Organic apples may be firmer and have better storability than apples grown conventionally, a Washington State University study suggests. In the study, organically grown apples were firmer on average both at harvest and after storage.
The trial took place in a four-acre plot within a commercial 50-acre conventional apple orchard in Washington’s Yakima Valley. The Golden Delicious trees in the experiment were planted in 1994 and farmed under one of three systems: organic, integrated, and conventional. In 1999, the trees were grafted over from Golden Delicious to Gala because of problems with fruit russeting. The first stage of the study compared the profitability of the three systems and found the organic plot to be the most profitable at the premiums that existed at the time.
In 2002 and 2003, Gregory Peck, Dr. Preston Andrews, and colleagues at WSU compared the quality of fruit from the different production systems. Andrews said the study would have begun a year sooner if the crops had not been damaged by a hailstorm. It had to end after two years because the orchard was sold.
For the two years, fruit was assessed at harvest, after three months in regular atmosphere, and after three and six months in controlled atmosphere storage. Overall, organic apples from the storage treatments in 2002 were 0.2 pounds firmer than the conventional apples, but were 2.5 pounds firmer the following season. Andrews said not only was the average firmness higher, but the apples were firmer overall so that there were fewer soft apples that failed to meet minimum firmness standards and had to be thrown out. For example, after six months in CA storage, only 10 percent of the organic apples were below the minimum firmness, compared with 36 percent of the conventional apples.
A nutrient analysis showed that the organic apples had lower nitrogen levels in the fruit tissue than the conventional fruit, which could explain the lower firmness of the conventional fruit. Because of economic constraints, the organic treatment did not receive a nitrogen application between 1995 and spring of 2003, though the conventional received synthetic fertilizer. Organically certified fertilizers, such as composted manures, are bulky and difficult to apply in orchards without specialized equipment or sufficient labor, the study’s authors point out.
The lack of nitrogen in the organic treatment appeared to have detrimental effects on yield and tree growth, however, as the organic trees were smaller than the conventional.
In 2002, yields were only a third of the volume of those from the conventional trees, although fruit size was larger. In 2003, the organic trees yielded more than the conventional, but had the smallest fruit size.
Andrews said inconsistent yields in the organic treatment were probably the result of several factors, including unsatisfactory crop load management, higher pest pressures, zinc deficiency, and lower leaf and fruit nitrogen levels. Although lime sulfur and fish oil was used for bloom thinning, no postbloom thinner was available for the organic treatment.
In 2003, organic fruit was skewed towards smaller sizes, but there were no differences in color grade either year between the treatments.
The study showed a clear difference in antioxidant content of organic and conventional apples, with the organic fruit having the most total antioxidants. In 2003, the organic apples had 10 percent more total antioxidants than conventional apples of the same size.
According to the authors of the study, one possible explanation for the higher level of antioxidants is that the herbicide glyphosate, applied only to the conventional plots, inhibited production of antioxidants in the fruit. Other researchers have found that high nitrogen levels are correlated with low flavonoid concentrations in the skin of apples, which is another possible reason for the higher total antioxidants in the organic fruit, Andrews reports.
At harvest, panels of consumers evaluated the fruit. In 2003, they rated the organic apples firmer than conventional apples, but conventional apples sweeter and more flavorful than organic. After the fruit had been stored, however, they said that organic apples were firmer, more flavorful, had better texture, and were more acceptable overall than the conventional apples, though the organic apples were more tart. The organic apples often provided a more favorable eating experience for the panelists after being stored long-term and held at room temperature for a time.
In both 2002 and 2003, the conventional fruit produced more flavor volatiles after storage than the organic fruit. However, this difference was not detected by the consumer panelists. They rated organic apples more acceptable after storage, perhaps because of the superior firmness and texture. It may also be that the sweetness and tartness of the fruit masked any flavor differences, Andrews said.
The percentage of unmarketable fruit was higher overall than would be expected in a commercial orchard, perhaps because all the apples were harvested, regardless of visible damage, such as bird pecks, sunscald, or severe russeting.
The organic fruit had significantly more damage from codling moth in 2002, but the amount of total pest damage was similar to conventional because the western flower thrips caused more damage to conventional fruit. In 2003, there was more insect damage in the organic treatment.
The researchers concluded that the organic system had the potential to grow high-quality Gala apples with minimal inputs soon after being top-grafted. "Many of the challenges associated with organic apple production will likely be overcome as new products and technologies become available to support the expanding production of organic apples," they stated.