The effect of rice aging on the freeze–thaw stability of rice flour gels

Interaction of anthocyanins, soluble dietary fiber and waxy rice starch: Their effect on freeze-thaw stability, water migration, and pasting, rheological and microstructural properties of starch gels

This study aimed to investigate the effect of the interaction of black rice anthocyanins (BRA), soluble dietary fiber from extruded rice bran (ES) and waxy rice starch (WRS) on the physicochemical properties of starch gels, including gelatinization properties, rheological properties, freeze-thaw stability, water migration, molecular structure and gel microstructure. The results showed that the pasting temperature (PT) of the mixtures was increased, and the peak viscosity (PV), trough viscosity (TV), final viscosity (FV) and setback viscosity (SV) were significantly reduced when ES and BRA were added to WRS in different proportions (ES:BRA, 4:0, 4:0.4, 4:1, 4:2, 8:0, 8:0.8, 8:2, 8:4). Both ES and BRA could enhance the viscosity of WRS gels, and ES exhibited strong ability on improving the strength of gels. The presence of ES and BRA improved the water retaining capacity of WRS gels, but weakened the freeze-thaw stability. ES, BRA and WRS formed non-covalent bonds (hydrogen bonds) through hydrophilic groups during gelatinization, which improved the gel properties. In addition, the steric hindrance formed by ES and BRA inhibited starch retrogradation. These results might contribute to the development of starch-based food formulations with good quality.

Verification of rice quality during storage after drying with hot air and radio frequency heating

The objectives of the study were to observe the milling and cooking qualities of paddy rice dried with hot air (HA) and hot air and radio frequency heating (HA/RF) at 38 °C and 42 °C, and to observe these qualities after 6 months of storage under average temperature and RH of 28.4 °C and 70%, respectively. During storage, the average moisture content of paddy rice decreased from 13.66% to 11.37% in HA, 13.66% to 11.40% in HA/RF38, and 13.58% to 11.63 in HA/RF42. The milling qualities of rice were affected by the RF heating temperature and storage period. Rice dried with HA/RF38 and HA/RF42 could be safely stored for up to 5 months and 4 months, respectively, with satisfactory fissure percentage and head rice yield. The whiteness index significantly increased from 63.37 ± 0.58 to 64.46 ± 0.75 at HA, 62.78 ± 0.97 to 63.75 ± 1.55 at HA/RF38, and 62.77 ± 1.90 to 64.45 ± 0.95 at HA/RF42 during storage. For cooking qualities, elongation ratio (ER) was affected by RF and storage period, while texture profiles and pasting properties were only affected by storage period. The ER increased from month 3, by 10%, 11%, and 11% in HA, HA/RF38, and HA/RF42. The hardness of cooked rice reached its peak value between months 4-5. However, adhesiveness decreased as the storage period increased. The peak viscosity and setback increased with increasing storage period while breakdown conversely decreased. This study showed that hot air drying and RF heating temperatures of 38 °C could replace hot air drying without undesirable changes in milling and cooking properties during storage up to 5 months. Therefore, this is a promising drying technology for the rice milling industry.

Effect of pre-swelling and freezing/thawing cycles on the structure of molecular, morphological, and functional properties of potato starch

This study aimed to investigate the effect of pre-swelling at 55°C for 1 hr followed by freezing-thawing cycles (PFTCs), and freezing-thawing cycles (FTCs) in the starch granules to improve the freeze-thaw stability and evaluate its impact on the molecular, morphological, and functional properties of potato starch (PS). FTCs at 1 cycle and 7 cycles were applied for both treated PS. Microscopical structure, thermal, molecular, and functional properties (i.e., swelling power, solubility, shear viscosity, and gel strength) were comprehensively analyzed. In terms of granule structures, treated PS by FTC showed a slightly affected on the surface of starch granules, while treating PS by PFTC showed an affected in the form of small cracks and holes in the outer surface of starch granules. The gelatinization enthalpy (∆H_gel ) values decreased in the treated PS compared with the native. Thus, decreasing was systemically increased with the number of applied cycles from 1- to 7-cycle. The viscosity of treated PS decreased systematically with molecular degradation or the physical modification, with remarkable reduction, particularly at a higher shear rate (150°C). Treated PS by FTC showed a clear difference (p ≤ .05) in gel values compared with the native at disintegration temperature 115°C. Finally, the degradation of the molecular properties showed significant differences between the native and treated PS either by the FTC or PFTC in molecular weight of starch and amylose without debranching and after debranching by pullulanase enzyme. PRACTICAL APPLICATIONS: Freezing is one of the standard preservation methods used for ready-to-eat products. When this type of food's exposed to more freeze-thaw cycles, the phase separation will be increased due to the increase in retrogradation of amylopectin. To avoid such changes during frozen storage, native potato starch (PS) was modified using both pre-swelling followed by freezing-thawing cycles (PFTCs) and freezing-thawing cycles (FTCs) at 1- and 7-cycle to enhance starch properties, such as swelling power, solubility, shear viscosity, and gel strength. The findings of this study might add to the theoretical understanding of modified PS and act as a guideline for modified starch manufacturing.

Impact of thermo-sonication on quality indices of starch-based sauces

In this study, ultrasonication, a physical, relatively cheap, and environmentally benign technology, was investigated to characterize its effect on functional properties of rice starch and rice starch-based sauces. Temperature-assisted ultrasound treatment improved the granular swelling power, fat and water absorption capacities, and thermal properties of rice starch, signifying its suitability in the formulation of starch-based sauces. Rheological characterization of the formulated sauces revealed a shear-thinning flow behavior, well described by the Ostwald de Waele model, while viscoelastic properties showed the existence of a weak gel. Results indicated that ultrasonication significantly enhanced the pseudoplastic behavior of starch-based sauces. Additionally, textural analysis showed that textural attributes (stickiness, stringiness, and work of adhesion) were also improved with ultrasonication. Moreover, enhanced freeze/thaw stability was also achieved with ultrasound-treated starch-based sauces. Overall, the results from this study show that ultrasound-treated starches can be used in the formulation of sauces and potentially other food products, which meets the requirements for clean label and minimally processed foods.

Effect of molecular structure on phase transition behavior of rice starch with different amylose contents

Phase transition behaviors in starch-water system and molecular structures of rice starches isolated from four Korean cultivars with different amylose contents were investigated and the importance of structural features affecting starch phase transitions was also explored. The Dodam starch with the highest average chain length of amylopectin (26.1), the highest proportion (24.3 %) of long chains (DP ≥ 37), and the lowest proportion (17.5 %) of short chains (DP 6-12) displayed the highest gelatinization and retrogradation temperatures. Enthalpies of ice freezing and melting, and glass transition temperature (T_g') of rice starches increased with increasing amylose content and decreasing proportion of short amylopectin chains because these structural features are related to a higher thermal stability of the starches. Ice melting temperature was also influenced by amylopectin chain structures. The results suggest that the phase transition behaviors of rice starches were highly influenced by their amylose content and amylopectin chain length distribution.

Fabrication of kappa-carrageenan hydrogels with cinnamon essential oil/hydroxypropyl-β-cyclodextrin composite: Evaluation of physicochemical properties, release kinetics and antimicrobial activity

A novel antimicrobial gel composed of κ-carrageenan (KC) and a cinnamon essential oil (CEO)/hydroxypropyl-β-cyclodextrin (HPCD) composite was developed. The CEO/HPCD composite was characterized by UV-visible spectrophotometry and Fourier-transform infrared spectroscopy (FT-IR), and the changes in the principal components of CEO upon encapsulation by HPCD were analyzed by gas chromatography-mass spectrometry (GC-MS). The physicochemical properties, release kinetics and antimicrobial activity of the fabricated gels were investigated. The hardness of the KC gels increased with composite concentration in the range of 1.0-3.0% (w/v) and thereafter decreased. A similar trend was observed for the gumminess and chewiness, whereas the gel springiness remained essentially constant. The CEO/HPCD composite also enhanced the fluidity of the system, and the syneresis was positively correlated with the composite concentration. The controlled release of CEO from the gels was affected by the relative humidity (RH) and CEO content. The Ritger-Peppas model indicated that the CEO release kinetics from the gels proceeded through a combination of diffusion and framework erosion. The KC gel containing 5% CEO/HPCD composite displayed effective antimicrobial activity, prolonging the shelf life of sliced bread by at least two days. The reported gels may have potential applications as a promising material for food preservation.

Effects of sucrose on pasting, thermal, rheological and textural properties of native and alcohol-alkali-treated waxy rice starch

In this work, the physicochemical properties of native waxy rice starch (WRS) and alcohol-alkali-treated waxy rice starch (AAT-WRS) were studied in the presence of sucrose. The results indicated that the addition of sucrose improved the transparency and freeze-thaw stability of WRS pastes and AAT-WRS pastes. Differential scanning calorimetry showed that the gelatinization temperatures of WRS increased with increased sucrose concentration, but the gelatinization enthalpy increased at low concentration of sucrose and decreased at high concentration. Rheological measurements indicated that sucrose addition had no significant effect on the pseudoplastic shear-thinning behaviors of WRS pastes and AAT-WRS pastes, but changed the apparent viscosity. Dynamic moduli (G' and G″) values of WRS pastes and AAT-WRS pastes with or without sucrose showed frequency dependency and sucrose addition dependency. The elastic behavior was dominant over viscous in the WRS-sucrose mixed pastes, while the AAT-WRS-sucrose mixed pastes was the opposite. The textural paraments of WRS and AAT-WRS before or after retrogradation increased with the increasing concentration of sucrose. These results suggested that sucrose potentially changed the physicochemical properties of WRS and AAT-WRS.