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ARS Home » Southeast Area » Dawson, Georgia » National Peanut Research Laboratory » Research » Publications at this Location » Publication #320570

Research Project: Postharvest Systems to Assess and Preserve Peanut Quality and Safety

Location: National Peanut Research Laboratory

Title: Nondestructive Determination of Moisture Content in Dry Fruits by Impedance and Phase angle measurements

item Kandala, Chari
item Holser, Ronald
item SUNDARAM, JAYA - University Of Georgia
item PUPPALA, NAVEEN - New Mexico State University

Submitted to: Journal of Sensor Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/21/2015
Publication Date: 12/25/2015
Citation: Kandala, C., Holser, R.A., Sundaram, J., Puppala, N. 2015. Nondestructive Determination of Moisture Content in Dry Fruits by Impedance and Phase angle measurements. Journal of Sensor Technology. 5:73-80.

Interpretive Summary: United stated is the second largest producer of cherries in the world, and has a thriving export market for dry fruits such as cherries and blueberries. Drying the fruits to a lower moisture content (mc) of below 10% from the wet produce having about 40% moisture, facilitates extending their self life considerably. Dried fruit with longer shelf life can be exported without the risk of spoilage, and would be available round the year anywhere in the world for including in several food products such as cakes and puddings that would enhance their flavor. Cherries and blueberries have high moisture contents when harvested and they are dried to safe mc levels by passing hot air over them at controlled relative humidity. During this process the mc has to be measured several times. Presently used methods are either vacuum-oven or Karl Fisher titration. Both methods are time consuming and destructive. The capacitance sensing method described here is nondestructive and time saving. No sample preparation is needed as for the other two methods. Earlier field trials have proved that this method would be useful for the dry-fruit industry. This method was tested successfully for cherries and blueberries and can be extended to other types of fruits such as raspberries.

Technical Abstract: Impedance (Z), and phase angle (') of a cylindrical parallel-plate capacitor with dry fruits between the plates was measured using a CI meter (Chari’s Impedance meter), at 1 and 9 MHz . Capacitance, C was derived from Z and ', and using the C, ', and Z values of a set of cherries whose moisture content (MC) values were later determined by the vacuum hot air-oven method, a calibration equation was developed. Using this equation, and their measured C, ', and Z values, the MC of a group of cherries, not used in the calibration, was predicted. The predicted values were compared with their air-oven values. Similar predictions were done using the same method on blueberries. The method worked well with a good R2 value, and a low standard error of prediction (SEP) in the measured moisture range, between 5% and 30% for cherries, and 9% and 22% for blueberries.