Studies on tuber starches III. Impact of annealing on the molecular structure, composition and physicochemical properties of yam (Dioscorea sp.) starches grown in Sri Lanka

Effects of Continuous and Cycled Annealing on the Physicochemical Properties and Digestibility of Water Caltrop Starch

The effects of treatment time of continuous annealing (ANN) and cycle numbers of cycled ANN on the structural, physicochemical, and digestive properties of water caltrop starch were studied under 70% moisture at 65 °C. It was found that continuous and cycled ANN have no significant effects on the morphology of starch granules. However, the relative crystallinity and content of resistant starch increased pronouncedly, possibly due to crystalline perfection, which also led to the rise in gelatinization temperature and the narrowed gelatinization temperature range of starch. The treatment time in continuous ANN generally showed a pronounced effect on the rheological properties of water caltrop starch. During pasting, the breakdown viscosity and setback viscosity of all treatment decreased, implying that ANN modified starch was less susceptible to the condition in heating and continuous shearing, and less likely to cause short-term retrogradation. In contrast, peak viscosity decreased with increasing treatment time of continuous ANN, indicating crystalline perfection restricted the swelling of starch granules and viscosity development during pasting process, which was consistent with the results of steady and dynamic rheological evaluation. All ANN-modified samples showed pseudoplastic behavior with weak gel viscoelastic characteristic. Under a total annealing time of 96 h, the pasting and rheological properties of water caltrop starch were essentially less affected by annealing cycle numbers. However, multistage ANN showed stronger resistance to enzyme hydrolysis.

Effects of enhanced starch-xanthan gum synergism on their physicochemical properties, functionalities, structural characteristics, and digestibility

The limited and unstable interactions between potato starch (PS) and xanthan gum (XG) by simple mixing (SM) lead it difficult to induce substantial changes in starchy products. Structural unwinding and rearrangement of PS and XG by critical melting and freeze-thawing (CMFT) were used to promote PS/XG synergism, and the physicochemical, functionalities, and structural properties were investigated. Compared to "Native" and SM, CMFT promoted the formation of large clusters with a rough granular surface and wrapped by a matrix composed of released soluble starches and XG (SEM), thus making the composite more compact to thermal processes, such as the significantly decreased WSI and SP, and increased the melting temperatures. The enhanced synergism of PS/XG after CMFT effectively decreased the breakdown viscosity from ~3600 (Native) to ~300 mPa·s and increased the final viscosity from ~2800 (Native) to ~4800. CMFT significantly increased the functional properties of PS/XG composite, including water/oil absorptions and resistant starch content. CMFT caused the partial melting and loss of large packaged structures in starch (XRD, FTIR, and NMR), and the melting and the loss of crystalline structure controlled at approximately 20 % and 30 %, respectively, are the most effective for promoting PS/XG interaction.

Properties Comparison of Oxidized and Heat Moisture Treated (HMT) Starch-Based Biodegradable Films

Starch-based biodegradable films have been studied for a long time. To improve starch properties and to increase film characteristics, starch is commonly modified. Amongst different types of starch modifications, oxidation and heat moisture treatment are interesting to explore. Unfortunately, review on these modifications for film application is rarely found, although these starch modifications provide interesting results regarding the starch and film properties. This paper aims to discuss the progress of research on oxidized and heat moisture-treated-starch for edible film application. In general, both HMT and oxidation modification on starch lead to an increase in film's tensile strength and Young's modulus, suggesting an improvement in film mechanical properties. The elongation, however, tends to decrease in oxidized starch-based film, hence more brittle film. Meanwhile, HMT tends to result in a more ductile film. The drawback of HMT film is its lower transparency, while the opposite is observed in oxidized films. The observation on WVP (water vapor permeability) of HMT starch-based film shows that the trend of WVP is not consistent. Similarly, an inconsistent trend of WVP is also found in oxidized starch films. This suggests that the WVP parameter is very sensitive to intrinsic and extrinsic factors. Starch source and its concentration in film, film thickness, RH (relative humidity) of film storage, oxidation method and its severity, plasticizer type and its concentration in film, and crystallinity value may partly play roles in determining film properties.

Physicochemical, structural, and rheological characteristics of corn starch after thermal-ultrasound processing

Thermal-ultrasound treatment is a green technology that can significantly alter the structural and functional properties of starches. This research extend the effect of at different temperatures (25 °C, 45 °C, and 65 °C) and times (30 and 60 min) on the physicochemical, structural, and rheological properties of corn starch was studied. Amylose content, solubility, swelling power, and the least gelling content increased with increasing temperature and time. Starch treated at 45 °C for 30 min had the lowest syneresis among all treatments. Thermal-ultrasound treatment at 25 °C and 65 °C for 60 min caused increasing paste clarity. Microscopic observations demonstrated that the starch granules were agglomerated at 65 °C. Although the crystallinity of samples decreased from 35.42% to 8.94%, the storage modulus was more than the loss modulus during the frequency sweep test. Pasting properties showed that pasting temperatures shifted to higher values after treatment. Nonetheless, the maximum viscosity decreased, and the final viscosity of the treated samples demonstrated that short-term retrogradation could deteriorate. Results showed that thermal-ultrasound is a viable technique for starch modification compared to conventional thermal and ultrasound treatments.

Hydrothermal modifications of nonconventional kithul (Caryota urens) starch: physico-chemical, rheological properties and in vitro digestibility

Effect of hydrothermal modifications (autoclaving, annealing and heat moisture treatment) on physico-chemical, rheological properties and in vitro digestibility of kithul starch was studied. Annealing and heat moisture treatment decreased swelling index, solubility and increased crystalline properties as compared with autoclaving. Autoclaving, annealing and heat moisture treatment caused significant morphological damages such as large holes and fissures on the kithul starch, in addition, granules changed from oval to donut shape. Heat moisture treatment formed higher number of agglomerated starch granules. Light transmittance decreased after hydrothermal modifications. Autoclaving and annealing increased the pasting viscosities (except break down viscosity) of kithul starch. A significant increase (p ≤ 0.05) in peak temperature, conclusion temperature and enthalpy was found in annealed and heat moisture treated kithul starches. The digestibility of kithul starch decreased with increasing resistant starch after annealing and heat moisture treatment. Autoclaved, annealed and heat moisture treated kithul starches exhibited higher value of storage modulus (G') and loss modulus (G″) than native kithul starch. It entail to higher firmness of modified starch gel. The current study showed that the remarkable changes formed by hydrothermal modifications increased the industrial acceptance of kithul starch.

Kithul palm (Caryota urens) as a new source of starch: Effect of single, dual chemical modifications and annealing on the physicochemical properties and in vitro digestibility

The objective of this study was to determine the effect of physical and chemical modifications on the physicochemical and in vitro digestibility of kithul starch. Starch isolated from kithul flour (Caryota urens) was subjected to physical and chemical modifications. The starch modification was verified by the presence of functional groups using Fourier transform Infrared spectral analysis (FT-IR). X-ray Diffraction (XRD) pattern revealed that the kithul starch is A- type and the modifications did not change the crystalline pattern. However, the relative crystallinity showed significant changes. Chemical modifications increased the swelling and solubility. Pasting and thermal parameters of all modified starches showed significant changes as compared to native starch (NS). Acetylated oxidised starch (AOS) showed highest paste viscosities. Higher enthalpy of gelatinization (∆H_gel) and paste viscosity attributed to perfection and ordering of amorphous regions in annealed starch (ANS). All modifications significantly increased the resistant starch (RS) content than native starch (NS), which indicates its lower digestibility. The current study showed the single, dual chemical modifications and annealing, effectively modified the physicochemical and in vitro digestibility of kithul starch.

Impact of hydrothermal modifications on the physicochemical, morphology, crystallinity, pasting and thermal properties of acorn starch

Native acorn starch had high purity and the granules were mainly elliptical and spherical with the mean diameter of 7.32 μm. Hydrothermal modifications slightly changed the morphology. The solubility, swelling properties and amylose leaching of acorn starch were mostly influenced by Heat-moisture treatment (HMT). XRD pattern of native starch (C-type) did not change on hydrothermal modifications, but native and annealing (ANN) modified starches showed the most crystallinity. DSC results showed that the gelatinization temperatures and enthalpy of native starch were 59.9, 71.3, and 80.6 °C and -14.9 mJ/mg, respectively, and hydrothermal treatments generally increased the gelatinization temperatures. Regarding to RVA results, peak, breakdown, trough, setback, and final viscosities of native starch were 415, 143, 272, 168, and 440 RVU, respectively, and viscosity parameters of native starch were mainly more than those of hydrothermally modified starches. Generally, the intensity of the effects of hydrothermal modifications followed the order: HMT > dual modifications > ANN.

Changes in physicochemical properties and in vitro digestibility of common buckwheat starch by heat-moisture treatment and annealing

Heat-moisture treatment (HMT) and annealing (ANN) were applied in the test to investigate how they can affect the physicochemical properties and in vitro digestibility of common buckwheat starch (CBS). In the practice, these two modification methods did not change typical 'A'-type X-ray diffraction pattern of CBS. However, the gelatinization temperature, amylose content, and relative crystallinity increased and peak viscosity value and gelatinization enthalpy of CBS declined significantly. Both the solubility and swelling power, which were temperature dependent, progressively decreased along with the treatments. Remarkable increase in slowly digested starch and resistant starch level was found at the same time. Besides, the decreases of rapidly digested starch and total hydrolysis content by using HMT were greater than by using ANN. The results indicated that the ANN and HMT efficiently modified physicochemical properties and in vitro digestibility of CBS and were able to improve its thermal stability, healthy benefits and application value.