Effects of extraction methods on the digestibility, cytotoxicity, prebiotic potential and immunomodulatory activity of taro (Colocasia esculenta) water-soluble non-starch polysaccharide

Abstract In this study, water-soluble non-starch polysaccharide (WS-NSP) from taro corm (Tc-WS-NSP) extracted using conventional extraction (Tc-WS-NSP-CE) and improved conventional extraction (Tc-WS-NSP-ICE) methods was used to compare the effects of these in vitro on the digestibility, cytotoxicity in HT-29 cells, prebiotic action on probiotic strains Lactobacillus acidophilus, Bifidobacterium breve, and Bifidobacterium infantis, and immunomodulatory activity measured by the ability to regulate the production of the pro-inflammatory chemokine IL-8 following TNF-α stimulation of HT-29 cells. Tc-WS-NSP-ICE was more resistant to digestion with lower digestibility (4.1%) compared to Tc-WS-NSP-CE (11.5%). Digested Tc-WS-NSP-ICE had higher carbohydrate (98.4 ± 0.9 g/100g) and lower protein (2.1 ± 0.3 g/100g) contents than the carbohydrate (96.4 ± 0.2 g/100g) and protein (5.4 ± 0.3 g/100g) contents of Tc-WS-NSP-CE. Digested Tc-WS-NSP-CE and Tc-WS-NSP-ICE contained the monosaccharides arabinose, galactose, glucose and mannose, the functional groups –OH, C=O, -COOH, –CH3, nitro and amino groups in their FTIR spectra, and were highly amorphous. The extraction methods did not significantly affect the cytotoxicity to HT-29 cells and the ability to enhance the growth of the probiotics L. acidophilus, B. breve, and B. infantis of the undigested and digested Tc-WS-NSP-CE and Tc-WS-NSP-ICE samples. The use of the ICE method resulted in a Tc-WS-NSP exhibiting better immunomodulatory activity than the CE where undigested (20.7%) and digested (25.0%) Tc-WS-NSP-ICEs demonstrated higher IL-8 down-regulation capacities than undigested (18.3%) and digested (22.2%) Tc-WS-NSP-CEs. Overall, the study demonstrated that extraction method can affect, and specifically enhance some property (i.e., digestibility) and biological activity (i.e., immunomodulatory activity) of the extracted biomaterial.