Hydrocolloids Decrease the Digestibility of Corn Starch, Soy Protein, and Skim Milk and the Antioxidant Capacity of Grape Juice

Abstract

Hydrocolloids have many applications in foods including their use in dysphagia diets. We aimed to evaluate whether hydrocolloids in foods affect the digestibility of starch and protein, and their effects on antioxidant capacity. The thickening hydrocolloids: locust bean gum and carboxymethyl cellulose, and the gel-forming agents: agar agar, konjac-glucomannan, and Hot & Soft Plus were blended with corn starch and soy protein, skim milk, or grape juice and were examined for their in vitro-digestability by comparing the reducing sugar and trichloroacetic acid (TCA)-soluble peptide, for antioxidant capacity by total polyphenol contents and the 2,2-diphenyl-1-picrylhydrazyl radical scavenging activity. The hydrocolloids resulted in a decrease in starch digestibility with the gel-forming agents. Hydrocolloids diminished TCA-soluble peptides in skim milk compared to soy protein with the exception of locust bean gum and decreased free radical scavenging capacities and total phenolic contents in grape juice. Our findings may provide evidence for the use of hydro-colloids for people at risk of nutritional deficiencies such as dysphagia patients.

Keywords: hydrocolloids; in vitro-digestability; locust bean gum.

Fig. 1

Apparent viscosity of food samples with CMC and LGB before in vitro digestion. Solutions consisting 100 mL of each specimen were used to measure the viscosity using a Viscometer. Control, 2% corn starch; CMC, 1% carboxymethyl cellulose; LBG, 1% locust bean gum. Results are expressed as mean±SD of at least three independent experiments. Different letters (a–e) represent significant differences (P < 0.05) among all groups by ANOVA.

Fig. 2

Reducing sugar content of corn starch samples with thickening or gel-forming agents after in vitro digestion. To measure the content of reduced sugars, a solution containing 3,5-dinitrosalicyclic acid sodium sulfite, and sodium hydroxide was mixed in a 1:1:1 (v/v/v) ratio. After 5 min of boiling, the tube was cooled in an ice water bath, and the absorbance was measured at 595 nm with a UV-Vis plate reader. A standard curve was generated using maltose. Control, 2% corn starch with no addition of hydrocolloids; CMC, 1% carboxymethyl cellulose; LBG, 1% locust bean gum; AA, 0.5% or 0.8% agar agar; KG, 0.5% or 0.8% konjacglucomannan; HS, 0.5% or 0.8% hot & soft plus. The results are expressed as mean±SD of at least three independent experiments. Different letters (a–d) represent significant differences (P < 0.05) among all groups by ANOVA.

Fig. 3

TCA-soluble peptide contents in soy protein and skim milk prepared with thickening or gel-forming agents after in vitro digestion. The digestibility of the proteins was examined by measuring the TCA-soluble peptides using a BCA protein assay kit. Control, 4% soy protein or 4% skim milk with no addition of hydrocolloids; CMC, 1% carboxymethyl cellulose; LBG, 1% locust bean gum; AA, 0.5% or 0.8% agar agar; KG, 0.5% or 0.8% konjacglucomannan; HS, 0.5% or 0.8% hot & soft plus. The results are expressed as mean±SD of at least three independent experiments. Different letters (a–d) represent significant differences (P < 0.05) among all groups by ANOVA.

Fig. 4

Total polyphenol content and DPPH free radical scavenging capacity in grape juice mixed with thickening or gel-forming agents after in vitro digestion. To determine the total polyphenolic content, the colorimetric Folin-Ciocalteu method was used. The calibration curve was constructed using gallic acid. The total phenolic compound amount was determined by comparison to the curve, and the results are expressed as mg equivalents of gallic acid/g of sample. A 70% ethanol solution was used as the control solution. Control, 20% grape juice with no addition of hydrocolloids; CMC, 1% carboxymethyl cellulose; LBG, 1% locust bean gum; AA, 0.5% or 0.8% agar agar; KG, 0.5% or 0.8% konjacglucomannan; HS, 0.5% or 0.8% hot & soft plus. The results are expressed as mean±SD of at least three independent experiments. Different letters (a–d) represent significant differences (P < 0.05) among all groups by ANOVA.