Optimization of Vacuum Frying for Black Glutinous Rice Crackers

This study aimed to optimize vacuum frying parameters, frying temperature (80–120 °C) and frying time (10–20 min), using response surface methodology (RSM) to maximize the quality of rice crackers from black glutinous rice. Vacuum frying temperature and time had no significant (p > 0.05) effect on protein, fiber, total anthocyanin content, and total flavonoid content. An increase in frying temperature increased the expansion ratio and total phenolic content (TPC), while decreasing bulk density and DPPH. Extending frying time significantly (p ≤ 0.05) increased fat content. Increasing both frying temperature and time reduced hardness, moisture, and water activity, and significantly changed color. These trends were evaluated using regression models with R2 values ranging from 0.858 to 0.999. Based on the developed models, the optimal condition was estimated at approximately 110 °C for 10 min, graphically predicting rice crackers with 23.32%db fat, hardness of 4.83 N, and TPC of 2.63 mg GAE/g. Compared with atmospheric frying (160 °C, 10 min), the optimal vacuum frying condition (110 °C, 10 min) reduced fat by 36.16%, decreased hardness by 68.65%, and increased TPC by 95.49%, suggesting that vacuum frying can produce black glutinous rice crackers with lower fat, higher antioxidant compounds, and greater crispiness under these specific parameters.