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Food Chemistry in Canned Tomatoes

Author: Asst. Prof. Dr. Nyam Kar Lin (Lecturer, UCSI University)

Canned foods offered an affordable and convenient way to people to get the needed-nutrients. Canning, the process of placing foods in jars or cans and heating properly to a specified temperature, is a way to preserve many different foods. The high heat destroys microorganisms and inactivates enzymes to preserve the safety and quality of the food. We live in a century where the variety of canned food is immense, and we are responsible for what we eat. We decide what we are about to eat and how it will affect our bodies. Canned food provides longer shelf life to food. Most of the canned fruits and vegetables are preservative-free. The canning process (high temperatures and sterile containers) destroys organisms that would cause spoilage. Canned food remains safe as long as the container remain intact. The two main differences of fresh food and canned food are flavour and health benefits. We need to discuss from food chemistry aspect when discuss the flavour and health benefits of canned food. The main components that concern in food chemistry carbohydrates, lipids, and protein, but it also includes areas such as water, vitamins, minerals, enzymes, food additives, flavors, and colors.

It is essential to ones to get balance diet. Most of the people do not have enough vegetable consumption per day. For a person who needs 2,000 calories a day to maintain weight and health, this translates into nine servings or 4½ cups per day (2 cups of fruit and 2½ cups of vegetables). Unfortunately, most people do not have home gardens capable of supplying the recommended 5–13 daily servings year round. Besides that, modern people are too busy to get themselves fresh vegetable. Canned vegetables save food preparation time because they are already being cut, sliced, peeled and pre-cooked, it just requiring reheating. Be sure to avoid overcooking to prevent the escape of water-soluble vitamins – steaming or microwaving is better than boiling for a long time. Lets imaging, coming home after a tough day's work, throwing your briefcase on the chair and opening up canned vegetables to cook in the pan with some other quick-cooking ingredients is just great. Canned vegetables can be a convenient solution if you run out of a vegetable or want to expand a recipe to serve more people. Vegetables and fruit contain essential vitamins, minerals, and fiber that may help protect you from chronic diseases, including stroke and maybe other heart diseases, and some cancers. Many people think that canned foods have too much salt, too many preservatives and poor taste, but canned food can be part of a healthy and tasty diet. Tomato is one of the most common canned vegetable.

Tomatoes are an excellent source of vitamin A, and a good source for vitamin C. Processing tomatoes is considered a “Super Food” because they are nutrient dense. Four ounce tomato supplies about one-third of the recommended daily allowance for vitamin C, plus contains beta-carotene, potassium, folic acid, and other B vitamins, iron, and fiber. Tomatoes are a naturally low-calorie food. Canned tomatoes are usually packed the same day the tomatoes are picked. Because canning factories are only a few miles from the farms where the tomatoes grow, the tomatoes stay on the vine or bush until they are fully ripe, so they do not lose valuable nutrients being moved and stored. However, fresh tomatoes can move as many as few thousand miles to reach the shop where they are sold! To make it through the trip, they must be picked when not yet ripe and not yet at their best nutritionally. While they are in the truck, warm temperatures and storage duration cause them to lose nutrients as well. By the time you buy the vegetables in the grocery store, they are be 10-14 days old and may have lost up to 90% of their nutrients, especially some vitamins such as Vitamin A and Vitamin C. Tomatoes is heated to destroy bacteria and then sealed in cans within hours of harvesting. Washing, peeling, and other steps in the canning process remove almost any pesticide residues left on unprocessed tomatoes. Tomatoes should be consumed immediately after opening it for maximum flavor and nutritional value.

During the canning process, which involves cutting, peeling and quick cooking, tomatoes do lose some nutrients; but once they are canned, the nutrient levels stay the same for at least 2 years. One half cup of canned tomatoes provides 118 mg of lycopene. Lycopene is a type of carotenoids, which found in red fruits, including watermelon, guava, pink grapefruit, and perhaps its most well-known source, tomatoes. Carotenoids are associated with protecting against heart disease, some types of cancer and age-related macular degeneration, according to the Linus Pauling Institute compared to just 3.7 mg found in one medium fresh, uncooked tomato (USDA 2005). Carotenoids help to prevent macular degeneration, an age-related eye disease. Vitamin is required for your hair, skin, fingernails and organs. It has antioxidant qualities that help heal, repair and rejuvenate. Canned tomato cultivars have "significantly higher" amounts of vitamin E and carotenoids compared with the fresh tomatoes that are typically eaten (Joy et al. 2007).

Lycopene in processed tomato is four times more bioavailable than in fresh tomatoes. A study was designed in which tomato and other dietary sources of lycopene were removed from the diets of postmenopausal women for a period of 4 weeks, to see what effect lycopene restriction would have on bone health. At the end of 4 weeks, women in the study started to show increased signs of oxidative stress in their bones and unwanted changes in their bone tissue. The study investigators concluded that removal of lycopene-containing foods (including tomatoes) from the diet was likely to put women at increased risk of osteoporosis. Tomato lycopene (and other tomato antioxidants) may have a unique role to play in this area. Besides this, lycopene is known as a powerful antioxidant that decreases cancer and heart-disease risk. For this reason, canned tomato is a preferable source as opposed to raw tomatoes.

Dietary carbohydrates are an essential part of any person's diet. Carbohydrate provides the body with energy. However, carbohydrate will transform into glucose in our body after the digestion. Therefore, eating too many calories can lead to weight gain. There is 4.8 g carbohydrates in a fresh tomato and about 7.3 g carbohydrates in a 3.5-oz. can of tomatoes. Regular canned tomatoes do not have any additives, but stewed tomatoes sometimes have additives like sugar, which can increase the carbohydrate count even more. One of the main concerns on the canned food is the sodium content. There is only 6 mg of dietary sodium in a medium-sized tomato. Tomatoes are naturally low in sodium. Yet canned foods often use sodium, or salt, as a preservative and flavoring agent. There are 132 mg of sodium in 3.5 oz. of canned tomatoes, and 564 mg of sodium in 1 cup of stewed tomatoes. The maximum sodium limit per day is 1500 mg or less to protect the health.

The resin linings of tin cans contain bisphenol-A, a synthetic estrogen that has been linked to ailments ranging from reproductive problems to heart disease, diabetes, and obesity. Bisphenol-A is an industrial chemical that has been present in many canned goods since the 1960s. It helps to protect the integrity of cans and prevent microbial contamination of food. Unfortunately, acidity (a prominent characteristic of tomatoes) causes BPA to leach into the food. Consumers should choose the tomatoes in glass bottles (which do not need resin linings) to prevent the present of BPA.

While canned foods are usually regarded as less nutritious than fresh or frozen products, research reveals that this is not always true. Over 1,500 food products are available in a canned state, lending convenience and diversity to those with a busy lifestyle. The sodium content in commercially-canned foods has been significantly reduced, up to 40% over old canning methods. Most canned foods are also now available in low-salt, no-salt, low-sugar, and no-sugar preparations for those with special dietary needs and/or those who want a more natural flavor. Fresh and frozen foods are the recommended forms in order to obtain the most nutritional benefit with the least side effects. However, canned foods can be healthful as well, particularly if they create a tendency to include more fruits and vegetables to the dinner plate.

References:
1. US Department of Agriculture, Agriculture Research Service. USDA National Nutrient Database for Standard Reference, Release 18. Nutrient Data Laboratory Homepage. Http://www.ars.usda.gov/ba/bhnrc/ndl. 2005

2. Joy, .R., Diane, M.B., and Christine, M.B., 2007. Nutritional comparison of fresh, frozen, and canned fruits and vegetables. Journal of the Science of Food and Agriculture, 87, 930-944.