Issue link: http://read.dmtmag.com/i/769560
www.goodfruit.com Good Fruit Grower JANUARY 15, 2017 33 Bacterial levels: The 'log' view T o understand bacterial contamination, it helps to know how researchers talk about an increase or reduction in bacterial levels. Ines Hanrahan, proj- ect manager for the Washington Tree Fruit Research Commission, offered this guidance: Say you have one bacterium on one apple and it increases to 10 bacteria. That would be considered a 1-log increase (in science-speak). An increase to 100 bacteria would be a 2-log increase, and so on, increasing by factors of 10 for each log increase. Now for a reduction. Say you have 10,000 bacteria on an apple, and you reduce the bacteria levels by 90 percent. That would be a 1-log reduction. A 99 percent reduction would be a 2-log reduction, continuing on to 99.9 percent, 99.99 percent and 99.999 percent, a five-log reduction that would, in the science world, effectively be considered a "kill step." Or to put it another way, say you have 10,000 apples. They're all contami- nated. If you clean the apples, but 1,000 are still contaminated, you've had a 1-log reduction. A 2-log reduction would mean 100 apples are still contami- nated, and a 3-log reduction would mean 10 apples are still contaminated. A 4-log reduction: Only one bad apple left in the bunch, but still short of a kill step. —S. Dininny RA, CA and CA with ozone at 70 to 80 parts per billion. In all three storage situations, the apples saw a significant reduction in Listeria in the first six weeks and only a gradual reduction over the next 12 weeks. However, the biggest drop in those first six weeks came in the CA room with ozone, where apples saw an almost 99.99 percent reduction in bacteria levels — one step short of what would be considered a "kill step" in the industry. The RA storage and CA storage without ozone saw reduction of only about 99 percent. Zhu stressed that these are early results and that more testing is needed before researchers can draw any conclusions. Said Ines Hanrahan, project manager for the Washington Tree Fruit Research Commission: "This is the first study of its kind, and we are very pleased with the initial results. We are hoping to be able to repeat this study while including more orchards and apple varieties of concern, such as Granny Smith." In 2016, Zhu inoculated 750 Granny Smith apples with Listeria monocytogenes (aka the "real" pathogenic strain) in a WSU laboratory in Pullman, Washington, then stored the apples at different temperatures: —1 degree Celsius (33 degrees Fahrenheit, a typical cold storage temperature). —4 degrees C (36 to 38 degrees F, often employed for Honeycrisp). —10 degrees C (50 degrees F, often used to temperature condition Honeycrisp in preparation for storage). The study showed there was very little die off of bacteria in the first eight weeks, regardless of whether a low dose or high dose of bacteria was applied and regardless of temperature. Zhu said the researchers were unable to establish a stable ozone level in the first two to three weeks of this study; conducting experim ents in commercial facilities means there will always be some unexpected variables. Overall, it's too early to draw conclusions, Hanrahan said. Fuji and Granny Smith apples from the 2016 harvest are in storage for another year of study this year. • "This is the first study of its kind, and we are very pleased with the initial results. We are hoping to be able to repeat this study while including more orchards and apple varieties of concern, such as Granny Smith." — Ines Hanrahan SAND MEDIA FILTRATION 815 Wallace Way Grandview, WA 509-882-2060 2410 N. 4th Ave. Pasco, WA 509-547-1761 800-959-1535 1155 S. Broadway Othello, WA 509-488-5623 800-595-1536 81156 Hwy 395 N Hermiston, OR 541-567-6370 BEST IN CLASS PERFORMANCE Protect your irrigation systems from troublesome algae and organic matter with LAKOS sand media filters, which feature a unique underdrain design for maximum performance. • The most effective filtration available • Industry-leading lowest pressure loss • Longer operating cycles and less backwashing saves water and energy • 15-year warranty on internal components • Growsmart ® by Lindsay MULTI-CONTROL provides exclusive filter flush capabilities