Role of phytate in oat beta-glucan extracts in starch hydrolysis

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Title: Role of phytate in oat beta-glucan extracts in starch hydrolysis
Author: Yang, Lingxi
Other contributor: Helsingin yliopisto, Maatalous-metsätieteellinen tiedekunta, Elintarvike- ja ympäristötieteiden laitos
University of Helsinki, Faculty of Agriculture and Forestry, Department of Food and Environmental Sciences
Helsingfors universitet, Agrikultur- och forstvetenskapliga fakulteten, Institutionen för livsmedels- och miljövetenskaper
Publisher: Helsingin yliopisto
Date: 2018
Language: eng
Thesis level: master's thesis
Discipline: Food Science
Food Science
Food Science
Abstract: Oat β-glucans are water soluble non-starch polysaccharides. The health benefits of β-glucan including reduction of post-prandial glycemic response are correlated to its ability of forming viscous solutions. Phytate has also been reported to reduce starch digestion due to its potential of binding starch-digestion-related enzymes such as α-amylase or enzyme co-factors. The previous study showed that a significant amount of phytate was found in both oat β-glucan extract and highly purified β-glucan. The aim of this research was to study the role of residual phytate in the oat β-glucan extracts in starch hydrolysis. Oat β-glucan (OBG) was extracted from oat bran concentrate. OBG with phytate-removal treatment (OBG-PR) was prepared with ion-exchange resin and dialysis. The content of β-glucan, phytate and starch in OBG and OBG-PR were determined with Megazyme kits. The protein and calcium content was also measured. Before adding into the gelatinized wheat starch solution, the β-glucan solutions or phytic acid solution were pre-incubated with porcine pancreatic α-amylase. The starch hydrolysis was induced at physiological pH 6.9 and 37°C. Aliquots were collected at 20 min and 120 min digestion time. Digested starch was calculated based on the released glucoses. Both OBG and OBG-PR inhibited the starch hydrolysis. OBG contained a higher amount of phytate. And it had a stronger inhibitory effect (46%) than that of OBG-PR (34%). Pure phytic acid showed a comparable inhibitory effect on the starch hydrolysis as the OBG intrinsic phytic acid did, when the pure phytic acid was used at the same level as the concentration of intrinsic phytic acid in OBG. The decrease of intrinsic calcium in OBG-PR was found due to the ion-exchange and dialysis process. Consequently, the same amount of calcium was added to OBG-PR. The inhibitory effect of phytic acid on starch hydrolysis was completely reversed by the addition of calcium. Moreover, degradation of β-glucan by lichenase increased starch hydrolysis rate, which confirmed the role of β-glucan viscosity in the reduction of starch hydrolysis. In summary, the residual phytic acid of oat β-glucan, in addition to viscosity, reduced starch hydrolysis, while calcium contributed to promote starch hydrolysis.
Subject: Oat β-glucan
Phytic acid
Starch hydrolysis

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