Nondestructive Evaluation of Pickling Cucumbers Using Visible-Infrared Light Transmission

A nondestructive method was developed utilizing a modified Trebor 101 watercore tester to evaluate the internal quality of pickling cucumbers. The method involved measuring the relative amount of visible-infrared light passing through the longitudinal midsection of whole cucumber fruit. Light transmission was quantified on a unitless sigmoid scale from 1 to 10, with light transmission and scale values positively related. Immediately after hand harvest, size 3F (47 to 51 mm in diameter) cucumbers exhibited transmission values between 2 and 3, regardless of cultivar. Following a mechanical-stress treatment, which simulated bruising incurred during harvesting and handling of cucumbers, the internal quality of the fruit declined and was associated with an increase to a value of 6 in light transmission compared to non-stressed fruit. Light transmission increased as the severity of stress applied to the fruit increased, and high light transmission values were evident throughout a 48 h storage period at room temperature. Light transmission values increased as fruit diameter decreased, but values within a particular size class of undamaged, hand-harvested fruit were consistent. Machine-harvested fruit (size 3F), evaluated just before processing, exhibited light transmission values from 2 to 8, but the majority of fruit fell within the transmission range of 2 to 3. When fruit exhibiting different light transmission values were speared (cut longitudinally into sixths), processed, and then visually evaluated by panelists, spears prepared from fruit exhibiting high transmission values were judged to be of lower quality than those prepared from fruit exhibiting low transmission values. Visible-infrared light transmission may be a valuable tool for detecting poor quality cucumbers before processing, and could allow the mechanical selection of high quality fruit on a large scale basis. Internal product quality is an important concern of the pickling cucumber industry. The processed product is considered to have high quality if it has seeds intact within the seed cavity, sharp edges at cut surfaces, and firm mesocarp and carpel tissue. By contrast, low quality processed products may have loose seeds or other cucumber tissue floating freely in the jar, ragged edges at cut surfaces, and have damaged or soft regions. These negative qualities can be attributed to environmental factors (Thomas and Staub, 1992), mineral nutrition (Frost and Kretchman, 1989; Staub et al., 1988), harvest methods (Marshall et al., 1972), postharvest handling (Miller et al., 1987), and storage procedures (Miller et al., 1987; Thomas and Staub, 1992) that adversely affect the cucumbers before processing. Since growers and processors cannot control all of these factors to produce a uniformly high quality fruit, cucumbers of high and low quality are present in shipments of fruit destined for processing. Hence, a method to rapidly evaluate the quality of individual cucumbers, with the intent of separating high and low quality fruit before processing, would be of value to the pickling cucumber industry. Peroxidase activity and delayed light emission (DLE) have been investigated as possible indicators of fresh cucumber quality. Hammerschmidt and Marshall (1991) found that when damaged cucumbers were dipped into a solution of guaiacol and hydrogen peroxide, the solution became darker in color than a solution into or publication 7 Apr. 1995. Accepted for publication 29 June 1995. d research support provided in part by state and federal funds appropriThe Ohio State Univ., Ohio Agricultural Research and Development rnal article no. 178-94. We thank Mark Jameson and Bonnie Borchert nt technical assistance. The cost of publishing this paper was defrayed the payment of page charges. Under postal regulations, this paper ust be hereby marked advertisement solely to indicate this fact. reprint requests should be addressed. SOC. HORT. SCI. 120(6):1063-1068. 1995. which undamaged cucumbers were dipped. This test was based on increased peroxidase activity evident after bruising (Miller and Kelley, 1989), and the water soluble nature of the enzyme. From a practical perspective, the peroxidase method is not desirable since it is slow and the resultant fruit are unsuitable for processing, due to guaiacol contamination. Hence, only a few fruit in a shipment of cucumbers can be evaluated by this method. As an alternative Abbott et al. (1991) tested whether DLE could be used to evaluate fresh cucumber quality. They found that DLE could consistently distinguish bruised from nonbruised cucumbers because nonbruised fruit exhibited significantly higher maximum values for DLE. However, DLE values increased during storage regardless of bruising, and storage temperature significantly affected maximum DLE values. The determination of DLE requires sophisticated instruments and the cucumbers must be stored in the dark for at least one hour before evaluation. Therefore, the DLE method may not be readily applicable to commercial situations. While conducting research on the effects of bruising on pickling cucumbers Miller et al. (1987) and Abbott et al. (1991) noted that water-soaked lesions were present throughout bruised fruit. Later observations showed that these lesions could be visualized through an infrared lens while the cucumber was backlit or sidelit with an incandescent lamp, and that these bruises were most transparent to light at wavelengths between 900 and 1100 nm (A.R. Miller and K. Norris, unpublished). These observations led to the hypothesis that infrared light transmission could be used to detect cucumbers with bruises and low internal quality. This paper describes the modification of a Trebor 101 watercore tester, which has output predominately in the infrared region of the light spectrum, for determining relative light transmission through pickling cucumbers. This modified instrument was then used to test the hypothesis that light transmission can be used to evaluate the