Amy Simonne

Effects of Nitrogen Rates on Chemical Composition of Yellow Grape Tomato Grown in a Subtropical Climate

ABSTRACT Grape tomatoes (Lycopersicon esculentum Mill.) are gaining popularity among consumers because of their flavor, sweetness, potential health benefits, and ease of consumption. Most grape tomatoes are indeterminate varieties. Hence, current production practices (including fertilization rates) may need to be adjusted to larger plants, longer growing seasons, and harvests over several months of the indeterminate varieties. The responses of physical (color and moisture content) and chemical [vitamin C, pH, total titratable acidity (TTA), carotenoids, and soluble solid content (SSC)] parameters for ‘Honey Bunch’ yellow grape tomato to nitrogen (N) rates were evaluated. In Spring 2005, tomatoes were grown on a Lakeland fine sand in North Florida using plasticulture and N rates of 0, 78, 157, 235, 314, and 392 kg/ha. Tomatoes were harvested fully ripen on 81 and 105 d after transplanting (DAT = 0 on March 24th), and uniform 20-fruit samples were carefully selected. Increasing N rate significantly reduced vitamin C concentration from 44 to 35 mg/100 g and TTA from 0.47% to 0.38% citric acid, but did not significantly affect lutein (mean = 0.26 micro-g/g) and β-carotene (mean = 0.82 micro-g/g) concentrations or color. Response of pulp pH to N rate was significant but within the narrow 4.5 to 4.7 range. Soluble solid contents decreased as N rate decreased for the first harvest (8.1 to 5.6 for 0 to 392 kg/ha of N), but increased for the second harvest (6.9 to 10.1 for 0 to 314 kg/ha of N). Overall, N rate did not have a marked effect on selected quality parameters, suggesting that variety and/or other environmental factors may be more important than N rate in determining chemical composition of grape tomato.

NITROGEN SOURCE AFFECTS CRUNCHINESS, BUT NOT LETTUCE YIELD

While nitrogen (N) form affects growth and yield of many vegetables crops, previous studies suggested that N-form may affect lettuce (Lactuca sativa L.) quality more than growth and yield. The objectives of this research were to evaluate the effect of the N-source used as injection material on the field performance and sensory attributes of three lettuce types. Three lettuce types (Romaine, butterhead and looseleaf) where grown with plasticulture and sidedressed with weekly injections of calcium nitrate, potassium nitrate, or ammonium nitrate, each at a rate of 7 kg N ha−1 week−1. All lettuce type reached marketable size 49 days after transplanting. N-source effect on marketable yield and head number was not significant (P>0.05). After harvest, lettuce samples were prepared for sensory evaluation. In a quiet session, panelists (n=36) were instructed to rate each sample for bitterness, sweetness, crunchiness, and overall preference on a 9-cm Hedonic scale. Sensory ratings were similar for all three lettuce types. Panelist found that crunchiness of calcium nitrate-fed plants (4.8 cm) was significantly (P=0.05) higher than that of plants receiving potassium nitrate (4.4 cm) or ammonium nitrate (4.2 cm). These results suggest that while growers may use ammonium nitrate because of its cost, they should consider using calcium nitrate to enhance lettuce crunchiness.

Prevalence of Escherichia coli O157:H7 From House Flies (Diptera: Muscidae) and Dairy Samples in North Central Florida1

Abstract Efficient detection of enterohemorrhagic Escherichia coli O157:H7 is important to monitor the safety of food products obtained from cattle, and it has been primarily accomplished by analyzing manure samples by selective cultivation techniques, PCR, and ELISA. As each technique suffers from different biases, there may be value in using multiple methods and samples to increase detection efficiency. Difficulties associated with cattle manure sampling can be circumvented by isolation of E. coli O157:H7 from house flies, Musca domestica (L.), which present as an important vector for spreading diseases. Thus, isolation of pathogens directly from house flies provides information about the potential human health impact that house fly dispersal can have because of pathogen distribution. House flies can disperse from dairy farms, where E. coli O157:H7 endemically thrive in cattle, to restaurants where food is prepared and served. Here, we report that detecting E. coli O157:H7 in house flies was 2.7 times more frequent than in manure from nearby dairy farms. Flies appear to offer a promising alternative in efforts to detect E. coli O157:H7 in dairy farms, restaurants, processing plants, and other establishments.