Processed fruits and vegetables have been long considered to have lower nutritional
value than their fresh commodities due to the loss of vitamin C during processing.
This research group found vitamin C in apples contributed < 0.4% of total antioxidant
activity, indicating most of the activity comes from the natural combination of phytochemicals.
This suggests that processed fruits and vegetables may retain their antioxidant activity
despite the loss of vitamin C. Here it is shown that thermal processing elevated total
antioxidant activity and bioaccessible lycopene content in tomatoes and produced no
significant changes in the total phenolics and total flavonoids content, although
loss of vitamin C was observed. The raw tomato had 0.76 +/- 0.03 micromol of vitamin
C/g of tomato. After 2, 15, and 30 min of heating at 88 degrees C, the vitamin C content
significantly dropped to 0.68 +/- 0.02, 0.64 +/- 0.01, and 0.54 +/- 0.02 micromol
of vitamin C/g of tomato, respectively (p < 0.01). The raw tomato had 2.01 +/- 0.04
mg of trans-lycopene/g of tomato. After 2, 15, and 30 min of heating at 88 degrees
C, the trans-lycopene content had increased to 3.11+/- 0.04, 5.45 +/- 0.02, and 5.32
+/- 0.05 mg of trans-lycopene/g of tomato (p < 0.01). The antioxidant activity of
raw tomatoes was 4.13 +/- 0.36 micromol of vitamin C equiv/g of tomato. With heat
treatment at 88 degrees C for 2, 15, and 30 min, the total antioxidant activity significantly
increased to 5.29 +/- 0.26, 5.53 +/- 0.24, and 6.70 +/- 0.25 micromol of vitamin C
equiv/g of tomato, respectively (p < 0.01). There were no significant changes in either
total phenolics or total flavonoids. These findings indicate thermal processing enhanced
the nutritional value of tomatoes by increasing the bioaccessible lycopene content
and total antioxidant activity and are against the notion that processed fruits and
vegetables have lower nutritional value than fresh produce. This information may have
a significant impact on consumers' food selection by increasing their consumption
of fruits and vegetables to reduce the risks of chronic diseases.