Survival of Listeria innocua and Native Microflora in Sanitizer-Treated Wild Blueberries (Vaccinium Angustifolium)

Figures & data

Figure 1. Custom-built pilot-scale processing line and setup for treatment of inoculated wild blueberries

A. Sanitizer immersion of inoculated wild blueberries in a sterilized steam pan, B. perforated tray with inoculated wild blueberries after immersion, C. mock processing line showing spray bars (a) used to spray sanitizer treatments and perforated conveyer belt (b).

Figure 2. Reduction of L. innocua on inoculated wild blueberries immersed in sanitizer for increasing time intervals

Data represent mean reduction of L. innocua population after immersion treatment with sanitizer (n = 3), error bars represent standard deviation, black (30 s), light gray (1.5 min), dark gray (3 min), striped (5 min), initial population 4.3 log CFU/g.

Figure 3. Reduction of native yeast on wild blueberries immersed in sanitizer for increasing time intervals

Data represent mean reduction of yeast population after immersion treatment with sanitizer (n = 3), error bars represent standard deviation, black (30 s), light gray (1.5 min), dark gray (3 min), striped (5 min), superscripts indicate significant differences (p < .05) across all treatments, initial population 7.0 log CFU/g.

Figure 4. Reduction of L. innocua on inoculated wild blueberries sprayed with sanitizer for increasing time intervals

Data represent mean reduction of L. innocua population after spray treatment with sanitizer (n = 3), error bars represent standard deviation, black (30 s), light gray (1.5 min), dark gray (3 min), striped (5 min), initial population 4.3 log CFU/g.

Figure 5. Reduction of native yeast on wild blueberry spray treated with sanitizer for increasing time intervals

Data represent mean reduction of yeast population after spray treatment with sanitizer (n = 3), error bars represent standard deviation, black (30 s), light gray (1.5 min), dark gray (3 min), striped (5 min), superscripts indicate significant differences (p < .05) across all treatments, initial population 7.0 log CFU/g.

Figure 6. Reduction of L. innocua on inoculated wild blueberries sequentially sprayed with sanitizer

Data represent mean reduction of L. innocua population after subsequent spray treatment with sanitizer (n = 3), light gray (spray 1), black (spray 2), superscripts indicate significant differences (p < .05) across treatments, initial population 4.5 log CFU/g.

Figure 7. Reduction of native yeast on wild blueberries sequentially sprayed with sanitizer

Data represent mean reduction of yeast population after subsequent spray treatment with sanitizer (n = 3), light gray (spray 1), black (spray 2), superscripts indicate significant differences (p < .05) across all treatments, initial population 7.1 log CFU/g.

Figure 8. Reduction of L. innocua on inoculated wild blueberries sequentially immersed then sprayed with sanitizer

Data represent mean reduction of L. innocua population after subsequent spray treatment with sanitizer (n = 3), light gray (immersion), black (spray), superscripts indicate significant differences (p < .05) between sanitizer treatments and water, initial population 4.5 log CFU/g.

Figure 9. Reduction of native yeast on wild blueberries sequentially immersed then sprayed with sanitizer

Data represent mean reduction of yeast population after immersion-spray treatment with sanitizer (n = 3), error bars represent standard deviation, light gray (immersion), black (spray), superscripts indicate significant differences (p < .05) between sanitizer treatments and water, initial population 7.1 log CFU/g.

Table 1. Positive coliforms detected in sanitizer-treated, frozen wild blueberries

Coliforms	Pre-treatment	Post-treatment	24 h after freezing
Water–water	4/6	2/6	2/6
Water–chlorine	1/6	3/6	1/6
PAA–PAA	0/6	4/6	1/6
Chlorine–chlorine	2/6	3/6	0/6
Chlorine–PAA	2/6	3/6	0/6

Results from three trials before and after treatment, detection limit 10 CFU/g.

Table 2. Survival of L. innocua in sanitizer-treated, inoculated wild blueberries after 2 weeks of frozen storage

Treatment	Survival (10 g)
Water–water	2/3
Water–chlorine	2/3
PAA–PAA	3/3
Chlorine–chlorine	2/3
Chlorine–PAA	2/3

Results from three trials after treatment, detection limit 1 CFU/10 g.

Figure 10. Reduction of L. innocua on inoculated wild blueberries immersed then spray treated with sanitizer followed by freezing

Data represent mean reduction of L. innocua population after immersion-spray treatment with sanitizer and frozen storage for 48 h (n = 3), light gray (immersion), white (spray), black (24 h after freezing), initial population 6.4 log CFU/g.

Figure 11. Reduction of native yeast on wild blueberries immersed then spray treated with sanitizer followed by freezing

Data represent mean reduction of L. innocua population after immersion-spray treatment with sanitizer and frozen storage for 48 h (n = 3), light gray (immersion), white (spray), black (24 h after freezing), initial population 6.5 log CFU/g.