Miki Yoshimura

Rheological studies on mixtures of corn starch and konjac-glucomannan

Abstract Rheological properties of corn starch (CS) and konjac-glucomannan (KM) mixtures (total polysaccharide concentration: 3.50 wt%, CS KM ratios: 10 0 , 9 1 , 8 2 , 7 3 , 6 4 ) were studied as a function of mixing ratio and storage time by measuring storage and loss shear moduli and by observing the large deformation and fracture behaviour. The viscoelastic behaviour of dispersions of CS plus water (2.10–3.50 wt%, 3.50 wt% = 10 0 ) was intermediate between a weak gel and an elastic gel, and dispersions of KM plus water (0.35–1.40 wt%) showed a behaviour similar to a concentrated polymer solution. The behaviour of CS and KM mixture was intermediate between a concentrated polymer solution and a weak gel. KM does not interact synergistically with CS to promote the formation of ordered structure. The breaking stress for CS and KM mixtures increased slowly with storage time than for CS alone. KM prevented syneresis of corn starch during storage.

Rheological study and a phase diagram on mixture of corn starch and konjac glucomannan

Publisher Summary This chapter demonstrates how storage (G′) and loss (G″) shear moduli are measured for mixtures of corn starch (CS) and konjac glucomannan (KM) (total polysaccharide concentration—3.50 wt%, CS / KM ratios: 10/0, 9/1, 8/2, 7/3, 6/4). The viscoelastic behavior of aqueous dispersions of CS (2.10–3.50 wt%, 3.50 wt%=10/0) is an intermediate between a weak gel and an elastic gel, and aqueous dispersions of KM (0.35–1.40 wt%) shows a behavior similar to a concentrated polymer solution. The behavior of dispersions of CS and KM mixtures is an intermediate between a concentrated polymer solution and a weak gel. Storage modulus of a CS/KM mixture (constant KM content) as a function of the added CS shows a maximum at a certain CS content. These results suggest that phase separation of the two polymers occur. This is confirmed by confocal laser scanning microscopy. The microstructure of these mixtures is found to be CS continuous under most conditions. This is explained as a consequence of the starch forming a weak gel even when the KM phase volume appears to dominate the microstructure. Under the conditions of this study the KM behaves as a concentrated polymer solution which is trapped by weak gels of CS. The chapter describes the addition of hydrocoUoid to starch is known to increase the viscosity of starch and influence the gelatinization and retrogradation of starch.

Rheological Studies on Gelation Kinetics of Powdered Soybean in the Presence of Glucono-δ-Lactone

Rheological properties on gelation kinetics of powdered soybean in the presence of glucono-δ-lactone (GDL) were studied by dynamic viscoelastic measurements, compression tests, differential scanning calorimetry (DSC), and observation of the network structure by confocal laser scanning microscopy (CLSM). The gelation time became shorter, and the rate constant of gelation increased with increasing concentration of powdered soybean and GDL. The rupture strain, rupture stress, rupture energy, storage modulus, and loss modulus increased with increasing the concentration of powdered soybean. In protein concentration of 4.4–6.9 % range, the storage modulus was proportional to 2.3 power of protein concentrations. It is indicated from CLSM that the network structure of the powdered soybean curd increased with the increasing concentration of powdered soybean. The network structure of the powdered soybean curd could be correlated well with the results obtained from rheological measurements. A non-heated dispersion of powdered soybean showed two endothermic peaks in the temperature range studied by heating DSC (20–140 °C). It is suggested that a heated dispersion of powdered soybean formed a stronger gel with increasing concentration of powdered soybean. The powdered soybean curd was coarser and more heterogeneous than soybean curd (tofu) by CLSM. The powdered soybean (SP) curd showed a smaller rupture strain and rupture energy than soybean curd (tofu) at the almost same protein concentration. It was suggested that ingredients such as insoluble dietary fiber other than soybean protein don’t contribute to the network structure.

Quality of Potatoes by Sous Vide Processing

真空調理中の成分変化を明らかにするため, ジャガイモを用い, 真空度 (30,100Torr) と加熱温度 (70, 80, 90,100℃) の成分に及ぼす影響を調べ, さらに貯蔵中の品質に及ぼす温度の影響についても検討した。1) 30Torrで真空包装したジャガイモの加熱温度による硬さの経時変化をみると, 温度が高いほど早く軟化した。70℃では軟化したが褐変とともに異臭が生じ加熱温度として適当ではなかった。2) ジャガイモの硬さは90℃および80℃では真空度による差がみられなかったが, 100℃加熱では真空度が高いほど軟らかくなった。3) ジャガイモの総アスコルビン酸含量は100℃加熱では真空度により差はみられなかった。しかし, 100℃ならびに90℃加熱では, 袋詰め試料は, 未包装試料よりも総アスコルビン酸含量が高かった。酸化型アスコルピン酸含量は違いがみられなかった。4) 糖含量はいずれの温度でも真空度による違いはみられなかった。袋詰め試料と未包装試料を比較すると, 100℃加熱では差がみられなかったが, 90℃, 80℃と温度が低いほど未包装試料の含量が低下した。5) 真空調理したジャガイモの20℃貯蔵では貯蔵3日から微生物が検出され, 5日を超えると初期腐敗の段階に達した。貯蔵温度が低くなるほど微生物の繁殖が抑えられ, 5℃ならびに10℃では貯蔵7日まで微生物の繁殖は認められなかった。6) 貯蔵に伴い還元型アスコルビン酸が減少し, 酸化型アスコルビン酸が増加した。特に20℃でこの傾向が顕著にみられた。還元糖含量は貯蔵温度による違いはみられず, 貯蔵に伴い漸増した。以上の結果から, ジャガイモを真空調理する場合は90℃以上の温度で真空度は高い方がよいと考えられた。また, 貯蔵する場合5℃付近の低い温度で7日以内とするのが望ましいと考えられた。

Quality Changes of Cooking in Hypobaric-packaged Winter squash

真空調理中の成分変化を明らかにするため, カボチャ果実を用い, 真空度 (30,100Torr) と加熱温度 (70, 80,100℃) の成分に及ぼす影響について検討した。1) カボチャ果実の加熱後の表面色は100℃, 80℃では, いずれの真空度でも良好であったが, 70℃加熱の100Torrおよび常圧試料で褐変が生『じた。2) カボチャ果実の硬さは80℃および70℃では真空度による差がみられなかったが, 100℃加熱では真空度が高いほど軟らかくなった。3) カボチャ果実の総アスコルビン酸含量は100℃加熱では真空度による差はみられなかった。しかし, 80℃並びに70℃加熱で, 真空包装されたカボチャ果実は, 常圧およびContro1よりも総アスコルビソ酸含量が高かった。酸化型アスコルビン酸含量は真空度が高いほど低い傾向にあった。4) 糖含量はいずれの温度でも真空度による違いはみられなかった。袋詰め試料とControlを比較すると, 100℃加熱では差がみられなかったが, 80℃, 70℃と温度が低いほど含量が低下した。以上の結果からカボチャ果実を真空調理する場合は80℃以上の温度で真空度は高い方がよいと考えられた。