Web Release Date: April 17,
Thermal Processing Enhances the Nutritional Value of Tomatoes by Increasing Total Antioxidant Activity
and
Department of Food Science and Institute of Comparative and Environmental Toxicology, Stocking Hall, Cornell University, Ithaca, New York 14853
Received for review November 26, 2001. Revised manuscript received March 8, 2002. Accepted March 8, 2002.
Abstract:
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 
mol of vitamin C/g of tomato. After 2, 15,
and 30 min of heating at 88 
C, the vitamin C content significantly dropped to 0.68 ± 0.02, 0.64 ±
0.01, and 0.54 ± 0.02 mol 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 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 mol of vitamin C
equiv/g of tomato. With heat treatment at 88 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 mol 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.
Keywords: Phenolics; antioxidant; phytochemicals; fruits; vegetables; processing; tomato
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