Low-field nuclear magnetic resonance (LF-NMR) study of water migration during carrot drying

Experimental Objective

 

To investigate changes in water states of carrots during infrared drying under different conditions using low-field nuclear magnetic resonance (LF-NMR) technology.

Experimental Materials

 

Carrot samples dried for different durations under various conditions.

Experimental Instrument

 

PQ001 low-field NMR analyser with a 25mm coil diameter, magnet temperature set to 32℃.

Sample Preparation

 

A total of 15 samples with different treatments or drying conditions, as shown in Table 1, were placed in infrared drying equipment for varied durations. After drying, samples were removed, weighed, and placed into the 25mm probe coil for T2 relaxation analysis.

Experimental Parameters

 

T2 measurement: TR = 3000ms, TE = 0.6ms, NECH = 8000.

Experimental Method

 

T2 measurement: Signals were acquired using NuMag LF-NMR analysis software with the CPMG sequence, followed by inversion analysis.

Analysis and Results

 

T2 Relaxation Analysis of Carrots with Different Slice Thicknesses

T2 relaxation spectra of carrot samples dried for different durations are shown below:

Figure 1: T2 relaxation spectra of carrots dried for different durations

As seen in Figure 1, 3–4 peaks appear during drying. These peaks are labelled T21, T22, T23, and T24 according to their emergence order. Peaks T21 and T22 (0.1–10ms) represent bound water, T23 (10–100ms) represents less mobile water, and T24 (>100ms) represents free water. In the early drying stage, three peaks are observed; as drying continues, four peaks emerge. Changes in the number of peaks likely reflect deepening drying, structural changes within the sample, and migration of some bound water, resulting in two distinct bound water peaks.

Conclusion

 

Slice thickness, material thickness, drying temperature, radiation distance, and power density all influence the migration and transformation of water states during carrot drying to varying degrees. Detailed changes are documented in the full experimental report.