Rapid field assay for pineapple fruit acidity

Abstract

The sugar-to-acid ratio of pineapple (Ananas comosus L.) contributes toward giving the fruit its unique flavor. This ratio is an important indicator of both commercial and organoleptic ripeness, and it is useful in determining a harvest date. Citric acid is the major acid in pineapple and usually is determined by titration to a specific pH endpoint, while sugars are determined as total soluble solids by re-fractometry. Both acid and sugar levels vary with the season in the year-round production cycle. Acid titration is slow and difficult to perform in the field. A digital acidity meter based upon diluted juice conductivity was evaluated for potential field use. The readings obtained from the meter varied with clone and fruit potassium concentration. The meter had utility for field use to evaluate fruit quality and harvest date. Because fruit potassium levels can vary between harvests, the meter should be recalibrated on a regular schedule to adjust for potential crop management and seasonal effects.