The law of water migration in food drying process was studied by low field NMR

Introduction

Drying is an important part in food, medicine and other materials processing, can prolong the shelf life, keep the original quality and taste of the modern food processing method, drying process in the different phase transformation, spatial distribution of moisture content, migration influence the quality of dry food, taste, nutrition, etc., and the low field nuclear magnetic resonance (NMR) technology is the study of moisture movement, phase state.

Low-Field NMR:

With the development of the magnet technology, nuclear magnetic resonance (NMR) technology to high field (1.5 ~ 3 T) and low (0.2 ~ 0.5 T) two direction, including low field nuclear magnetic resonance (NMR) analysis and imaging (low field nuclear magnetic resonance analysis and imaging, LF – NMR/MRI) device is small in size, good stability, low equipment cost, the resolution requirements not demanding analysis of agricultural products and food safety detection field more and more attention.

The process of moisture transfer is an important step to improve the drying efficiency and quality. Through the method of sampling and weighing and model prediction, the overall moisture content of materials can be generally inferred, but the uniformity of moisture cannot be reflected.

Low-field NMR technology is a powerful means to study the content, state, distribution, migration, diffusion and interaction with other molecules of water molecules, and the characteristics of water are the key factors affecting the quality of food, so the NMR technology using water molecules as probes is widely used in food drying.

Lf-NMR/MRI technology can not only provide the total signal strength of water, but also effectively analyze the composition and distribution of water, and can reflect the drying state of fruit and vegetable materials in three-dimensional space. At present, there are more and more reports on studying the drying process of fruit and vegetable materials by LF-NMR/MRI.

Lf-NMR/MRI can provide the spatial distribution of water changes in free water, non-flowing water and bound water as well as the water activity degree, providing more comprehensive water flow information.