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In order to elucidate the mechanisms of citric acid in fresh‐cut potato browning inhibition, various concentrations of immersion solutions were prepared using either citric or sulfuric acid for pH ≤ 4 and sodium hydroxide for pH > 7. Dipping potato slices in water (control, pH = 5.84) allowed severe browning to develop during 6 days of storage at 5C. Citric acid at concentrations >0.5% inhibited browning on the cut surfaces of fresh‐cut potato without affecting the antioxidant content or PPO activity, and induced the highest increase of tissue pH during storage. Dipping in 1 or 2% citric acid (pH 2.42 and 2.24) reduced all color changes equally, resulting in the lowest discoloration scores. Acidification of the immersion solution using H2SO4 also reduced discoloration, as NaOH solutions with pH > 7, but neither was as effective as citric acid. Further reducing the pH of 0.5% citric acid from 2.59 to 2.24 with H2SO4 also did not improve browning inhibition. Practical Application Acidification or alkalization of the immersion solution using inorganic compounds reduces browning of potato slices, although not as efficiently as citric acid, by reducing PPO activity. Citric acid reduces browning of potato slices, without affecting PPO activity, either by bonding with phenolic substrates or PPO enzyme to form complexes, or by generating the formation of other compounds, as implied by the pH increase of the surface tissue. No correlation between the total phenolic content, antioxidant capacity, and discoloration score were observed. This research shows that the effectiveness of citric acid in reducing browning in fresh‐cut plant tissues is not predominately due to acidification, and that the effectiveness of citric acid as an antibrowning agent cannot be duplicated by simple pH adjustment of the immersion solution—either below or above the PPO optimum range.

Quality changes of bunched and topped radishes (Raphanus sativus L.) during postharvest storage were investigated. Bunched radish plants, topped roots and detached leaves were stored at 5 or 10C for 9 days. Yellowing and wilting of leaves during storage at 10C were the main visual quality deteriorations in bunched radishes. Leaf detachment reduced respiration and ethylene production rates and weight loss of roots, and resulted in lower ascorbic acid, antioxidant capacity and phenolic content especially during storage at 10C. Root color did not change during storage, with or without leaf detachment. Leaf color did not change at 5C, whereas lightness and chroma increased and hue angle decreased at 10C, with larger changes observed in detached leaves. H2O2 content as well as peroxidase, ascorbate peroxidase and catalase activities in the root tissue were unaffected by leaf detachment, but increased during storage especially at 10C after 9 days of storage. PRACTICAL APPLICATIONSRadishes are marketed with the leaves attached on the enlarged root, which is the edible part of the plant, or are topped so that leaves are removed from the root. Consumers prefer to purchase radishes with the leaves attached because their green color is an indication of freshness. In retail market, higher than recommended temperatures are often encountered, resulting in yellowing of leaves; therefore, plants are topped and only the root is distributed. However, the effects of storage temperature as well as the removal of leaves on nutritional compounds of the edible roots have not been investigated and need to be determined, because nutritional quality is of increasing interest to the consumers. This study provides information on the effect of temperature and leaves removal on metabolism and quality of radish plants during storage, which can be applicable to sustain the quality and increase commercial marketing of radishes. bs_bs_banner Journal of Food Quality

Enzymatic browning is a serious quality limitation for fresh-cut potato (Solanum tuberosum L.) that has been successfully controlled by heat treatment in other commodities. The use of brief heat treatments with 55 °C water (HW) applied to ‘Russet Burbank’ tubers for 10, 20, 30, or 40 min before cutting was evaluated for potential implementation to control tissue browning. After heat treatment, tubers were held at 20 °C for 0 or 1 day before peeling and slicing. Control tubers were not previously immersed in hot water. All slices were placed in perforated plastic bags and stored at 5 °C for 6 days. Exposure to HW for 30 or 40 min caused severe heat injury. Browning developed in all treatments as indicated by color measurements and discoloration scores (index of extent of discolored area on the slice surface) during storage. Hot water treatment for 10 min best reduced browning, but only when treated tubers were stored intact for 1 day at 20 °C before cutting, as indicated by discoloration scores and changes in L*, a*, and Ho values, which were significantly different from either the control or the other HW treatments. Generally, the severe browning that developed in control slices during storage was associated with significant increases of 25% and 71% in phenolic content and antioxidant capacity, respectively. On the other hand, phenolic synthesis increased by only 6.25% to 13.2% in HW-treated slices during storage and polyphenoloxidase (PPO) activity was 24% to 31% lower compared with the activity before storage. Immersing potato tubers in 55 °C water for 10 to 20 min followed by storage at 20 °C for 1 day before processing reduced but did not prevent browning of peeled slices in terms of color changes and discoloration score. There was no significant correlation between browning and phenolic content or PPO activity.

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