Effect of using riceberry flour and xanthan gum on physical properties and estimated glycemic index of steamed rice cakes: optimization by D-optimal mixture design approach.

Riceberry, a Thai black rice variety (Oryza Sativa L.) has been developed with the aim to provide high iron and low glucose to consumers. Therefore, riceberry could potentially be used to produce healthier processed foods. In this regard, a D-optimal mixture design was employed for the optimization of the steamed rice cakes which included ten combinations of riceberry flour (RF), xanthan gum (XG) and glutinous rice flour (GRF). The influence of RF substitution for GRF with XG addition on the texture, physicochemical and sensory properties, as well as the estimated glycemic index (eGI) of the steamed rice cakes, were studied. The results demonstrated that RF, XG, and GRF had a noticeable effect on eGI, textural, and sensory properties of the steamed rice cakes. XG was the variable that most affected hardness, adhesiveness, cohesiveness, and gumminess of the steamed rice cakes by the positive effect. XG had a negative effect on hydrolysis index and eGI. The optimum mixture obtained on a basis of overall liking, hardness, adhesiveness, gumminess, and eGI value contained 39% RF, 1% XG, and 60% GRF with desirability equal to 0.673. For filling, the red bean paste with 100% isomaltulose substitution for sucrose indicated the lowest value of eGI and the highest score of the overall liking. The optimum steamed rice cakes stuffed with the red bean paste used isomaltulose as a sucrose replacer were classified as the medium GI food.

Optimization of ultrasonic-assisted extraction of polysaccharides from purple glutinous rice bran (Oryza sativa L.) and their antioxidant activities.

Purple glutinous rice bran (Kum Doi Saket rice (KUM)) contains high content of edible polysaccharides and anthocyanins and has an excellent antioxidant activity. This research aimed to optimize the extraction of crude polysaccharides from defatted purple glutinous rice bran using an ultrasonic-assisted extraction (UAE) and compared with a hot water extraction (HWE). Results showed that optimal extraction condition was as follows: a defatted rice bran to water ratio of 1:20 w/v, extraction temperature and time of 70 °C for 20 min. Under the optimal extraction condition, the yield of polysaccharide of UAE (4%) was significantly higher than that obtained from the HWE (0.8%). Additionally, antioxidant activities of extracted polysaccharide including IC50 value DPPH, IC50 value ABTS, and FRAP value were 1.09 mg/mL, 2.80 mg/mL and 197 µM Fe2+/g, respectively. It is suggested that the UAE process is promising method to decrease the processing time and to enhance extracted polysaccharide yields by 4 times.

Effect of extraction and concentration processes on properties of longan syrup.

Longan (Dimocarpus longan Lour.) syrup is a novel liquid sweetener produced from longan, one of the traditional and economic fruits in the Northern of Thailand. In this research, the effect of extraction and concentration processes on properties of longan syrup was investigated. There were two extraction methods (juice extractor and hydraulic press) and three concentration methods (direct heating, steam heating and vacuum evaporation). Results overall showed that the extraction method had no significant (p ≥ 0.05) effect on longan syrup properties, while concentration resulted in the quality changes of longan syrup. Concentration using direct heating of longan juice caused reduction of sucrose content, and longan syrup dark in color. The headspace volatile compounds of longan syrup were sampled using direct headspace technique and further characterized using gas chromatography-mass spectrometry. The identified volatile compounds could be divided into two groups of aroma characteristics which were (1) floral aroma: 3-methybutyl acetate, (ß)-ocimene and 2-phenylethyl alcohol and (2) caramel aroma: butyraldehyde, furfural and benzaldehyde. 2-Phenylethyl alcohol, contributing to floral odor, was retained using vacuum evaporation as a concentration method. Result revealed that the optimal concentration process for longan syrup production was vacuum evaporation, providing the highest floral volatile and lowest caramel volatile. Sensory tests confirmed that longan flavor of the syrup produced from the vacuum evaporation process had significantly higher hedonic scores than other processes.