**3. Results**

#### *3.1. Fruit Visual Quality and Texture*

To determine the effect of ECPTM treatment on fruit quality and texture, qualitative visual assessment to determine percent sound fruit, and quantitative measurements on fruit compression and skin puncture were performed (Figures 1–3). Since fruit were shipped from the site of harvest in Alma, GA, to the irradiation facility in Pocatello, ID, an unshipped control was included along with the shipped but untreated control (shipped to the treatment facility but receiving 0 kGy irradiation) to

compare changes in fruit quality associated with shipping. In general, shipping did not affect fruit visual quality and texture characteristics (Figures 1–3). There were no significant effects of ECPTM on visual quality in 'Farthing' in both trials compared with the control (Figures 1A and 2A).

**Figure 1.** Effect of Electronic Cold-PasteurizationTM on percent sound fruit (**A**), compression (**B**), and puncture (**C**) for 'Farthing' blueberries in trial 1. Treatments included an unshipped control (UNS; not shipped to the irradiation facility) and four levels of irradiation; no irradiation control (0), 0.15, 0.5, and 1.0 kGy. Evaluations were conducted 6, 13, and 25 days after irradiation treatment. Fruit were stored at 2 to 4 ◦C under high relative humidity until assessments were performed. An initial fruit quality assessment was performed after harvest shown as a horizontal dashed line. Means within the same storage times after treatment followed by the same letter are not significantly different from each other based on one-way analysis of variance (α = 0.05).

**Figure 2.** Effect of Electronic Cold-PasteurizationTM on percent sound fruit ( **A**), compression (**B**), and puncture ( **C**) for 'Farthing' blueberries in trial 2. Treatments included an unshipped control (UNS; not shipped to the irradiation facility) and four levels of irradiation; no irradiation control (0), 0.15, 0.5, and 1.0 kGy. Evaluations were conducted 6, 13, and 25 days after irradiation treatment. Fruit were stored at 2 to 4 ◦C under high relative humidity until assessments were performed. An initial fruit quality assessment was performed after harvest shown as a horizontal dashed line. Due to low number of fruit, measurements were not performed for fruit treated at 1 kGy at 13 days after treatment. Means within the same storage times after treatment followed by the same letter are not significantly different from each other based on one-way analysis of variance (α = 0.05).

**Figure 3.** Effect of Electronic Cold-PasteurizationTM on percent sound fruit (**A**), compression (**B**), and puncture (**C**) for 'Rebel' blueberries in trial 2. Treatments included an unshipped control (UNS; not shipped to the irradiation facility) and four levels of irradiation; no irradiation control (0), 0.15, 0.5, and 1.0 kGy. Evaluations were conducted 6 and 13 days after irradiation treatment. Fruit were stored at 2 to 4 ◦C under high relative humidity until assessments were performed. An initial fruit quality assessment was performed after harvest shown as a horizontal dashed line. Means within the same storage times after treatment followed by the same letter are not significantly different from each other based on one-way analysis of variance (α = 0.05).

Fruit texture, measured using compression, indicated that a higher dose of irradiation resulted in a loss of firmness in 'Farthing' in both trials at various times after treatment (Figures 1B and 2B). Compared with unshipped and 0-kGy controls, a decrease in firmness was small but statistically significant with the 1.0-kGy treatment. Compared with the 0-kGy control, there was a 0.03 N decrease in firmness in the 1.0-kGy treatment at 6 and 13 days after treatment in trial 1; trial 2 showed a 0.03 N and 0.06 N at 6 and 25 days after treatment, respectively. Similarly, irradiation at 1.0 kGy resulted in a decrease in skin toughness, measured by the skin puncture force, relative to the controls in 'Farthing' in both trials. Compared with the 0-kGy control, there was a 0.04 to 0.06 N decrease in skin puncture force in the 1.0-kGy treatment at 6, 13, and 25 days after storage; trial 2 showed a 0.07 N decrease in skin puncture force at 6 and 25 days after treatment. (Figures 1C and 2C).

Comparison of fruit texture between varieties in the unshipped control at the initial and later time-points during postharvest storage indicated that 'Rebel' exhibited lower firmness and skin puncture force than 'Farthing'. 'Rebel' fruit could not be evaluated for postharvest quality attributes at 25 days after treatment due to poor quality. Visual quality of ECPTM -treated fruit of 'Rebel' did not differ from that in the control treatments (Figure 3A). There were no significant differences in fruit compression among treatments at both time points during postharvest storage (Figure 3B). Skin toughness was not different among treatments at 6 days after irradiation (Figure 3C). At 13 days after treatment, fruit irradiated at 0.5 and 1.0 kGy had lower values than the 0-kGy control, but were not different from the unshipped control suggesting that skin toughness did not change due to ECPTM in 'Rebel'.

#### *3.2. Total Soluble Solids Content, Titratable Acidity, and Weight*

There were no effects of irradiation on total soluble solids content or titratable acidity in 'Farthing' and 'Rebel' at various times after treatment (Table 1). In general, fruit weight did not change during postharvest storage. Similarly, no significant change in fruit weight was observed at various times after irradiation treatment compared with both unshipped and the 0-kGy controls in 'Farthing' and 'Rebel' (Table 2).


**Table 1.** Total soluble solids (TSS) content and titratable acidity (TA) of 'Farthing' and 'Rebel' blueberry fruit subjected to Electronic Cold-PasteurizationTM followed by different cold storage periods.

a Treatments included an unshipped control (UNS, not shipped to the irradiation facility) and four levels of irradiation; no irradiation control (0), 0.15, 0.5, and 1.0 kGy. Fruit were stored at 2 to 4 ◦C under high relative humidity until TSS and TA measurements were performed. An initial fruit quality assessment was done after harvest (day 0). Due to low number of 'Farthing' fruit in trial 2, no assessment was performed at 13 days after irradiation for fruit treated at 1.0 kGy. In case of Rebel, almost 100% decay in fruit resulted in no assessment at 25 days after treatment. One-way analysis of variance indicated no significant differences among irradiation levels within a given storage period after treatment in each trial (α = 0.05).


**Table 2.** Weight of 'Farthing' and 'Rebel' blueberry fruit subjected to Electronic Cold-PasteurizationTM followed by different cold storage periods.

a Treatments included an unshipped control (UNS, not shipped to the irradiation facility) and four levels of irradiation; no irradiation control (0), 0.15, 0.5, and 1.0 kGy. Fruit were stored at 2 to 4 ◦C under high relative humidity until weight measurements were performed. An initial fruit quality assessment was done after harvest (day 0). Due to low number of 'Farthing' fruit in trial 2, no assessment was performed at 13 days after irradiation for fruit treated at 1.0 kGy. In case of Rebel, almost 100% decay in fruit resulted in no assessment at 25 days after treatment. For every trial, means within the same storage times after treatment followed by the same letter are not significantly different from each other based on one-way analysis of variance (α = 0.05). Nonsignificant values are denoted by ns.

#### *3.3. Microbial Load on Fruit after Treatment*

Microbial loads on the fruit surface were determined for samples collected 6 days after ECPTM treatment. Microbial population densities were highest for total aerobic bacteria and total yeasts (up to ~10<sup>5</sup> CFU/g of fruit), followed by total molds; colony counts were lowest for coliforms (Table 3). Only a single sample of 'Rebel' showed presence of *E. coli* (at 2.7 CFU/g fruit), and therefore no statistical analysis was possible for *E. coli*. Microbial loads were similar across the two trials of 'Farthing', but were considerably higher for 'Rebel', which had very soft fruit and also the highest microbial counts (Table 3).

ECPTM significantly reduced total aerobic bacteria (by between 0.5 and 1 log units) in each of the three cultivar × trial combinations, but typically only at the 1.0-kGy irradiation level (Table 3). Yeast counts were similarly reduced in all cases, but again significant only for the 1.0-kGy level. Total surface mold counts were not reduced by irradiation in any of the cases. Population densities of coliform bacteria were not impacted on 'Farthing', but were reduced significantly and by over 2 log units on 'Rebel' (Table 3), which had the highest microbial loads in general.


**Table 3.** Surface microbial load, in log (colony-forming units per g of fruit), on 'Farthing' and 'Rebel' blueberry fruit subjected to Electronic Cold-PasteurizationTM 6 days after treatment.

a Treatments included an unshipped control (UNS, not shipped to the irradiation facility) and four levels of irradiation; no irradiation control (0), 0.15, 0.5, and 1.0 kGy. Fruit were stored at 2 to 4 ◦C under high relative humidity until wash platings were performed. Means within the same trial and column followed by the same letter are not significantly different from each other based on one-way analysis of variance (α = 0.05). Nonsignificant values are denoted by ns.

#### *3.4. Postharvest Disease Incidence on Fruit after Treatment*

Postharvest disease incidence was determined at 6 and 13 days after treatment in trial 1 and for the 6-day post-treatment period in trial 2, each followed by a 4-day fruit exposure at room temperature to allow infections to develop. Anthracnose (caused by *Colletotrichum acutatum*), *Botrytis cinerea*, *Alternaria* sp., *Aureobasidium pullulans*, *Phomopsis vaccinii*, and *Cladosporium* sp. were observed on postharvest fruit; no significant effects of ECPTM on disease incidence were observed, neither at low decay incidence levels (<5% as observed with 'Farthing'), nor at high levels (~15% as observed with 'Rebel') (Table 4).


**Table 4.** Postharvest disease incidence, in percent, on 'Farthing' and 'Rebel' blueberry fruit subjected to Electronic Cold-PasteurizationTM 6 or 13 days after treatment plus 4 days at room temperature.

a Treatments included an unshipped control (UNS, not shipped to the irradiation facility) and four levels of irradiation; no irradiation control (0), 0.15, 0.5, and 1.0 kGy. Fruit were stored at 2 to 4 ◦C under high relative humidity, followed by 4 days at room temperature, until disease assessments were performed. An initial fruit quality assessment was done after harvest (day 0). The 13-day assessment was not included in trial 2 due to low number of fruit in Farthing and nearly 100% decay in 'Rebel'. Means within the same trial and column followed by the same letter are not significantly different from each other based on one-way analysis of variance (α = 0.05). Nonsignificant values are denoted by ns.
