Effects Of Different Cooking Methods And Storage Conditions On The Rice Starch Digestibility

Seven types of rice with different levels of amylose were selected to study the effect of different cooking methods, chilling and freezing on the digestibility of their starches. An in vitro enzymatic starch digestion method was applied in order to estimate the expected glycemic index (GI) in vivo based on the kinetics of starch hydrolysis in vitro. First, samples were cooked with different cooking methods to investigate the effect of cooking on the starch digestibility; second, samples were steamed and stored at temperatures of 4 and -20°C in order to simulate certain storage conditions of cooked rice. The results indicated significant differences in terms of starch digestibility or GI of the seven types of rice studied and the digestibility of their starches were further affected by different cooking methods. These differences can be attributed to the formation of resistant starch (RS). Steaming increased the RS formation in each type of rice. Cooking the rice with excess water, combi oven and rice cooker contributed only to small changes in the formation of RS. The proximate compositions of the rice before and after cooking were similar for all cooking methods. The amylose content of rice has an obvious impact on the rice starch digestibility due to its positive correlation with formation of RS. Starch hydrolysis was found to be rapid and complete for the waxy and low amylose rice rather than for the intermediate and high amylose rice. Chilling of steamed rice promoted the formation of RS more than freezing. The GI ranged between 68 and 98 for steamed rice and between 63 and 82 for chilled and frozen rice. Storing steamed rice at 4°C and -20°C gradually increased the formation of RS and reduced the estimated GI for all the seven types of rice. A high decrease in starch hydrolysis after chilling and freezing was found among the waxy rice. Thermal properties of rice that have undergone steaming, chilling and freezing showed a shift of the gelatinization temperature to a higher value. The pasting properties of steamed and chilled or frozen rice samples showed increased pasting temperatures and decreased peak viscosity compared to those of raw rice. The raw rice starches had the characteristic A-type crystalline pattern, with diffraction peaks at 15.2, 17.2, 17.9 and 23.2° (2θ). The steaming, chilling and freezing treatment on rice caused weak peak formation at 16° and 20° (2θ) representing crystalline B-type and V-amyloselipid complexes. Steaming, chilling and freezing of rice had reduced the relative crystallinity (RC) value

Combination of saponification and dispersive liquid–liquid microextraction for the determination of tocopherols and tocotrienols in cereals by reversed-phase high-performance liquid chromatography

A simple sample preparation technique coupled with reversed-phase high-performance liquid chromatography was developed for the determination of tocopherols and tocotrienols in cereals. The sample preparation procedure involved a small-scale hydrolysis of 0.5 g cereal sample by saponification, followed by the extraction and concentration of tocopherols and tocotrienols from saponified extract using dispersive liquid–liquid microextraction (DLLME). Parameters affecting the DLLME performance were optimized to achieve the highest extraction efficiency and the performance of the developed DLLME method was evaluated. Good linearity was observed over the range assayed (0.031–4.0 μg/mL) with regression coefficients greater than 0.9989 for all tocopherols and tocotrienols. Limits of detection and enrichment factors ranged from 0.01 to 0.11 μg/mL and 50 to 73, respectively. Intra- and inter-day precision were lower than 8.9% and the recoveries were around 85.5–116.6% for all tocopherols and tocotrienols. The developed DLLME method was successfully applied to cereals: rice, barley, oat, wheat, corn and millet. This new sample preparation approach represents an inexpensive, rapid, simple and precise sample cleanup and concentration method for the determination of tocopherols and tocotrienols in cereals

Combination of saponification and dispersive liquid–liquid microextraction for the determination of tocopherols and tocotrienols in cereals by reversed-phase high-performance liquid chromatography

A simple sample preparation technique coupled with reversed-phase high-performance liquid chromatography was developed for the determination of tocopherols and tocotrienols in cereals. The sample preparation procedure involved a small-scale hydrolysis of 0.5 g cereal sample by saponification, followed by the extraction and concentration of tocopherols and tocotrienols from saponified extract using dispersive liquid–liquid microextraction (DLLME). Parameters affecting the DLLME performance were optimized to achieve the highest extraction efficiency and the performance of the developed DLLME method was evaluated. Good linearity was observed over the range assayed (0.031–4.0 μg/mL) with regression coefficients greater than 0.9989 for all tocopherols and tocotrienols. Limits of detection and enrichment factors ranged from 0.01 to 0.11 μg/mL and 50 to 73, respectively. Intra- and inter-day precision were lower than 8.9% and the recoveries were around 85.5–116.6% for all tocopherols and tocotrienols. The developed DLLME method was successfully applied to cereals: rice, barley, oat, wheat, corn and millet. This new sample preparation approach represents an inexpensive, rapid, simple and precise sample cleanup and concentration method for the determination of tocopherols and tocotrienols in cereals

Effect of wall materials on the spray drying efficiency, powder properties and stability of bioactive compounds in tamarillo juice microencapsulation

Hydro- and lipo-soluble bioactive compounds, such as anthocyanins and carotenoids, in tamarillo juice were microencapsulated using different wall materials, such as maltodextrin (MD), n-octenyl succinic anhydride modified starch, from waxy maize for high load encapsulation (OSA 1), low viscosity gum Arabic alternative (OSA 2), resistant maltodextrin (RMD) and gum Arabic (GA). The wall materials were characterized according to their physicochemical and functional properties, molecular weight distribution and encapsulation efficiency using X-ray diffractometry. The tamarillo powders obtained after spray drying were evaluated for their physicochemical and thermal properties, phenolic content, flavonoid content, antioxidant capacity and storage stability. Although there were significant differences in terms of the encapsulation efficiencies of the wall materials, yield, physical properties and storage stability of the spray dried powders, all of the wall materials successfully encapsulated the hydro- and lipo-soluble bioactive compounds. The viscosity, amorphous region and molecular weight of the wall material had positive influences on the encapsulation efficiency, powder properties and storage stability of the encapsulated tamarillo juice. The storage stability of the powders depended on their water activity, hygroscopicity and glass transition temperature (Tg). The tamarillo powders showed greater anthocyanin and carotenoid degradation in the presence of light at 25 °C compared to the powders stored in the dark at 4 °C. GA and OSA 1 resulted in the highest encapsulation efficiency for both the hydro- and lipo-soluble bioactive compounds, while OSA 1 and MSB showed the greatest storage stability. Reductions in the antioxidant activity, phenolic content and flavonoid content during storage will contribute to the degradation of anthocyanins and carotenoids

Rapid reversed-phase chromatographic method for determination of eight vitamin E isomers and gamma-oryzanols in rice bran and rice bran oil

Rice bran and rice bran oil contain high amounts of lipid soluble phytochemicals such as tocopherols, tocotrienols and γ-oryzanols with potential health benefits. A reversed-phase high-performance liquid chromatographic method for the quantitation of these phytochemicals was developed. These phytochemicals were extracted using rapid one-step methanol extraction and separated on a Kinetex pentafluorophenyl phase column for quantitation using fluorescence and ultraviolet detectors. Separation was carried out within 20 min at a flow rate of 1.0 mL/min using a gradient elution of mobile phase consisting of methanol and water at column temperature of 30 °C. A good separation of all eight tocol isomers was achieved while the γ-oryzanols were separated near to baseline. Extraction yields of tocopherols, tocotrienols and γ-oryzanols from saponification medium with different pH conditions were studied. Total γ-oryzanols extracted from alkaline medium were significantly lower than those from the neutral and acidic mediums (p  0.9994), low detection limit (3–34 ng/mL) and high precision (RSD < 7.5 %) with satisfactory recovery (R% = 81–116 %). The advantages of this method over available reverse-phase methods are the better resolution of β and γ tocol isomers with the γ-oryzanols, usage of non-halogenated mobile phase and shorter analysis time, and it is compatible with the standard laboratorial chromatographic equipment

Physicochemical characteristics of Nigella seed (Nigella sativa L.) oil as affected by different extraction methods.

The physicochemical properties of crude Nigella seed (Nigella sativa L.) oil which was extracted using Soxhlet, Modified Bligh-Dyer and Hexane extraction methods were determined. The effect of different extraction methods which includes different parameters, such as temperature, time and solvent on the extraction yield and the physicochemical properties were investigated. The experimental results showed that temperature, different solvents and extraction time had the most significant effect on the yield of the Nigella oil extracts. The fatty acid (FA) compositions of Nigella seed oil were further analyzed by gas chromatography to compare the extraction methods. The C16:0, C18:1 and C18:2 have been identified to be the dominant fatty acids in the Nigella seed oils. However, the main triacylglycerol (TAG) was LLL followed by OLL and PLL. The FA and TAG content showed that the composition of the Nigella seed oil extracted by different methods was mostly similar, whereas relative concentration of the identified compounds were apparently different according to the extraction methods. The melting and crystallization temperatures of the oil extracted by Soxhlet were -2.54 and -55.76 °C, respectively. The general characteristics of the Nigella seed oil obtained by different extraction methods were further compared. Where the Soxhlet extraction method was considered to be the optimum process for extracting Nigella seed oil with a higher quality with respect to the other two processes

Antioxidant properties, degradation kinetics and storage stability of drinks prepared from the cooking water of pigmented rice

Pigmented rice, consisting of black rice and red rice, is known to contain antioxidant compounds in its bran that tend to leach out into the water during cooking. As the rice is usually cooked in excess water which is discarded after cooking, the purpose of this study is therefore, to evaluate the rice cooking water as an antioxidant drink in terms of its antioxidant properties, storage stability and anthocyanin degradation kinetics. The results showed that the percentages of antioxidant extractability from pigmented rice into the cooking water were 88.42 and 103.26%, respectively for red rice and black rice, respectively. However, red rice drink possessed significantly (p<0.05) higher antioxidant activity than black rice drink, except for its total monomeric anthocyanin content. The drinks showed good microbiological stability throughout 12 weeks of storage when kept at 4°C, while those stored at 25°C lasted for 4 weeks. There was a significant decrease of antioxidant content, chroma and pH and increase in L value and hue angle, while less significant changes were observed for total soluble solids and viscosity of the drinks during the storage stability study. The degradation of anthocyanins in both drinks kept at different temperatures followed first-order reaction kinetics. According to the findings of this study, black rice and red rice cooking water have the potential of being new antioxidant drinks

Functional and preliminary characterisation of hydrocolloid from tamarillo (Solanum betaceum Cav.) puree

Hydrocolloid from tamarillo (Solanum betaceum Cav.) puree was extracted using water and characterised for the first time. Proximate compositions of the extracted hydrocolloid were also determined. Functional characteristics such as water-holding capacity, oil-holding capacity, emulsifying activity, emulsion stability, foaming capacity and stability of the hydrocolloid were evaluated in comparison to that of commercial hydrocolloids. Its functional groups and degree of esterification were determined using Fourier Transform Infrared (FT-IR) spectroscopy. Monosaccharide profiling was done using reverse-phase high pressure liquid chromatography (RP-HPLC). Screening of various fruits for high hydrocolloid yield after water extraction resulted in tamarillo giving the highest yield. The yield on dry weight basis was 8.30%. The hydrocolloid constituted of 0.83% starch, 21.18% protein and 66.48% dietary fibre with 49.47% degree of esterification and the monosaccharides identified were mannose, ribose, rhamnose, galacturonic acid, glucose, galactose, xylose and arabinose. Higher oil-holding capacity, emulsifying activity and emulsion stability compared to commercial hydrocolloids propose its possible application as a food emulsifier and bile acid binder. Foaming capacity of 32.19% and good foam stabilisation (79.36% of initial foam volume after 2 h of foam formation) suggest its promising application in frothy beverages and other foam based food products. These findings suggest that water-extracted tamarillo hydrocolloid can be utilised as an alternative to low methoxyl pectin