New Analytical Strategies for Quality Control and Classification of Apple Juices Using Digital Image Processing (DIP) Combined with Machine Learning (ML)

Apple juice is widely consumed for its pleasant sensory attributes and nutritional value. However, due to its high commercial value, this beverage, particularly whole juice, is susceptible to fraud and adulteration. This underscores the need for rapid, noninvasive analytical strategies to ensure product authenticity and quality. This study reports, for the first time, the application of smartphone-based image analysis combined with machine learning as a low-cost and nondestructive approach for both classifying apple juice types and predicting the actual juice content in apple-based beverages. Images of nine whole juice (WJ), four reconstituted juice (RE), and five nectar (NE) samples were analyzed to develop models capable of discriminating beverage categories and estimating apple juice concentration. Classification models generated using <i>k</i>-nearest neighbors (<i>k</i>NN) and extreme gradient boosting (XGBoost) algorithms achieved good global accuracies of 95.9% (99.1% and 100.0% in training and 95.9% in testing), with cross-validation accuracies of 98.7% and 95.5%, respectively. Predictive models constructed from calibration curves (5-100% apple juice) combined with commercial samples yielded good estimates for coefficients of determination (<i>R</i> ² = 93.1-93.5% in testing, 97.7-96.2% in training, and 91.9-92.4% in cross-validation) and root-mean-square errors (RMSE = 8.0-8.2%) for models generated by XGBoost and CatBoost, respectively. These findings demonstrate the scientific novelty and practical feasibility of integrating smartphone imaging with machine learning for the quantitative analysis of apple juice. The proposed approach represents a rapid, accurate, and cost-effective alternative for industrial quality control and regulatory inspection.