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  • Author or Editor: D. D. Hamann x
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Abstract

A method is described and test results reported for sorting blueberries with low-frequency vibration. Separation was dependent on fruit firmness which is affected by roughness of handling and other softening factors.

Firmness, as measured by compressing blueberries 0.2 cm between flat plates, statistically explained 58 to 72% of the variation in frequency for removal of berries from a vibrating trough with constant energy input. When comparing ripeness with frequency for sorting, light transmittance (∆OD; 740-800 nm) values, which indicate anthocyanin pigment concentration, explained only 10% of the variation in sorting frequency.

Berries of several cultivars and harvest dates were vibration sorted and tested for susceptibility to decay. Sorting frequency statistically explained 75% of the variation in decay level. Thus, the vibration method should be suitable for sorting blueberries into groups of different shelf life.

Open Access

Abstract

An Instron Universal Testing Machine was modified to measure firmness of blueberry fruit. Each blueberry was compressed between 2 flat surfaces for 1/4 its diameter at 1 cm/minute. Compression curves were linear. Small, green, unripe blueberries were extremely firm, softened appreciably as they ripened from the green to red stages but softened relatively little thereafter. Smaller blueberries tended to be slightly more firm than larger ones. Firmness varied from one harvest to another within a year and from one year to another. The firmness of fruit of some cultivars was almost double that of others. Firmness as measured by the Instron compared well (r = 0.70* and 0.81 *) with field (“chewing” or mastication) scores made by the breeder as part of his regular program. Blueberries dropped upon hard boards softened (bruised) in proportion to the distance of fall. Small increments (10.2 cm or 4-inch) of fall softened blueberries as much as large increments (40.6 cm or 16-inch) as long as the total distance (sum of increments) of fall was constant. Regardless of cultivar, size, ripeness, or initial firmness, the firmness of blueberries after a standard fall (8 drops of 40.6 cm or 16 inches each) can be predicted if their initial firmness (X) is known (Y = −0.590 + 0.627X). Bruised blueberries decayed more than those not bruised. Firmness of blueberries decreased when they were warmed and increased when they were cooled; this effect was a reversible, physical phenomenon.

Open Access