Nutritional impact of phytosanitary irradiation of fruits and vegetables

5.2Stone fruit

Limited studies have been published on the effects of irradiation on nutrient composition of stone fruit. The available published and unpublished data are summarised in Table 6.2. Mitchell et al. (1992) assessed the effect of irradiating nectarines and peaches, but vitamin C analyses were not performed for irradiated fruit due to low levels in control fruit (<10 and <5 mg/100 g, respectively) (Mitchell et al. 1992).
Unpublished data from DAFF QLD (2012) tested the effects of irradiation with 0.15, 0.6 and 1.0 kGy on apricot, cherry, peach and plum. Fruits were assessed one day after irradiation, and after 14 (apricot and cherry), 21 (nectarine), 28 (peach) or 35 (plum) days cold storage. In apricot, peach and plum there was no significant effect of irradiation at any dose on total vitamin C or -carotene levels. Similarly, in white nectarines there was no significant effect of irradiation on AA, while β-carotene levels were below the limit of detection in all fruit. In cherries irradiated with 0.6 kGy, total vitamin C and -carotene levels decreased by 46% and 17%, respectively, after 14 days storage. In contrast, there was no effect of irradiation with 0.15 kGy or 1 kGy on total vitamin C or -carotene levels in cherries. Some of the other analyses showed a similar pattern (glucose, energy) in the 0.6 kGy treated cherries, but the reason for these inconsistent results was unclear. For all these analyses, total vitamin C data were at the lower detection limit of the assay, and were considerably lower than values reported in nutrient data tables.
Whole apricots

In fresh apricots irradiated at 0.5 and 1.0 kGy, the -carotene concentration increased after 10 days storage (Egea et al. 2007). In the same study there was a significant decrease of approximately one-third in AA content in apricots irradiated with 1.0 kGy after 3 days storage, and although levels remained lower throughout the 13 day experimental period, they were not significantly different to controls at day 7, 10 or 13. There was no difference in AA levels between apricots irradiated with 0.5 kGy and non-irradiated controls. Total vitamin C data were not reported in this study; therefore it is uncertain whether the decrease observed was a result of AA oxidation or destruction.

Dried apricots

In dried apricots, irradiation with 1-3 kGy had no effect on total vitamin C levels immediately or after 6 months of storage (Hussain et al. 2011). After 12 and 18 months, total vitamin C levels were significantly higher in fruit irradiated with ≥2 kGy (5-6% and 20-23%, respectively). These differences were attributed to irradiated apricots maintaining lower moisture content. During the 18 month storage period, AA levels decreased 59% in non-irradiated controls, and 46-55% in irradiated fruit. -Carotene levels exhibited a dose-dependent increase immediately after irradiation in dried apricots (1 kGy; +10%, 3 kGy; +29%). During 18 months storage, -carotene levels decreased ~30% in control and irradiated fruit, but remained significantly higher in fruit irradiated with all doses. However, the applicability of these data to fresh fruit is limited due to the important influence of water content on effects of irradiation (Diehl 1995).

Cherries

Irradiation of cherries with 0.3 kGy did not significantly affect AA levels either immediately after irradiation, or after cold storage of 30 and 60 days, or 60 days cold storage followed by 2 days at 20C (Akbudak et al. 2008). In contrast, irrespective of irradiation, storage decreased AA levels by a mean of 51% (30 days), 58% (60 days) and 65% (60 days cold, 2 days 20C) under normal atmospheric conditions. Losses of AA were diminished by controlled atmosphere during storage, but this effect was also unaffected by irradiation.

Other non-vitamin bioactive compounds

In fresh apricots, there was no effect of irradiation on antioxidant capacity (Egea et al. 2007). Irradiation of dried apricots with 3 kGy increased total phenols and flavonoids (Hussain et al. 2013). Akbudak et al. (2008) examined anthocyanin levels in cherries following irradiation and storage. In non-irradiated fruit, anthocyanin levels increased during storage under normal atmospheric conditions. This increase was attenuated in irradiated fruit, with anthocyanin levels 21% lower than non-irradiated cherries (Akbudak et al. 2008).

Table 6.2 Effects of irradiation on radiation-sensitive nutrients in stone fruit

Fruit	Dose	Carotene	Vitamin C	Other components	Analysis method / Reference
Apricot	0.5 and 1.0 kGy	No change	1 kGy; -30%* at day 3, no significant difference after 7 d	Antioxidant capacity: no change	AA by HPLC. Egea 2007
Apricot	0.15, 0.6, 1.0 kGy	No change	No change	n.d.	-carotene and total vitamin C by HPLC DAFF QLD, 2012
Apricot (dried)	1.0, 1.5, 2.0, 2.5, 3.0 kGy	+10%* to +30%*	No change ≤6 mo. 12 mo; ≥2 kGy +5%* 18mo; ≥2 kGy +20%*	3 kGy; phenols: +12%* flavonoids: +16%*	-carotene and total vitamin C by HPLC. Hussain 2011 Hussain 2013
Cherry	0.3 kGy	n.d.	No change	Anthocyanins: 21%	AA by spectrophotometry Akbudak 2008
Cherry	0.15, 0.6, 1.0 kGy	0.15, 1.0 kGy; no change 0.6 kGy; -6 to -17%	0.15, 1.0 kGy; no change 0.6 kGy; -39%* to -46%*	n.d.	-carotene and total vitamin C by HPLC DAFF QLD, 2012
Peach	0.15, 0.6, 1.0 kGy	No change	No change	n.d.
Plum	0.15, 0.6, 1.0 kGy	No change	No change	n.d.
Nectarine	0.15, 0.6, 1.0 kGy	Not detected	No change	n.d.	AA by titration, -carotene by HPLC DAFF QLD, 2012

*significant difference. n.d.: not determined