高乳清蛋白含量营养棒在储藏初期的小分子迁移及对其质地硬化的影响

Migration of small molecules and its effect on texture hardening in high- protein nutritious bars made of WPI during early storage

高蛋白营养棒在储藏过程中的硬化问题,严重限制了此类食品的货架期。引起这类食品硬化的机制十分复杂。本研究采用乳清分离蛋白/水/甘油组成的简化模型体系,通过调整溶剂中水与甘油的比例,改变体系的储藏稳定性,并采用质构仪、激光共聚焦显微镜和低场核磁共振,研究小分子迁移对其储藏初期硬化的影响。结果表明,随着溶剂中甘油比例的逐渐增加,体系储藏初期硬度变化趋势从"基本不变"逐步转变为"迅速硬化"。在乳清蛋白的纯水体系中,蛋白颗粒完全溶解,体系均匀稳定而未发生显著的分子迁移,硬度几乎不变;随着溶剂中甘油比重的增加,体系内逐渐出现未完全水合的蛋白颗粒,小分子物质从体相向颗粒内部迁移,致使分子流动性显著降低,体系微结构发生改变从而导致质地不断硬化。由此推测,小分子迁移是高蛋白营养棒储藏初期迅速硬化的重要因素。

High- protein nutritious bars are suffering from texture hardening, which limits their shelf life. The mechanisms for the hardening of high-protein nutritious bars are rather complicated.In this research, protein bar model systems were prepared with WPI ,water,and glycerol.By adjusting the proportion of water and glycerol in the solvent fraction,a series of models with different storage stability were obtained.Texture analyzer, confocal laser scanning microscope, and low-field nuclear magnetic resonance were used to investigate the relationship between migration of small molecules and texture hardening of the systems in the early stage of storage.it was suggested that the changes in texture of the model system converted from ＂keeping constant＂ to ＂hardening rapidly＂ as the proportion of glycerol in solvent increased. WPI-water system formed a uniform structure without undissolved protein particles.Migration of small molecules or change of microstructure was not observed and the system kept soft during the early stage of storage. However, as the proportion of glycerol was increased, undissolved protein particles could be observed and the small molecules such as glycerol and water migrated into the particles during the storage,which caused texture hardening.In conclusion,the migration of small molecules was a key factor for the rapid hardening of high-protein nutrition bars in the early stage of storage.