Bioactive Polyphenols from Southern Chile Seaweed as Inhibitors of Enzymes for Starch Digestion

Abstract

The increment of non-communicable chronic diseases is a constant concern worldwide, with type-2 diabetes mellitus being one of the most common illnesses. A mechanism to avoid diabetes-related hyperglycemia is to reduce food digestion/absorption by using anti-enzymatic (functional) ingredients. This research explored the potential of six common Chilean seaweeds to obtain anti-hyperglycemic polyphenol extracts, based on their capacity to inhibit key enzymes related with starch digestion. Ethanol/water hot pressurized liquid extraction (HPLE), which is an environmentally friendly method, was studied and compared to conventional extraction with acetone. Total polyphenols (TP), antioxidant activity, cytotoxicity and inhibition capacity on α-glucosidase and α-amylase were analyzed. Results showed that the Durvillaea antarctica (cochayuyo) acetone extract had the highest TP content (6.7 ± 0.7 mg gallic acid equivalents (GAE)/g dry seaweed), while its HPLE ethanol/water extract showed the highest antioxidant activity (680.1 ± 11.6 μmol E Trolox/g dry seaweed). No extract affected cell viability significantly. Only cochayuyo produced extracts having relevant anti-enzymatic capacity on both studied enzymes, showing a much stronger inhibition to α-glucosidase (even almost 100% at 1000 µg/mL) than to α-amylase. In conclusion, from the Chilean seaweeds considered in this study, cochayuyo is the most suitable for developing functional ingredients to moderate postprandial glycemic response (starchy foods), since it showed a clear enzymatic inhibition capacity and selectivity.

Keywords: cochayuyo; enzyme inhibition; hypoglycemic effect; seaweed polyphenols; starch digestion.

Figure 1

HT-29 cell viability at different dry extracts concentrations: (A) the ethanolic extract at 24 h incubation; (B) the ethanolic extract at 48 h incubation; (C) the acetone extract at 24 h incubation; (D) the acetone extract at 48 h incubation. Each point represents the mean of viable cells ± SD (n = 2). The dashed line is the cell viability using the positive control (DMSO 16.7%). The 100% viability was assigned to the cell culture without extracts.

Figure 2

Percentages of the α-amylase activity under different concentrations of ethanol (A) and acetone (B) extracts (µg/mL). The points represent the average enzymatic activity (%) ± standard deviation (n = 3).

Figure 3

Percentages of α-glucosidase activity under different concentrations of ethanol (A) and acetone (B) extracts (µg/mL). Points represent the average enzymatic activity (%) ± standard deviation (n = 3).

Figure 4

Macroalgae used in this study. The red macroalgae species (A) Pyropia sp., (B) M. laminarioides, (C) Gelidium sp., (D) Nothogenia sp.; and the brown macroalgae species (E) D. antarctica and (F) L. spicata. (Photograph by Mauricio Palacios- IDEAL Center).