Postharvest Flux and Genotype × Environment Effects for Onion-induced Antiplatelet Activity, Pungency, and Soluble Solids in Long-day Onion during Postharvest Cold Storage

Two mild and two pungent onion (Allium cepa L.) selections (hereafter referred to as cultitypes), W420B, W424B, MSU8155B, and Exhibition, were grown at two locations in two states (Wisconsin and Oregon) during 1994 and 1995. Onion bulbs were harvested, stored at 4 °C and sampled for antiplatelet activity, pungency, and soluble solids 10 days after harvest and every 40 days during a 210-day postharvest storage period. Significant cultitype × state and cultitype × year interactions were detected. However, these were primarily due to the change in rank of cultitypes within the mild or pungent group. Averaged over all environments, antiplatelet activity was significantly greater in 1994 compared to 1995 for all cultitypes. Significantly greater antiplatelet activity was measured for three out of four cultitypes grown in Oregon compared to Wisconsin. During postharvest storage, antiplatelet activity increased 61% and 56% across all cultitypes and across both states during 1994, and across all cultitypes in Wisconsin during 1995, respectively. Although pungency determination can be a good indicator for relative rankings of different cultitypes for antiplatelet activity, changes in pungency were not correlated with changes in antiplatelet activity during postharvest storage. Results demonstrate cultitype, environment, duration of postharvest storage and genotype × environment interactions influence pungency, soluble solids, and antiplatelet activity, which should be considered when assessing onion-induced antiplatelet activity. Knott, 1934). In a study by Randle (1992), pungency ranged from 1.6 for mild to 13.0 μmol pyruvate/g fresh weight for pungent onions, depending on the cultivar and sulfur substrate conditions (Randle, 1992). Since organosulfur compounds responsible for antiplatelet activity and pungency are synthesized from a common precursor, the ACSOs (Block, 1992), pungency may be an indicator of antiplatelet activity. Previous studies have evaluated the relationship between total dissolved solids (TDS) and total dry matter with pungency (Bedford, 1984; Randle, 1992). Higher TDS tend to be correlated with higher pungency and a correlation with increased antiplatelet activity can be hypothesized. Solids contribute to the flavor, texture, and storability of onions. Solids are measured by the refractive index of onion extract on a refractometer and are highly correlated (r = 0.96) to dry matter content (Mann and Hoyle, 1945). High levels of TDS in onions are desirable for dehydration and in certain cases are associated with good storability. Storability, the maintenance of high quality onion bulbs during storage, is of great importance to both producers and consumers of onions since onions are generally stored at temperatures slightly >0 °C after harvest so they can be sold at favorable market prices during the winter months. Studies relating dry matter content and storage characteristics have shown that high dry matter content is related to good storability (Suzuki and Cutliffe, 1989). Total dry matter percentage values of various onion cultivars ranged from 3.03 to 20.10 g per 100 g bulb material, depending on sulfur conditions of growth media and phenotype (Randle, 1992). High sulfur substrate conditions increased pungency in cultivars with high pyruvic acid measurements but were associated with reduced dry matter or TDS measurements (Randle and Bussard, 1993a, 1993b). Postharvest changes in these variables have been documented in several studies as the ratios of organosulfur compounds, pungency and solids change during storage and also depend on storage temperature, time of harvest, cultivar, and postharvest handling before storage (Hurst et al., 1985; Kopsell and Randle, 1997; Miedema, 1994; Mikitzel and Fellman, 1994). Allium species have historically been used by many cultures in folk medicine and in traditional cuisine (Augusti, 1990; Block, 1992; Lawson, 1993). Onion has been suggested as a treatment for a variety of human ailments. Native onion sulfoxides have lipidlowering effects, fibrinolytic effects, and antiplatelet activity (Augusti, 1990). Platelet aggregation contributes to the risk of thromboembolic diseases due to agglutination and fusion of blood platelets obstructing the flow of blood in vessels supplying organs or tissues (Mustard and Packham, 1970). Several Allium-derived compounds have an inhibitory effect on platelet aggregation and may potentially be used to treat or prevent thromboembolic conditions. Organosulfur compounds responsible for the distinct aromas and flavors in onion are synthesized from a common precursor, the Salk(en)yl-L-cysteine sulfoxides (ACSOs). Upon crushing of onion bulb tissue, the ACSOs are hydrolyzed by alliinase into a suite of thiosulfinates (Lancaster and Shaw, 1989). Concentration of ACSO and alliinase varies with onion cultivar and is also influenced by environmental factors (Lancaster and Shaw, 1989; Randle, 1992). Pungency, an indicator of the strength of onion flavor, is commonly measured by the pyruvic acid method (Randle and Bussard, 1993b; Schwimmer and Weston, 1961) in which reaction of 2,4-dinitro phenyl-hydrazine (DNPH) with NaOH is used to detect the presence of pyruvic acid. In one of the earliest studies addressing the effects of environment and cultivar on onion pungency, investigators observed that, although cultivar has the most pronounced effect, genotype × environment effects were important in explaining variability (Platenius and