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

M.L.A. STRAUSS, N.P. JOLLY, M.G. LAMBRECHTS AND P. VAN RENSBURG. 2001. Aims: The objective of this study was to investigate what types of enzymes are being produced by non-Saccharomyces yeasts isolated from grapes in South Africa vineyards and clarified grape juice. These enzyme profiles could pave the way for attributing specific effects in wine to some of these enzymes produced by so-called wild yeasts associated with grape must. Methods and Results: In this study 245 yeast isolates, belonging to the genera Kloeckera, Candida, Debaryomyces, Rhodotorula, Pichia, Zygosaccharomyces, Hanseniaspora and Kluyveromyces were screened for the production of extracellular pectinases, proteases β-glucanases, lichenases, β-glucosidases, cellulases, xylanases, amylases and sulphite reductase activity. These yeasts, representing 21 species, were previously isolated from grapes and clarified grape juice. The production of all extracellular hydrolytic enzymes screened for was observed except β-glucosidase activity. The amount and range of enzymes produced varied with different isolates of the same species. Conclusion: This study clearly revealed the potential of non-Saccharomyces wine yeasts to produce a wide range of useful extracellular enzymes during the initial phase of wine fermentation. Significance and Impact of the Study: Enzymes produced by indigenous yeasts associated with grapes and juice might be harnessed to catalyse desired biotransformations during wine fermentation.

https://onlinelibrary.wiley.com/doi/pdf/10.1046/j.1365-2672.2001.01379.x

Screening for the production of extracellular hydrolytic enzymes by non‐Saccharomyces wine yeasts

Consumption of fruit and vegetable products has dramatically increased in the United States by more than 30% during the past few decades. It is also estimated that about 20% of all fruits and vegetables produced is lost each year due to spoilage. The focus of this chapter is to provide a general background on microbiological spoilage of fruit and vegetable products that are organized in three categories: fresh whole fruits and vegetables, fresh-cut fruits and vegetables, and fermented or acidified vegetable products. This chapter will address characteristics of spoilage microorganisms associated with each of these fruit and vegetable categories including spoilage mechanisms, spoilage defects, prevention and control of spoilage, and methods for detecting spoilage microorganisms.

http://seward.co.uk/resources/wp-content/uploads/sites/3/2013/03/food-microbiology-fruit-vegetable-TVC-stomacher-400.pdf

Microbiological Spoilage of Fruits and Vegetables

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.

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.

The Formation of Carbonyl Compounds in Cucumbers

Although investigations have dealt with softening of brined cucumbers since 1899 (Aderhold), the studies have been primarily concernied with proving the bacterial theory of spoilage. Much effort has been directed toward implicating the aerobic bacilli as the responsible agents (Kossowicz, 1908; LeFevre, 1919; Fabian and Johnson, 1938; Faville and Fabian, 1949; Demain and Fabian, 1950, Unpublished Experiments; and Vaughn et al., 1954). The nature of the acid fermentation of cucumbers presents three important obstacles to serious consideration of the much-studied aerobic bacillus theory of softening spoilage: (1) the salt content of the fermenting brines; (2) the acidic condition of the brine aind accompainying drop in pH resulting from early and rapid development of the lactic acid bacteria; and (3) the low oxygen tension of the brine attested to by excellent grow-th of the microaerophilic, lactic acid bacteria. SucK conditions wrould indeed be highly restrictive if niot wholly inhibitive for growth by aerobic, sporeforming bacteria of the genius Bacillus. Thus it is niot surprising that populations for these organisms have niot beeii demonstrated in cucumber fermentations brined under conditions typical of the industry. Early brining studies (UInpublished) by Etchells anid Jones (1940), conducted with replicated 45-gallon barrel lots at a commercial pickle plant in easterni North Carolina, confirmed the above conclusion that cucumber fermentations offer a rather unfavorable environment for development of aerobic bacilli. Heavy inocula of washed cells of young cultures of Bacillus mesentericus fuiscas (Bacillus stibtilis) failed to develop when added to cucumber fermentations at the outset, and the cured brine-stock showed no loss of firmness over uninoculated controls. Furthermore, in other experiments, broth filtrates from the above organism, when added to cucumber fermentations at the start, did not cause softening

Populations and softening enzyme activity of filamentous fungi on flowers, ovaries, and fruit of pickling cucumbers.

Interest in the use of sorbic acid (2,4-hexadienoic acid) as a food preservative and fungistatic agent was stimulated by Gooding in 1945 and by the report of its harmlessness as a dietary component by Deuel et al. (1954). The numerous reports which followed, especially those which dealt with sorbic acid as a selective inhibitor of certain microorganisms (Emard and Vaughn, 1952; York and Vaughn, 1954, 1955; Hansen and Appleman, 1955; Borg et al., 1955, 1956; Costilow et al., 1955) prompted this study. The present report is concerned with the inhibitory action of sorbic acid in cultural media at different pH levels for certain species of bacteria, yeasts, and filamentous fungi which, for the most part, are associated with the growing cucumber or the commercial cucumber fermentation. Sorbic acid falls into a group of short-chain organic acids, which, together with their salts, have been shown to exhibit antimicrobial properties. Such properties, for many of these acids, have been demonstrated for over fifty years; for reviews see: Wyss et al. (1945), Wyss (1948), Schelhorn (1953), Ingram et al. (1956), Grubb (1957). Hoffman et al. (1939) investigated the fungistatic properties of normal saturated and unsaturated fatty acids containing from 1 to 14 carbon atoms and used as test organisms a mixed culture of common bread molds such as Aspergillus niger, A. glaucus, Rhizopus nigricans, and Penicillium frequentans. Sorbic acid was not in-

Influence of sorbic acid on the growth of certain species of bacteria, yeasts, and filamentous fungi.

A process is described for the controlled fermentation of sliced, large cucumbers which results in improved firmness of the tissue. The cucumbers are sliced, blanched in water, cooled, brined in a solution of NaCl and calcium acetate at pH 4.3–4.6 and inoculated with a Lactobacillus plantarum starter culture. The fermentation is essentially complete within 1 wk at 27°C. Buffering of the brines with calcium acetate had the dual advantage of insuring complete fermentation, and firming of the cucumber tissue. Heated slices, when brined at 0–6.5% NaCl according to this process, were firm after 3 months’ storage; whereas, unheated slices became soft at lower levels of NaCl. The process offers a possible means of reducing or eliminating the problem of soft centers in large cucumbers. The process also improved the firmness of small, whole cucumbers.

T. A. Bell

Papers

The Formation of Carbonyl Compounds in Cucumbers

Populations and softening enzyme activity of filamentous fungi on flowers, ovaries, and fruit of pickling cucumbers.

Influence of sorbic acid on the growth of certain species of bacteria, yeasts, and filamentous fungi.

Controlled fermentation of sliced cucumbers

BLOATER FORMATION IN BRINED CUCUMBERS FERMENTED BY Lactobacillus plantarum