Search

The effect of temperature on phenolic accumulation in fresh-cut pitaya fruit was reported during storage at 5, 10 and 15 °C. Fresh-cut pitaya fruit were treated with ROS production inhibitor (diphenyliodonium iodide, DPI) or elicitor (glucose/glucose oxidase, G/GO) and the total soluble phenolics (TSP) content, antioxidant activity (AOX), phenylalanine ammonia lyase (PAL) activity, as well as ROS production and antioxidant enzymes activity were determined. Results showed that higher storage temperature promoted the production of ROS, enhanced the accumulation of TSP and improved the AOX of fresh-cut pitaya fruit. Moreover, treatment with DPI dramatically inhibited ROS generation, PAL activity and TSP accumulation, while G/GO treatment significantly increased ROS level, PAL activity and TSP accumulation. These results demonstrate that phenolics accumulate with increasing temperature and confirm previous report of ROS effects on wound induced phenolic accumulation in pitaya fruit.

The single and combined effects of UV-B (1.5 kJ m −2 ) and UV-C (4.0 kJ m −2 ) radiation treatments were studied on the phenylalanine ammonia-lyase (PAL) activity, phenolic content and antioxidant capacity (TAC) of shredded fresh-cut carrots during 72 h at 15 °C. Non-irradiated samples were used as control (CTRL). PAL activity of UV-B and CTRL samples was increased by approximately 760% after 72 h while increases of 120–140% in the remaining radiation treatments were found. Chlorogenic acid represented 70% of the sum of phenolic compounds of initial samples. UV-B treatment showed the highest phenolic accumulation with 498% after 72 h, regarding its initial value, while single and combined UV-C treatments achieved an accumulation of 440%, which was similar to CTRL samples. Such phenolics data were highly correlated (R 2 = 0.82) to total antioxidant capacity throughout storage. Conclusively, UV-B treatment achieved the highest phenolic compounds accumulation and related antioxidant capacity in shredded carrot during 3 days at 15 °C. Furthermore, the use of UV-C treatment with sanitizing purposes combined with UV-B radiation did not negatively affect the accumulation of bioactive compounds, achieving similar enhancements to CTRL samples.

The main problem affecting the quality of fresh-cut sunchoke tubers is cut surface discoloration. Pre- and post-cutting hot water and ethanol treatments were evaluated for their potential to inhibit discoloration, color changes, and associated phenolic metabolism in tuber slices stored in air at 5 °C. Some of the treatments tested inhibited discoloration and changes in a * and hue color values. Slices that were post-cut treated with hot water at 50 °C for 6–8 min or 55 °C for 3–4 min and pre-cut treated with water at 50 °C for 20–25 min maintained good color for 8–12 days at 5 °C. Post-cut ethanol fumigation (150–750 μL/L for 5 h at 5 °C) can prevent discoloration for 30 d at 5 °C. Post-cut dips with ethanol solutions (3, 5, 8 or 10% for 5 min) increased shelf-life twofold or longer compared to untreated slices. Ethanol fumigation retarded the onset of wound-induced respiration rates as well as reducing maximum rates. A post-cut 10% ethanol dip also reduced respiration rates and reduced PAL activity and total phenolics. Ethanol dips had no effect and hot water treatments had no persistent effect on microbial loads over 12 d.

This study characterizes dehydration and white blush processes, structural alterations and synthesis of phenolic compounds (lignin and suberin), in relation to development of white blush on baby carrot surfaces. Carrots were minimally processed as baby carrots and kept on polypropylene trays with or without polyvinyl chloride (PVC) film at 5 ± 2 °C, 90 ± 5% RH. During storage, baby carrots that were not wrapped with PVC film were rehydrated 1, 1.5, 15 and 17 h after minimal processing. Fresh-cut baby carrots were evaluated for white blush index, sensory analysis (visual scores), fresh matter loss, phenylalanine ammonia-lyase (PAL) activity and structural and histochemical changes. Increases in white blush index and subjective visual scores on the carrot surface occurred in the first hours, when the material was kept on trays without PVC film and after 3 and 6 d, when stored on trays covered with PVC film. Visual assessment of white blush resulted in a more accurate assessment than instrumental evaluation because it allowed the perception of minor differences between distinct white blush levels, especially at the tips. Hydrating baby carrot surfaces for 1 and 1.5 h after processing allowed partial absorption of water by tissues and the orange color was reestablished on the surface. Fifteen hours after processing, even after rehydration, the color did not return to the original orange standard. The rapid increase in PAL activity in the secondary phloem of baby carrots, compared to that of whole carrots, suggested a physiological response as a result of abrasion. Dehydration and structural alterations of the more superficial cell layers were the main causes of white blush in baby carrots that was not related to lignin accumulation, but rather to synthesis of non-structural phenolic compounds.

Intact heads and cut leaf midrib tissue of crisphead lettuce ( Lactuca sativa , L., cv. ‘Salinas’ and ‘Vanguard’) were kept in air or air +5%, 10%, or 20% CO 2 for 10 or 20 days at 2.5°C and then transferred to air at 20°C for 12 hrs to study CO 2 effects on phenolic metabolism and fermentative products. Exposure of cut midribs to 20% CO 2 increased extractable activity of phenylalanine ammonia-lyase (PAL) when assayed at its optimum pH (8.5). However, under the 20% CO 2 treatment PAL activity was reduced as a result of a decrease in cytoplasmic pH. Total phenolic content of cut midribs was reduced under 20% CO 2 -enriched atmosphere probably due to this decrease in PAL activity. The phenolic content rapidly increased after the tissue was transferred from 20% CO 2 at 2.5°C to air at 20°C when cytoplasmic pH returned to its normal value and the PAL activity was restored. Such effects of CO 2 on PAL and phenolics were of lower magnitude in intact heads, probably due to their lower sensitivity to phenolic metabolism. Off-flavor developed in the intact heads exposed to 20% CO 2 , which was associated with increased concentrations of ethanol and acetaldehyde. When exposed to 20% CO 2 , levels of ethanol and acetaldehyde in cut midribs were only about half of those in intact heads.