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By Mike Thornton, Plant Scientist, and Nora Olsen, Extension Potato Specialist, University of Idaho
Recent studies indicate that consumers are becoming more demanding about the quality of the food they buy. The potato industry has a lot riding on consumer perceptions of fresh potato quality as their brand is prominently displayed on each bag. In the produce department, potato quality is most often initially judged by appearance and then by shelf-life after the purchase is made. Defects that negatively influence appearance and shelf-life can, therefore, adversely damage consumers’ perceptions and lead them to have second thoughts about purchasing potatoes in the future.
To get a better understanding of fresh potato quality, the Idaho Potato Commission has been funding a research project with a few main objectives: 1) identify the most common types of defects that lead to quality issues; 2) document the months of the shipping season and shipping destinations where quality issues are most common; and 3) determine the extent to which defect levels change between the time of packing and arrival at the distribution center. This project started in February 2018 and will run through June 2021, and encompasses parts of the 2017, 2018, 2019 and 2020 potato crops.
Types of Defects
Throughout this project, we have been working closely with the fresh pack industry to look at the most common defects associated with quality notices (downgrades and rejections) for loads arriving at produce distribution centers of one of the largest retailers in the U.S. One of the first things we learned is that the types of defects causing most of the quality issues are not constant from month to month or year to year.
For example, during the winter of 2018, blackspot, shatter bruise, dry rot and soft rot were the most reported defects. But by that summer, pressure bruise was the defect most associated with quality issues as the remaining potatoes in storage were packed and shipped. In the fall of 2019, conditions were very cold, leading to a lot of shatter bruise and blackspot, as well as soft rot in lots that were affected by frost. However, once those initial lots with frost damage were gone, the level of soft rot dropped substantially.
Season and Region
It was interesting to see that the number of quality notices can spike at certain times of the year, but again that pattern was not always consistent. We saw a sharp increase in quality notices in April 2018, but that was followed by a steep reduction one month later. In contrast, in the past two winters, we have seen a smaller increase in quality notices around February, but then a leveling off in quality issues after that point.
One of the more consistent trends we have seen in this project is that there is a definite geographic bias in terms of the location of distribution centers that tend to have the most quality reports. For example, during the August 2018 to January 2019 period, approximately 50 percent of the rejections/downgrades were from six distribution centers located in the Southeast and 15 percent from two located in the Midwest. The remaining 35 percent of the notices were spread evenly across the remaining 19 distribution centers. This indicates that transportation duration may be having a bigger impact on arrival quality than previously realized.
Changes in Transit
To better understand the changes in potato quality that are occurring along the supply chain, we tracked six loads from a single packing shed to several distribution centers in the West, Northeast and Southeast. We took subsamples from 5-pound consumer poly bags off the packing room floor, put some of the bags into a walk-in cooler to hold at the same temperature as the set point of the truck, and then met the truckload on the day the potatoes were delivered to the distribution center.
For all three sets of samples, we peeled about 200 potatoes to determine the types and number of both scorable and non-scorable defects. We also stashed temperature and humidity recording devices within the pallets on each load to get a better handle on actual conditions inside the trucks.
The results were eye opening in that for two of the six loads, the temperature conditions inside the truck never reached the set point. One case was due to a malfunctioning thermostat, and in the other case, the reefer unit was switched in transit to intermittent operation, which caused the potatoes to cool very slowly. This is a very small sample size, but it does raise the importance of checking on trucks to ensure they are operating in the desired manner. Another surprising result was the range of temperatures among pallets on a truck. We commonly saw 3 to 4 degrees Fahrenheit temperature difference between pallets located in the front compared to the back of the truck.
In terms of quality, we saw a measurable increase in both blackspot and shatter bruise between packing and arrival at destination. This is not surprising as potatoes are likely to experience impact damage any time they are handled, including during the packing operation. In most situations, the increase was not associated with an increase in scorable defects, which is good news. The exception was in the incidence of potatoes cutting black underneath a visible pressure bruise depression on the surface (Fig. 1). For some reason, we saw three times more of these pressure bruises cutting black at the distribution center compared to the packing shed.
Interestingly, the potatoes sampled in the packing shed and placed into a walk-in cooler for the same number of days as the truck journey did not show any increase in this defect. This indicates that something unique to the conditions in the truck (vibration, temperature fluctuation, oxygen level or other factors) is causing an increase in pressure bruise defect levels.
It is clear that focusing on bruise prevention is still the best way to ensure that consumers remain satisfied with the quality of fresh potatoes. That message needs to be emphasized throughout the handling chain from harvest through arrival at the supermarket if we are going to maximize appearance and shelf-life.
To help with education efforts, we have posted articles, bulletins and videos focusing on bruise prevention at www.uidaho.edu/potatoes.
