Response Surface Optimization of the Preparation Process of Compound Yogurt with Cistanche deserticola and Jujube and Evaluation of the Antioxidant Activity of Compound Yogurt with Biosensors

The preparation process of compound yogurt with added cistanche and jujube was optimized using single-factor experiments and response surface curve analysis by applying evaluation indicators including taste, texture, odor, and color. Besides, a rapid evaluation of the antioxidant activity of the compound yogurt was performed by employing the DPPH free radical scavenging system and electrochemical biosensors. Results of the single-factor experiments and response surface analysis indicated that the quality of the compound yogurt was optimal when the percentages of jujube juice, cistanche juice, and honey were 18%, 8%, and 5%, respectively. This composition achieved a sensory score of 92.2, which was close to the predicted score of 92.5. Under the same optimized conditions, the evaluation of the antioxidant activity with the preparation of DNA/CS-N-G/GCE biosensor obtained through the layer-by-layer modified glassy carbon electrode assembly of DNA, chitosan, and nitrogen-doped graphene indicated that L-ascorbic acid, compound yogurt, and plain yogurt present peak current values of 6.5×10⁻⁵、8.5×10⁻⁵ and 1.05×10⁻⁴ A, respectively. This represented a decreasing trend in antioxidant activity. Further validation of DPPH free radical scavenging experiments showed that the IC₅₀ value of L-ascorbic acid, compound yogurt and plain yogurt were 4.54, 15.65 and 22.94 mg/mL, respectively. This was consistent with the results of the evaluation of the compound yogurt using the biosensor, and there was no significant difference between the two methods. Therefore, the addition of cistanche and jujube extracts into plain yogurt significantly enhanced the inhibition of damage to DNA by free radicals, thus improving the antioxidant activity in the compound yogurt. The constructed sensor could be used for the rapid evaluation of antioxidant activity of compound yogurt.