Gelation Properties of Okra's Extract And Its Application In Strawberry Jam

The mucilage of okra (Abelmoschus esculentus (L.) Moench), containing high amount of gum and pectin, possesses the structure of rhamnogalacturonan which has thickening properties [1,2]. Pectin in okra is a low-methoxy type, which forms gel with calcium ion at low sugar concentration. The aim of this research is to study the application of okra's extract as a thickening agent and to reduce sucrose content in strawberry jam. Firstly, the optimum temperature for the extraction of the okra was investigated. Physical analyses were determined by % yield, flowing distance (viscosity) and color values (Hunter L* a* b*). It was found that at four different extracting temperatures, i.e, 50, 60, 70 and 80 °C, the optimum temperature for the extraction was 60 °C. Then, gelation properties of the okra's extract were investigated in 3 different concentrations of sucrose at 50, 60 and 70% (by weight of okra's extract) and 3 different concentrations of calcium chloride at 2, 2.5 and 3% (by total weight). Secondly, the physical analysis results showed that the sugar content at 50% and the calcium chloride concentration at 2% had the highest viscosity. Finally, an appropriate ratio of the okra's extract to reduce sucrose content in strawberry jam was further studied at either 60:40, or 40:60, or 80:20 (by sucrose weight) and the pectin content was varied at 0.5 and 1% (by total weight). The jam with the ratio of sucrose to okra's extract at 40:60, and of pectin at 0.5%, possessed the highest spreadability and the lowest viscosity. Additionally, at this concentration the sensory scores in appearance and spreadability were higher than those of the control.

[1] Woolfe, M.L, Chaplin, M.F. and Otchere, G. J. Sci. Fd Agric. 1977; 28: 519 – 529.

[2] Bhat, U.S, Tharathan, R.N. Starch 1987; 39: 165 – 167.