Non-destructive Fruit Firmness Evaluation Using Vision-Based Tactile Information

During postharvest storage, fruit firmness usually decreases due to respiration and bruise, the former of which indicates the fruit ripeness while the latter negatively influence consumers' taste preference. This paper presents a portable and low-cost device using vision-based tactile information to evaluate fruit firmness in a non-destructive manner. The device consists of a camera, LED lights, and a soft sensing layer with small bumps to capture detailed tactile information of the fruit. Two working modes are designed and a CNN-LSTM architecture is developed to relate the tactile information to fruit overall firmness or detect local firmness distortion. According to the experimental results, an R2 up to 92.9% was achieved for the evaluation of the overall firmness of Cuixiang kiwifruit, and accuracy of 98.0% was obtained for the detection of local firmness distortion of Fuji apples. These results demonstrate the efficacy of the proposed solution to evaluate fruit firmness featuring high precision, and its non-destructive and potable nature is also anticipated to be favorable by the fresh fruit market.