处理能有效保证加工后的调理猪肉干具备更好的品质，该结果为调理猪肉干在干燥过程中的品质控制及高效加工提供了理论基础。

Quality changes and its mechanism of conditioned pork jerkys under different drying methods

Abstract: The present study was conducted to clarify the quality changes and the influencing mechanism of conditioned pork jerkys under different drying. Porcine longissimus doris muscles of Chinese hybrid pigs (Doroc×Landrace×Yorkshire, n=8) were collected at 24 h postmortem, and then cut into the slices (4 cm×5 cm×3 mm). Three types of drying were assigned, including Hot Air Drying (HAD), Vacuum Freeze Drying (VFD), and Convection Oven Drying (COD). An in vitro digestibility test was then performed on the dried samples to analyze the drying rate, shear force, color, water activity, consumer sensory comment, and protein. Moreover, the Low-Field Nuclear Magnetic Resonance (LF-NMR) and environmental Scanning Electronic Microscopy (SEM) were applied to characterize the water distribution and microstructure changes of pork jerkys. Furthermore, the Partial Least Squares Regression (PLSR) was employed to reveal the influence of different drying on quality changes in the conditioned pork jerkys. The results showed that the drying presented a significant effect on the drying rate, shear force, water activity, color, and protein digestibility of the conditioned pork jerkys (P<0.05). The shortest drying time was achieved from the COD group, which was much lower than that from another two groups (P<0.05). Specifically, the migration and evaporation rates of water in the cytoplasm and extracellular space of samples were promoted effectively, resulting in a 33% increase in drying rate, compared with other groups. The reason was that the thermal convection in the cavity was generated to form the continuous thermal cycles in the convection oven. In quality indicators, the shear force, water activity, and redness values (29.96 N, 0.637, and 2.49) of samples treated with the VFD were much lower than those with the rest drying (P<0.05), whereas, there were higher values of brightness (L*), color intensity (C*), protein digestibility in the gastric fluid (PGD) and total protein digestibility (PTD) in the VFD group. The SEM images showed that the muscle fibers in the samples were formed a loose and porous structure after treated with the VFD. The microstructure in the VFD samples greatly contributed to the loss of intramuscular water, leading to the explosion of some contact regions of protease. As such, the samples in the VFD group behaved the changes of shear force, water activity, and protein digestibility. Simultaneously, the LF-NMR showed that the bound water was the main component of internal moisture in the conditioned pork jerkys, while the relaxation time of bound water (T2b) in the COD samples was the shortest (P<0.05), resulting in the best water-holding capacity. There was a lower degree of oxidation, cross-linking and aggregation in the protein of the COD samples (P<0.05), whereas, the protein digestibility and sensory scores reached the highest value (P<0.05). The PLSR analysis further confirmed that the application of COD was more suitable for the processing of conditioned pork jerkys, resulting from the lower degree of muscle oxidation and higher value of in vitro digestibility. The finding can provide a strong theoretical basis for the quality control and efficient processing of conditioned pork jerkys during drying.