STABILITY of FROZEN STARCH PASTES: EFFECT of FREEZING, STORAGE and XANTHAN GUM ADDITION

ABSTRACT. Starch pastes act as protective systems of the solid elements in precooked frozen foods, minimizing their dehydration and chemical changes during storage. the effect of xanthan gum (0.3 % w/w) on corn starch and wheat flour pastes (10 % w/w), frozen at different freezing rates and stored between -5 and -20C, was analyzed. Freezing modified the quality attributes of the starch pastes increasing exudate production, structure deterioration and rheological changes compared to the unfrozen samples. Starch pastes showed a pseudoplastic behavior and apparent viscosities decreased in frozen samples. High freezing rates led to smaller ice crystals (indirect microscopic observation) and the absence of starch retrogradation. Starch retrogradation and ice recrystallization, both contributed to the deterioration of the frozen paste during storage (spongy structure, marked decrease of apparent viscosity and increase of syneresis). the addition of xanthan gum minimized spongy structure formation, exudate production and rheological changes; however, no protective effect was observed on ice crystal sizes and on amylopectin retrogradation by Differential Scanning Calorimetry.     

Effect of freezing rate and frozen storage on starch–sucrose–hydrocolloid systems

Model food systems based on starch (100 g kg⁻¹), sucrose (150 g kg⁻¹) and water (750 g kg⁻¹) with and without the addition of a low proportion of hydrocolloid (xanthan gum, guar gum or sodium alginate) were gelatinised, frozen at different rates and stored to analyse textural changes by oscillatory rheometry. Differential scanning calorimetry (DSC) was used to analyse gelatinisation, amylopectin retrogradation and glass transition temperatures. Sucrose had a significant effect on the increase in the gelatinisation temperature as well as on the decrease observed in glass transition values. The onset temperature of the second step of the glass transition, corresponding to the heat capacity change close to ice melting (denoted Tg_im in the present work), ranged between −23.0 and −22.2 °C. Rheological viscoelastic tests showed an increase in the dynamic moduli G* and G ′ after slow freezing and during storage at −19 °C (T > Tg_im) in starch–sucrose systems that is related to sponge formation due to amylose retrogradation. DSC studies confirmed that also amylopectin retrogradation occurs during storage; however, samples containing gums did not develop the spongy appearance. Storage at the usual commercial temperatures (close to −18 °C, slightly above Tg_im) affects the quality of aqueous starch–sucrose pastes without gums owing to amylose and amylopectin retrogradation. However, when hydrocolloids are included in the formulations, the usual storage conditions allow the maintenance of acceptable textural attributes. © 2000 Society of Chemical Industry     

Long-term stability of waxy maize starch/xanthan gum mixtures prepared at a temperature within the gelatinization range

The retrogradation behavior of waxy maize starch pastes with added xanthan gum was investigated. The pastes were prepared with or without added xanthan gum at two starch concentrations (5:100 and 7:100), at two temperatures within the gelatinization range (70 °C or 72 °C) and at acid or neutral pH. The evolution of the macrostructure (texture, flow behavior and syneresis), microstructure (oscillation rheology) and molecular aggregation (pulsed-field NMR) of the pastes was followed up in an 8 week period during cold storage (7 °C). Heating temperature was found to have a profound effect on the long-term stability of the pastes. Pastes prepared at 70 °C behaved as flocculated dispersions of largely intact, swollen granules which resulted in stable structural properties during the preservation period. At 72 °C, a higher degree of gelatinization and degradation was observed, resulting in structurally unstable systems due to association and crystallization of amylopectin. Especially for these systems, xanthan gum was found to enhance the gelation process, probably due to phase separation. Although xanthan gum may restrict the granule disruption during preparation, this beneficial effect on the freshly prepared pastes did not result in an improved stability during storage.     

Morphological,thermal and rheological properties of starches separated from rice cultivars grown in India

Morphological, thermal and rheological properties of starches separated from five rice cultivars (PR-106, PR-114, IR-8, PR-103 and PR-113), varying in amylose content, were studied. Amylose contents of starches separated from PR-103, IR-8, PR-106, PR-114 and PR-113 were 7.83, 15.62, 16.05, 16.13 and 18.86%, respectively. The granular size, measured using a Scanning Electron Microscope, varied from 2.4 to 5.4 μm in all rice starches. PR-103 starch, with lowest average granular size, amylose content and solubility, had the highest swelling power, while PR-113 starch, with the highest average granular size and amylose content had the lowest swelling power. PR-103 starch showed highest transition temperatures, enthalpies of gelatinization, peak height index, range and enthalpies of retrogradation. The retrogradation (%) was observed to be highest in PR-113 starch and lowest in PR-103 starch. The changes in rheological parameters of rice starches during heating were measured using a Dynamic rheometer. PR-113 rice starch showed the highest G′, G″ and breakdown in G′ values, whereas PR-103 starch showed the lowest values for these parameters. Turbidity value of gelatinized pastes from all rice starches progressively increased up to the 3rd day during refrigerated storage, PR-103 starch paste showed the lowest turbidity value and PR-113 starch showed the highest value. The syneresis (%) of starch pastes, from different rice cultivars during storage at 4 °C, was also measured. The syneresis of starch pastes from all rice cultivars, except PR-103, increased with storage. PR-103 starch paste showed negligible syneresis during storage.     

Classification of Rice Starch Amylose Content from Rheological Changes of Starch Paste after Cold Recrystallization

Following storage at 4°C for 24 h (recrystallization) rice starch pastes with low and medium amylose content exhibited a lower increase in consistency index, shear stress and Casson plastic viscosities than pastes with high amylose content. On the other hand, high amylose rice starch showed a higher degree of retrogradation than rice starch of lower amylose content.     

Influence of hydroxypropylation on retrogradation properties of native,defatted and heat-moisture treated potato starches

Recent studies have shown that defatting and heat-moisture treatment cause structural changes within the amorphous and crystalline regions of potato starch. Furthermore, the alkaline reagents (NaOH and Na₂SO₄) used during hydroxypropylation has been shown to cause structural changes within the amorphous and crystalline regions of native, defatted and heat-moisture treated starches. In this study, we have compared (using different techniques) the retrogradation properties of potato starch before and after physical (defatting and heat-moisture treatment), and chemical (alkaline treatment and hydroxypropylation) modification. Turbidity measurements showed that changes in turbidity during storage (4°C for 24 h and then at 40°C for 29 days) of native, defatted and heat-moisture treated gelatinized starch pastes were influenced by the interplay of two factors: (1) interaction between leached starch components (amylose–amylose, amylose–amylopectin, amylose–amylopectin), and (2) interaction between granule remnants and leached amylose and amylopectin. In alkali treated gelatinized native, defatted and heat-moisture treated starch pastes, turbidity changes on storage was influenced by aggregation of granule remnants. Hydroxypropylation decreased the rate and extent of increase in turbidity during storage of native, defatted and heat-moisture treated starches. The change in turbidity during storage of hydroxypropylated starch pastes was influenced by the interplay between: (1) steric effects imposed by hydroxypropyl groups on chain aggregation, (2) aggregation between small granule remnants, and (3) settling of large granule remnants beneath the path of the spectrophotometer beam. Stored gelatinized pastes of native, defatted and heat-moisture treated starches gave a `B' type X-ray pattern. A similar pattern was also observed after alkaline treatment, and hydroxypropylation. However, the X-ray intensity of the strong reflection at 5.2 Å decreased after alkaline treatment and hydroxypropylation. The retrogradation endotherm (monitored by differential scanning calorimetry) occurred after 2 days storage in native, defatted and heat-moisture treated starches. A similar trend was also observed after alkaline treatment. However, the retrogradation endotherm appeared only after 7 days in hydroxypropylated starches. The enthalpy of retrogradation in all starches decreased on alkaline treatment and hydroxypropylation.     

Effects of Cationization on Functional Properties of Pea and Corn Starches

Amylography, scanning electron microscopy and storage tests demonstrated that native pea starches were highly resistant to granule disintegration during heating in dilute slurries, resulting in low hot paste viscosity, high retrogradation and syneresis. Cationization at degrees of substitution of 0.02 to 0.05 reduced the pasting and gelatinization temperatures, increased peak viscosities and set-back on cooling but eliminated syneresis after storage at 4°C and − 15°C. The principal effects of cationization were to promote rapid granule dispersion at low pasting temperatures, yielding a molecular dispersion of amylose and amylopectin on heating to 95°C. On cooling, the gel structures were firm and the cationic groups controlled the realignment of starch chains during low temperature storage.     

Changes in rheological properties of hydroxypropyl potato starch pastes during freeze—thaw treatments. III. Effect of cooking conditions and concentration of the starch paste

The effects of different cooking conditions and concentrations on the freeze-thaw stability of hydroxypropyl potato starch (molar substitution 0·125) paste were investigated by dynamic rheological measurements and syneresis determination. The cooking conditions of the starch were chosen by taking the starch pastes at peak consistency (SP/Peak), at half breakdown consistency (SP/HB), after being held at 95°C for 15 min (SP/95°C) and after the whole pasting cycle (SP/25°C) in the Brabender Amylograph. The concentration effect was studied with the starch pastes after a whole pasting cycle at 35, 50 and 65 g kg^?1. Depending on cooking conditions and concentration, the rheological responses in changes of complex modulus (G*) and phase angle () of the starch pastes, with regard to the number of freeze-thaw cycles, differed considerably. This indicated that the starch pastes had undergone various structural changes during freeze-thaw treatments. With an increased extent of pasting, and with an increased starch concentration, the rheological responses indicative of the destabilisation process of the starch pastes were, in general, delayed. The number of freeze-thaw cycles required for the appearance of a peak in G*, related to the first syneresis, was one, two, five and six for SP/Peak, SP/HB, SP/95°C and SP/25°C, respectively. For the starch pastes at 35, 50 and 65 g kg^?1, it was four, six and seven cycles, respectively. Based on these rheological data, it was suggested that the amount of inter-mingled amylose and amylopectin in the dispersion of hydroxypropyl starch paste is the main controlling factor, which plays a critical role in the rheological response as well as in the syneresis.     

Effect of Cultivation Conditions on Retrogradation of Sweetpotato Starch

Sweetpotatoes were grown under four cultivation conditions, i. e. early planting and early harvesting (I, E‐E), standard (II, STD), early planting and late harvesting (III, E‐L), and late planting and late harvesting (IV, L‐L). Retrogradation of the starch isolated from fresh roots was estimated by the hardness and syneresis rate after two weeks of storage at 5 °C. A significant difference in retrogradation among the cultivation conditions and cultivars was observed. The starch tended to exhibit slower retrogradation in late harvesting, where the temperature was low. The differences in amylose content and the proportion of short unit‐chains (DP 9‐11) of amylopectin among cultivation conditions were also significant. Starch retrogradation was positively correlated with the proportion of chains with DP 12‐14 but negatively correlated with the proportion of DP 9‐11. Moreover, there was no significant correlation between amylose content and retrogradation. These results indicate that the main factor for retrogradation under any cultivation condition is the proportion of short unit‐chains of amylopectin. The best performance of sweetpotato starch as a food ingredient would be achieved by selecting both the proper cultivar and cultivation conditions.     

Influence of selected hydrocolloids on triticale starch rheological properties

The aim of the study was to define the influence of selected nonstarch polysaccharides (guar gum, xanthan gum and arabic gum) on several rheological properties of triticale starch pastes/gels, at constant polysaccharide concentration (6.5 g/100 g). These included pasting characteristics, flow curves at 50 °C and mechanical spectra at 25 °C. It was found that the presence of a gum in a system modified the rheological properties of triticale starch gels/pastes, depending on the type and concentration of the gums. In the case of guar and xanthan gums, higher pasting viscosity was observed and the shear stress was increased compared with native starch. The presence of guar gum reduced the degree of thixotropy hysteresis, negative values for this being found for systems with xanthan in spite of their shear‐thinning behaviour. Systems containing arabic gum displayed lower values of pasting and flow viscosity. The type and concentration of gums added to the polysaccharide influenced the viscoelastic properties of the gels.     

Effect of modified tapioca starch and xanthan gum on low temperature texture stability and dough viscoelasticity of a starch-based food gel

This work investigated the effect of modified tapioca starch and xanthan gum on dough viscoelasticity and texture stability during storage at 4 °C of starch sheets for Chinese shrimp dumplings. Hydroxypropylated starch and hydroxypropylated-crosslinked starch were used to substitute for tapioca starch in the control formulation, and xanthan gum was added to adjust the formulation. During storage, texture of the control became firmer due to amylopectin retrogradation confirmed by differential scanning calorimetry and X-ray diffraction. Conversely, gel sheets containing modified starches showed less texture change. Dough viscoelasticity of the formulations substituted by hydroxypropylated starch were much softer and easier to deform than that of the control one. Dough with hydroxypropylated-crosslinked starch was, however, stiffer and more strain-resistant. Moreover, the formulation comprising the mixture of both types of modified starches and xanthan gum gave dough viscoelasticity similar to that of the control, and provided gel sheet the least texture change. Consequently, this modified formulation could be beneficial for the application of frozen/chilled dumpling wrappers.     

Changes in Starch Properties of Corn Tortillas during Storage

Starch properties of corn tortillas were characterized during storage. Tortillas were chopped into pieces, macerated with ethanol, centrifuged, extracted again with ethanol, centrifuged, dried, and ground into flour to dehydrate and stabilize starch. Water absorption and water solubility at 25°C, starch pasting properties, and amount and molecular weight of starch extracted at 95°C in water were quantified. Increased levels of soluble amylopectin and increased cold paste viscosity distinguished fresh (0, 0.5, and 1 h) from aged (120 h) tortillas. Water solubility at 25°C decreased continuously during storage; whereas, water absorption increased 0.5 h after baking and then decreased during storage. Rapid changes in starch properties were stabilized using the dehydration procedure and clearly distinguished by pasting viscosities and other methods. Measured starch properties were consistent with very rapid associations (retrogradation) of amylose and rapid associations of amylose and amylopectin yielding insoluble structures in corn tortillas. Retention of some starch crystal nuclei after baking facilitated starch associations that yielded rapid structural changes in corn tortillas.     

Resistant Starch Content and Structural Changes in Maize (Zea mays) Tortillas During Storage

Storage of maize products such as tortillas may cause starch retrogradation and lead to resistant starch (RS) formation. This study was carried out to determine if storage of maize tortillas under refrigerated conditions enhanced RS content and/or modified RS structure. Improved Costeño variety maize grain was nixtamalized and processed into tortillas which were stored for five and ten days at 5°C. Total resistant starch (TRS) and retrograded resistant starch (RRS or RS3) contents were determined on raw and nixtamalized maize grain and tortillas stored for zero, five and ten days. Differential scanning calorimetry (DSC), X‐ray diffraction (XRD) and near‐infrared (NIR) spectroscopy were use to evaluate structural changes in retrograded resistant starch isolated from each sample type. Total starch content was 67 ± 1.5% for all samples, TRS ranged from 3.3% in the raw grain at 7.2% in tortillas stored for ten days, while RRS starch content ranged from 0% in the raw grain to 3.2% in tortillas stored for ten days. DSC showed endothermic transitions corresponding to amylopectin and amylose retrogradation, at 31.9 and 139.7°C in RRS from tortillas stored for five days, and at 47.9 and 146°C in RRS from tortillas stored for ten days. These values agreed with the higher total RS content recorded after prolonged storage. XRD revealed a starch crystallinity of 13.7% in tortillas stored for five days and 15.3% in those stored for ten days. NIR spectroscopy analysis showed evidence of structural changes in polymeric order that were more pronounced in RRS of tortillas stored for ten days, due to increase in crystalline region.     

In vitro availability of starch in heat‐treated potatoes as related to genotype,weight and storage time

The objective of the study was to determine the influence of potato variety, weight and storage time after lifting on the glycaemic index (GI) and resistant starch (RS) content predicted from measurement of the rate and extent of in vitro starch hydrolysis, respectively. The potatoes were either boiled, or boiled and subjected to different heat‐cycling conditions selected to promote retrogradation of amylose or amylopectin, respectively. The hydrolysis indices (HI) and predicted GIs of all 19 potato products were high and fell within narrow ranges of 122–144 and 118–138, respectively. No correlation between average weight of the potato tuber and HI was found. Furthermore, there was no difference in HI between potatoes stored for 1–3 or 8–10 months, nor between varieties of new potato and winter potato. However, the HI was significantly lowered by temperature cycling at conditions known to promote retrogradation of amylopectin (6 °C, 48 h) compared with 6 °C for 24 h followed by 70 °C for 24 h. RS content was already substantial in boiled potatoes, 4.5 g 100 g^?1 (starch basis), and could be increased further by temperature cycling, the highest yield obtained, 9.8 g 100 g^?1 (starch basis), following heat treatment at 6 °C for 24 h followed by 70 °C for 24 h; that is at conditions known to favour amylose retrogradation. Copyright © 2004 Society of Chemical Industry     

Effect of the Extent of Conversion and Retrogradation on the Digestibility of Potato Starch

The effect of starch conversion on the susceptibility of potato granules to α‐amylase was studied by direct sampling at different pasting times corresponding to different points on the RVA profile of a 6.4% (w/w) suspension of starch in distilled water. Native granules showed high resistance to α‐amylase with 8.6 ± 0.4% digestibility for a 6 h incubation period with the enzyme. When the suspension was heated to 60 °C, the digestibility increased to 53.5 ± 0.7% although, at this temperature, there was still no noticeable increase in the measured viscosity (≤0.040 Pa · s). The material sampled after a pasting time corresponding to the RVA peak viscosity showed a digestibility of 88.4 ± 0.5%. This suggested, owing to the expected retrogradation of amylose on cooling, the quasi‐total susceptibility of amylopectin to enzymatic digestion at this pasting stage. The effect of ions on the swelling of potato starch was used to assess whether the decrease of the swelling of the granules in the presence of NaCl was paralleled by an increase in resistance to α‐amylase. A small (∼6.1%) but significant decrease in the digestibility of pasted starch was observed in the presence of salt. Finally, the effect of the retrogradation of the amylopectin fraction on its digestibility was assessed in extruded potato starch ribbons containing 35% (w/w) water and stored at different temperatures. After 14 days of storage, the digestibility decreased from 77.0 ± 0.9% in the freshly extruded samples to between 28.0 ± 1.7% and 42.1 ± 0.3%, depending on the storage temperature. This suggested a measurable difference in the α‐amylase susceptibility between the A and B polymorphs of retrograded amylopectin.     

Thermal and rheological properties of tapioca starch gels with and without xanthan gum under cold storage

Changes in the thermal and rheological properties of tapioca starch (TS) with and without xanthan gum (Xan) (total polysaccharide concentration = 25% w/w) were investigated using a differential scanning calorimeter, Rheolograph Gel and Texture Analyser. The gelatinization temperatures of TS shifted to higher values with the Xan concentration. Xan enhanced the retrogradation of TS during the initial stage of storage but retarded the process for a further storage time at 5 °C. The onset temperature of all reheated TS/Xan gels decreased with increasing storage time indicating thermally unstable structure formation after a longer storage time. Storage Young’s moduli (E′) of the TS and TS/Xan gels stored at 5 °C increased with increasing storage time. The E′ values became more temperature dependent with storage time due to the weak cross-linkage of amylopectin molecules in the gels but became less dependent in the system containing Xan. TS/Xan gels kept for 14 days showed lower Young’s moduli than TS gels from the compression test confirming retardation of the retrogradation process by Xan. The results suggested that Xan could retard the retrogradation of TS gels for longer storage times.     

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.     

Effect of Freezing on Functional and Textural Attributes of Cress Seed Gum and Xanthan Gum

Consumer habits have undergone great changes, motivated by the new social lifestyle. These changes have promoted the increase in the production of frozen foods; and as a result, many food applications of some hydrocolloids are limited due to functional loss during freezing. In this study, the effect of freezing treatments (?18 °C for 24 h and ?30 °C for 15 h) on rheological, emulsifying, foaming, and textural characteristics of cress seed gum as a new source of hydrocolloid in comparison with xanthan gum as a commercial gum were investigated. The results demonstrated that cress seed gum had significantly lower viscosity than xanthan gum solution, and the freezing treatments did not have significant impact on rheological properties of both products. Conversion of water to ice leads to an increment in molecular association and improved textural characteristics. The high tendency of cress seed gum chains to associate is attributed to its high mannose to galactose ratio. High stability of cress seed gum and similarity with xanthan gum make it attractive for use in frozen foods as a novel gum to provide specific functionality, minimize the negative effect of freezing, and reduce production costs.     

Impacts of Low and Ultra-Low Temperature Freezing on Retrogradation Properties of Rice Amylopectin During Storage

Amylopectin retrogradation is a serious problem in starch-based ready meals. In the current research, rice amylopectin was frozen by low temperature (−20, −30, and −60°C) and ultra-low temperature (−100°C), and then stored at 4°C for 21 days or at −18°C for up to 5 months to evaluate the retrogradation properties. Amylopectin retrogradation enthalpy of rice was determined by a differential scanning calorimetry. The results showed that low temperature and ultra-low temperature freezing can effectively retard amylopectin retrogradation during the freezing process and during frozen storage (−18°C) for at least 5 months. However, rice amylopectin still retrograded after the freezing process during chill storage at 4°C. The methods of low and ultra-low temperature freezing combined with frozen storage might be potentially very useful for food industry to produce high quality starch-based ready to eat meals.     

Modeling of Retrogradation of Waxy and Normal Corn Starches

Retrogradation behavior of waxy and normal corn starch gels stored at 5 and 21°C were investigated for 50 days by differential scanning calorimetry. The extend of retrogradation can be expressed as the ratio of retrogradation and gelatinization enthalpy values and these were 70–78% for normal corn starch and 39–68% for amioca stored at two temperatures. Higher retrogradation rates were observed at 5°C for both waxy and normal corn starch. Kinetic data were evaluated by considering retrogradation as consecutive reactions in series and by Avrami Equation. High R² values (0.97–0.98) indicated that both models can be used for prediction. The comparison of rate constants obtained by Avrami Equation indicated that both temperature and amylose content of starch affected the recrystallization rate. By the kinetic model based on consecutive reactions in series, it was proven mathematically that the rate limiting step in recrystallization of starch gels is the nucleation.