Screening and Structural Characterization of Auricularia auricula Polysaccharides for Their Ability to Improve Rehydration Characteristics of Dehydrated White Radish

Polysaccharides from Auricularia auricula (AAP) were extracted by hot water extraction and fractionated by sequential precipitation with 10% and 80% (final concentration) ethanol into two fractions (named AAP-10 and AAP-80, respectively). Each fraction was further separated into three subfractions: AP-10-Ⅰ, AAP-10-Ⅱ, AAP-10-Ⅲ, AAP-80-Ⅰ, AAP-80-Ⅱ and AAP-80-Ⅲ. Each of the six polysaccharides was vacuum infiltrated into white radish before dehydration and rehydration. The effects of these polysaccharides on the rehydration characteristics of white radish were investigated by measuring the rehydration ratio, expansibility, water-holding capacity (WHC), color and texture parameters. Polysaccharides that greatly differed in their ability to improve the rehydration characteristics of dehydrated radish were selected for structural characterization. The results showed that compared with dehydrated radish without osmotic treatment, treatment with AAP could improve the rehydration characteristics of dehydrated radish in varying degrees. The effect of AAP-80-Ⅲ was most pronounced among the six polysaccharides. The rehydration ratio of radish treated with AAP-80-Ⅲ was 7.32, the expansibility was 3.22 mL/g, and the water-holding capacity was 87.2%; it had better color (L* value of 62.68 ± 0.17, a* value of −1.06 ± 0.02, and b* value of 4.23 ± 0.09), hardness (1746.14 ± 11.9) N and chewiness (1207.09 ± 9.39) N. AAP-10-Ⅰ could also improve the rehydration characteristics of dehydrated radish, but the difference was not significant. AAP-10-Ⅰ and AAP-80-Ⅲ contained neither protein nor nucleic acid, and both had hydrophilic functional groups. But the molecular mass of AAP-80-Ⅲ was less than that AAP-10-Ⅰ, and so AAP-80-Ⅲ could more easily penetrate into radish tissue. Moreover, arabinose accounted for a larger proportion in the monosaccharide composition of AAP-80-Ⅲ, which increased the water-holding capacity of radish tissue. Based on the above results, AAP-80-Ⅲ can effectively improve the rehydration characteristics of dehydrated radish.