NMR study of fresh cut salads: Influence of temperature and storage time on leaf structure and water distribution in escarole

Abstract

Consumption of fresh‐cut vegetables has rapidly increased over the past decades. Among salads, escarole is one of the most popular varieties. Specific packaging limits gas exchange and consequently water loss and bacterial respiration, increasing the shelf life of salads. Although the major cause of quality loss for minimally processed salads is the leaf textural changes, this aspect has rarely been investigated. Therefore, investigating structural changes of leaves during storage is important in order to understand and minimize quality loss of salads. In this study, we focused on the impact of storage duration and temperature on the escarole leaf structure. The complex leaf structure was investigated by relaxation NMR, via transverse relaxation times, which allows the specific description of vacuolar water compartment of the cell. The storage duration (maximum 12 days) and temperatures (4°C, 7°C, 10°C, and 12°C) have been chosen in order to represent the conditions registered in factory. The results showed that the temperature did not have significant impact on the salad structure during the first week. During the second week, changes in the water distribution and changes in the relaxation time T2 have been observed. The changes in transverse relaxation times associated with vacuolar water are related to lost of cell membrane and wall integrity. The NMR results confirmed the effect of storage temperature on the degradation process of the cell before visual detection of the salad leaf degradation. The present study confirmed the sensibility of NMR relaxometry for monitoring water changes in the leaf.

A Global Non-Invasive Methodology for the Phenotyping of Potato Under Water Deficit Conditions using Imaging, Physiological and Molecular Tools

“…As expected, all T 2 distributions measured in the leaves displayed several distinct peaks (data not shown). NMR data were interpreted in line with results obtained for oilseed rape, tobacco and escarole [14][15][16]. In the following, only relaxation peaks associated with the vacuole water pool (either one or two peaks characterized by the longest T 2 relaxation times, depending on leaf age and condition) are presented.…”

“…Equally, other tools have now become available for the in situ characterization of leaf and tuber development and its disturbance under stress. Indeed, the capacity of Nuclear Magnetic Resonance (NMR) relaxometry to evaluate in detail the water distribution associated with the cell and tissue structures of oilseed rape, tobacco and lettuce leaves has been recently demonstrated [14][15][16]. NMR transverse relaxation time, which is particularly sensitive to variations in the water properties of plant tissues, was used to study changes in cell water status and distribution.…”

Impact of storage time and temperature of salad heads on the quality of fresh-cut Cichorium endivia

“…11A), each corresponding to particular water fractions. According to Sorin et al (2019), the two fast relaxing peaks correspond to 1) water inside starch granules and cell walls and 2) chloroplast water. The third and fourth peaks were characterized by relaxation times of approximately 130 and 350 ms and relative signal intensities of 19 and 72 %, respectively.…”

“…These peaks are associated with the vacuolar water of cells with distinct volume distributions (peaks 3 and 4 for small and large vacuoles, respectively, Sorin et al 2019). In the following section, only the relaxation peaks associated with the vacuole water pools are analyzed.…”

Quantitative MRI analysis of structural changes in tomato tissues resulting from dehydration

“…The usefulness of nuclear magnetic resonance (NMR) for obtaining information on water distribution and transfers in plant tissues during physiological or physical processes has been demonstrated in numerous studies. [1][2][3][4][5][6][7][8][9] Indeed, multi-exponential transverse relaxation reflects the behavior of water protons in different environments, allowing it therefore to provide information about subcellular water compartmentation in plant tissues. Although a large number of these studies have been carried out using NMR, there is a growing body of work that adopts a similar approach using magnetic resonance imaging (MRI), [10][11][12][13][14][15][16][17][18] thanks to the methodological advances made in recent years.…”