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Thursday, September 02, 2010

Organic Strawberries Are Better

Consumers who buy organic fruits and vegetables because they think they're tastier, more nutritious and better for the environment are getting what they're paying for, according to a study published online in the journal PLoS One Wednesday.

The finding is based on a detailed comparison of organic and conventional strawberries from 13 pairs of neighboring farms in Watsonville, Calif., where 40% of the state's strawberry crop is produced. A team of ecologists, food chemists, soil scientists and other experts analyzed a variety of factors before concluding that the organic berries — and the dirt they were raised in — were superior.

When susceptibility to fungal post-harvest rots was evaluated, organic strawberries had significantly longer survival times (less gray mold incidence) than conventional strawberries (Figure 1). When strawberries were exposed to a two-day shelf-life interval, the percent loss in fresh weight was significantly less for the organic berries than for the conventional berries (Table 2). These results indicate that the organic strawberries would have a longer shelf life than the conventional strawberries because of slower rotting and dehydration, perhaps due to augmentation of cuticle and epidermal cell walls. There were no fungicides applied to the organic strawberry fields for post-harvest control of gray mold (Botrytis cinerea), in contrast to multiple fungicide applications to the conventional fields. Although sulfur was applied to the organic fields to control powdery mildew (Sphaerotheca macularis), sulfur sprays are ineffective against gray mold. This suggests that the organic strawberries may have been more resistant or avoided infection by means other than fungicides (e.g., systemic-acquired resistance).

Strawberries from organic farms were significantly smaller (by 13.4%) than those from conventional farms, but had significantly greater dry matter content (by 8.3%) (Table 2). Fruit firmness and external color intensity (C*) were similar between conventional and organic berries, but organic berries were darker red (significantly lower L* and hab) than conventional berries. Although their darker red color did not result in a preference for the appearance of organic over conventional ‘Lanai’ and ‘San Juan’ strawberries by consumer-sensory panels, these panels did prefer the appearance of organic ‘Diamante’ berries to their conventional counterparts (Table 3).

Organic strawberries had significantly higher total antioxidant activity (8.5% more), ascorbic acid (9.7% more), and total phenolics (10.5% more) than conventional berries (Table 2), but significantly less phosphorus (13.6% less) and potassium (9.1% less) (Table 1). Specific polyphenols, such as quercetin and ellagic acid, showed mixed or no differences (Table 4). Strawberries are among the most concentrated sources of vitamin C and other antioxidant compounds in the human diet. Dietary antioxidants, including ascorbic acid (i.e., vitamin C) and phenolic compounds offer significant potential human health benefits for protection against diseases. For example, Olsson et al. reported decreased proliferation of breast and colon cancer cells by extracts of organically grown strawberries compared to conventional berries, with ascorbic acid concentrations correlated negatively with cancer cell proliferation. Although the greater potassium concentration in the conventional strawberries is a plus, strawberries are not among the richest sources of potassium or even phosphorus. Interestingly, less phosphorus in the diet may be considered desirable, given the negative effects of the increasing U.S. consumption of phosphorus on vitamin D and calcium metabolism, and the resulting potential risk to bone health.

Using hedonic/intensity ratings, consumer-sensory panels found organic ‘Diamante’ strawberries to be sweeter and have preferable flavor, appearance, and overall acceptance compared to conventional ‘Diamante’ berries (Table 3). Organic and conventional ‘Lanai’ and ‘San Juan’ berries were rated similarly. Sensory results of sweeter tasting ‘Diamante’ strawberries were confirmed by higher soluble solids content measured in the laboratory (Table 5).

Soils were sampled and analyzed from the top (0–10 cm) and bottom (20–30 cm) of the raised mounds in June 2004 and 2005. The organically managed surface soils compared to their conventional counterparts contained significantly greater total carbon (21.6% more) and nitrogen (30.2% more) (Table 6). Organic matter (total carbon) can have a beneficial impact on soil quality, enhancing soil structure and fertility and increasing water infiltration and storage. Levels of extractable nutrients were similar in the two systems, with the exception of zinc, boron, and sodium being significantly higher and iron being notably higher in the organically farmed surface soils.

Organically managed surface soils also supported significantly greater microbial biomass (159.4% more), microbial carbon as a percent of total carbon (66.2% greater), readily mineralizable carbon (25.5% more), and microbial carbon to mineralizable carbon ratio (86.0% greater) (Table 6). These indicate larger pools of total, labile, and microbial biomass C and a higher proportion of soil total and labile C as microbial biomass. All measures of microbial activity were significantly greater in the organically farmed soils, including microbial respiration (33.3% more), dehydrogenase (112.3% more), acid phosphatase (98.9% more), and alkaline phosphatase (121.5% more). The organically farmed soils had a significantly lower qCO2 metabolic quotient, indicating that the microbial biomass in the organically farmed soils was 94.7% more efficient or under less stress than in the conventionally farmed soils. These same differences, except for qCO2, alkaline phosphatase, iron, boron, and sodium, were also observed in soils from the bottom of the mounds (20–30 cm depth).

"Almost every major indicator is favoring the organic strawberries," said lead author John Reganold, who studies sustainable agriculture at Washington State University in Pullman.

The critics pointed out that organic farming usually entails higher costs and lower yields, two issues that weren't addressed in the study because they do not factor into consumers' buying decisions. In an interview, Reganold said that the Watsonville strawberry farmers who used organic methods grew about 25% fewer strawberries than their conventional counterparts.

Reganold said he chose to study strawberries because they are a popular, nutritious and economically valuable crop. But their dietary value should not be taken out of context, said Sean Clark, a professor of agriculture and natural resources at Berea College in Kentucky: The average American eats only 8 pounds of the berries per year.

"We eat considerably more potatoes, apples and bananas per capita annually," Clark said. "Changing what people eat — increasing fruits and vegetables and decreasing meats, fats and total daily calories, for example — could have a more profound impact on public health and longevity than switching from conventional to organic strawberries."

posted by CASFS 2006 @ 8:08 PM


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