3.2.3. Alpha-amylase inhibition
Figure 7A shows the α-amylase inhibitory effect of 3% husk emulsion with 0, 5, 10, 15 and 20% w/w inulin addition at 5 mg/ml. Inhibitory activity increased with increasing inulin concentration from 0% to 15%. The α-amylase inhibitory activity of the emulsion gel at 20% inulin was not significantly different (p>0.05) from that of 15% inulin concentration. The inhibitory activity of 3% husk emulsion gel with 20% inulin at 5 mg/ml on α-amylase was 16.06 ± 3.03%.
(Place for figure 7)
Fig. 7 Inhibitory potency of (A) 3% psyllium husk emulsion in the presence of different concentration of inulin at 200X dilution, and (B) puree samples with incorporated 5% or 10% husk-20% inulin emulsion gel against α-amylase (1 U/mL) activity at 1% starch concentration. Different letters represent significant different at p<0.05.
The α-amylase inhibitory activity of puree samples (salmon, chicken, chicken stew or beef) with 5% w/w and 10% w/w husk-20% inulin emulsion gel (Fig. 7B), showed that all puree samples can delay α-amylase activity. The inhibitory activity of puree samples with 10% w/w replacement by the emulsion gel was higher than that of puree with 5% w/w replacement. Amongst the purees with 10% w/w replacement by husk-20% inulin emulsion gel, the chicken stew had the highest amylase inhibition (21.14%), followed by salmon and chicken (14.12 and 12.68% inhibition, respectively). The beef had the lowest amylase inhibition of 7.93%. Guo et al. (2020) reported that the hydroxyl (-OH) and carboxyl groups (-COOH) on the polysaccharides branched chain can interact with the amino acid residues of digestive enzymes (α-amylase and α-glucosidase), thus inhibiting their activity. In addition, Ahmed & Urooj (2010) concluded that dietary fiber, such as wheat bran and psyllium husk, can bind glucose, and thereby inhibit amylase activity. Previous α-amylase inhibitory activity indicated that soluble fibers can capsulate α-amylase and starch, thereby reducing starch accessibility to the enzyme (Ou et al., 2001).
Our result indicates that incorporation of husk-20% inulin emulsion gel will be beneficial to delay dietary starch breakdown in food product and thereby maintain their consistency with addition of starch-based thickener during oral digestion.