食品中核磁共振状态图的应用(英文)

食品中质量感官指标和货架期与它的理化特性有关,水是食品原料中重要组成部分,它的含量与食品的理化特性有关,并在其中扮演着重要角色。“玻璃态转化” 的概念是在研究食品原料和产品理化特性的聚合物理论时提出的。食品玻璃态转化状态图通常用来描述水含量与食品理化特性的关系。状态图能有效地反映在不同温度和水分含量下的物质的理化特性。本文提出一个新的观念-“核磁共振状态图” 概念,核磁共振状态图是指核磁共振弛豫时间(通常指自旋-自旋弛豫时间或T2)和温度之间的曲线图,它放映食品的核磁共振弛豫现象与食品的理化特性关系。我们在研究时发现这条曲线图与物质的许多理化特性有着良好的相关性。利用核磁共振状态图可以在以下方面得到应用:(1)通过分析产品的成分,确定产品变化的规律;(2)预测产品的理化性质的变化(质地、粘性、结块、水分和油脂的迁移等)的趋势,营养成分降解和微生物代谢与食品中水分活度之间的关系;(3)结合核磁共振成像技术能很好地帮助理解水分(特别游离水分)对食品的质量与安全的影响。本文描述了核磁共振的基本原理、核磁共振弛豫现象的特征与食品特性的关系,并为研究食品体系提供新的研究方法和途径。

NMR State Diagram Concept of Food Products

The sensory quality and shelf stability of food products are closely related to their physiochemical properties. The glass transition concept borrowed from polymer science has been applied to the study of physiochemical properties of food materials and products. Water is seen as a plasticizer of solids, and therefore plays a key role in the characteristics of food materials. A state diagram based on the glass transition concept usually describes the relationship between water content (or solid content) and temperature-dependence of physiochemical properties (e.g., phases). State diagrams are useful in characterizing material behavior at various temperatures and water contents.The present paper demonstrates a new concept, called "NMR State Diagram", which is based on the relationships between NMR (nuclear magnetic resonance) relaxation and temperature dependence of physiochemical properties. An NMR state diagram is a curve of NMR relaxation time (usually spin-spin relaxation time or T2) against temperature. Our studies have shown excellent correlations between curves characteristics and many physiochemical properties. The potential applications of this NMR State Diagram concept may include: (1) ingredients screening, useful for product formula development, (2) prediction of physiochemical changes (texture, viscosity, caking, water and fat migration, etc), chemical degradation of nutrients and microbiological activity, which are associated with mobility of water and polymers, (3) Combined with MRI (magnetic resonance imaging) techniques, the concept would greatly improve our understanding of quality and safety of food products, especially intermediate moist foods (IMF). In this conceptual paper, the basic principles of NMR, theoretical aspects of NMR relaxation and its relations to food properties, methodology, and data from real food systems are presented.