Effect of repeated freezing-thawing on structural,physicochemical and digestible properties of normal and waxy starch gels

The normal and waxy corn starch gels were subjected to repeated freeze–thaw treatment at 0, 1, 2, 3, 4,5 and 6 cycles with an interval of 24 h, and the effects on structural, physicochemical and digestible properties were investigated. The normal starch gels formed a honeycomb structure while waxy starch gels exhibited a lamellar structure, and the number of holes and lamellas increased with increasing cycles. The X-ray analysis showed that the A-type pattern of starches was converted into the B-type after treatment, and their relative crystallinity increased with the number of increased freeze–thaw cycles. The hardness increased in both normal and waxy starch. The solubility and pasting breakdown viscosity decreased in normal starch while they increased in waxy starch. The pasting peak time, peak viscosity, and setback viscosity increased in normal starch but decreased in waxy starch. The rapidly digested starch (RDS) and slowly digested starch (SDS) content in normal starch increased and non-digestible starch (RS) content decreased whereas the RDS, SDS and RS content in waxy starch was almost unchanged as the freeze–thaw cycles increased. In the meantime, the molecular weight of both normal and waxy starch decreased with freeze–thaw treatment. Therefore, the repeated freeze–thaw treatment can change the physicochemical and digestible properties which could be a basis for starch-based food processing.     

颗粒状冷水可溶淀粉糊性质的研究

在常压下,用醇解法制备了不同溶解度的颗粒状冷水可溶淀粉系列,并对玉米、木薯和马铃薯原淀粉及其不同溶解度的颗粒状冷水可溶淀粉糊的性质进行了研究。试验证明,相对于原淀粉糊,醇解法制备的颗粒状冷水可溶玉米淀粉糊的表观粘度和冻融稳定性有所提高,凝沉性降低;颗粒状冷水可溶木薯和马铃薯淀粉糊的表观粘度、凝沉性和冻融稳定性均降低。三种颗粒状冷水可溶淀粉糊的透明度大大提高,且随着溶解度提高其透明度增大。     

Selected Physicochemical Properties of Starch Isolated from Fermented Sorghum Flour

Starch was isolated from fermented sorghum flour (24 h natural lactic acid fermentation), and water retention, starch solubility, clarity of starch pastes and freeze‐thaw stability were measured. In comparison with starch isolated from unfermented sorghum flour, fermentation increased the solubility of the starch and decreased the water retention, but it had no effect on the freeze‐thaw stability of the starch. There was no substantial difference in the starch paste clarity between the two samples. Storage of starch pastes at lower temperature (4°C) resulted in a very low clarity of starch.     

Physicochemical properties of octenyl succinic anhydride‐modified potato starch with different degrees of substitution

BACKGROUND: Esterified starch is an important type of modified starch. In particular, octenyl succinic anhydride‐modified starch (OSA starch) is widely used in the food industry. However, there has been little research on the properties of products with different degrees of substitution (DS). Therefore the aim of this study was to analyse the physicochemical properties of products with different DS. RESULTS: OSA starch samples with different DS were prepared from potato starch. Two new peaks were observed in the Fourier transform infrared spectrum, one at 1724 cm^?1 due to C?O and one at 1572 cm^?1 due to RCOO? . Emulsifying capacity and emulsion stability improved with increasing DS. Rheological analysis showed the occurrence of the ‘shear‐thinning’ phenomenon, the viscosity of the sample with DS = 0.0211 being even lower than that of native starch. A decrease in syneresis rate from 88.3% (native starch) to 39.0% (DS = 0.0211) indicated that freeze–thaw stability was improved. CONCLUSION: The physicochemical properties of OSA potato starch were better than those of native potato starch. Freeze–thaw stability, emulsifying capacity and emulsion stability improved with increasing DS. Viscosity increased at lower DS but decreased at DS = 0.0211. Copyright © 2009 Society of Chemical Industry     

Influence of xyloglucan on gelatinization and retrogradation of tapioca starch

Dynamic and steady shear rheometry and differential scanning calorimetry (DSC) were used to investigate effects of xyloglucan (XG) on gelatinization and retrogradation of tapioca starch (TS). The viscosity of TS/XG pastes immediately after gelatinization increased with increasing XG content at the total polysaccharide concentration of 3.5%. Gelatinized TS alone showed pseudoplastic flow at low shear rates and dilatant behavior at higher shear rates (about >1 s⁻¹), while mixtures with XG did not show dilatancy. Mechanical spectra of TS pastes containing XG were more liquid-like than those of TS pastes without XG. XG provides shear stability to the TS during storage. Increases in dynamic moduli during storage at 5 °C were suppressed in the presence of XG. In contrast, the retrogradation ratio determined based on DSC increased more rapidly in the presence of XG. These results suggest that XG forms a continuous liquid phase in a mixture to impart better mechanical stability during storage but to accelerate re-ordering of starch polysaccharides by effectively reducing the amount of water available for starch.     

Effect of rice ageing and freeze‐thaw cycle on textural properties of cooked rice (Oryza sativa L.) cv. Khao Dawk Mali 105

This study investigated the effect of rice grain ageing (0.7–12 months) and freeze‐thaw 1–5 cycles on the textural properties of cooked rice. The cooked rice from aged rice grains was freezing and thawing up to five cycles. Ageing of the rice grain increased the hardness and decreased the stickiness of the cooked rice. Repeated freeze‐thaw cycles caused an increase in hardness and a decrease in stickiness of aged cooked rice. Scanning electron micrographs showed a rough surface on the cooked rice after repeated freeze‐thaw cycles, especially for cooked rice from rice aged for 12 months. Differential scanning calorimetry and X‐ray diffraction showed increased starch retrogradation with increased freeze‐thaw cycles. The gelatinisation temperature and gelatinisation enthalpy increased when rice was aged for longer periods. Thus, ageing of rice and the number of freeze‐thaw cycles influence the textural properties of cooked rice.     

Influences of chitosan on freeze–thaw stability of Arenga pinnata starch

This study aims to investigate chitosan (CS) with five different molecular weight (Mw) on freeze–thaw stability of Arenga pinnata starch (APS) gel subjected to five freeze–thaw cycles (FTC). The syneresis of APS gels was reduced by adding CS and the APS gel with high Mw CS had lower syneresis duo to a higher water holding capacity (P < 0.05). The addition of CS significantly decreased the hardness and molecular ordered structure of APS gel. In addition, CS could improve the microstructural stability. The results suggested that CS could effectively improve the freeze–thaw stability of APS gel, and CS with higher Mw might have more practical utility to improve stability of APS gel.     

Molecular Background of Technological Properties of Selected Starches

Selected starches, i.e. waxy maize, amaranth, quinoa, wheat, millet and buckwheat starches, were investigated with respect to their technological properties such as gelatinization, stability to mechanical stress, resistance to conditions and stability in continuous freeze/thaw cycles. Technological properties are correlated with molecular features such as branching characteristics in terms of iodine-complexing potential, molar mass, occupied glucan-coil volume, packing density of glucan coils and rheological properties. Waxy maize and amaranth starches were found to be amylopectin-type short-chain branched (scb) glucans with weight average molar masses M_w = 17 × 10⁶ g/mol and 12 × 10⁶ g/mol, respectively. Waxy maize starch had a high gelatinization potential, high viscosity at 95 °C (340 mPas) low stability at acidic conditions, average stability to shearing and good freeze/thaw stability. For amaranth starch a viscosity of 122 mPas at 95 °C, low resistance to acid, but high stability to applied shearing and even high freeze/thaw stability was determined. Investigated quinoa starch was classified as scb-type glucan, however, the branches are significantly longer than those of waxy maize and amaranth. With a M_w = 11 × 10⁶ g/mol and a viscosity of 187 mPas at 95 °C, this sample is comparably resistant to acidic conditions and to shearing, but instable in freeze/thaw experiments. Wheat, millet and buckwheat starches contain significant percentages of amylose-type long-chain branched (lcb) glucans (22.1, 32.1 and 24.3 %, respectively) with M_w values of 5 × 10⁶ g/mol, 12 × 10⁶ g/mol and 15 × 10⁶ g/mol, respectively. Wheat starch, with a viscosity of 107 mPas at 95 °C, shows low stability under acidic conditions, but high stability to shearing. Wheat and millet starches, but not buckwheat starch, form weak gels in the course of subsequent freeze/thaw cycles. Millet starch, with a viscosity of 101 mPas at 95 °C was found to be moderately stable under acidic conditions and to shearing. Buckwheat starch with a viscosity of 230 mPas at 95 °C shows no acid resistance and is instable upon shearing but performs very well in freeze/thaw experiments.     

Biochemical and physicochemical changes in catfish (Silurus glanis Linne) muscle as influenced by different freeze–thaw cycles

Freeze–thaw cycles affected the biochemical and physicochemical properties of catfish fillets. When the number of freeze–thaw cycles increased, the activities of α-glucosidase and β-N-acetyl-glucosaminidase increased (P<0.05). No increase in non-heme iron content was observed (P>0.05); however the heme iron content decreased (P<0.05). This suggested that the freeze–thaw process caused damage of the cell and hemeprotein, resulting in the release of pro-oxidants. No differences in metmyoglobin and autolysis products (P>0.05) were found as affected by freeze–thaw cycles. After 3 days of chilled storage (2–4°C), a small non-significant increase in non-heme iron content was observed with a concomitant decrease in heme iron. Thiobarbituric acid-release substance increased significantly (P<0.05), especially for the fillets subjected to five freeze–thaw cycles. Components with spectral characteristics similar to hydrogen peroxide-activated hemoproteins were detected with a concomitant decrease in metmyoglobin content in five-cycle freeze–thawed samples after 3 days of storage. The freeze–thaw process therefore has a detrimental effect on the quality of catfish fillets, particularly after chilled storage.     

马铃薯氧化淀粉性质及表征

采用马铃薯淀粉为原料,FeSO4为催化剂,H2O2为氧化剂干法制备氧化淀粉,对氧化淀粉溶解度及其糊的表观粘度、透明度、冻融稳定性、凝沉性等性质进行研究。结果表明,与原淀粉相比,马铃薯氧化淀粉溶解度、透明度增大,表观粘度降低,冻融稳定性增强,凝沉性减弱;并对氧化淀粉结构进行表征。     

Influence of Xanthan–Curdlan Hydrogel Complex on Freeze‐Thaw Stability and Rheological Properties of Whey Protein Isolate Gel over Multiple Freeze‐Thaw Cycle

The effect of adding xanthan–curdlan hydrogel complex (XCHC) at 2 concentrations (0.25 and 0.5% w/w) on the freeze‐thaw stability of heat‐induced whey protein isolate (WPI) gel was investigated. Samples were stored at 4 °C for 24 h before subjected to 5 freeze‐thaw cycles alternating between ?16 °C (18 h) and 25 °C (6 h). Adding XCHC to the WPI solution resulted in the reduction of a significant amount of syneresis up to 5 repeated freeze‐thaw cycles. Addition of XCHC decreased the amount of syneresis from 45% in the control sample (pure WPI gel) to 31.82% and 5.44% in the samples containing 0.25% and 0.5% gum, respectively, after the 5th freeze‐thaw cycle. XCHC increased the storage modulus (G′) of the gels and minimized the changes of the G′ values over the 5 freeze‐thaw cycles, indicating improvement of the stability of the system. Furthermore, the minimum protein concentration for gel formation decreased in the presence of the XCHC. Scanning electron microscopy (SEM) images showed that addition of XCHC resulted in the formation of a well‐structured gel with numerous small pores in the network, which consequently improved the water retention ability during the temperature abuses up to 5 freeze‐thaw cycles. These results have important implications for using XCHC in the formulation of the frozen WPI‐based products with improved freeze‐thaw stability and rheological properties.     

Gelatinization and rheological properties of rice starch/xanthan mixtures: Effects of molecular weight of xanthan and different salts

Effects of molecular weight (M_w) of xanthan (XG) and salts (0.1 M NaCl or CaCl₂) on the pasting, thermal, and rheological properties of rice starch (RS) were studied. A series of five XG samples, having various M_w, was prepared by homogenization of native XG solutions in the presence or absence of salts. The presence of salts greatly reduced the intrinsic viscosities, [η], of all XG solutions. Rapid visco-analysis (RVA) data showed that XG addition increased the peak, breakdown, final, and setback viscosities of RS, either in the presence or absence of salts, whereas the pasting temperatures were unaffected. Differential scanning calorimetry (DSC) demonstrated that the gelatinization temperatures of RS were unaffected by XG addition but slightly increased by CaCl₂ addition, whereas the gelatinization enthalpies (ΔH) were significantly decreased by additions of XG and salts. Dynamic shear data revealed weak gel-like behaviour in all paste samples in which their rigidity was decreased by XG addition. Flow tests showed that all pastes exhibited time-dependent shear-thinning (thixotropic) with yield stress behaviour in which the hysteresis loop areas were significantly decreased by XG addition, whereas the other rheological parameters varied differently among the samples, with and without added salt. In general, the effects of XG addition on the pasting and rheological properties of RS were more pronounced with increasing M_w of XG and these effects depended on salts added.     

Improving the freeze–thaw stability of emulsions via combining phosphatidylcholine and modified starch: A combined experimental and computational study

Phosphatidylcholine (PC)-coated emulsion was unstable during the freezing process. This study aimed to investigate the influences of octenyl succinic anhydride modified starch (OSAS) to PC weight ratios on the properties of the OSAS–PC complex and freeze–thaw stability of oil-in-water (O/W) emulsions. The results of molecular dynamics (MD) simulation indicated that electrostatic interaction was dominant in the complex. When OSAS/PC weight ratios were 5:5, 6:4, and 3:7, the complex showed a relatively low interfacial tension, high interfacial layer thickness, and high apparent viscosity at low shear rate. Z-average diameter in emulsions increased from 175.8 to 270.0 nm and zeta-potential increased from –49.2 to –29.7 mV, when OSAS/PC weight ratio varied from 0:10 to 7:3. OSAS–PC complex in weight ratios of 3:7 and 5:5 remarkably improved the freeze–thaw stability of emulsions (no creaming and aggregates), which may be related to a thick and dense interfacial layer. These findings indicated that the freeze–thaw stability of PC-stabilised emulsions could be improved by OSAS with low levels.     

The physicochemical and binder properties of starch from Persea americana Miller (Lauraceae)

Avocado starch was extracted from the kernels of the fruit Persea americana Miller (Fam. Lauraceae) and evaluated for its potential as an alternative to maize starch as a pharmaceutical excipient. Its physicochemical and thermal properties were evaluated and compared with those of maize starch. Granules prepared with avocado and maize starch pastes as binder were evaluated for their flow, friability and compaction characteristics. The average yield of starch extracted from the fresh kernels of P. americana was 20.5 ± 0.55% w/w. The scanning electron micrograph (SEM) showed that avocado starch has two characteristic granule shapes; triangular and circular both having an approximate equal distribution. The triangular shaped granules are larger (28 to 32 µm) than the circular (6 to 9 µm). The foaming capacity of avocado starch was 19.05 ± 0.6%, its swelling, moisture uptake and paste clarity were generally lower than that of the maize starch. Avocado starch gel exhibited an extent of syneresis after freeze–thaw that increased cumulatively with increase in number of freeze–thaw cycles. The glass transition (T_g) and gelatinisation temperatures for avocado starch were higher than that of maize starch. The melting temperatures (T_m), ash value, as well as the various densities of avocado starch showed similarities with those of maize starch. The granules prepared with avocado starch pastes as binder showed superior compactibility and mechanical strength to those of maize starch but with similar flow characteristics. Avocado starch generally showed distinct physicochemical and binder properties with some similarities to the standard maize starch.     

青冈属淀粉糊特性研究

采用偏光显微镜、分光光度计、旋转粘度计等分析仪器 ,对青冈属淀粉糊特性进行了较详细的研究。试验结果表明 ,糊化温度分别为云山青冈淀粉 67.0～ 76.5℃、大叶青冈淀粉64.5～ 75 0℃ ,细叶青冈淀粉 65 5～ 75 0℃。青冈属淀粉糊具有酶解率偏低、透明度低、凝沉稳定性较强、冻融稳定性很好的特性。在 pH值 6 0～ 8 0范围内青冈属淀粉糊粘度较高 ,温度和转速对糊粘度有一定影响 ,浓度对糊粘度有非常显著的影响     

Improving effect of xanthan and locust bean gums on the freeze-thaw stability of white sauces made with different native starches

The effect of adding xanthan gum and locust bean gum at low concentrations (0.15% w/w) on the freeze/thaw stability of white sauces prepared with native starches from four different sources (corn, waxy corn, potato, and rice) was investigated. Linear viscoelastic properties were taken as structural indicators and these and syneresis as indicators of the freeze/thaw stability of the sauces. The pasting properties of the starch in the sauce system were also studied. Both hydrocolloids reduced the structural changes occurring after thawing, xanthan gum being more effective than locust bean gum. In corn and potato sauces, the most affected by the freeze/thaw cycle, the appearance of syneresis and the increase in viscoelastic functions were significantly reduced by both hydrocolloids. In general, the addition of hydrocolloids affected peak, hot peak and cold peak viscosities and reduced relative total setback. The results regarding the possible effects of hydrocolloid addition to white sauce systems are discussed in molecular terms.     

Thermal and rheological properties of tapioca starch and xyloglucan mixtures in the presence of sucrose

The influence of sucrose on thermal and rheological properties of tapioca starch (TS)–tamarind seed xyloglucan (XG) mixtures was investigated. Rapid visco-analysis profiles of 5% w/w TS/XG dispersions at different mixing ratios revealed that peak and final viscosities increased with increasing sucrose and XG contents. Loss tangent of each mixing ratio of TS/XG pastes determined from dynamic rheometry exhibited a lower value with increasing sucrose, suggesting solid-like properties contributed from the dissolved sucrose in the systems. Gelatinization temperatures of 25% w/w TS/XG at mixing ratios of 10/0 and 9/1 increased with increasing sucrose content whereas the gelatinization enthalpy of pastes increased in the presence of high sucrose concentration. Sucrose increased the stiffness and hardness of the 25% w/w TS/XG gels (mixing ratios of 10/0, 9.5/0.5 and 9/1) from the compression test. These results suggest that sucrose delays the gelatinization of TS and XG mixtures and strengthens the gels by increasing the elastic component.     

Combined effect of autoclaving‐cooling and cross‐linking treatments of normal corn starch on the resistant starch formation and physicochemical properties

Normal corn starch (NCS) was treated by both autoclaving‐cooling and cross‐linking to produce resistant starch (RS). The RS yield, crystalline structure, as well as other physicochemical properties of the modified starch were investigated. The yield of RS was 12.2% by four autoclaving‐cooling cycles, and it could be further increased up to 31.0% by the subsequent cross‐linking using sodium trimetaphosphate/sodium tripolyphosphate. The scanning electron microscopy images clearly illustrated that the granular structure of native starch was disrupted and a continuous network with irregular shape was formed after autoclaving‐cooling cycles. The subsequent chemical cross‐linking appeared to make the network structure more compact and dense. X‐ray diffraction patterns showed that B‐ and V‐types coexisted in all the modified corn starches, and all these modified starches exhibited very low viscosity which remained almost constant regardless of temperature changes.     

马铃薯淀粉基脂肪模拟物性质研究

以马铃薯淀粉为原料,在不同条件下对其进行酶法水解制备低DE值脂肪模拟物,并对DE值在2.0～4.1之间脂肪模拟物水溶性、持水性、冻融稳定性、回生现象和表观粘度进行测定;结果表明,DE值在2～3的马铃薯淀粉基脂肪模拟物具有较好水溶性、持水性、冻融稳定性、凝胶强度,不易发生回生凝沉现象。     

The influence of different stabilizers and salt addition on the stability of model emulsions containing olive or sesame oil

Stabilizers are widely used in low-fat emulsion production. However, food industry pays attention to ingredients, such as resistant starch (RS) that also present substantial benefits to human health. Low-fat model emulsions of either olive or sesame oil that also contained xanthan gum (XG), whey protein concentrate (WPC), and undigested (resistant) starch (RS) were produced and stored at 5 °C. Salt was added in selected samples. A multiple light scattering technique was applied for investigating destabilization phenomena. Microscopic observations and droplet size measurements took place. Rheological properties performing a heating–cooling cycle experiment (5–25–5 °C) were measured. Olive oil emulsions presented the greatest stability and the lowest droplet size. RS plays the role of solid particle stabilizer, mainly entrapped in the matrix of the continuous phase. By salt addition stability was significantly improved, whereas droplet size was decreased. Those samples had a more pronounced elastic character and significantly greater viscosity values than their counterparts without salt.