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K.H.S. Peiris and S.J. Kays

Centella asiatica, the Asiatic pennywort, is an herbaceous perennial indigenous to the southeastern United States. In some Asian countries, it is valued as an important vegetable and is widely cultivated. In addition, it is considered an important medicinal herb due primarily to the pentacyclic phytochemical, asiaticoside, which effectively treats a variety of skin diseases. Information on the botany, photochemistry, medicinal, nutritional value, and cultivation of the crop is reviewed. This species may warrant preliminary field and consumer acceptance tests as a speciality vegetable in the United States.

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K.H.S. Peiris, J.L. Mallon, and S.J. Kays

Respiratory rate was measured and vital heat calculated for 18 specialty vegetables {arugula or roquette [Eruca sativa Miller], banana flower bud [Musa ×paradisiaca L. var. paradisiaca], bitter gourd [Momordica charantia L.], cassava [Manihot esculanta Crantz], chayote [Sechium edule (Jacq.) Swartz], Chinese chive [Allium tuberosum Rottler ex Sprengel], Chinese water chestnut [Eleocharis dulcis (Burm. f.) Trin. ex Henschel], drumstick [Moringa oleifera Lam.], giant or elephant garlic [Allium scorodoprasm L.], guar [Cyamopsis tetragonoloba (L.) Taub.], hyacinth bean [Lablab purpurus (L.) Sweet.], Jerusalem artichoke [Helianthus tuberosus L.], jicama [Pachyrhizus erosus (L.) Urban], methi [Trigonella foenum-graecum L.], salsify [Tragopogon porrifolius L.], tindora [Coccinia grandis (L.) Voigt], tomatillo [Physalis ixocarpa Brot. ex Hornem.], and tumeric [Curcuma longa L.]} at 0, 5, 10, and 20 °C. Respiration rates increased more or less exponentially with increasing storage temperature in all the vegetables tested, CO2 varying from 28 to 302 mg·kg−1·h−1 at 20 °C for tumeric and drumstick, respectively. At 0 °C, the same products had the lowest and highest respiration rates of the products measured (i.e., CO2 at 4.5 and 28 mg·kg-1·h−1, respectively). Among the vegetables tested, above-ground plant parts such as leaves, fruit, and flowers generally had higher respiration rates than subterrancan storage organs such as roots, corms, and tubers. Vital heat produced ranged from 49 J·kg-1·h-1 for tumeric at 0 °C to 3272 J·kg-1·h-1 for drumstick at 20 °C.

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K.H.S. Peiris, G.G. Dull, R.G. Leffler, and S.J. Kays

Spatial variation in soluble solids content (SSC) of fruits of apple (Malus ×domestica Borkh. cv. Red Delicious), cantaloupe (Cucumis melo L. Cantaloupensis group), grapefruit (Citrus paradisi Macf. cv. Indian River Ruby Red), honeydew melon (Cucumis melo L. Inodorus group), mango (Mangifera indica L. cv. Hayden), orange (Citrus sinensis L. Osbeck. cv. Valencia), peach (Prunus persica L. Batsch. cv. Windblow), pineapple (Ananas comosus L. Merr. cv. Kew) and tomato (Lycopersicon esculentum Mill.), and of bulbs of onion (Allium cepa L. Cepa group) and in dry-matter content (DMC) of potato (Solanum tuberosum L. cv. Russet Burbank) tubers was measured along three directional orientations (i.e., proximal to distal, circumferentially midway along the proximal to distal axis, and radially from the center of the interior to the outer surface). The pattern and magnitude of constituent variation depended on the type of product and the direction of measurement. Radial and proximal to distal variation was greater than circumferential variation in all the products tested. Honeydew had the highest radial variation with a SSC difference of 6.0 % and a cv of 22.8%, while tomato displayed lower radial variation with a cv of 1.0%. Pineapple had a proximal to distal SSC difference of 4.6% with a cv of 13.8%, while the difference in tomato was 0.6% with a cv of 5.1%. Circumferential variation of SSC in all products tested was <2% with cv ranging from 1.1% to 3.8%. The results confirm that considerable constituent variability exists within individual fruit and vegetable organs. This variability may affect the accuracy of calibration equations and their prediction capability. Therefore, within-unit constituent variability should be meticulously assessed when an NIR spectrometric method is being developed for the nondestructive quality evaluation and sorting of a product.

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K.H.S. Peiris, G.G. Dull, R.G. Leffler, and S.J. Kays

A nondestructive method for measuring the soluble solids content (SSC) of individual processing tomatoes (Lycopersicon esculentum Mill.) was developed using NIR spectrometry. A diode array fiber optic spectrometer was used to measure NIR transmittance. Each fruit was scanned at two locations on opposite sides midway along the proximal-distal axis. After scanning, each fruit was processed and pureed, and SSC was determined using a refractometer. Multiple linear regression (MLR), partial least squares (PLS) regression, and neural network (NN) calibration models were developed using the second derivatives of averaged spectra from 780 to 980 nm. The validation results showed that NN calibration was better than MLR or PLS calibrations. The NN calibration could estimate the processed SSC of individual unprocessed tomatoes with a standard error of prediction of 0.52% and could classify >72% of fruit in an independent population within ±0.5% of SSC.

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K.H.S. Peiris, G.G. Dull, R.G. Leffler, and S.J. Kays

A nondestructive method for measuring the soluble solids (SS) content of peaches [Prunus persica (L.) Batsch] was developed using near-infrared (NIR) spectrometry. NIR transmittance in the 800 to 1050 nm region was measured for four cultivars of peaches (`Blake', `Encore', `Red Haven', and `Winblo'), over a period of three seasons (1993 through 1995). Each fruit was scanned on both halves keeping the suture away from the incident light beam. Soluble solids contents of flesh samples taken from corresponding scanned areas were determined using a refractometer. Multiple linear regression models using two wavelengths were developed with second derivative spectral data and laboratory measurements of SS content. Multiple correlation coefficients (R) for individual cultivar calibrations within a single season ranged from 0.76 to 0.98 with standard error of calibration (SEC) values from 0.35% to 1.22%. Selected spectra and corresponding SS data in individual cultivar calibration data sets were combined to create season and cultivar calibration data sets to cover the entire range of SS contents within the season or within the cultivar. These combined calibrations resulted in R values of 0.92 to 0.97 with SEC values ranging from 0.37% to 0.79%. Simple correlations of validations (r) ranged from 0.20 to 0.94 and the standard error of prediction (SEP) ranged from 0.49% to 1.63% while the bias varied from -0.01% to -2.62%. Lower r values and higher SEP and bias values resulted when individual cultivar calibrations were used to predict SS levels in other cultivar validation data sets. Cultivar calibrations, season calibrations and the overall calibration predicted SS content of all validation data sets with a smaller bias and SEP and with higher r values. These results indicate that NIR spectrometry is suitable for rapid nondestructive determination of SS in peaches. Feasible applications of the method include packinghouse sorting of peaches for sweetness and parent and progeny fruit quality assessment in peach breeding programs. Using this technique fruit may be sorted into two or three sweetness classes. The technique may also potentially be extended to other fruit.