Evaluation of in-line sensors for prediction of soluble and total solids/moisture in continuous processing of fruit juices

Abstract Three inline sensors: Near-infra red (NIR) (Protonics P-112, Katrina Inc, Hagerstown, MD); Guided Microwave (Epsilon Industrial Inc, Austin, TX) and Maselli refractometer (Maselli Measurements Inc, Stockton, CA) were evaluated for continuous measurement of soluble and total solids/total moisture in continuous processing of (8–16 Brix) apple, grape, pear, apple-cherry and apple-banana juices in a pilot scale processing unit. Experiments were conducted in the temperature range 21–65 °C, back pressure of 0–204 kPa, flow rate of 0.756–4.536 kilolit/h, and acidity of 0.3 to 0.6% malic acid, and pH range of: 3.2–3.9. The sensors were calibrated by off-line measurement of soluble solids from an Abbe refractometer and total solids/moisture by standard vacuum oven method. The process temperature was found to have great effect on the prediction of these sensors. The effects of acidity, back pressure and flow rate were negligible. High correlation coefficients were obtained for calibration curves of the soluble and total solids in different juices. Maselli refractometer gave excellent results for soluble solids under different operating conditions. NIR Katrina analyser and GM Epsilon spectrometer gave good results for soluble and total solids. The sensors were found to give reproducible results after prolonged use and were not found to have any deposits or buildups. The present research shows that these sensors can satisfactorily be used for in-line processing of different juices in industries.