Variable Temperature Nuclear Magnetic Resonance and Magnetic

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Variable Temperature Nuclear Magnetic Resonance and Magnetic Resonance Imaging System as a Novel Technique for In Situ Monitoring Food Phase Transition Yukun Song, Shasha Cheng, Huihui Wang, Bei-Wei Zhu, Dayong Zhou, Peiqiang Yang, and Mingqian Tan J. Agric. Food Chem., Just Accepted Manuscript • DOI: 10.1021/acs.jafc.7b04334 • Publication Date (Web): 02 Jan 2018 Downloaded from http://pubs.acs.org on January 3, 2018

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Journal of Agricultural and Food Chemistry

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Variable Temperature Nuclear Magnetic Resonance and Magnetic Resonance

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Imaging System as a Novel Technique for In Situ Monitoring of Food Phase

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Transition

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Yukun Song, †, ‡ Shasha Cheng,†, ‡ Huihui Wang,†, ‡ Bei-Wei Zhu,†, ‡ Dayong Zhou,†, ‡

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Peiqiang Yang§ and Mingqian Tan*,†, ‡

7 8

†

9

Seafood, Dalian Polytechnic University, Qinggongyuan1, Ganjingzi District, Dalian

School of Food Science and Technology, National Engineering Research Center of

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116034, Liaoning, China

11

‡

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Dalian116034, Liaoning, China

13

§

Engineering Research Center of Seafood of Ministry of Education of China,

Suzhou Niumag Analytical Instrument Co., Suzhou 215163, Jiangsu, China

14 15

*Corresponding

author

(Tel&

Fax:

+86-411-86318657,

16

[email protected], ORCID: 0000000275350035).

17 18 19 20 21 22 1

ACS Paragon Plus Environment

E-mail:

M.

Tan,


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ABSTRACT:

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A nuclear magnetic resonance (NMR) and magnetic resonance imaging (MRI)

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system with a 45 mm variable temperature (VT) sample probe (VT-NMR-MRI) was

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developed as an innovative technique for in situ monitoring of food phase transition.

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The system was designed to allow for dual deployment either in a freezing (-37 oC) or

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a high temperature (150

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VT-NMR-MRI system is that it is able to measure the water states simultaneously in

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situ during food processing. The performance of the VT-NMR-MRI system was

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evaluated by measuring the phase transition for salmon flesh and hen egg samples.

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The NMR relaxometry results demonstrated that the freezing point of salmon flesh

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was -8.08 oC, and the salmon flesh denaturation temperature was 42.16 oC. The

34

protein denaturation of egg was 70.61 oC and the protein denaturation occurred at

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24.12 min. Meanwhile, the use of MRI in phase transition of food was also

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investigated to gain internal structural information. All these results showed that the

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VT-NMR-MRI system provided an effective means for in situ monitoring of phase

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transition in food processing.

o

C). The major breakthrough of the developed

39 40 41

Key words: VT-NMR-MRI, phase transitions, freezing point, denaturation

42

temperature

43 44 2


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INTRODUCTION

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Nuclear magnetic resonance (NMR) is based on the measurement of resonant

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radiofrequency absorption by non-zero nuclear spins in the presence of an external

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static magnetic, and magnetic resonance imaging (MRI) is performed with a NMR

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instrument equipped with magnetic gradient coils to spatially gather the data，which is

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able to provide internal structure information without any disruption to the sample.1,2

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The non-destructive and structural analytical ability of NMR and MRI makes them

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powerful analytical tools for a wide range of applications to monitor water mobility,

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such

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fermentation,13,14 drying,15,16 and freeze-thaw17,18 in food processing. However, the

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NMR or MRI measurements of food samples are usually carried out after food

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processing at different temperatures or processing environment. Thus, it can’t reflect

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the real water state of food sample in situ because of the high dependence on tissue

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state, temperature and humidity for NMR or MRI signal.19 Therefore, it is highly

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desirable to monitor the relaxation time or structure changes simultaneously when

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food samples are being processed like heating, drying or cooling, among others.

as

cooking,3,4

storage,5-7

water

absorption,8

salting,9,10

baking,11,12

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In recent years, attempts have been to explore the in situ monitoring of water

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dynamics in food processing using the NMR instrument equipped with a variable

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temperature (VT) sample probe. García et al.14 analyzed changes of water distribution

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and mobility in sausages at different manufacturing times using a Maran benchtop

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pulsed NMR analyzer (Resonance Instruments, Witney, UK) equipped with an 18 mm

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VT sample probe. Engelsen et al.20 studied the kinetics of the bread baking process by 3



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a Maran benchtop pulsed NMR analyser (Resonance Instruments) with an 18 mm VT

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sample probe controlled by a continuous flow (500 L/h) of dried air with an

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operational range from -50 to 150 oC. Greiff et al.21 used a Bruker minispec mq 20

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(Bruker Optik GmbH, Ettlingen, Germany) NMR possessing a 10 mm VT sample

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probe to investigate the physicochemical parameters and measure sodium and

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potassium contents in low-salt brines and fish. Kovrlija et al.22 studied starch

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transformation using a time domain Bruker spectrometer (The Minispec; Bruker SA,

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F-67166, Wissembourg, Germany) with 10 mm diameter NMR tubes regulated by a

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VT unit (BVT3000). However, the drawbacks of these instrument are that the VT

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sample probe is very small (diameter less than 18 mm), so that the size of testing

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sample is limited in obtaining information about whole food sample. Moreover,

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VT-NMR-MRI was rarely studied for simultaneous imaging of food internal structure.

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The development of a VT-NMR-MRI instrument with larger size VT sample probe

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remains to be a challenging task for food processing.

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Food processing may involve phase transition process, such as protein

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denaturation, starch gelatinization, and liquid water into ice (freezing point), which

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plays an important role in understanding the mechanism of food quality changes.

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Phase transition can significantly affect the structure, enzyme activity and dynamics

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of biopolymers through ligand binding, conformation variation, crystal formation and

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alike.23-25 The final food quality (texture, color, water holding capability, etc) is highly

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relied upon the degree of phase transition. Therefore, it is imperative to in situ

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monitor the phase transition during food processing. There are many methods 4


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available for studying the phase transitions, such as differential scanning calorimetry

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(DSC),26 Fourier transform (FT)-Raman spectroscopy,27 dynamic thermal analysis

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(DTA), dynamic mechanical thermal analysis (MTA) and dynamic mechanical

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analysis (DMA).28 However, DSC suffers from sample size limitations, and

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FT-Raman spectroscopy only reflects changes of sample surface. DTA, MTA and

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DMA are all sample destructive methods. From this point of view, VT-NMR-MRI

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may provide more information in dissecting of the food phase transition in a fast and

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non-destructive manner.

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In this study, a VT-NMR-MRI instrument equipped with a 45 mm VT sample

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probe was developed to in situ study the water dynamics in food processing (heating

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and cooling). The sample probe temperature was operated in the range of -37 to 150

100

o

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The temperature of the sample probe was measured at the airflow rate of 47 to 240

102

L/min to investigate the performance of the instrument. The in situ monitoring of

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phase transition of fish and whole hen egg was investigated with the developed

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VT-NMR-MRI instrument. The freezing point and denaturation temperature of

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salmon flesh, as well as denaturation temperature and time of whole hen eggs were

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evaluated to demonstrate its application in phase transition monitoring during food

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processing.

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EXPERIMENTAL

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INSTRUMENT

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C by a temperature control unit via a continuous dried airflow from 0 to 240 L/min.

The schematic diagram of VT-NMR-MRI instrument, which included a VT 5



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system, key NMR and MRI scanner (Niumag Analytical Instrument Corporation,

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Suzhou, China), is shown in Figure 1. The VT system comprises of a dry air generator

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unit (Shandong Hongrun Air Compressor Technical Co., Ltd, Shandong, China), a

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refrigerating unit (Hangzhou Xuezhongtan Technical Co., Ltd, Zhejiang, China),

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electrical resistance heater unit and a temperature control unit (Figure 1 and Figure

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S1). The dry air generator unit is consisted of an air compressor with the ability to

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provide a maximum of 270 L min-1 compressed air, and a dryer filling with 13 X

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molecular sieves to remove the moisture avoiding its frozen in refrigerating unit. The

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dry air can be cooled to a minimum temperature of -60 oC by the refrigerating unit,

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and heated up to 200 oC by the electrical resistance heater unit. A three-way valve was

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used to allow delivering the dry air to the refrigerating unit. The dry air passes

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through the refrigerating unit when the temperature is set below the 32 oC of

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permanent magnet. The regulation of the air temperature is controlled by a

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temperature sensor. Finally, the refrigerated or heated air is transported to the sample

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probe through a polyethylene pipe wrapped in a 15 mm thick heat insulation foam

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allowing the temperature of sample probe to vary from -37 to 150 oC.

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The key NMR scanner was equipped with a 60 mm sample probe (Figure S2) at

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32 oC adopts a magnetic field strength of 0.5 T corresponding to a proton resonance

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frequency of 21.16 MHz. It included an industrial control computer (ICC),

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temperature control (TC) unit 1 and a radiofrequency (RF) unit. As shown by the

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schematic

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polytetrafluoroethylene (PTFE) tube, 45 mm in diameter, was mounted as sample

diagram

in

Figure

1

(b)

and

Figure

6


S2,

a

7.5-mm

thick

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probe. PTFE was selected because of its excellent thermal insulation performance

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without proton signal interference for NMR measurement. The PTFE tube is able to

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maintain the temperature of permanent magnet in NMR at 32 ± 0.02 oC when the

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temperature of sample probe changed from -37 to 150 oC. The MRI function is

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performed by adding a gradient unit with NMR instrument. (Figure 1)

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MATERIALS AND METHODS

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Materials. Fresh Atlantic salmon (Salmo salar L.) flesh and hen eggs

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were purchased from a local market at Dalian, China. The salmon flesh was cut

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into 20×20×20 mm (12.61 ± 2.18 g) size and each egg was about 43.50 ±1.35 g.

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The VT-NMR-MRI measurements were carried out immediately after

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purchasing the test samples.

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Determination of freezing point and thermally-induced denaturation

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temperature of salmon flesh. The freezing point and thermally-induced denaturation

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temperatures of salmon flesh were measured by the developed VT-NMR-MRI unit by

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monitoring the water dynamics in the temperature range of -20 to 10 oC and 30 to 60

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o

150

Aorun Microwave Technology Ltd., Nanjing China) was used to record the core

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temperature of salmon flesh. The sample was frozen or heated in the sample probe

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with an airflow rate of 75.0 ± 5 L min-1, and NMR relaxation data were collected

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every 2 oC interval. For comparison, the freezing point and denaturation temperature

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of salmon flesh were also measured by DSC (Q20, TA Instruments, New Castle, DE,

C, respectively. A single channel fiber-optic temperature measuring system (ORW-Y,

7



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USA) using deionized water as a reference. For determination of freezing point,

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samples were equilibrated for 10 min at 10 oC, and cooled to -20 oC at 2 oC /min. For

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denaturation temperature determination, samples were equilibrated for 20 min at 20

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o

C, followed by ramping up to 60 oC at 1oC /min.

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Transversal (T2) relaxation was measured by the Carr-Purcell-Meiboom-Gill

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(CPMG) pulse sequence with a time delay between 90 and 180º pulses (τ-value) of

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300 µs. Data from 1000 echoes were acquired from 8 scan repetitions. The repetition

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time between two succeeding scans was set to 3000 ms. Single-exponential fitting of

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CPMG decay curves were performed using MultiExp Inv analysis software.

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Single-exponential fitting analysis was performed on the relaxation data in the

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software of simultaneous iterative reconstruction technique (SIRT) algorithm.

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T1 weighted images of the salmon flesh were obtained by a spin-echo (SE)

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sequence. The following scanning protocols were used: slice width, 5 mm; average,

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8; T1 weighted image echo time (TE) of 14 ms and repetition time (TR) of 100 ms.

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Signal intensity was measured and analyzed using a software Osirix (OsiriX Life

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v.7.0.4, Geneva, Switzerland).

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Determination of denaturation temperature and time for hen egg. The

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whole hen egg was placed in the sample probe and heated by hot air from 55 to

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90 oC with a step of 5 oC for 30 min. The air flow rate was 75.0 ± 5 L min-1.

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The spin-spin relaxation time (T2) was measured at every temperature rise of 5

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o

C. As for the denaturation time measurement, the egg was heated at

8


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denaturation temperature. The NMR data were collected by the VT-NMR-MRI

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every 5 min for the first 30 min, and every 10 min for the last 30 min.

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The NMR and MRI parameters of egg were similar to those of the salmon flesh

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with a slight modification with the echoes of 5000, and the repetition time 3000 ms

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during spin-spin relaxation time measurements. The TE of 14 ms and TR of 600 ms

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were used for T1 weighted image. An average T2-relaxation time can be defined as

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T2m.29 = ∑ , ,

183 184

∑ = 1

The fractions di and T2,i were obtained from the CPMG signals by a

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multi-exponential curve fitting.

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RESULTS AND DISCUSSION

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Performance testing of VT-NMR-MRI instrument. Larger varying

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temperature interval enables to study the proton states and mobility in more practical

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food processing industry, particularly in freezing, drying, heating and baking, with

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non-destructive NMR technique in a fast manner. The low-temperature and

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high-temperature modes of VT-NMR-MRI were designed. To assess the control

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temperature ability of the developed instrument, the stability of instrument at the

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extreme temperature of the sample probe was investigated at an air pressure in the

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range of 0.05-0.40 Mpa, corresponding with an airflow rate varying from 47 to 240

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L/min.

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The temperature is highly dependent on the airflow rate as shown in Table 1. In

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low-temperature mode, the sample probe temperature changed from -37.0 to -22.5 oC 9



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when the airflow rate varied from 47 to 240 L/min with a constant fluctuation

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temperature of 0.02 oC. The minimum temperature was -37.0 oC when the airflow was

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210 L/min. The temperature did not decrease with increasing pressure because of

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larger volume airflow leading to insufficient cooling by the refrigerator. Therefore, the

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cooling range of the VT-NMR-MRI instrument was measured to be in the range of

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-37.0 oC to ambient temperature. In high-temperature mode, the temperature was kept

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at 150 oC when the airflow rate was in the range of 47 to 130 L/min. The temperature

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decreased when the airflow rate increased continuously, and 47 L/min was sufficient

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to raise temperature to 150 oC. Table S1 in the supplementary material lists the

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comparison of the performance with some typical apparatuses with this work. The

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VT-NMR-MRI instrument coupling of NMR and MRI with a relatively large sample

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probe is useful to obtain more information about the testing food samples.

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(Table 1)

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Determination of freezing point of salmon flesh. The protein denaturation of

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salmon is a representative example during food processing. Usually the salmon flesh

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was frozen during storage, and cooked at relative high temperature when eaten. The

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salmon fish was selected as a typical food product to evaluate the performance of the

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VT-NMR-MRI system in this study. The freezing point is associated with a

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considerable change in molecular mobility and relaxation time in amorphous food

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solids. Fig. 2a shows the T2 relaxation spectral change of salmon flesh sample in

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freezing process of -20 to 10 oC. Significant change of different water populations

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was identified. Only one population T22 was present above 0 oC, however, T21 and T23 10


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were observed below -2 and -4 oC, respectively. The reason is probably that the

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outside of the salmon flesh was frozen first, and then the inside step by step. The

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water mobility dramatically decreased, resulting in the conversion from T22 to T21 and

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T23. The water distribution and transformation played an important role in reflecting

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states of the salmon flesh samples during the freezing process. The change of different

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water populations was identified as displayed in Fig. 2b, which further shows the

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presence of the water population T21 and T23 at temperature below -2 oC. By

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single-exponential fitting of the transverse relaxation time, T2 relaxation time was

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obtained as a function of temperature shown in Fig. 2c. The T2 relaxation did not

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change above 0 oC, but decreased significantly below 0 oC. The slope curve of the T2

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relaxation in the range of -8 to 0 ºC exhibited an intersection at -8.08 oC with that of

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the T2 relaxation time within -20 to -10 ºC. The inflection point where the two lines

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meet was regarded as the corresponding state transitions temperature.30 Additionally,

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DSC analysis was carried out to confirm the inflection point obtained from the

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relaxation time curve in evaluating the state transition temperature. Fig. 2d shows the

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DSC thermogram of salmon flesh; a single exothermic peak was observed at around

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-8.27 oC which was quite close to -8.08 oC assessed by the VT-NMR-MRI. It is

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noteworthy that DSC determines the enthalpy and temperature changes between a

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sample and reference during the phase and state transitions of food systems.31 The

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freezing point occurs in a certain temperature range, although it is often referred to as

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a single temperature value.32 Therefore, the VT-NMR-MRI equipment is useful in

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determining the freezing point of food samples. Besides, the VT-NMR-MRI in this 11



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work can measure the sample with a diameter of about 45 and 60 mm height (~ 100 g),

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but the DSC only can determine the state transition temperature for food sample with

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a weight of about 5~ 500 mg. Therefore, the value determined by VT-NMR-MRI is

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more versatile and representative for the actual practical industrial applications.

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Furthermore, T1 weighted image was conducted every 2 oC during the entire

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freezing process from -20 to 10 oC to provide internal structural changes of the

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freezing salmon flesh samples. As shown in Figure 2e, the pseudo-color images

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clearly show the proton signal changes during the whole freezing process, in which

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the difference between outside and inside of salmon flesh was visualized. Different

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colors represent different H proton density, and red color means high H proton density

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while blue color means low H proton density. In general, the signals of the MRI

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mainly originate from the water or fat in salmon flesh. The T1 weighted image of

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salmon flesh showed no significant difference above 0 ºC. A gradual change of the

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sample below 0 ºC was observed which indicated a continuous bondage of water

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freedom, and there was only stripe-like signal in the frozen sample below -6 ºC which

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was assigned to fat. This result was consistent with that of the NMR analysis. MRI is

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a good method to detect the internal structure and water distribution in salmon flesh

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samples in situ in a rapid, and non-destructive manner.

260

(Figure 2.)

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The most frequently used methods to measure the freezing point of foods are the

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cooling curve method33 and DSC34. However, the small sample size (5-500 mg) in

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DSC analysis is difficult to obtain the representative information for the whole 12


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sample.35 Both of these two methods can’t provide the water state and distribution

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during freezing point measurements. The VT-NMR-MRI not only can accurately

266

measure a representative sample, but also detect the internal structure and water

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distribution by MRI.

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Determination of heat denaturation temperature for salmon flesh. The

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transverse relaxation spectra with the heating temperature show the denaturation

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process of salmon flesh (Fig. 3a). It can be seen that there were two peaks of T21 and

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T22, and no obvious change for relaxation time T21 during the whole heating process

272

(Fig. 3b). The T22 decreased dramatically from 1217.38 to 240.94 ms within 40 oC,

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and then tended to remain constant. The single-exponential fitting of the transverse

274

relaxation times (T2) as a function of heating time is shown in Fig 3c. The T2 curve

275

displayed a decreased trend below 34 oC, and then increased dramatically from 34 to

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42 oC, followed by a significant decrease in the range of 42 to 60 oC. The transition

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position representing the denaturation was observed at 42.16 oC. Fig. 3d shows the

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DSC thermogram of salmon flesh during the heating process. A prominent peak

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around 41.53 oC was observed. The only endothermic peak was due to the

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denaturation of the salmon flesh upon heating, which was correlated to the contraction

281

and the increase of elasticity of salmon flesh. That is to say, the heat transfer

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temperature measured by VT-NMR-MRI was very close to that of DSC. T1 weighted

283

image was conducted every 2 oC during the whole heating process from 30 to 60 oC.

284

As shown in Fig. 3e, unfortunately, the pseudo-color images only show the proton

285

signal and not any change during the entire heating process. This is probably because 13



286

the water dynamics in salmon flesh changed slightly which was not identified by the

287

T1 weighted images.

288

(Figure 3.)

289

Determination of hen egg denaturation temperature. The protein

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denaturation is a process in which the advanced structure of protein

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disintegrates while its primary sequence remains unchanged by heating

292

treatment. Taking hen eggs as example, the multi-exponential fitting of the

293

transverse relaxation spectra along with the heating temperature are shown in

294

Fig. 4a. Three peaks were observed before heating for 70 min, and they

295

changed to two peaks from 70 to 75 min, finally merged into a single peak. As

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specified by Fig. 4b, there are three water populations, T21, T22 and T23, for egg

297

samples at 55 oC. T21 was the shortest fraction with a relaxation time of

298

approximately 1.59 ms at 55 oC, which didn’t change until 70 oC. It increased

299

dramatically from 2.38 to 15.34 ms when the temperature reached 75 oC, and

300

then disappeared. T22 was the middle fraction with a relaxation time of

301

approximately 18.04 ms, which increased dramatically from 12.93 to 65.03 ms

302

when the temperature was 75 oC, and then changed slightly. The last fraction

303

T23 decreased dramatically from 333.13 to 98.85 ms within 70 oC, and then was

304

merged into T22.The denaturation involves only the modification of the native

305

structure of a protein without cleavage of peptide bonds within the amino acid

306

sequence.29 An average T2-relaxation time (T2m) at different heating time was

307

used to measure the denaturation of egg samples (Fig. 4c). A clear inflection 14


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point was observed at 70.61 oC, which was assigned to the denaturation

309

temperature of whole egg.

310

As show in Fig. 4d, the photographs of eggs heated at different

311

temperatures clearly showed that the solidification of egg white and yolk

312

occurred at approximately 65 and 70 oC, respectively. This further demonstrates

313

that the analysis of protein denaturation by non-destructive VT-NMR-MRI is

314

valid. MRI enabled visualization of the inter structure of egg to reflect the

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protein state in a non-destructive manner during heating. The T1 weighted

316

pseudo-color images in Fig. 4e show that the contrast enhancement varied for

317

eggs upon heating process at different temperatures. It can be noted that the red

318

color of egg yolk at 70 oC changed significantly when compared with those

319

below 65 oC, demonstrating that the gelation or denaturation of egg protein had

320

occurred. This is probably because the mobility of protons was reduced when

321

the protein denatured, resulting in an increased contrast enhancement. By using

322

MRI technique, the denaturation of egg protein can be monitored directly

323

without any sample destruction occurring. From this point, MRI is considered

324

as a supplementary technique in assessment of egg protein denaturation. The

325

quantitative results in Fig. 4f further confirm the MRI intensity changes at

326

different temperatures. The relative intensity of egg yolk increased dramatically

327

below 70 oC, and then increased slightly, indicating a significant protein

328

denaturation at the first 70 oC. The intensity of egg white and whole egg

329

increased continuously during heating, indicating reduced water mobility due to 15



330

protein denaturation. The previous research was focussed on the analysis of egg

331

white or yolk denaturation by DSC,36 but the whole eggs gelation upon heating

332

has rarely been reported because of the limited size of its sample probe. Herein,

333

the VT-NMR-MRI can evaluate the whole egg thermal behavior in terms of

334

molecular interaction during its denaturation transition.

335

(Figure 4.)

336

Hen egg protein denaturation time measurement. Protein denaturation

337

occurs as soon as the temperature reaches a certain point which may take time

338

for the initial conversion to completion. The relaxation time changes can give a

339

clue for egg protein denaturation time by VT-NMR-MRI technique. Fig. 5a

340

shows the transverse relaxation spectra at 70.61 oC for different time periods. It

341

can be noted that there were three proton populations, T21, T22 and T23. No

342

obvious change for relaxation time T21 during 60 min heating process was

343

found, and T22 didn’t change within about 15 min, and then increased

344

significantly around 15-20 min (Fig. 5b). The T23 didn’t change within 10 min,

345

and then decreased from 636.38 to 460.59 ms, disappeared after heating for 15

346

min. The average relaxation timeT2m at each time point was plotted for the egg

347

samples (Fig. 5c). T2m didn’t change within the first 10 min, and then decreased

348

dramatically from 10 to 25 min, followed by a gradual decrease until 60 min.

349

The intersection point 24.12 min of the two fitting lines was calculated through

350

linear regression, and the corresponding temperature was assigned as the

351

denaturation time. To confirm the results, the photographs of eggs heated at 16


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different times are displayed in Fig. 5d, which clearly shows that the

353

solidification process of egg white and egg yolk had occurred around 20 - 25

354

min. This demonstrates that the analysis of protein denaturation by

355

non-destructive VT-NMR-MRI is acceptable.

356

(figure 5.)

357

Furthermore, the internal structure of egg was analyzed by MRI to reflect

358

the protein denaturation in a non-destructive manner during different heating.

359

The T1 weighted pseudo-color images in Fig. 5e show that the contrast

360

enhancement increased significantly around 20 - 25min, demonstrating that the

361

gelation or denaturation of egg protein had occurred. This is possibly because

362

the mobility of protons was reduced when the protein denatured, resulting in an

363

increased contrast enhancement. By using the MRI technique, the denaturation

364

of egg protein can be monitored directly without sample destruction. From this

365

point, MRI is considered as a supplementary technique in assessment of egg

366

protein denaturation. The quantitative results in Fig. 5f further confirmed the

367

MRI intensity change at different times.

368

In summary, A VT-NMR-MRI equipment with a 45 mm variable temperature

369

radiofrequency sample probe was developed. The sample probe temperature is

370

controlled by a continuous flow of dried air variable at -37 to 150 oC. The

371

VT-NMR-MRI unit was tested for monitoring phase transitions during food

372

processing. The freezing point of salmon flesh was -8.08

373

denaturation temperature was 42.16 oC, consistent with those using the DSC method. 17


o

C, and its heat


Page 18 of 31

374

Using the whole egg as a model, the protein denaturation temperature was

375

approximately 70.61 oC after heating for about 24.12 min. All results showed that

376

the phase transitions of protein food like fish and egg can be monitored by the

377

VT-NMR-MRI, and the developed method may have potential for assessing other

378

phase transitions during food processing.

379 380

AUTHOR INFORMATION

381

Corresponding Author

382

*(M. Tan) Phone & Fax: +86-0411-86318657. E-mail: [email protected].

383

Funding

384

This work was supported by the National Key Research and Development

385

Program of China (2017YFD0400103, 2015YFD0400404) and the National Key

386

Scientific

387

(2013YQ17046307). We thank Prof. F. Shahidi for correcting and spelling grammar

388

mistakes.

389

Notes

390

The authors declare no competing financial interest.

391

REFERENCES

392

(1) Kirtil, E.; Oztop, M. H. 1H nuclear magnetic resonance relaxometry and magnetic

393

resonance imaging and applications in food science and processing. Food Eng.

394

Rev. 2016, 8, 1-22.

395

Instrument

and

Equipment

Development

Project

of

China

(2) Schmidt, S. J.; Sun, X.; Litchfield, J. B. Applications of magnetic resonance 18


Page 19 of 31


396 397 398

imaging in food science. Rev. Food Sci.1996, 36, 357-385. (3) Zhang, L.; McCarthy, M. J. NMR study of hydration of navy bean during cooking. LWT - Food Sci. Technol. 2013, 53, 402-408.

399

(4) Bertram, H. C.; Whittaker, A. K.; Shorthose, W. R.; Andersen, H. J.; Karlsson, A.

400

H. Water characteristics in cooked beef as influenced by ageing and high-pressure

401

treatment - an NMR micro imaging study. Meat Sci.2004, 66, 301-306.

402

(5) Sánchez-Valencia, J.; Sánchez-Alonso, I.; Martinez, I.; Careche, M. Low-field

403

nuclear magnetic resonance of proton (1H LF NMR) relaxometry for monitoring

404

the time and temperature history of frozen hake (Merluccius merluccius L.)

405

Muscle. Food Bioprocess Tech. 2015, 8, 2137-2145.

406

(6) Bosmans, G. M.; Lagrain, B.; Ooms, N.; Fierens, E.; Delcour, J. A. Storage of

407

parbaked bread affects shelf life of fully baked end product: a ¹H NMR study.

408

Food Chem. 2014, 165, 149-156.

409

(7) Sánchez-Alonso, I.; Martinez, I.; Sánchez-Valencia, J.; Careche, M. Estimation of

410

freezing storage time and quality changes in hake (Merluccius merluccius, L.) by

411

low field NMR. Food Chem. 2012, 135, 1626-1634.

412

(8) Lin, S.; Yang, S.; Li, X.; Chen, F.; Zhang, M. Dynamics of water mobility and

413

distribution in soybean antioxidant peptide powders monitored by LF-NMR.

414

Food Chem. 2016, 199, 280-286.

415

(9) Aursand, I. G.; Gallartjornet, L.; Erikson, U.; Axelson, D. E.; Rustad, T. Water

416

Distribution in Brine Salted Cod (Gadus morhua) and Salmon (Salmo salar): A

417

Low-Field 1H NMR Study. J. Agr. Food Chem. 2008, 56, 6252-6260. 19



418

(10) Aursand, I. G.; Veliyulin, E.; Böcker, U.; Ofstad, R.; Rustad, T.; Erikson, U.

419

Water and salt distribution in Atlantic Salmon (Salmo salar) studied by low-field

420

1

421

and brine salting. J. Agr. Food Chem. 2009, 57, 46-54.

H NMR, 1H and 23Na MRI and light microscopy: effects of raw material quality

422

(11) Pojić, M.; Musse, M.; Rondeau, C.; Hadnađev, M.; Grenier, D.; Mariette, F.;

423

Cambert, M.; Diascorn, Y.; Quellec, S.; Torbica, A.; Hadnađev, T. D.; Lucas, T.

424

Overall and local bread expansion, mechanical properties, and molecular

425

structure during bread baking: effect of emulsifying starches. Food Bioprocess

426

Tech. 2016, 9, 1287-1305.

427

(12) Engelsen, S. B.; Jensen, M. K.; Pedersen, H. T.; Norgaard, L.; Munck, L.

428

NMR-baking and multivariate prediction of instrumental texture parameters in

429

bread. J. Cereal Sci. 2001, 33, 59-69.

430

(13) Li, T.; Tu, C.; Rui, X.; Gao, Y.; Li, W.; Wang, K.; Xiao, Y.; Dong, M. Study of

431

water dynamics in the soaking, steaming and solid-state fermentation of glutinous

432

rice by LF-NMR: a novel monitoring approach. J. Agr. Food Chem. 2015, 63,

433

3261-3270.

434

(14) Garcia Garcia, A. B.; Larsen, L. B.; Cambero Rodriguez, M. I.; Cruz Diaz, K. P.;

435

Bertram, H. C. Proteolysis process in fermented sausage model systems as

436

studied by NMR relaxometry. J. Agr. Food Chem. 2015, 63, 3039-3045.

437

(15) Li, M.; Wang, H.; Zhao, G.; Qiao, M.; Li, M.; Sun, L.; Gao, X.; Zhang, J.

438

Determining the drying degree and quality of chicken jerky by LF-NMR. J. Food

439

Eng. 2014, 139, 43-49. 20


Page 20 of 31

Page 21 of 31


440 441

(16) Xu, D.; Min, Z.; Aruns, M.; Wang, S. Microwave freeze drying of sea cucumber (Stichopus japonicus). J. Food Eng. 2010, 96, 491-497.

442

(17) Ali, S.; Zhang, W.; Rajput, N.; Khan, M. A.; Li, C. B.; Zhou, G. H. Effect of

443

multiple freeze-thaw cycles on the quality of chicken breast meat. Food Chem.

444

2015, 173, 808-814.

445

(18) Ding, X.; Zhang, H.; Wang, L.; Qian, H.; Qi, X.; Xiao, J. Effect of barley

446

antifreeze protein on thermal properties and water state of dough during freezing

447

and freeze-thaw cycles. Food Hydrocolloid 2015, 47, 32-40.

448

(19) Bottomley, P. A.; Foster, T. H.; Argersinger, R. E.; Pfeifer, L. M. A review of

449

normal tissue hydrogen NMR relaxation times and relaxation mechanisms from

450

1-100 MHz: dependence on tissue type, NMR frequency, temperature, species,

451

excision, and age. Med. Phys. 1984, 11, 425-448.

452

(20) Engelsen, S. B.; Jensen, M. K.; Pedersen, H. T.; Nørgaard, L.; Munck, L.

453

NMR-baking and multivariate prediction of instrumental texture parameters in

454

bread. J. Cereal Sci. 2001, 33, 59-69.

455

(21) Greiff, K.; Fuentes, A.; Aursand, I. G.; Erikson, U.; Masot, R.; Alcaniz, M.; Barat,

456

J. M. Innovative nondestructive measurements of water activity and the content

457

of salts in low-salt hake minces. J. Agr. Food Chem. 2014, 62, 2496-2505.

458 459 460 461

(22) Kovrlija, R.; Rondeau-Mouro, C. Hydrothermal changes of starch monitored by combined NMR and DSC methods. Food Bioprocess Tech. 2016, 1-17. (23) Yamamoto, N.; Kuwata, K. Regulating the conformation of prion protein through ligand binding. J. Phys. Chem. B 2009, 113, 12853-12856. 21



462

(24) Balasubramanian, S.; Devi, A.; Singh, K. K.; Bosco, S. J.; Mohite, A. M. Crit.

463

Application of glass transition in food processing. Rev. Food Sci. 2016, 56,

464

919-936.

465

(25) Svanidze, A. V.; Huth, H.; Lushnikov, S. G.; Kojima, S.; Schick, C. Phase

466

transition in tetragonal hen egg-white lysozyme crystals. Appl. Phys. Lett.2009,

467

95, 604.

468

(26) Tolstorebrov, I.; Eikevik, T. M.; Bantle, M. A DSC determination of phase

469

transitions and liquid fraction in fish oils and mixtures of triacylglycerides. Food

470

Res. Int. 2014, 58, 132-140.

471

(27) Chen, Z. P.; Fevotte, G.; Caillet, A.; Littlejohn, D.; Morris, J. Advanced

472

calibration strategy for in situ quantitative monitoring of phase transition

473

processes in suspensions using FT-Raman spectroscopy. Anal. Chem.2008, 80,

474

6658-6665.

475

(28) Laaksonen, T. J.; Roos, Y. H. Thermal, dynamic-mechanical, and dielectric

476

analysis of phase and state transitions of frozen what doughs. J. Cereal Sci. 2000,

477

32, 281-292.

478

(29) Goetz, J.; Koehler, P. Study of the thermal denaturation of selected proteins of

479

whey and egg by low resolution NMR. LWT - Food Sci. Technol. 2005, 38,

480

501-512.

481 482 483

(30) R. Ruan, Z. L., P. Chen, V. Huang, S. Almaer, I. Taub. Pulse NMR study of glass transition in maltodextrin. J. Food Sci., 64, 6-9. (31) Sablani, S. S.; Syamaladevi, R. M.; Swanson, B. G. A review of methods, data 22


Page 22 of 31

Page 23 of 31


484

and applications of state diagrams of food systems. Food Eng. Rev. 2010, 2,

485

168-203.

486

(32) Pitombo, R. N.M.; Lima, G. A.M.R. Nuclear magnetic resonance and water

487

activity in measuring the water mobility in Pintado (Pseudoplatystoma

488

corruscans) fish. J. Food Eng. 2003, 58, 59-66.

489

(33) Seetapan, N.; Limparyoon, N.; Gamonpilas, C.; Methacanon, P.; Fuongfuchat, A.

490

Effect of cryogenic freezing on textural properties and microstructure of rice

491

flour/tapioca starch blend gel. J. Food Eng. 2015, 151, 51-59.

492

(34) Bainy, E. M.; Corazza, M. L.; Lenzi, M. K. Measurement of freezing point of

493

tilapia fish burger using differential scanning calorimetry (DSC) and cooling

494

curve method. J. Food Eng. 2015, 161, 82-86.

495

(35) Rahman, M. S.; Guizani, N.; Alkhaseibi, M.; Alhinai, S. A.; Almaskri, S. S.;

496

Alhamhami, K. Analysis of cooling curve to determine the end point of freezing.

497

Food Hydrocolloid. 2002, 16, 653-659.

498

(36) Ibanoglu, E.; Ercelebi, E. A. Thermal denaturation and functional properties of

499

egg proteins in the presence of hydrocolloid gums. Food Chem. 2007, 101,

500

626-633.

501 502 503 504 505 23



506 507 508 509 510 511 512 513 514 515 516 517 518

FIGURE CAPTIONS.

519

Figure 1. Overall equipment (a) and schematic diagram (b) of VT-NMR-MRI. ICC:

520

industrial control computer, TC: temperature control, RF: radiofrequency.

521

Figure 2. Changes of T2 relaxation spectra (a) and relaxation parameters T21, T22 and

522

T23 (b), representative plot for relaxation time (T2) versus temperature (c), DSC

523

thermogram (d) and T1 weighted images (e) of salmon flesh in freezing process from

524

-20 to 10 oC.

525

Figure 3. Changes of T2 relaxation time spectra (a) and relaxation parameters T21 and

526

T22 (b) of the salmon flesh upon heating at different temperatures. Single-exponential

527

fitting of the transverse relaxation times (T2) at different heating time(c), and DSC 24


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Page 25 of 31


528

thermogram (d), and the T1 weighted images (e) of salmon flesh in heat transfer

529

process.

530

Figure 4. T2 relaxation spectra (a) of egg, transverse relaxation times of T21, T22 and

531

T23 fractions of egg (b), average relaxation times T2m as a function of temperature for

532

eggs (c), photographs of egg at different temperatures (d) and T1 weighted

533

pseudo-color images of egg (e) during heating at different temperatures and the

534

corresponding histogram of relative intensity of the T1 weighted images of egg (f).

535

Figure 5. T2 relaxation spectra (a) of egg, transverse relaxation times of T21, T22 and

536

T23 fractions of egg (b), average relaxation times T2m as a function of heating time for

537

eggs (c), photographs of egg with different times (d) T1 weighted pseudo-color images

538

of egg (e) during heating at different times and the corresponding histogram of

539

relative intensity of the T1 weighted images of egg (f).

540

Table 1 Performance of VT-NMR-MRI instrument

541

Pressure (MPa) 0.05 0.10 0.15 0.20 0.25 0.30 0.35 0.40

Airflow rate(L/min) 47±2 75±5 105±5 130±5 150±10 180±10 210±15 240±15

Low Temperature (oC) -22.5±0.2 -25.5±0.2 -30.5±0.2 -32.5±0.2 -34.5±0.2 -36.0±0.2 -37.0±0.2 -36.5±0.2

542 543 544 25


High Temperature (oC) 150±0.02 150±0.02 150±0.02 150±0.02 148±0.02 145±0.02 138±0.02 130±0.02


545 546

547 548

Figure.1

26


Page 26 of 31

Page 27 of 31


549 550

Fig. 2.

27



551 552

Figure 3.

28


Page 28 of 31

Page 29 of 31


553 554

Figure 4.

29



555 556

Figure 5.

557

30


Page 30 of 31

Page 31 of 31


TOC Air

Dry air

Temperature sensor

Three-way valves

Refrigerating

Flowmeter

Electrical resistance heater

Air compressor

RF coil

Exhuast


Variable Temperature Nuclear Magnetic Resonance and Magnetic

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