Influence of free‐air CO2 enrichment (FACE) on the eating quality of rice

Rice plants (Oryza sativa L cv Akitakomachi) were grown under free‐air CO₂ enrichment (FACE) in farmers' fields in Shizukuishi, Iwate, Japan during 1999 and 2000. The grains were harvested and subsequently analyzed for protein and amylose contents as well as the traits related to cooked‐rice viscosity. The cooked rice was also subjected to sensory evaluation. The protein content of rice grains grown under elevated CO₂ was significantly lower than that of rice grown under ambient conditions. In addition, CO₂ enrichment increased the whiteness of the grains in both brown and milled rice and reduced their surface hardness. Although the amylose content of rice grains was unaffected, starch pasting properties demonstrated that rice grains in elevated CO₂ had higher maximum viscosity and breakdown than those grown in ambient conditions. Sensory evaluation of cooked rice with respect to umami (deliciousness), appearance, aroma, hardness, stickiness and overall palatability index indicated that the sensory properties were not significantly altered by the CO₂ enrichment treatment. Therefore, we conclude that the growth of the rice cultivar Akitakomachi under elevated CO₂ concentration decreased the protein content, but did not change the palatability to a level that may be detected by sensory taste panel evaluation. Copyright © 2005 Society of Chemical Industry     

Rheological and Thermal Properties of Extruded Mixtures of Rice Starch and Isolated Soy Protein

Many foods gain new mechanical, thermal and textural properties after being processed due to interactions between carbohydrates and proteins. This effect is characteristic for each foodstuff. The properties of extruded isolated soy protein (ISP) and rice starch were studied considering the following extrusion variables: starch proportion with respect to ISP (0–100%), pH (3–9), moisture content (20–30%) and temperature (140–180ºC). The following characteristics were measured: Water absorption index (WAI), water solubility index (WSI), glass transition temperature (T_g), melting temperature (T_m), viscosity at 90ºC and at 50ºC, storage (G′), loss modulus (G′′) and tan δ. The results indicate that the extruded starch exhibits higher WAI and WSI values than untreated starch. For extruded ISP these values are much lower than for untreated ISP. Extrudates with higher starch proportion had higher T_g and T_m values; pH has a significant effect (p<0.05), at pH 3 higher T_g values were observed, and at pH 9 higher values of T_m. The highest viscosities at 90ºC and 50ºC were observed for extrudates with a higher starch proportion and pH 9. Extruded mixtures showed a more elastic than viscous behavior and an extruded 1:1 blend of starch‐ISP exhibited the behavior of a viscous liquid.     

Differences in physicochemical properties of kernels of two rice cultivars during grain formation

BACKGROUND: Rice varieties with similar apparent amylose content may have different grain qualities. The development of rice quality is a dynamic process that occurs with the formation of rice kernels. In this study, physicochemical properties during the grain formation period were investigated to interpret differences in grain quality between two non‐waxy rice cultivars, Wuyujing3 and 30you917, with similar apparent amylose content. RESULTS: There were significant differences in dynamic changes in 1000‐grain weight, amylose content and pasting and thermal properties during grain formation of the two cultivars. The difference in their apparent amylose contents from 5 days after anthesis (DAA) to 15 DAA was significant, except in the late grain‐filling stage. Wuyujing3 showed a slower increase in 1000‐grain weight than 30you917 from 10 to 25 DAA. The transition temperatures (T_o, T_p and T_c) of developing grain flour of Wuyujing3 were higher than those of 30you917 during the grain formation period. Wuyujing3 showed greater stickiness (higher breakdown and peak viscosity and lower positive setback) than 30you917 according to Rapid Visco Analyser (RVA) profiling. CONCLUSION: The results suggested that the differences in cooking and eating quality parameters of the two mature rices were determined by the differences in grain filling and the dynamic changes in the main rice quality components such as amylose content, grain weight and differential scanning calorimetry and RVA properties, which will help cultivators understand the physical basis of rice quality development. Copyright © 2011 Society of Chemical Industry     

Physical aging of glassy normal and waxy rice starches: effect of aging time on glass transition and enthalpy relaxation

Physical aging and glass transition characteristics of amorphous normal and waxy rice starches (11 and 15% moisture contents) were investigated under differential scanning calorimetry as function of aging time. Normal rice starch showed higher T_g than waxy rice starch. The T_g and ΔC_p at glass transition gradually increased with aging time, whereas fictive temperature was slightly reduced regardless of moisture content and starch type. The relaxation enthalpy and relaxation peak temperature increased with aging time until structural equilibrium was reached. Enthalpy increase was more significant in the early stage of aging whereas temperature increase was constant during the aging period tested (120 h). Aging kinetic analysis using Cowie and Ferguson model revealed that the amorphous normal and waxy rice starches behaved in different modes for the physical aging. Relaxation distribution parameter (β) of both starches was in a range of 0.3<β<0.7, but higher at a lower moisture content, and for normal starch than for waxy starch. Maximum relaxation enthalpy for normal starch (1.10 and 2.69 J/g, respectively, at 11 and 15% moistures) was higher than those of waxy starch (0.77 and 2.48 J/g). Based on the characteristic time (t_c), normal starch has slower progression toward an equilibrium than waxy starch. Overall results proved that physical aging kinetics were highly dependent on starch structure and composition.     

EFFECT OF DEFORMATION RATE AND MOISTURE CONTENT ON RICE GRAIN STIFFNESS1

Grains of brown rice, paddy variety IR-8, were subjected to two types of uniaxial compressive loading, constant displacement rate and sinusoidally varying stress, to determine behavior over a wide range of time scale. Grains from four different moisture level groups were used. With a time decrease from 120 to 1.6 × 10^?4s the relaxation modulus increased 15, 25, 16 and 20 fold at respective moisture contents of 12, 17, 22 and 27%. A master relaxation curve for each moisture content is presented. Understanding the viscoelastic behavior of brown rice as a function at time and moisture content is basic to the solution of stress-strain analysis problems.     

The impact of germination on the characteristics of brown rice flour and starch

BACKGROUND: In recent years, germinated brown rice as a functional food has received great attention with its improved sensory and nutritional properties. Particularly of interest are the high levels of γ‐amino butyric acid (GABA) which can be obtained during germination. However, more studies are needed to fully understand the effect of germination on the physicochemical properties of brown rice. RESULT: Germination altered the chemical composition of brown rice, resulting in an increase in reducing sugar and ash content, and a reduction in amylose. Solubility, paste viscosity, transition temperatures (T_o, T_p and T_c) and percentage of retrogradation (%Retrogradation) were decreased, while swelling power and turbidity were significantly increased. Scanning electron micrographs indicated that starch granules from germinated brown rice became smaller and less homogeneous. Moreover, germination shortened the chain length of amylopectin and amylose molecules. CONCLUSION: This investigation provides information on changes in the characteristics of rice flour and rice starch during germination, leading to a better understanding on the chemistry of brown rice germination. Copyright © 2011 Society of Chemical Industry     

Glass Transition and Sticky Point Temperatures and Stability/Mobility Diagram of Fruit Powders

Principal components present in fruits are low molecular weight sugars and some organic acids. They have low glass transition temperature (T _g) and are very hygroscopic in their amorphous state, so the dry product becomes sticky. Water acts as a plasticizer and decreases the glass transition temperature of the product with the increase in moisture content and water activity. To overcome this problem, ingredients having high T _g value, such as maltodextrin, and food grade anti-caking agents were added to prepare vacuum dried fruit powders. The relationship between T _g and a _w provides a simple method for prediction of safe storage temperature at different relative humidities environment. Food powders namely, mango, pineapple, and tomato (3–4% w.b moisture content) were produced by mixing with maltodextrin and tri calcium phosphate at predetermined levels before drying. The relationship among glass transition temperature (T _g), sticky point temperature (T _s), moisture content and water activity of the three powders was represented in a stability/mobility diagram to find out safe storage conditions. Glass transition temperature of the fruit powders were interpreted in terms of the Gordon-Taylor model for verification. Glass transition and sticky point temperatures were compared by plotting them in a graph against moisture content.     

Moisture Sorption of Amorphous Sugar Products

Moisture sorption into sugar glasses led to significant changes in the physico‐chemical properties. Increased moisture content reduced the glass transition temperature, T_g, although the effect was dependent on type of corn syrup. In general, higher corn syrup content and addition of a high‐maltose corn syrup resulted in slightly higher T_g for a given moisture content. Higher corn syrup concentration increased hardness, but also resulted in increased stickiness. Stickiness increased as a function of moisture until a maximum was reached, whereupon further moisture sorption reduced stickiness. A maximum in stickiness occurred when T^g values were still above room temperature, indicating that surface moisture was considerably higher than bulk moisture content.     

Plasticizing Effect of Water on Thermal Behavior and Crystallization of Amorphous Food Models

Dehydrated sugar solutions were used as models of thermal behavior of amorphous foods, and of the effect of temperature, moisture content and time on physical state of such foods. The transition temperatures determined were glass transition (T_g), crystallization (T_cr) and melting (T_m) which all decreased with increasing moisture. T_g of a sucrose/ fructose model had a slightly lower value than the empirical “sticky point,” at all moisture contents studied. Crystallization of sucrose was delayed by addition of fructose or starch. Crystallization above T_g was time-dependent, and the relaxation time of this process followed the WLF equation.     

Physical and Water Absorption Characteristics of Some Improved Rice Varieties

The physical and water absorption characteristics of paddy and brown rice from some early maturing Oryza sativa varieties and newly developed interspecific (O. sativa × Oryza glaberrima) rice varieties were studied. The physical dimensions (length, breadth and width, length/width ratio, equivalent diameter), grain surface area and volume, sphericity, 1,000-kernel weight, bulk and true densities as well as porosity were determined. A nonlinear moisture diffusion equation was used to model the water absorption curves of the rice varieties at 30–60 °C. Digital images of the rice grains were analyzed for their tristimulus color parameters (L*, a*, b*). The physical characteristics of the rice varieties differed significantly (p < 0.05). The rice grains were of medium size with length/width ratio ranging between 2.80 and 3.50. Notably, the New Rice for Africa variety WAB 450 aka NERICA 1 had the smallest 1,000-kernel weight and the highest husk/paddy weight ratio. The equilibrium moisture content was significantly influenced (p < 0.01) by the soaking temperature and the rice component being soaked. The hydration rate curves were generally characterized by two falling rate periods. The predicted water absorption curves were very close to experimental curves (0.91 < r ² < 1.00, p < 0.01). The interspecific variety (NERICA 1) had higher effective moisture diffusivity compared to the early maturing O. sativa varieties.     

Effect of amino acid,pH and mineral salts on glass transition and flow behaviour of soy protein concentrate

The objective of this study was to assess the effect of proline, mineral salts (NaCl and Na₂SO₄) and pH combined with moisture content on the glass transition temperature (T_g) and flow‐starting temperature (T_f) of soy protein concentrate (SPC). Initial screening of the variables based on fractional factorial design showed insignificant effect of NaCl on T_g and T_f. The design was extended to a face‐centred central composite design (CCD) excluding NaCl and data evaluated by use of response surface methodology. The established model for T_g (R² = 0.824) shows significant negative first‐order effects of moisture, proline and Na₂SO₄, and a positive interaction effect of moisture and Na₂SO₄. The T_f model (R² = 0.937) shows significant negative first‐order effects of moisture and proline, a positive first‐order and negative square effect of pH, and a negative interaction effect of moisture and proline. The main effect on T_g and T_f was 2.2 and 1.3 times higher, respectively, for moisture compared to proline. The study confirms that proline (or other free amino acids) can replace moisture as protein plasticiser in the extrusion process. Minor effects can also be obtained by reduction in pH.     

Resistant starch and thermal,morphological and textural properties of heat‐moisture treated rice starches with high‐, medium‐ and low‐amylose content

This study investigated the effects of heat‐moisture treatment (HMT) on the resistant starch content and thermal, morphological, and textural properties of rice starches with high‐, medium‐ and low‐amylose content. The starches were adjusted to 15, 20 and 25% moisture levels and heated at 110°C for 1 h. The HMT increased the resistant starch content in all of the rice starches. HMT increased the onset temperature and the gelatinisation temperature range (T_finish–T_onset) and decreased the enthalpy of gelatinisation of rice starches with different amylose contents. This reduction increased with the increase in the moisture content of HMT. The morphology of rice starch granules was altered with the HMT; the granules presented more agglomerated surface. The HMT affected the textural parameters of rice starches; the high‐ and low‐amylose rice starches subjected to 15 and 20% HMT possessed higher gel hardness.     

Influence of Heat‐Moisture Treatment and Acid Modifications on Physicochemical,Rheological, Thermal and Morphological Characteristics of Indian Water Chestnut (Trapa natans) Starch and its Application in Biodegradable Films

Water chestnut starch was subjected to acid modification and heat‐moisture treatment. Hydrochloric acid was used for acid modification at three different concentrations (0.25 M, 0.5 M and 1 M) for 2 h. Modifications did not alter the granule morphology. Heat‐moisture treatment (HMT) resulted in slight reduction in the granular size of the starch granules. Acid modification lowered the amylose content, swelling power, water‐ and oil‐binding capacity but improved the solubility of starch to a considerable level. Light transmittance of acid‐modified (AM) starches improved significantly. A significant reduction in peak, trough, final and setback viscosity was observed by acid‐thinning. In case of heat‐moisture treated starch the final viscosity (F_v) was found to be even higher than the peak viscosity (P_v). Native water chestnut starch exhibited a lower onset temperature (T_o) and peak temperature (T_p) of gelatinization than the corresponding acid‐treated starches. Starch films prepared from native starch exhibited excellent pliability, whereas those prepared from AM and HMT starches showed good tensile strength. Starch films prepared from acid‐treated starches provided better puncture and tensile strength.     

Thermal Transition Properties of Spaghetti Measured by Differential Scanning Calorimetry (DSC) and Thermal Mechanical Compression Test (TMCT)

Glass transition temperature (T _g) of spaghetti sample was measured by thermal and rheological methods as a function of water content from 0 to 70 kg/100 kg spaghetti. In the cases of sample containing un-freezable water (i.e., amount of water which did not form ice even at very low temperature), calorimetric measurements performed by differential scanning calorimetry showed that the T _g values decreased from 142.8 to 42.7 °C when water content increased from 0 to 13.95 kg/100 kg spaghetti, respectively. Glass transition temperature increased with the increase of heating rate (2–50 °C/min) and reached to a nearly constant value above 30 °C/min. Thermal mechanical compression test showed relatively lower T _g values compared to the DSC values at low moisture contents, whereas at high moisture content T _g showed higher values. In the cases of samples containing freezable water (27–70 kg/100 kg spaghetti), glass transition shifts were merged with the ice melting endotherm. The freezing point, measured from the endothermic peak, decreased with the decrease of water content. In the state diagram, maximal freeze-concentration condition was determined as X_\texts￠ X_{\text{s}}^\prime =0.81 kg/kg spaghetti from the intersection of the extended freezing curve and a horizontal line passing thru T_\textm￠ T_{\text{m}}^\prime  = −10.3 °C.     

Effect of Heat‐Moisture Treatment on Structural and Thermal Properties of Rice Starches Differing in Amylose Content

Starches from glutinous rice (1.4% amylose), Jasmine rice (15.0% amylose) and Chiang rice (20.2% amylose) were exposed to heat‐moisture treatment (HMT) at 100 °C for 16 h and at different moisture levels (18, 21, 24 and 27%). The effect of heat‐moisture treatment on structural and thermal properties of these three rice starches was investigated. The HMT did not change the size, shape and surface characteristics of rice starch granules. The A‐type crystalline pattern of rice starches remained unchanged after HMT. The relative crystallinity (RC) and the ratio of short‐range molecular order to amorphous (RSA) of heat‐moisture treated glutinous and Jasmine rice starches decreased with increasing moisture level of the treatments. In contrast, the RC of the treated Chiang rice starch remained practically unchanged. A peak of crystalline V‐amylose‐lipid complexes was clearly presented in all treated Chiang rice starches. The peak became progressively stronger with increasing moisture level of the treatment. Differential scanning calorimetry (DSC) of all treated rice starches showed a shift of the gelatinization temperature to higher values. Increasing moisture level of the treatments increased the onset gelatinization temperature (T_o) but decreased the gelatinization enthalpy (ΔH) of rice starches. A broad gelatinization temperature range (T_c‐T_o) with a biphasic endotherm was found for all treated Chiang rice starches and Jasmine rice starch after HMT₂₇ (HMT at 27% moisture level). Additionally the (T_c‐T_o) of treated Chiang rice starches increased linearly with increasing moisture level of the treatments.     

Measurement of Glass-Rubber Transition Temperature of Rice by Thermal Mechanical Compression Test (TMCT)

TMCT (Thermal Mechanical Compression Test) was applied to measure the T_g-r (glass-rubber transition temperature) of rice flour and individual rice kernels at low moisture content (2.4–19.5% wet basis). As expected, T_g-r decreased with increasing moisture content. The T_g-r temperatures measured by TMCT were comparable with those measured by DSC (Differential Scanning Calorimetry), TMA (Thermo-mechanical Analysis), and DMTA (Dynamic Mechanical Thermal Analysis) as reported in the literature. These results indicated that the TMCT technique could be applied to measure the glass-rubber transition of a single grain of rice or the rice in powder form. The sensitivity of the test was observed higher for the rice kernel than rice flour. TMCT technique has the advantage of usefulness and cost-effectiveness compared with the other techniques.     

Popping of amaranth grain (Amaranthus caudatus) and its effect on the functional,nutritional and sensory properties

The popping of amarunth grain (Amaranthus caudatus var INIAP‐Alegría) by hot air processing was studied. A household corn popper adapted to control heating and airflow was used. The effects of temperature, load, airflow and moisture on the popping capacity and on the functional properties, nutritional quality, crude protein content, lysine content and sensory texture of the poppei grain were investigate. The yield, expansion volume and density of popped grain showed that the optimal conditions for the popping process were 240 °C, 22 g load, 0.013 m³ s^?1 airflow and 12% grain moisture. The proportion of popped grain with butterfly shape was highest (p < 0.05) at 220 °C, 22 g load, 0.014 m³ s^?1 airflow and 14% grain moisture. The functional and physic‐chemical properties of popped grain obtained by various treatments showed completely gelatinised starch. The total, available and resistant starch contents were similar among the different treatments. The enzymatic degradation of starch was 65% within 5–15 min of incubation with α‐amylase. The crude protein content was almost 15% for all the treatments, while the total lysine content was 45.2–48.0 mg g^?1 protein. The in vitro availability of protein of popped grain obtained at 0.013 m³ s^?1 airflow and 14% grain moisture was above 84%. The highest available lysine value was found for popped grain obtained at 0.014 m³ s^?1 airflow, 18–22 g load and 12–14% grain moisture. However, six of the eight treatments had available lysine contents that varied between 41.2 and 47.4 mg g^?1 protein. Sensory analyses showed that the treatments with the highest popping capacity produced grains with high crunch and expansion capacities. © 2002 Society of Chemical Industry     

Mechanical and water vapour barrier properties of edible gellan films

Edible films based on gellan were developed. Of the plasticizers tested, glycerol was found to be the most suitable with respect to mechanical properties and transparency. The mechanical properties (tensile and puncture), water vapour permeability (WVP) and glass transition temperature (T_g) were examined for gellan films as a function of glycerol concentration. The lowest effective glycerol concentration was ∼60% (film dry weight basis); below this concentration, the films tended to be brittle and difficult to handle, whereas films with more than ∼75% glycerol tended to be sticky. Addition of glycerol to gellan films increased extensibility (tensile elongation and puncture deformation) moderately, but decreased tensile strength, elastic modulus and T_g, and increased WVP of the films. Increasing the a_w caused marked decreases in tensile strength and elastic modulus, but decreased tensile elongation only slightly. In general, tensile strength and elastic modulus appeared to be more sensitive to changes in glycerol content and a_w than puncture strength.     

Material Properties and Glass Transition Temperatures of Different Thermoplastic Starches After Extrusion Processing

Four different starch sources, namely waxy maize, wheat, potato and pea starch were extruded with the plasticizer glycerol, the latter in concentrations of 15, 20 and 25% (w/w). The glass transition temperatures of the resulting thermoplastic products were measured by Dynamic Mechanical Thermal Analysis (DMTA). Beside mechanical and structural properties also the transition temperatures of the materials were evaluated during tensile and impact tests. Above certain glycerol contents, dependent on the starch source, a lower glass transition temperature T_g resulted in decreased modulus and tensile strengths and increased elongations. Lowering the T_g at different glycerol contents did not influence the impact strength. When the amylose/amylopectin ratio increased a decrease in T_g was found. For pea, wheat, potato and waxy maize starch the T_g was 75 °C, 143 °C, 152 °C and 158 °C, respectively. Therefore products with higher percentages of amylose are more flexible. The shrinkage of the specimens made by injection molding was considerable compared to the specimens made by pressing.     

Iron content and availability studies in some Sri Lankan rice varieties

Thirty‐eight rice varieties, grown in Low Country Wet Zone, during Yala (2006) and Maha (2006/2007) seasons were screened for stable high iron rice varieties and were statistically analysed. Iron contents ranged 1.89–3.73 mg 100 g^?1 and varied significantly (P < 0.05) with variety and season. Selected fifteen high iron rice varieties, at degree of polishing 8–10% were analysed for iron, zinc and phytate. High iron contents in endosperm were observed in Suduru Samba (0.47 mg 100 g^?1), Basmati 370 (0.37 mg 100 g^?1), Kalu Heenati (0.42 mg 100 g^?1), Rathu Heenati (0.44 mg 100 g^?1) and Sudu Heenati (0.37 mg 100 g^?1). Phytate contents of polished rice varieties ranged from 200–300 mg 100 g^?1. Large reduction in iron content (84.5–93.6%) was observed in polished rice while the reduction in phytate content (18.9–40.8%) was low. Percentage dialyzability of iron in selected endosperm high iron rice varieties ranged from 1.73 to 8.71. Dialysability of iron in cooked polished rice did not show a relation to the phytate content in raw rice.