High-humidity hot air impingement blanching alters texture, cell-wall polysaccharides, water status and distribution of seedless grape

Jun Wang, Arun S. Mujumdar, Li-Zhen Deng, Zhen-Jiang Gao, Hong-Wei Xiao, G.S.V. Raghavan

Index: 10.1016/j.carbpol.2018.04.023

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Abstract

Blanching pretreatment plays an essential role in fruits and vegetables processing to obtain excellent final products. The purpose of current work was to characterise the texture, cell-wall polysaccharides and water distribution of grapes pre- and post- high-humidity hot air impingement blanching (HHAIB). The cell-wall pectins nanostructure, water status and distribution of samples were determined by atomic force microscopy (AFM), low field nuclear magnetic resonance (LF-NMR) and magnetic resonance image (MRI), respectively. Results revealed that blanching caused significant berry tissue softening which was accompanied by an increase of water-soluble pectin (WSP, from 39.57 to 57.44 g/100 g fresh weight) and a decrease of chelate-soluble pectin (CSP, from 79.34 to 53.78 g/100 g fresh weight) and sodium-carbonate-soluble pectin (NSP, from 364.23 to 187.64 g/100 g fresh weight) concentration. Obvious depolymerization and degradation was observed in cell-wall polysaccharides nanostructure in blanched berries. The length frequencies of WSP chains are mainly distributed in the range of 0.51-2.00 μm, while it was 1.01-2.00 μm for the CSP chains of blanched samples. LF-NMR transverse relaxation time and MRI analysis indicated that HHAIB treatment resulted in a water loss and migration from berry interior to surface tissue. The findings in present study provide a deeper understanding in tissue softening and moisture variation of blanched berries.