Effect of gamma irradiation on physicochemical characteristics and microbiological quality at different ratio of tapioca and potato starches of flat rice noodle

Abstract

Flat rice noodle is classified under non-wheat noodles due to the absence of gluten and required gelatinization of starch during processing. It is also very susceptible to spoilage and has a short shelf-life because of the high moisture content. This study was conducted to investigate and compare the effect of gamma irradiation on the physicochemical characteristics and microbiological quality of containing two different starches. Tapioca starch (TS) and potato starch (PS) were incorporated into the formulations at 3 levels (3%, 8% and 11%) and was irradiated at 4 doses of 0 (control), 4, 6, and 8 kGy with dose rate of 42.78 Gy/min by using 60Cobalt. Total plate count (TPC) was performed where samples were stored at 8°C and examined for day 1, 3, 5, and 7. Results showed that all doses of irradiation did not significantly (p>0.05) affected the moisture content and water activity of samples. However, gamma irradiation significantly (p<0.05) decreased the pH value, cooking yield, lightness, and hardness of the samples; whereas it significantly (p<0.05) increased the cooking loss, colour (a* and b*), and breaking length. Meanwhile, cooking yield, lightness, and hardness of samples containing PS were higher compared to samples containing TS. Moisture content for samples containing both TS and PS was higher compared to samples containing single starch. TPC showed that irradiation was able to control microbial growth. Moreover, no microbial load was detected on samples irradiated at 8 kGy until day 7. It was thus shown that increased doses in gamma irradiation could improve microbiological quality of flat rice noodles