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A computer video image analysis system was used to quantify changes in oxidative browning of developing ‘Redskin’ peach fruit [Prunus persica (L.) Batsch]. Oxidative browning of endocarp tissue occurs rapidly at the onset of Stage I and decreases in rate and intensity during development, with little or no browning occurring by the time endocarp sclerification begins at the onset of Stage II. Conversely, little or no browning occurs in mesocarp tissue during early development, but browning increases in rate and intensity through endocarp sclerification. In this study, net oxidative browning was correlated with net polyphenyl oxidase (PPO, EC 1.10.3.2) and peroxidase (POD, EC 1.11.1.7) enzyme activity of the tissues as quantified by image analysis of PPO and POD histochemical staining reactions. Image analysis revealed localized areas of activity within the tissue.

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-flavor and maintain the original pulp color and nutritional value for a longer period of time ( Murata et al., 1995a ; Podsedek et al., 2000 ). The objective of the present work was to quantify enzymatic browning, PPO activity, and six target phenolic

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blemish-free. Considering the importance of these relationships, surprisingly little is known about the mechanical properties of apple skin. The objective of this study was to quantify the mechanical properties of the skin (cuticle, epidermis, and

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test for sweet cherry fruit skin was described by Bargel et al. (2004) . Excised fruit skin segments were pressurized from the inner side and the extent of bulging for each pressure increment was quantified. Brüggenwirth et al. (2014) modified the

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Abstract

The carbohydrate reserves in plant tissue have been correlated with all phases of plant growth and development. Consequently, several methods have been developed to quantify those reserves. The methods for starch determination are either direct (iodine staining) or indirect (the conversion of starch to sugars by chemical or enzymatic hydrolysis). Chemical methods involve hydrolysis of subunit bonds with either a strong acid or base, and enzymatic methods use catalytic proteins specifically to cleave the subunit bonds.

Open Access

synthesis occurs with the formation of N-methylputrescine from putrescine by the enzymatic activity of putrescine N-methyltransferase (PMT) (EC 2.1.1.53) ( Hashimoto and Yamada 1994 ). From this point, several diverging pathways are observed among various

Open Access

The tearing and burning sensations associated with raw onion consumption are caused by (Z,E)-propanethial S-oxide, the lachrymatory factor (LF). The LF is produced from the hydrolysis of S-1-propenyl-L-cysteine S-oxide (PREN), the dominant flavor compound in onions. Current methodology for LF quantification was optimized for Granex-type onions using a 2-min incubation time to allow for maximum formation. In this study, data were taken on PREN hydrolysis of `Dehydrator #3' and `Granex 33' at harvest and during storage and were compared to LF formation. `Dehydrator #3' PREN hydrolysis was 98% complete 5 s after cellular disruption at each sampling date. However, using the 2-min incubation procedure, only 10.25 μmol of LF was recovered from the hydrolysis of 30.11 μmol of PREN at harvest, thereby underestimating LF for this cultivar. Percent PREN hydrolysis for `Granex 33' was lower than `Dehydrator #3' during the enzymatic reaction at each sampling date, suggesting slower PREN hydrolysis activity. At harvest, 6.96 μmol of LF were recovered from 12.54 μmol of PREN hydrolyzed. After 2 storage months, however, micromol of LF were equal to micromol of PREN. LF quantification is currently being considered by the onion industry as a direct measurement of gross onion pungency. This data suggests that more optimization of LF quantification is needed before it can be applied to a broad range of cultivar types.

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The accumulation of total soluble sugars (TSS) and starch and their relationship to flower bud hardiness were studied in three Forsythia taxa: Forsythia ×intermedia `Spectabilis', Forsythia ×intermedia `Lynwood', and F. suspensa. Taxon hardiness was based on the mean temperature at which low temperature exotherms (LTEs) occurred during thermal analysis. Ethanol-extracted soluble sugars were quantified with anthrone, and starch was enzymatically digested and quantified with Trinder reagent. Qualitative changes in sugar content were determined with high-performance liquid chromatography and co-chromatography of authentic standards. Quantitative and qualitative changes in sugar content, similar for the three taxa, were observed in conjunction with fluctuations in flower bud hardiness, although neither TSS nor starch were correlated with mean LTE temperature. TSS was higher in acclimated than nonacclimated buds. However, after deacclimation began, sugars continued to increase with mean LTE temperature. Buds lacked starch except for a brief period during deacclimation. Galactose, stachyose, raffinose, and an unidentified carbohydrate were positively correlated with hardiness (P = 0.005, 0.001, 0.005, and 0.001, respectively).

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Onion (Allium cepa L.) pungency changes during storage. To better understand these flavor changes, seven onion cultivars representing different storage duration, photoperiodic requirement, and flavor intensity were greenhouse grown and the bulbs stored for 3 or 6 months at 5±3 °C, 0.8 to 1.1 kPa vapor pressure deficit. Bulbs were evaluated using high-pressure liquid chromatography quantification for changes in S-alk(en)yl cysteine sulfoxide (ACSO) flavor precursors and γ-glutamyl peptide (γ-GP) biosynthetic intermediates before storage and monthly thereafter. Before and during storage, cultivars differed in total ACSO, (+) S-methyl-L-cysteine sulfoxide (MCSO), trans-(+)-S-(1-propenyl)-L-cysteine sulfoxide (PRENCSO), (+) propyl-L-cysteine sulfoxide (PCSO), S-2 carboxypropyl glutathione (2-CARB), and γ-L-glutamyl-S-(1-propenyl)-L-cysteine sulfoxide (γGPECSO) concentration. During storage MCSO generally decreased while PRENCSO increased in concentration for most cultivars. The linear increase in PRENCSO concentration during storage was accompanied by a linear decrease in γGPECSO concentration. While not measured in this study, these trends indicate γ-glutamyl transpeptidase activity throughout bulb storage. γ-Glutamyl transpeptidase was previously reported to be active only in the later stages of bulb storage or during bulb sprouting. Changes in ACSO and γ-GP compounds during storage did not follow previously reported changes during storage for enzymatically formed pyruvic acid (EPY) for these cultivars. To better understand what causes flavor changes in onions during storage, future investigations should include analysis of the enzymes involved in flavor development and ACSO hydrolysis products.

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Fruit of pepper (Capsicum annuum L.) is hollow by nature, which limits its water reservoir capacity, and as such, small amounts of water loss result in loss of freshness and firmness, which reduce fruit quality, shelf life, and market value. In order to understand the basis for water loss from fruit, 10 pepper accessions with wide variation in water loss rate were used to study physiological and biochemical factors associated with postharvest water loss in ripe pepper fruit during storage. Postharvest water loss rate in ripe pepper fruit stored at 20 °C, and 85% relative humidity, was found to be associated with cell membrane ion leakage, lipoxygenase activity, and total cuticular wax amount. Total cuticular wax amounts were highest in the high-water-loss pepper fruit, and lowest in the low-water-loss fruit. However, total cuticle amount (isolated enzymatically and quantified gravimetrically), total cutin monomer amount, and the amount of individual cutin monomer and wax constituents (determined using gas chromatography mass spectrometry) indicated no direct association with postharvest water loss rates. Fruit fresh weight, pericarp weight, pericarp surface area, pericarp thickness, initial water content, and dry matter were highly associated with each other, but less so with water loss rate. Fruit of accessions displaying high fruit water loss rate matured and ripened earlier than fruit of accessions displaying low-water-loss rate. Cell membrane ion leakage and lipoxygenase activity were higher after storage than immediately after harvest. Pepper fruit total cuticle wax amount, lipoxygenase activity, and cell membrane ion leakage were directly related to postharvest water loss rate in pepper fruit during storage.

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