Teruo Nakakuki

Effect of raw and heat–moisture-treated high-amylose corn starches on the process of digestion in the rat digestive tract

High-amylose corn starch (HAS) is widely known as a resistant starch foodstuff. We developed heat-moisture-treated high-amylose corn starch (HMT-HAS) that was more resistant to enzymatic hydrolysis. Resistant starch contents of HAS and HMT-HAS using the enzymatic-gravimetric method were found to be 30% and 65% respectively. Rats were given 10% ordinary corn starch (CS), HAS or HMT-HAS by meal feeding for 10 days. The caecum contents increased and the caecal pH was lower after their diets were supplemented with HAS and HMT-HAS. Starch contents increased in the upper and the lower small intestine with HAS and HMT-HAS. Caecal starch with HAS and HMT-HAS was more than that with CS. Particularly, caecal starch with HMT-HAS was seven times more than that with HAS. There were no differences in starch content in the large bowel between CS and HAS, but the content increased with HMT-HAS. These results suggested that HAS and HMT-HAS were resistant to digestion and absorption in the small intestine, and any indigestible starches reached the caecum. In the caecum, HAS was hydrolysed almost completely by intestinal bacteria; however, some HMT-HAS escaped bacterial hydrolysis. This escaped HMT-HAS reached the large bowel and was excreted in the faeces.

Effect of Raw and Heat-Moisture Treated High-Amylose Corn Starch on Fermentation by the Rat Cecal Bacteria

Resistant starch content of high-amylose corn starch (HAS) was doubled by heat-moisture treatment. Resistant starch content of HAS and heat-moisture treated high-amylose corn starch (HMT-HAS) were 31.8 and 67.3%, respectively, as determined by enzymatic-gravimetric method. Effects of the two types of high-amylose corn starches, HAS and HMT-HAS, on starch fermentation, microflora, pH, short chain fatty acid (SCFA) content and β-glucuronidase activity in the cecal content have been investigated. Rats were given ordinary corn starch (OCS; control), HAS or HMT-HAS at 10% level for 10-13 days. The cecal and colorectal contents weights were larger in HAS and HMT-HAS groups than in the OCS group. The cecal contents weight did not differ between HAS and HMT-HAS groups, while the colorectal contents weight was higher in the HMT-HAS group than in the HAS group. The upper and lower small intestinal and cecal starch contents were significantly higher in the HAS and HMT-HAS groups than in the OCS group, whereas there were no differences between colorectal starch content in group OCS and HAS. Starch excretion in feces was significantly higher in groups HAS and HMT-HAS than in group OCS, the increase in the HMT-HAS group was especially remarkable. The composition of the cecal microflora was not effected by the diet. β-Glucuronidase activities in rats fed HAS or HMT-HAS decreased. SCFA concentration was higher in groups HAS and HMT-HAS than in group OCS, and the cecal pH was lower in groups HAS and HMT-HAS than in group OCS.

Maltopentaose-Forming Amylase-Mediated p-Nitrophenyl α-Maltohexaoside formation in an Aqueous-Organic Solvent System :A Substrate for Human Amylase in Serum

A maltopentaose-forming amylase [EC 3.2.1.1] from Bacillus licheniformis effectively produced p-nitrophenyl α-maltohexaoside (3) through a transglycosylation reaction from maltohexaose as a donor and p-nitrophenyl α-glucoside (1) as an acceptor in an aqueous solution containing hydrophilic organic solvents. The enzyme specifically transferred from maltohexaose to the 4-position of 1. The yield of 3 depended on the kind of donor, concentration of solvent, pH, and temperature. By the addition of solvents such as dimethyl sulfoxide and 1-butanol, respectively, effects of acceleration on transferase activity of the enzyme and improvement of acceptor solubility were achieved, and resulted in a great increase in the formation of 3.

Crystallization and preliminary X-ray study of γ-­type cyclodextrin glycosyltransferase from Bacillus clarkii

A gamma-cyclodextrin glycosyltransferase (EC 2.4.1.19) from Bacillus clarkii was crystallized using the hanging-drop vapour-diffusion method at 293 K. X-ray diffraction data were collected to 2.2 A. The crystal belongs to space group R3, with unit-cell parameters a = b = 211.6, c = 52.7 A. The asymmetric unit contains one protein molecule, with a corresponding V(M) of 3.03 A(3) Da(-1) and a solvent content of 59.4%. Molecular replacement was successfully carried out using a homology model based on the three-dimensional structure of the CGTase from Thermonanaerobacterium thermosulfurigenes EM1 as a search model.

Subsite Structure of Maltogenic Amylase from Thermomonospora viridis TF-35

We estimated the subsite structure of the maltogenic amylase from Thermomonospora viridis TF-35 (TVA). TVA has six subsites, and the catalytic site is between the 3rd and 4th subsite. The subsite affinities, A -3, A -2, (A -1+A +1), A +2 and A +3 were calculated to be 0.47, 2.31, 0.49, 2.45, and 0.17 kcal mol-1, respectively.

Preventive Effect of Oligosaccharides against Denaturation of Carp Myofibrillar Protein Caused by Freeze-Drying

0～3.7%の間の濃度のオリゴ糖共存下でコイ筋原繊維懸濁液を凍結乾燥すると,筋原繊維Ca2+-ATPaseは,初期の数時間後まで速やかに失活して最小値に達し,後期はその値を維持した.そこで初期の筋原繊維Ca2+-ATPaseの失活の一次反応速度(kD)を求めると,logkDと濃度は反比例するので,その勾配(e)を防止効果として表した.また,後期における筋原繊維Ca2+-ATPaseの残存活性の対数値と濃度の間には比例関係が成立するので,凍結乾燥による筋原繊維Ca2+-ATPaseの失活を完全に阻止するために必要なオリゴ糖の濃度の理論値を外挿して求めた.その結果,e値の高いオリゴ糖ほど凍結乾燥による筋原繊維Ca2+-ATPaseの失活を阻止する最小濃度は低いこと,またいずれのオリゴ糖も5～9%の添加で十分効果をあげることができることが示された. これに対して,log kDとモル1農度も反比例するのでその直線の勾配を別の防止効果(E値)として平均分子量当りの変性防止効果の強さを表し,高純度のグルコースおよびオリゴ糖と比較した.その結果,フジオリゴは,数種類の糖が混合しているが,その糖組成中に保護効果の強いマルトテトラオース,あるいはそれ以上の重合度を有するオリゴ糖が多く含まれるもの,さらに防止効果の弱いグルコース,マルトースの含量が少ないものほど変性防止効果は強いと思われた.