Lycopene in Tomatoes: Chemical and Physical Properties Affected by Food Processing

Abstract

Lycopene is the pigment principally responsible for the characteristic deep-red color of ripe tomato fruits and tomato products. It has attracted attention due to its biological and physicochemical properties, especially related to its effects as a natural antioxidant. Although it has no provitamin A activity, lycopene does exhibit a physical quenching rate constant with singlet oxygen almost twice as high as that of beta-carotene. This makes its presence in the diet of considerable interest. Increasing clinical evidence supports the role of lycopene as a micronutrient with important health benefits, because it appears to provide protection against a broad range of epithelial cancers. Tomatoes and related tomato products are the major source of lycopene compounds, and are also considered an important source of carotenoids in the human diet. Undesirable degradation of lycopene not only affects the sensory quality of the final products, but also the health benefit of tomato-based foods for the human body. Lycopene in fresh tomato fruits occurs essentially in the all-trans configuration. The main causes of tomato lycopene degradation during processing are isomerization and oxidation. Isomerization converts all-trans isomers to cis-isomers due to additional energy input and results in an unstable, energy-rich station. Determination of the degree of lycopene isomerization during processing would provide a measure of the potential health benefits of tomato-based foods. Thermal processing (bleaching, retorting, and freezing processes) generally cause some loss of lycopene in tomato-based foods. Heat induces isomerization of the all-trans to cis forms. The cis-isomers increase with temperature and processing time. In general, dehydrated and powdered tomatoes have poor lycopene stability unless carefully processed and promptly placed in a hermetically sealed and inert atmosphere for storage. A significant increase in the cis-isomers with a simultaneous decrease in the all-trans isomers can be observed in the dehydrated tomato samples using the different dehydration methods. Frozen foods and heat-sterilized foods exhibit excellent lycopene stability throughout their normal temperature storage shelf life. Lycopene bioavailability (absorption) can be influenced by many factors. The bioavailability of cis-isomers in food is higher than that of all-trans isomers. Lycopene bioavailability in processed tomato products is higher than in unprocessed fresh tomatoes. The composition and structure of the food also have an impact on the bioavailability of lycopene and may affect the release of lycopene from the tomato tissue matrix. Food processing may improve lycopene bioavailability by breaking down cell walls, which weakens the bonding forces between lycopene and tissue matrix, thus making lycopene more accessible and enhancing the cis-isomerization. More information on lycopene bioavailability, however, is needed. The pharmacokinetic properties of lycopene remain particularly poorly understood. Further research on the bioavalabili...

Lycopene and β-carotene are bioavailable from lycopene ‘red’ carrots in humans

“…Our hypothesis was that the lycopene from the high lycopene carrot was bioavailable, however, not as bioavailable as that from tomato paste. This hypothesis is based on studies that have indicated lycopene from processed tomato products is more bioavailable than raw tomatoes (Porrini et al, 1998;Bohm & Bitsch, 1999;Shi & Le Mague, 2000). In addition, these experiments allow us to examine the effect of carrot fiber on lycopene absorption.…”

“…The primary dietary source of lycopene is the tomato, with 85% coming from tomato products in the US (Arab & Steck, 2000). Lycopene, while having no provitamin A activity, is a potent antioxidant with twice the activity of b-carotene for quenching singlet oxygen and 10 times the in vitro antioxidant activity of a-tocopherol (DiMascio et al, 1989;Shi & Le Mague, 2000). Epidemiological evidence suggests an inverse association between dietary lycopene and the development of certain types of cancer (Agarwal & Rao, 2000).…”

“…Specifically for lycopene, these factors include: the amount of lycopene consumed, food matrix, dietary fiber and fat, interactions with other carotenoids, and interference with proper micelle formation (Castenmiller & West, 1998;Shi & Le Mague, 2000;van Het Hof et al, 2000;Tanumihardjo, 2002). Studies have indicated that the bioavailability of the cis-isomer of lycopene is greater than the all-trans isomer and heat processing improves bioavailability by increasing the cis-to trans-ratio (Stahl & Sies, 1996;Shi & Le Mague, 2000). Mechanical processing of tomato products, which helps to break down cell walls and release lycopene from the food matrix, also increases bioavailability (Hill & Rogers, 1969;Helzlsouer et al, 1989).…”

Tomato consumption and plasma lycopene concentration in people aged 65 y and over in a British national survey

“…However, the lycopene content of tomato products is highly variable, being affected by factors such as variety (Hart & Scott, 1995;Abushita et al, 2000), ripeness (Fraser et al, 1994), climate and geographical site of production (Scalfi et al, 2000) and processing (Tonucci et al, 1995;Shi & Le Maguer, 2000;Re et al, 2002). For Body mass index (mean, SE) 412 24.8(0.6) 24.2(0.9) 24.8(0.9) 24.5 (0.8) 26.2 (0.9) 26.2 (0.9) 23.3 (1.0) 25.8 (1.2) 0.4 a TCP=tomato-containing products.…”

“…fine chopping) that help to break down the plant matrix (e.g. chloroplasts and chromoplasts) to which lycopene was firmly bound previously (Stahl & Sies, 1992;Shi & Le Maguer, 2000).…”