Applications of NMR Spectroscopy: Volume 1

Atta-ur Rahman,M. Iqbal Choudhary

• Publisher: Bentham Science Publishers
• Year: 2015
• ISBN:
  9781608059621
• Topic: Sciences physiques
• Subtopic: Spectroscopie et analyse du spectre

Applications ofNMR Spectroscopy, Volume 1, originally published by Bentham and now distributed by Elsevier, presents the latest developments in the field of NMR spectroscopy, including the analysis of edible oils and lipid content in foods, the role of NMR spectroscopy in the human metabolomics and the diagnosis of autism-related disorders, protein-protein interactions, and NMR spectroscopy of chiral molecules.

The fully illustrated chapters contain comprehensive references to the recent literature. The applications presented cover a wide range of the field, such as drug development, medical imaging and diagnostics, food science, mining, petrochemical, process control, materials science, and chemical engineering, making this resource a multi-disciplinary reference with broad applications.

The content is ideal for readers who are seeking reviews and updates, as it consolidates scientific articles of a diverse nature into a single volume. Sections are organized based on disciplines, such as food science and medical diagnostics. Each chapter is written by eminent experts in the field.

• Consolidates the latest developments in NMR spectroscopy into a single volume
• Authored and edited by world-leading experts in spectroscopy
• Features comprehensive references to the most recent related literature
• More than 75 illustrations aid in the retention of key concepts

Section A

Food sciences

Chapter 1

Applications of Low-Field Pulsed Nuclear Magnetic Resonance Technique in Lipid and Food

Hong Zhang*; Lu Zhang; Xiaoyang Sun; Shichao Xie Wilmar (Shanghai) Biotechnology Research & Development Center Co., Ltd, Pudong, Shanghai, P. R China
^* Wilmar (Shanghai) Biotechnology Research & Development Center Co., Ltd. Shanghai, P. R. China; Tel: [phone]; Fax: [phone] [email protected]

Abstract

The ratio between liquid and solid portion of lipid can be determined quickly and accurately by low-field pulsed nuclear magnetic resonance (LFP-NMR) instrument. This analytical tool has become one of important techniques to characterize product physical properties especially related to fat melting behavior, mouth feeling, and cooling effect etc. in lipid and food application system. In lipid, it can be used to determine the solid fat content, evaluate the crystallization rate and the compatibility of lipid blends, monitor the enzymatic interesterification degree, and estimate the fat crystal type. As a nondestructive testing, LFP-NMR technique was also applied to analyze the particle size distribution of emulsion, the fat crystallization, and the quality control during food storage. LFP-NMR is not only applied to evaluate the fat crystallization, but also to analyze the crystallinity of sugar. These application progresses of LFP-NMR technique in lipid and food will be summarized in this chapter.

Keywords

Compatibility

crystallinity

crystallization rate

emulsion

foods

interesterification

lipids

low-filed pulsed NMR

particle size distribution

polymorphism

SFC

1 Introduction

Low-field pulsed nuclear magnetic resonance (LFP-NMR) is now a standard analytical technique which has been successfully applied in the study of lipid and food. LFP-NMR also known as time-domain NMR (TD-NMR) started about 40 years ago in the cooperation between Unilever Research (The Netherlands) and Bruker Physik AG. The idea was raised to build a small tabletop TD-NMR analyzer for the solid-to-liquid ratio analysis on fat compositions [1]. Nowadays, its applications do not only cover research and development but also quality and process control in the food supply chain. It has been used throughout all areas of food science and technology to characterize product physical properties especially related to fat melting behavior, mouth feeling, and cooling effect etc. [2-6].

LFP-NMR is a fast and accurate alternative method compared to the destructive conventional chemical methods to determine the content of water and fat simultaneously. The analysis is non-destructive, requires less space and does not require inflammable chemicals and expensive glassware. It is not only a standard technique for the determination of solid fat content (SFC), but also a well-established technique for routine analysis, e.g., determination of oil content of seeds, meals and meat, and determination of humidity in a variety of foodstuffs [7].

In 1960s, Conway first used NMR to analyze whole seed for oil content. Although wide-line NMR has been in use since 1980s for selecting seeds of higher oil content in plant-breeding programme, LFP-NMR provides a faster and more accurate approach for the determination of oil in seeds. Without weighing and oven drying the seeds, NMR takes about 10 sec per analysis. Seeds can subsequently be used in breeding programme [8].

A perfect process analytical method would be based on a robust, non-invasive and easy to handle customized technique operating in real-time. The ideal instrumentation comes without any need for calibration, is an absolute method, has a professional support, and is compliant to increasing regulatory requirements. A trend can be observed towards such an all-in-one device suitable for every purpose in NMR. Almost all types of food samples could be analyzed in the case the water content is minor (typically below 15%) [9]. However, samples with the high amounts of water/free water cannot be treated this way. The NMR signal from water will interfere with the oil signal. This is because the relaxation times of free water and oil are rather similar and chemical shift dispersion is obscured in LFP-NMR by the magnets inhomogeneity. Moreover, the selectivity in commonly used LFP-NMR pulse sequences is too small to guarantee a clear separation of signals. The classic approach was to pre-dry the samples either for example by an oven, chemical reagents like CuSO4 or via infrared or microwave drying processes, rendering the application a two-step approach. Under these circumstances, samples (like olives, sausages, fish, and meat) need to be pre-dried to remove free water.

Most common LFP-NMR applications are based on very simple NMR pulse sequences, like the free induction decay (FID) or the Hahn-echo acquisition. A Hahn-echo sequence is adapted to determine the total oil and moisture conte...