This research proposed a technique for detecting the sensitivity of benzoic acid (C6H5COOH) and copper sulfate (CuSO4), which is excessively used in foods. The novelty of this work is that it detects the sensitivity of two food additives with the same metasurface. Although it offers the benefits of miniaturization, minimal sample consumption, and cost-efficiency, it is an easier, faster, and nondestructive detection method than other traditional approaches. The proposed design is based on a polyimide substrate with an aluminum resonator that forms a star shape on the substrate. The transmission frequency of the metasurface was determined at 0.91 THz with a transmission coefficient of 36.6 dB. The metasurface sensor is insensitive to polarization and has a large angle of incident. The transmission spectrum shows that the amplitude of the transmission peaks usually changes with variations in the refractive index of the analytes. The proposed sensor effectively detects benzoic acid (C6H5COOH) with a sensitivity of 0.175 THz/RIU and, the sensitivity of the Copper Sulfate (CuSO₄) is 0.225 THz/RIU with the Q factor values of 12 and 10.55 respectively. These sensitivity results and transmission intensities of different analyte thicknesses show that this proposed THz metasurface sensor can be used to detect additives in foods.