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The effects of dual modification with ultrasound and annealing treatments on the properties and glycemic index of the Thai glutinous rice cultivar ‘RD6’.
(2019-01-01)
Kunyanee, K.
;
Luangsakul, N.
Glutinous rice is a popular food and an important source of carbohydrate, especially in the North and North-Eastern areas of Thailand. However, glutinous rice can be considered unhealthy because it has a high glycemic index (GI=75-92), which makes it unsuitable for people suffering with type II diabetes. Therefore, a method of processing glutinous rice that reduces its GI could make it a more acceptable food and more suitable for diabetics. Ultrasound, which applies mechanical waves with a frequency above 16 kHz, and annealing (ANN), which is a hydrothermal treatment, have both been successfully used to modify starch. Ultrasound impacts starch granules and can change molecular structure and properties. ANN can reduce starch hydrolysis and improve its relative crystallinity, which affected its thermal properties. Therefore, the combination of ultrasound and ANN treatments were investigated to determine their effects on the glycemic index of the Thai glutinous rice cultivar ‘RD6’. Samples of ‘RD6’ were treated with ultrasound, at 100% amplitude, for 15 min followed by storage at 4oC for 24 h and then exposed to ANN at 45, 50 or 55oC. The samples were then evaluated for their pasting properties (pasting temperature, pasting viscosity, breakdown, final viscosity and setback), gelatinization properties, starch hydrolysis and glycemic index. All the pasting properties of the ‘RD6’ samples that treated with ultrasound and ultrasound plus ANN had significantly (p<0.05) increased levels of all compared to the untreated samples (control). These treatments also significantly (p<0.05) increased onset temperature and gelatinization enthalpy, particularly the ANN at the higher temperatures (50 and 55oC). In addition, ultrasound plus ANN significantly (p<0.05) decreased starch hydrolysis and promoted a decrease in their glycemic index from (76.78-77.62) as compared to the control (84.14) and ultrasound alone (80.71), but none of these treatments reduced glycemic index to below 70, which is ranked as high.
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The utilization of ultrasound and chilling treatment to reduce GI in Thai glutinous rice (RD6)
(2018-12-01)
Kunyanee, K.
;
Luangsakul, N.
The source of carbohydrate in the North and North-Eastern areas in Thailand are predominantly based on glutinous rice which high glycemic index (GI75-92). Lower GI glutinous rice was interesting prospect to develop diabetics. There are modified methods to reduce GI by limit the accessibility of the digestive enzymes on starch molecule. The most common physical modification method used for reducing GI on starch are hydrothermal and gelatinization-retrogradation methods. Ultrasound is the sound wave at frequency exceeding audible threshold of the human hearing rang. It is studied on starch to change the molecular structure for improving some physicochemical properties. Therefore, this resecrch focused on the utilization of ultrasound and chilling treatment to reduce GI in Thai glutinousonrice (RD6). The glutinous rice was treated with ultrasound for 15 and 30 min and amplitude at 40, 70, and 100%. All of the ultrasound-treated rice was stored at 4 o Cfor 24 h. Then, thery were analyzed on the ratio crystalline to amorphous by FTIR, thermal properties by DSC, RVA pasting properties, and GI. With increasing time and amplitude of ultrasound, the ratio of crystalline to amorphous decreased from 0.779 to 0.662. The onset temperatureand enthalpy (∆H) decreased from 62.38 to 58.10 o C, and 1.81 to 0.70 J/g, respectively. The peak viscosity, and final viscosity from RVA increased from 3079 to 3838.67 cP and 2407.33 to 2922 cP, respectively. When increasing time and amplitude of ultrasound, the hydrolysis index (HI) and eGI slightly increased with longer time and higher amplitude than the others. The chilled samplesafter ultrasound treatment showed that the ratio of crystalline to amorphous, and ∆H increased while HI and eGI decreased when compared to unchilled ultrasound treated rice.
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Effect of oil addition on in vitro starch digestibility and physicochemical properties of instant rice
(2018-12-01)
Luangsakul, N.
;
Ritudomphol, O.
The most varieties of rice have high starch digestibility and glycemic index (GI), which is unsuitable for diabetics. The processes involved in the production of instant rice, not only make it more convenient for the consumer, but can also lower its starch digestibility and GI through the decrease in enzymatic accessibility to rice kernels. One way to control the enzymatic digestion of rice was increasing the amylose-lipid complex formation. The effect of oil addition during rice cooking on in vitro starch digestibility, GI and some physicochemical properties (thermal properties, X-ray diffraction patterns and pasting properties) of instant rice wasc studied. During rice cooking, 2 type of cooking oil, including coconut oil (C) and rice bran oil (R) at 2.5, 5 and 7.5% (w/w, on the basis of uncooked rice) were added to Sao Hai rice (SH), which had amylose content of 21.35 g/100g (dry weight basis, db). Thermal properties showed amylose-lipid complex dissociation peaks when rice was cooked with oil, and the highest enthalpy was found in the addition of oil at 2.5%. In X-ray diffraction patterns, cooked rice with oil which showed A+V type crystalline structure and the addition of rice bran oil at 2.5% exhibited the highest relative crystallinity (19.98%). The formation of amylose-lipid complex of cooked rice with oil reduced in vitro starch digestibility and eGI compared to cooked rice without oil. The addition of rice bran oil at 2.5% had the highest slowly digestible starch (SDS) and resistant starch (RS) contents, which were consistent with their lowest estimated glycemic index (eGI). The addition of oil to rice resulted in a lower peak viscosity (PV) and setback (SB), as compared to instant rice without oil.

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