Physiological response of ‘Fuji’ apples to irradiation and the effect on quality

Authors: KHESHTI, NASIM - Chapman University; MELO, ANDERSON - Chapman University; BACQUERO, ALAN - Chapman University; Obenland, David - Dave; PRAKASH, ANURADHA - Chapman University

Submitted to: Radiation Physics and Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/29/2019
Publication Date: 7/5/2019
Citation: Kheshti, N., Melo, A., Bacquero, A., Obenland, D.M., Prakash, A. 2019. Physiological response of ‘Fuji’ apples to irradiation and the effect on quality. Journal of Radiation Physics and Chemistry. 165. https://doi.org/10.1016/j.radphyschem.2019.108389.
DOI: https://doi.org/10.1016/j.radphyschem.2019.108389

Interpretive Summary: Irradiation is approved for quarantine treatment of apples exported from California to Mexico but the effects of treatment on apple quality had previously not been thoroughly described. ‘Fuji’ apples were irradiated at 377 Gy or 1148 Gy, and then stored for 7 days at 1 °C to simulate ground transportation to Mexico plus a further 7 days at ambient temperature to mimic retail and commercial storage. Irradiation suppressed ethylene production but increased the rate of respiration. The concentration of sugars was unaffected while that of acids decreased. Flavor volatiles were relatively unaffected at 377 GY but were diminished in concentration by the 1148 Gy treatment. Higher electrolyte leakage in treated apples indicated that some damage occurred due to irradiation but firmness was the only major quality factor impacted, although the loss of firmness was far less at 377 Gy than 1148 Gy. An irradiation treatment of 377 Gy is sufficient for quarantine purposes and, given its minimal impact on apple quality, can be a viable alternative to conventional phytosanitary treatments for ‘Fuji’ apples. Since prior treatments either take too long or cause damage this helps enable a new export market for this variety.

Technical Abstract: Irradiation at 250 Gy has been approved as a phytosanitary treatment for California apples destined for Mexico. In this study, we evaluated the effect of irradiation on the physiology of California ‘Fuji’ apples. ‘Fuji” apples were treated at 377 and 1148 Gy, then stored for 7 days at 1°C to mimic ground transportation to Mexico and another 7 days at ambient temperature to mimic retail and consumer storage. Irradiation suppressed ethylene production, especially in the 1148 Gy treated apples. This suppression coincided with a decrease in ACC oxidase activity (p<0.05). Respiration rate was increased and acid content was decreased, suggesting that organic acids, but not sugars, provided a substrate for increased respiration. An increase in electrolyte leakage indicated damage to the cell membrane, but the damage was not sufficient to cause changes in malondialdehyde (MDA). The effect of irradiation at 1148 Gy on alcohols and esters depended on storage time. Irradiation showed inhibitory effect on ester production after 14 days of storage while treatment at 377 Gy caused only minor changes in volatile compounds. Irradiation caused physiological responses in apples, but quality indices such as internal color, browning index, TSS and individual sugars were not affected. Loss of firmness was the only quality attribute impacted, but the firmness of the 377 Gy apples following 14 days of storage was not different (P>0.05) from fumigated or cold treated apples. Therefore, irradiation at doses 377 Gy or lower could be considered as a suitable alternative to conventional phytosanitary treatments for 'Fuji' apples.