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Ultrasound has been an extraction technique received much attention in recent years. This technique is proven to be able to increase extraction efficiency, shorten extraction time and maintain the activity of antioxidants especially polyphenols. Liquid state of the antioxidant mixture after extraction reduces the application of extracts containing bioactive compounds. This is due to the rapid decline in activity over time and higher transport costs for the liquid extracts with a large amount of water. Therefore, this study was focused on extraction process assisted by microwave to obtain the guava extracts and capsulated these extracts by the suitable carrier to remain the polyphenol activity. It could be seen that microwave was a potential method to extract the polyphenols in comparison with solid-liquid extraction. The cell structure of plant materials was significantly destroyed by microwave in order to release more polyphenols from inner parts of guava leaves. The total phenolic and flavonoid content were increased 12.7% and 36.5% when microwave applied in comparison with the solid-liquid extraction. The combined 20% maltodextrin and 10% arabic gum was the best way to maintain the polyphenol activity. The polyphenols were encapsulated by the combined maltose dextrin and arabic gum was 5.2% more than those of maltodextrin only. Color indices such as L*, a*, b* were significantly different between the powders capsulated by the maltose dextrin and the combined maltose dextrin and arabic gum. [ABSTRACT FROM AUTHOR]

The extraction of high-methoxyl pectin from amberella peels was studied. The best result was obtained with pH of 4.6, solid-liquid ratio of 1:38, extraction time of 9 min and microwave power of 600W in which the pectin content was 20%. Some characters of pectins were estimated. Pectins obtained by the combined oxalic acid and microwave showed DE value and galacturonic acid 7.3% and 100.6%; respectively, higher than those treated with hydrochloride acid. DA values were the same between both pectin samples. The lightness of pectins extracted by the combined oxalic acid and microwave was more suitable for food application than that of pectins obtain to the hydrochloride treatment. There were significant different in color co-ordinates between the pectins from hydrochloride treatment and that from the combined oxalic and microwave treatment. The viscosity and viscosity-average molecular weight of pectins of the combined oxalic acid and microwave were 120% and 161% higher than those of traditional method. Microwave irradiation could be damaged more cell walls of amberella peels to release a large amount of pectins and to reduce treatment time for minimizing the cost of extraction process. The combined oxalic acid and microwave is a good method to get more pectins from amberella peels. [ABSTRACT FROM AUTHOR]

Many synthetic pigments are now banned or limited in application to the foods because the evidence related to the ability to cause cancer and other adverse impacts on the health. Therefore, the study of natural colorants to replace the synthetic colors mentioned above is a challenge for many food scientists in Vietnam and around the world. Cam is abundant in rural area in the North of Vietnam. Currently, Cam leaves have been used as a popular pigment in Vietnam to replace synthetic colors in the traditional foods. Many studies have also shown that the dyes extracted from Cam leaves exhibited clear and beautiful appearance and durability during prolonged storage. Furthermore, the safety when using pigment of Cam leaves has been proven through the long history of the use and through the study of acute toxicity. Extracts of Cam leaves contain a large amount of pelargonidin, zizilan, carotenoids, ß-sitosterol. These compounds are asserted to cure the tuberculosis, eliminates phlegm, acute bronchitis, antitoxic, anti-inflammatory, windpipe infection, hepatitis and diabetes. In order to reduce the cost of using these extracts on food application, many extraction techniques have been introduced to maximum the amount of pigments obtained to Cam leaves. Among of them, ultrasound and microwave are potential ones because of their lower cost and shortly consumed time. [ABSTRACT FROM AUTHOR]