Nondestructive Quality Assessment

Today, the majority of internal quality assessments for lots of fruit are based on destructive tests on selected samples. From a relatively small number of samples, decisions are made about the remaining population. Retail customer requirements for specific internal quality conditions have become increasingly difficult to achieve. The invisible quality attributes that are being promoted and requested include firmness, texture, sweetness, flavor, and assurance of no internal decay or disorders. A number of technologies are being explored in the quest for methods to inspect individual fruit and pack only those which meet minimum criteria and customer expectations.

A nondestructive online method to replace the destructive pen-etrometer method of measuring firmness is being sought. A possible solution for fruit of moderate firmness, e.g., stone fruit, is being developed in the United Kingdom (http://www.sinclair-intl.com/). This nondestructive method uses an accelerometer in the form of a small bullet probe that taps the fruit and monitors the change in slope of acceleration of the probe during impact. Once developed, this technology can be quickly integrated in conjunction with the equipment that applies labels on individual fruit. For firmer fruit such as apples and pears, a company in the Netherlands (http://www.aweta.nl) is devel oping an acoustical device that taps fruit and measures the frequency at which it vibrates as a result of the nondestructive impact. A combination of the frequency and the weight of the fruit results in a measurement that can be used for sorting. Consumers can distinguish fruit of differing acoustic levels as firm or soft textured.

Near-infrared (NIR) is a technology that has just recently become commercially available for measuring the sugar content of stone and pome fruit (Figure P1.2). With NIR technology, an association is built between the patterns of the absorbed invisible wavelengths and the internal organic sugar molecules present in the flesh of a fruit. Computer modeling plays a large role in these systems. The operation and results of NIR are dependent on fruit temperature. Under stable operating conditions, NIR is accurate to within approximately a 1 percent sugar level. The reflectance method measures the sugar content near the surface of the fruit. Transmission requires more light but measures more tissue.

Magnetic resonance imaging (MRI) is another promising technique that has been explored. This technology is dependent on the influence of a strong magnetic field on hydrogen nuclei. Fruit are com-

FIGURE P1.2. Near-infrared technology measuring sugar content of apples on a commercial packing line (Source: Photo courtesy of Stemilt Growers, Wenatchee, WA.)

posed mainly of water (approximately 85 percent) and thus have an abundance of hydrogen atoms that respond to magnetism. MRI is a valuable technique that is commonly used in the medical field. It also works well for identifying internal defects in fruit. The drawbacks with this technique are its relatively slow speed and the significant costs associated with a need for multiple lanes to sort fruit at commercial rates.

Another accepted technique that is used widely in the medical field today is X-ray technology. Research in this area has shown positive results with identifying internal damage caused by tunneling insects. The technique has much potential for commercialization from a cost and speed standpoint. There is concern, however, regarding the perception of the public with respect to consuming fruit that have been irradiated.

The packing operation is a very critical step in the process of providing fruit to the consumer. Packing is unique to all other operations of growing, storing, handling, and distributing fruit. The packing line acts as a funnel of opportunity for selecting fruit with appealing characteristics, both external and internal, and thus providing the consumer with consistent satisfaction that produces repeat purchases.

Related Topics: FRUIT MATURITY; HARVEST; MARKETING; POST-HARVEST FRUIT PHYSIOLOGY; STORING AND HANDLING FRUIT

SELECTED BIBLIOGRAPHY

Abbott, J. A., R. Lu, B. L. Upchurch, and R. Stroshine (1997). New technologies for nondestructive quality evaluation of fruits and vegetables. Hort. Rev. 20:1-120.

Baritelle, A. L. and G. M. Hyde (2001). Commodity conditioning to reduce impact bruising. Postharvest Biology and Technol. 21:331-339.

Crisosto, C. H., D. Slaughter, D. Garner, and J. Boyd (2001). Stone fruit critical bruising thresholds. J. Amer. Pomological Soc. 55:76-81.

Lange, D. L. (2000). New film technologies for horticultural products. HortTechnol. 10:487-490.

LaRue, J. H. and R. S. Johnson (1989). Peaches, plums and nectarines: Growing and handling for fresh market, Pub. 3331. Davis, CA: Univ. of California Coop. Exten. Serv., Div. of Agric. and Nat. Resources.

Northeast Regional Agricultural Engineering Service (1997). Sensors for nondestructive testing: Measuring the quality offresh fruits and vegetables. Proceed ings from the sensors for nondestructive testing international conference. Ithaca, NY: NRAES.

Wills, R., B. McGlasson, D. Graham, and D. Joyce (1998). Postharvest: An introduction to the physiology and handling of fruit, vegetables and ornamentals, Fourth edition. Adelaide, South Australia: Hyde Park Press.

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