The color, flavor, texture, and the nutritional value of fresh-cut fruit and vegetable products are factors critical to consumer acceptance and the success of these products. In this chapter, desirable and undesirable quality attributes of fresh-cut fruit and vegetable products are reviewed. Both instrumental and sensory measurements for determining these critical quality attributes are discussed. The advantages and disadvantages of sensory and instrumental quality measurements are described. A review of typical unit operations involved in the production of fresh-cut products is presented. The effects of fresh-cut processing techniques and treatments on sensory quality, including the appearance, texture, flavor (taste and aroma) of vegetables, and fruits are detailed.

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Color, Flavor, Texture, and Nutritional Quality of Fresh-Cut Fruits and Vegetables: Desirable Levels, Instrumental and Sensory Measurement, and the Effects of Processing

The steam volatile components of Californian green bell peppers (Capsicum annum aar. grossum, Sendt) have been qualitatively analyzed using conventional and capillary gas-liquid chromatographic separation with characterization by mass, infrared, and in some cases ultraviolet and proton magnetic resonance spectra. Major components identified in oil obtained by vacuum steam-distillation-continuous-extraction included 2-methoxy-3-isobutylpyrazine, trans-p-ocimene, limonene, methyl salicylate, linalool, nona-trans,cis-2,6-dienal, deca-trans,trans2,4-dienal, and hex-cis-3-enol. Additional components detected in small amounts in the vacuum isolated oil but in much larger amounts in oil isolated at atmospheric pressure were non-1 -en-4one, non-trans-2-en-4-one, nona-trans,trans-2,5-dien4-one, 2-pentylfuran, and benzaldehyde. The identities of 24 components were confirmed by direct comparison of their spectral and gas chromatographic retention data with those of authentic samples. Tentative identification was obtained for an additional 19 components from their mass spectral fragmentation patterns. Odor thresholds in water solution were determined for major components. 2-Methoxy-3-isobutylpyrazine was found to possess an extremely potent odor with an odor threshold of 2 parts per 1012 parts of water. Generally about 70 to 80% of untrained sensory panelists (40) indicated that the odor of dilute water solutions of this compound was similar to that of fresh green bell peppers.

Characterization of some volatile constituents of bell peppers.

Using an automated rapid headspace solid phase microextraction (SPME) method for volatile extraction in cantaloupes, 86 compounds already reported for muskmelons were recovered and an additional 53 compounds not previously reported were identified or tentatively identified. The SPME method extracted a copious number of volatiles that can be analyzed to clearly differentiate between variety, growth stage, and stage of harvest ripeness. Most of the newly reported compounds in cantaloupe were esters and aldehydes that have already been demonstrated as flavor-related compounds in other products. All esters believed to have flavor impact increased progressively after pollination, and this trend continued with increasing harvest maturity. However, compound recovery often decreased when fruits were harvested over-ripe. Most aldehydes increased during early growth stages and then tapered off with increasing harvest maturity. The SPME method suitably recovered most compounds reported to impart characteristic flavor/aroma in muskmelons. SPME offers experimental flexibility and the ability to discover more compounds and address flavor quality changes in fresh-cut cantaloupe.

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Identification of volatile compounds in cantaloupe at various developmental stages using solid phase microextraction.

CHARACTERIZATION OF VOLATILE ODOR AND FLAVOR COMPOUNDS A. Isolation 1. Very low boiling compounds (b.p. below 40°C) 2. Low boiling compounds (b.p. 40-100°C) 3. High boiling compounds (b.p. 100-200°C) 4. Very high boiling compounds (b.p. above 200°C) 5. Isolation of classes of compounds 6. Comment B. Fractionation of flavor compounds 1. Free compounds 2. Derivatives C. Identification 1. Chromatography 2. Ultraviolet-visible spectra 3. Infrared spectra 4. Raman spectra 5. Mass spectra 6. Nuclear magnetic resonance spectra 7. Microscopy 8. Refractive index and density Page 181

Odor and flavor compounds from lipids.

12-Oxo- trans -10-dodecenoic acid ( trans -10-ODA) is an oxidation product of polyunsaturated fatty acids in plant tissues. The structural similarity of trans -10-ODA and traumatic acid, a compound considered to be a wound hormone, suggested that trans -10-ODA might be a precursor of traumatic acid. Both trans -10-ODA and traumatic acid were active in the Wehnelt bean assay. The results were more consistent with trans -10-ODA than with traumatic acid. Cucumber ( Cucumis sativus L. var. National Pickling) hypocotyls also showed a growth increase following treatment with trans -10-ODA, which suggested that trans -10-ODA has a more general influence on plant development than previously ascribed to traumatic acid. Runner beans ( Phaseolus vulgaris L. var. Kentucky Wonder) were analyzed for the presence of endogenous trans -10-ODA and traumatic acid. These are the beans from which traumatic acid was originally isolated in 1939. They contained trans -10-ODA but no traumatic acid. Young beans were a better source of trans -10-ODA than older beans and an increase in the esterified form of trans -10-ODA with age may have been due to a conversion of the free acid to the esterified form. The amount of endogenous trans -10-ODA increased when bean pod tissue was sliced and wounded. Rapid stirring and the presence of oxygen increased autooxidation of trans -10-ODA to traumatic acid in runner beans, which indicated that the compound identified as traumatic acid is formed by autooxidation of trans -10-ODA and that trans -10-ODA is a natural compound with growth-regulating properties. Enzyme extracts of runner beans synthesized trans -10-ODA from linoleic acid. No enzymic synthesis of traumatic acid was observed even when cofactors were added to the reaction mixture. This confirmed the conclusion that traumatic acid is formed by autooxidation of trans -10-ODA.

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Identification of Traumatin, a Wound Hormone, as 12-Oxo-trans-10-dodecenoic Acid.

SUMMARY

The carbonyl contents of benzene extracts of aqueous cucumber homogenates were estimated spectrophotometrically as the 2, 4-dinitrophenylhydrazones. A large increase in the formation of carbonyl compounds occurred when cucumbers were blended with water in the presence of oxygen. This formation of carbonyl compounds was prevented by three methods: blending the cucumbers at pH 1.0; blending in an oxygen-free atmosphere; and heating whole cucumbers to an internal temperature of 77°C before blending.



Chromatographic assays indicated that negligible amounts of the 2-enals, 2, 6-nonadienal, 2-nonenal, and P-hexenal are present in intact cucumbers; but a rapid synthesis of this class of carbonyl compounds occurred when fresh cucumbers were blended in the presence of oxygen. The most significant increase occurred in the formation of 2, 6-nonadienal, the aldehyde largely responsible for the flavor of fresh cucumbers. There were indications that ethanal and propanal were present in appreciable levels in intact cucumbers.



These observations suggest that the characteristic flavor components of fresh cucumbers are generated enzymatically as a consequence of cutting or mechanically rupturing the fruit.

W. Y. Cobb

Papers

The Formation of Carbonyl Compounds in Cucumbers