Starch digestion in the human body is typically viewed in a sequential manner beginning with α-amylase and followed by α-glucosidase to produce glucose. This report indicates that the two enzyme types can act synergistically to digest granular starch structure. The aim of this study was to investigate how the mucosal α-glucosidases act with α-amylase to digest granular starch. Two types of enzyme extracts, pancreatic and intestinal extracts, were applied. The pancreatic extract containing predominantly α-amylase, and intestinal extract containing a combination of α-amylase and mucosal α-glucosidase activities, were applied to three granular maize starches with different amylose contents in an in vitro system. Relative glucogenesis, released maltooligosaccharide amounts, and structural changes of degraded residues were examined. Pancreatic extract-treated starches showed a hydrolysis limit over the 12 h incubation period with residues having a higher gelatinization temperature than the native starch. α-Amylase combined with the mucosal α-glucosidases in the intestinal extract showed higher glucogenesis as expected, but also higher maltooligosaccharide amounts indicating an overall greater degree of granular starch breakdown. Starch residues after intestinal extract digestion showed more starch fragmentation, higher gelatinization temperature, higher crystallinity (without any change in polymorph), and an increase of intermediate-sized or small-sized fractions of starch molecules, but did not show preferential hydrolysis of either amylose or amylopectin. Direct digestion of granular starch by mammalian recombinant mucosal α-glucosidases was observed which shows that these enzymes may work either independently or together with α-amylase to digest starch. Thus, mucosal α-glucosidases can have a synergistic effect with α-amylase on granular starch digestion, consistent with a role in overall starch digestion beyond their primary glucogenesis function.
Thermal conductivity determination of food at temperatures >100 °C still remains a challenge. The objective of this study was to determine the temperature-dependent thermal conductivity of food using rapid heating (TPCell). The experiments were designed based on scaled sensitivity coefficient (SSC), and the estimated thermal conductivity of potato puree was compared between the constant temperature heating at 121.10 °C (R12B10T1) and the rapid heating (R22B10T1). Temperature-dependent thermal conductivity models along with a constant conductivity were used for estimation. R22B10T1 experiment using the k model provided reliable measurements as compared to R12B10T1 with thermal conductivity values from 0.463 ± 0.011 W m−1 K−1 to 0.450 ± 0.016 W m−1 K−1 for 25–140 °C and root mean squares error (RMSE) of 1.441. In the R12B10T1 experiment, the analysis showed the correlation of residuals, which made the estimation less reliable. The thermal conductivity values were in the range of 0.444 ± 0.012 W m−1 K−1 to 0.510 ± 0.034 W m−1 K−1 for 20–120 °C estimated using the k model. Temperature-dependent models (linear and k models) provided a better estimate than the single parameter thermal conductivity determination with low RMSE for both types of experiments. SSC can provide insight in designing dynamic experiments for the determination of thermal conductivity coefficient.
Four small intestinal α‐glucosidases, N‐ and C‐terminal subunits of maltase‐glucoamylase (MGAM) and sucrase‐isomaltase (SI), releases glucose from starch molecules at the final stage of digestion in the small intestine. In our previous study, we hypothesized that the digestibility at α‐glucosidase level is determined by the internal molecular structure of starch hydrolysates. We later reported that the branch pattern of starch internal molecules influences the digestion. The objective of this study is to further test the hypothesis that the branch amount and the distance between branches influence the rate and extent of glucose release from α‐amylase hydrolysate. Two starches [waxy (wx) maize and potato] with different internal structure were hydrolyzed by pancreatic α‐amylase. The hydrolysate consists of linear glucans and branched dextrin (α‐limit dextrin,α‐LD), and they were separated by size‐exclusion chromatography. α‐LD was digested by Ct‐MGAM in vitro, and the rate and extent of glucose release were examined. Both wx maize and potato hydrolysates consist of 30‐35% of α‐LD, and the molecular size of their α‐LD was DP (average degree of polymerization)13 and 17, respectively. The amount of released glucose from wx maize and potato α‐LD was 30 and 40 mg (p<0.05), and the rate of glucose release as represented by the catalytic efficiency was 0.13 and 0.28, respectively. In conclusion, α‐LD with longer distance between branches and loose branched structure (potato in this study) generated higher glucose amount at higher rate by Ct‐MGAM. In the future, starches with different type of internal structure needs to be further examined. This project was sponsored by Univ. of Idaho and Whistler Center for Carbohydrate Research at Purdue Univ.
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