Effect of hot-air oven dehydration process on water dynamics and microstructure of apple (Fuji) cultivar slices assessed by LF-NMR and MRI

Abstract

Non-destructive analysis of water dynamics during drying is of importance for quality control of food products. In this study, different water dynamics and migration in Fuji apple slices dried at various hot-air oven temperatures, i.e. 50, 60, 70, and 80 °C and air velocity at 0.2 m/s were monitored using low-field nuclear magnetic resonance (LF-NMR) and magnetic resonance imaging (MRI). Multi-exponential fitting of the transverse relaxation T₂ parameter demonstrated four distinct water peaks in all samples corresponding to strongly bound, lightly bound, entrapped/immobilized, and free water as follows: T₂₁ in the range of 0.01–1 ms, T₂₂ in the range of 1–10 ms, T₂₃ in the range of 10–100 ms, and T₂₄ in the range of 100–1000 ms, respectively. The water content was measured and analyzed by the traditional technique using the oven drying method. The overall results were highly significant, depicting that the transverse relaxation times T₂₄, signal per mass of the free water A₂₄, and water content significantly decreased (p< 0.05), while the color (L*, a*, b*) and shear force (SF) curves increased with extended drying. Furthermore, good correlations were observed between the LF-NMR parameters and color, water content, and SF in differently processed samples during the dehydration process. Scanning electron microscopy (SEM) and MRI provided the structural changes and spatial water distributions during the drying process. LF-NMR exhibited great potential in evaluating the various water dynamics and quality of Fuji cultivar apples during the drying process.

Abbreviations: AA: ascorbic acid; ANOVA: analysis of variance; CPMG: Carr-Purcell-Meiboom-Gill; DW: distilled water; F: Fuji; LF-NMR: low-field nuclear magnetic resonance; MRI: magnetic resonance imaging; SE: spin-echo; SEM: scanning electron microscopy; SF: shear force; SIRT: simultaneous iterative reconstruction technique; TE: echo time; TR: repetition time.

Keywords:

• Apple
• dehydration
• water dynamics
• LF-NMR
• MRI
• SEM

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

This work was supported by the National Key Research and Development Program of China (2017YFC1600802) and the National Key Scientific Instrument and Equipment Development Project of China (2013YQ17046307).

Notes on contributors

Tariq Kamal

Tariq Kamal is a Ph.D. student in the lab of Prof. Mingqian Tan at the School of Food Science and Technology, National Engineering Research Center of Seafood, Dalian Polytechnic University, China. He received a B.Sc (Hons) degree in Basic Agricultural Sciences and Master Degree with specialization in Agriculture and Food from The University of Agriculture, Peshawar-Pakistan, in 2011 and 2014, respectively. His research focuses on the analysis of water dynamics of fruits.

Yukun Song

Yukun Song is a Ph.D. student in the lab of Prof. Mingqian Tan at the School of Food Science and Technology, National Engineering Research Center of Seafood, Dalian Polytechnic University, China. He received his master degree from Dalian Polytechnic University, and bachelor degree (2012) in Jinzhou Medical University. His current research focuses on the non-destructive analysis of food quality.

Zhang Tan

Zhang Tan is a master student in the lab of Prof. Mingqian Tan at the School of Food Science and Technology, National Engineering Research Center of Seafood, Dalian Polytechnic University, China. He received his bachelor degree (2015) from Henan Agriculture University. He works on the analysis of duck eggs with low field nuclear magnetic resonance.

Bei-Wei Zhu

Bei-Wei Zhu is a Chair Professor of National Engineering Research Center of Seafood, Dalian Polytechnic University, China. She received her Ph.D. Degree from Okayama University, Japan. Her research focuses on the basic theory and application of deep processing of aquatic products. In 2013, she was selected as a member of the Chinese Academy of Engineering.

Mingqian Tan

Mingqian Tan is a full Professor of food science and technology at Dalian Polytechnic University, China. He received a BS and Master degree in Chemistry from Nanjing University of Science and Technology, China, and a Ph.D. in Analytical Chemistry from Chinese Academy of Sciences. He serves as an Editor Board member of Foods. He is the author or co-author of more than 120 papers/book chapters and 30 patents applications. His current research focuses on the non-destructive food analysis, food safety assessment and nutrition delivery system.

Tariq Kamal conducted the experiments and wrote the manuscript, Yukun Song and Zhang Tan carried out the data analysis of LF-NMR. Bei-Wei Zhu and Mingqian Tan designed the experiment and Mingqian Tan revised the paper.