Fortification of rice grain with gac aril (Momordica conchinchinensis) using vacuum impregnation technique

Abstract

© 2018 The Author(s). The objective of this research was to improve functional property of rice by fortification with gac aril using vacuum impregnation (VI) process. Effects of rice variety, preparation method and VI condition on gac aril fortified rice quality were investigated. Sao Hai (SH) and Khaw Dok Mali 105 (KDML 105) were prepared to achieve polished and unpolished rice. The samples were impregnated with 30% gac aril solution under VI condition (vacuum pressure 500 mmHg), 0% gac solution was used as a control. After drying, the samples were analyzed for physicochemical property i.e. texture, color L*, a* and b*, total fiber, lycopene, β-carotene and total phenolic (TPC) content and antioxidant activity (DPPH assay) as well as sensory quality (9-point hedonic scale). The results showed that both varieties of unpolished rice had higher hardness and darker colour than polished samples. Unpolished SH impregnated with gac aril showed the highest content of β-carotene (22.10±0.83 mg/g), lycopene (8.38±0.11 µg/g), and TPC (0.24±0.03 mg GAE/g) while antioxidant activity of all gac aril fortified samples were not significantly different (p>0.05) (DPPH value ranged 1.39-1.72 mmol TE/ g) and higher than control. However, sensory evaluation showed that gac fortified unpolished KDML 105 had the highest score of the overall acceptability. Based on all properties, unpolished KDML 105 was chosen for studying the suitable VI condition in further step. Unpolished KDML 105 was soaked in 30% gac aril solution under different vacuum pressures (0, 300 and 500 mmHg) and pressurizing techniques (single and pulse pressure). The dried samples were analyzed and it was found that the high vacuum pressure at 500 mmHg and pulse pressure gave the highest β-carotene (41.41 ± 4.53 mg/g), lycopene (25.07 ±1.74 µg/g) and TPC (0.21±0.03 mg GAE/g) content and DPPH value (2.91±0.90 mmol TE/ g), while physical properties, texture and sensory were not significantly different (p>95%). In addition, glycemic index (GI) of rice after VI process was decreased from 84.24 to 72.04. Finally, it can be concluded that non-polishing process, high vacuum pressure and pulse pressurizing are the suitable condition to prepare gac aril fortified rice. The health benefits of rice are improved with high antioxidant activity and lower GI.