Physicochemical properties of cross-linked-annealed wheat starch

Starch in its native form, may not be able to provide functional properties such as high or low temperatures and shear forces bearings expected in modern industries. Therefore, it is usually modified to make it compatible for different applications. The main aim of this research was to study the effects of dual modification using cross-linking and annealing on physicochemical properties of wheat starch. Therefore, starch was first cross-linked using different levels of POCl₃ (0, 0.1, 0.2, 0.4?%, w/w, starch basis) and then annealed at 40?°C for 72?h. Scanning electron micrographs showed the presence of some spots on the granules of the dual-modified samples. The results of differential scanning calorimetry showed that the onset, peak and conclusion temperatures and enthalpy increased upon dual modification. The X-ray diffraction pattern of the modified samples remained unchanged while water solubility and swelling decreased. The results of rapid visco analyzing showed lower peak, setback, breakdown and final viscosities for the dual-modified samples. These samples produced stronger gels as determined using a texture analyzer. In total, annealing of the cross-linked starch could enhance some of its functional properties for further applications.     

A switch point model for high-resolution moisture absorption isotherms of raw and pregelatinized starches

The goal of this work was to find or create a simple model of the experimental high-resolution water absorption isotherms, determined with the dynamic dewpoint isotherm method (DDI) for different forms of starch powder. The samples used were rice and cassava starches and their 1:1 mix, each in raw and pregelatinized forms. The adsorption isotherms were measured at both 25 and 35?°C temperatures for the water activity range 0.2–0.9. The results showed that the modern DDI method provided densely measured isotherms with consistent characteristics. In particular, a linear zone in the adsorption isotherms of starch powders can be identified and its extent estimated. It is also subjectively clear with the DDI resolution across all the samples tested. Aside from smallish distinction between raw and pregelatinized cases, the starches had very similar isotherms, which might represent a “generic starch flour isotherm”. This shape was very well fit by an initial linear segment and a final curved segment, with the critical transition at the switch point. The transition point results indicate that pregelatinization increases the demands on water barrier properties of the packaging.     

Crystallinity and Rheological Properties of Pregelatinized Rice Starches Differing in Amylose Content

Three rice starches with different amylose contents (Glutinous: 1.4%, Jasmine: 15.0% and Chiang: 20.2%) were pregelatinized in a double drum dryer at 110, 117 and 123°C. Starch crystallinity was determined by X‐ray diffractometry and Fourier transform infrared (FTIR) spectrometry. Rheological properties were assessed by a Rapid Visco Analyser (RVA) and rheometer. Pregelatinized starches obtained from Glutinous (PGS) and Jasmine rice (PJS) gave an RVA pasting profile with cold peak viscosity. At drum temperature 110°C, PGS and PJS showed X‐ray patterns that were indicative of amorphous structures. However, pregelatinized Chiang rice starch (PCS) exhibited RVA hot peak viscosity and the presence of an amylose‐lipid complex with remaining granule structure. The PCS had a lower water absorption index (WAI) and water solubility index (WSI) than PJS and PGS. After pregelatinization at increased drum temperature (117, 123°C), the PGS had a lower WAI, whereas PCS showed an opposite trend indicating lower degree of granule disruption. In addition, the cold peak viscosity of PGS and PJS decreased with increasing drum temperature. For all drum temperatures, the apparent viscosity at 25°C for PGS and PJS decreased with increasing shear rate, indicating shear‐thinning behavior.     

Effects of L-ascorbic acid on physicochemical characteristics of wheat starch

The main objective of this study was to determine the effects of l-ascorbic acid, as a permitted additive in bakery products, on characteristics of wheat starch. Suspensions of wheat starch (30%, w/w) in water containing 140 mg/kg ascorbic acid before and after gelatinization were prepared and studied using different techniques. The results of scanning electron microscopy showed that some spots appeared on the surface of the starch granules as a result of the addition of ascorbic acid. However, no changes in the starch crystalline pattern and its degree of crystallinity were observed by X-ray diffraction technique. For ungelatinized samples, no difference in the pasting properties of the samples was determined by the rapid visco analyzer, whereas for the gelatinized samples, peak and final viscosities decreased for the samples contained ascorbic acid. Determination of the intrinsic viscosities of the samples showed that addition of ascorbic acid to the gelatinized samples reduced the intrinsic viscosity. In general, it was found that ascorbic acid had some degradation effects on wheat starch molecules particularly after gelatinization.     

Key properties of iodine‐, iron‐ and zinc‐ fortified fish cracker: effects of ambient shelf storage on iodine retention and quality indicators

Multi‐micronutrient (MN)‐fortified fish cracker could be used as a means to improve iodine, iron (Fe) and zinc (Zn) status. We evaluated iodine stability as well as the quality and sensory properties of MN‐fortified fish cracker, at the fortification levels of 5.3 mg per 100 g for Fe and Zn and 260 μg per 100 g for iodine in the dough. On average, the overall retention of iodine after processing and storage for 4 months was ~65%. Fortification with KIO₃ + ZnO, or KIO₃ + ZnO + ferrous fumarate, significantly increased the loss of iodine during processing. The Fe compounds tended to promote iodine instability during storage and contributed to thiobarbituric reactive substances. Fortification did not affect linear expansion of the cracker. Triple‐fortified fish cracker with KIO₃, ferric pyrophosphate and ZnO exhibited both high iodine retention (92.7% for steaming + drying and 72.7% for storage) in the tropical conditions (30 ± 1 °C, 80 ± 5% R.H.) and achieved overall desirable sensory scores. Thus, such fortification of fish cracker might successfully supplement iodine, zinc and iron, while at the same time contributing to the palatability of cracker.     

Effect of Sago Starch Addition and Steaming Time on Making Cassava Cracker (Keropok)

This work was aimed at investigating the effects of steaming time and different fractions of sago starch (0, 6, 12, 18 and 24%) in mixtures with cassava starch on the properties of crackers as compared to cassava crackers. In the hydrothermal process, the steaming period was varied from 25 to 120 min. The properties of raw starches, half‐finished crackers (HFC) and puffed crackers (PC) were determined. Raw cassava starch had lower amylose content, smaller granule size, lower gelatinization and lower swelling power than sago starch. The properties of the raw starch mixtures varied according to the mixing proportions. Both sago starch content and steaming time influenced cracker quality, especially its expansion, which was related to the degree of gelatinization (DG). Increasing sago starch content caused decreased DG of HFC and hence decreased cracker expansion. Two groups of HFC were obtained; low DG (55–65%, 25‐45 min steaming time) and high DG (>80%, 60‐120 min steaming time) HFC. Generally the expansion increased as the DG increased – however, a too long steaming period (> 75 min) again reduced expansion, apparently the thinner starch gel allowed collapse of the air cells. No treatment gave complete gelatinization; which could be due to insufficient water for starch to gelatinize.