Effect of gamma irradiation on physicochemical properties and microbiological quality of wet yellow noodle fortified with water spinach (Ipomoea aquatica)

Abstract

Effect of gamma irradiation on physicochemical properties and microbiological quality of wet water spinach yellow (WYS) noodles were investigated. Water spinach has been substituted with the wheat flour at level 5%, 10% and 15% and irradiated at 0 kGy, 3 kGy, 5 kGy and 7 kGy with a dose rate of 34 Gy/minutes by using Cobalt-60. Gamma irradiation significantly decreased the cooking yield, hardness and lightness while significantly increased cooking loss and breaking length of WYS noodles. All doses of irradiation did not affect the moisture content, pH, water activity, greenness and yellowness of the noodles. Cross sections of WYS noodles were observed under VPSEM at 500X magnification and irradiation gave little changes to starch granules. Increasing substitution level of water spinach and irradiation dose showed elongated and clumped together. Moisture content and color of yellow noodles increased gradually on increasing the level of water spinach substituted. However, a decreasing trend was observed in breaking length, hardness, lightness and yellowness. Total plate counts of the WYS noodles that stored at 27°C were examined at day 0, 3 and 5. It showed that certain dose such as 7 kGy of irradiation able to reduce the bacteria count in noodles. On day 5, most of the samples showed high bacteria count more than 108 CFU/g was not safe to be consumed. In conclusion, gamma irradiation and substitution of water spinach gave significantly effect cooking properties, textural properties and lightness while no effect on moisture content, pH, water activity, greenness and yellowness of WYS noodles.