Issue link: https://read.dmtmag.com/i/76198
GOOD TO KNOW A research report from Yan Wang, Mid- Columbia Agricultural Research and Extension Center, Oregon State University M MAP could extend Bartlett season It might also reduce quality problems in export markets. odified atmosphere packaging is used to supplement low-temperature manage- ment of many fresh fruit and vegetable products. MAP may have the potential to extend the Bartlett pear marketing season and increase export distances to reach new mar- kets, perhaps increasing the total volume of Pacific Northwest pears that can be marketed each year. MAP bags, used inside the cartons, can delay ripening, reduce physiological disorders, and suppress decay. These benefits are derived primarily from the altered gas atmosphere surrounding the commodity that is cre- ated by the respiration of the product and the resistance of the packaging's polymeric film to oxygen and carbon dioxide diffusion. MAP also maintains high relative humidity, which reduces water loss, greatly improving the preservation of product quality and the potential storage duration. However, MAP can also cause undesirable effects such as fermentation and off-flavors if the oxygen concentra- tion decreases to a point that will not sustain aerobic respiration. Similarly, injury can occur if the carbon diox- ide concentration exceeds critical levels. Successful use of MAP requires that the gas permeability of the film is matched to the requirement of the commodity and the storage temperature, ensuring the creation of the specific gas atmosphere and relative humidity needed to maintain postharvest quality. One primary application for MAP with pears is ensur- ing high arrival quality of Bartlett pears shipped to distant markets. About one-third of the Pacific Northwest's pear production is exported. The major quality issues at arrival are advanced ripening, especially yellowing, and physio- logical disorders such as senescent scald (Figure 1A). Pear packers have experimented with MAP for maintaining quality of export fruit. However, MAP-related internal browning (Figure 1B)has presented a problem for buyers and receivers. Another application for MAP may be as a substitute for controlled atmosphere (CA) storage. In the Northwest, the majority of Bartlett pears are normally held for one to two months in refrigerated air (RA) or three to four FIGURE 1A. An example of senescent scald in non-MAP packed fruit. FIGURE 1B. MAP- related internal browning disorder of Bartlett pears at export market. months in CA. Regular atmosphere storage has an oxy- gen level of around 21% and a carbon dioxide level of 0.03%, whereas the typical CA atmosphere used for pears has an oxygen level of 2% and a carbon dioxide level of less than 1%. Some years, a portion of the crop can be stored for up to three months in RA and five months in CA. It may be possible to use MAP for maintaining quality similar to CA storage without the extensive investment in infrastruc- ture and instrumentation. The industry is also interested in expanding MAP to other pear cultivars such as Comice and Starkrimson. There is not sufficient information on optimum MAP conditions for these cultivars. Results The Columbia Gorge Fruit Growers has funded my research program to study the effects of MAP on pears during storage and transit. The experiments were done with four types of bags made by three different compa- nies. The major results of studies on the effects of MAP on Bartlett with different MAP bags and simulated transit conditions are reported here: Now's The Time To Sample! •Tree structure responding to optimal or stressed conditions Leaf Analysis shows •Nutrient uptake relative to healthy/ damaged cambium •Fruit mineral accumulation levels •Potential for storage disorders •Data for optimum storage segregation •Relationship to carbohydrate supply Fruit Analysis shows 1) AP bags that maintained an average internal atmos- phere of 12.3% oxygen and 5.6% carbon dioxide signif- icantly extended Bartlett pear storage life and maintained high eating quality without internal browning or other disorders for up to four months at 30°F (Figure 2).High carbon dioxide appears to play a major role in maintaining fruit quality because a reduction in oxygen concentration from 21% to 4 or 5% did not significantly reduce the respiration or eth- ylene synthesis rates in either unripe or ripened Bartlett pears. 2) MAP bags with higher gas permeability (18.0% oxygen and 1.5% carbon dioxide) had minimal effect in terms of delaying fruit yellowing and softening during cold storage. 3) MAP bags with internal gas atmosphere equilibrated at 2.2% oxygen and 5.7% carbon dioxide resulted in fruit with 25.5% and 62.3% internal breakdown after three and four months of cold storage, respectively. 4) During simulated transit conditions at temperatures of 35°, 40°, 45°, and 50°F for three weeks, pears in an MAP bag from LifeSpan developed internal browning at 45° and 50°F but not at 35° and 40°F, regardless of pretransit cold storage duration (1 and 3 months). For simulated transit at 35 and 40°F for three weeks, MAP slowed down ripening and prevented senescent scald (Figure 3). 5) The MAP-related internal browning observed in this study included two types of symptoms: classic pithy brown core and wet brown flesh (Figure 4). 509-662-1888 509-452-7707 Wenatchee, WA 98801 Union Gap, WA 9890 800-545-4206 www.cascadeanalytical.com 46 AUGUST 2012 GOOD FRUIT GROWER 6) LifeSpan MAP-packed Bartlett pears stayed firmer than 15 pounds during three weeks of simulated tran- sit at 35°F, regardless of storage durations of up to three months at 30°F. While MAP-packed fruit stayed firmer than 15 pounds when held at 40°F for three weeks in the early storage season (after 1 month of storage), firmness dropped below 15 pounds under the same transit conditions in the late storage season (after 3 months of storage at 30°F). These findings are signifi- cant because Bartlett pears with a firmness of less than 15 pounds would likely suffer vibration and/or impact bruising damage during transportation. www.goodfruit.com 1A 1B