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News

China: processing tomatoes with less waste

05/07/2024 - François-Xavier Branthôme
New processing methods developed by scientists in China could make the common tomato even more accessible and nutritious.

Public health campaigns around the world exhort people to eat more fruit and vegetables. With good reason. An estimated 3.9 million deaths worldwide were linked to inadequate fruit and vegetable consumption in 2017 alone, according to the World Health Organization.
Food scientist Xiaojun Liao and student Huanzhi Yang of China Agricultural University.

Incorporating fruit and vegetables into daily diets may seem like an easy way to reduce the risk of diseases, such as cancer and cardiovascular disorders. But encouraging greater consumption of fruits and vegetables, while minimizing the environmental impact of producing them is challenging.

To help tackle this problem, a team led by Xiaojun Liao, a professor of food science at China Agricultural University in Beijing, has developed a series of novel processing techniques to make tomatoes even more nutritious and accessible.

Green tomatoes
The team has also developed techniques to reduce the energy costs of processing fruits and vegetables, as well as methods to make use of as much of the produce as possible to minimize waste.
We can produce food that is both beneficial to health, and helps meet global demands for nutritious food, while reducing the burden on the environment,” says Liao. “To do this, we need to introduce green processing technologies, which involve comprehensive use of by-products and reduced food loss.”

Aside from the red varieties stocked in grocery aisles, tomatoes come in other vibrant hues ranging from green to purple. These colours come mainly from carotenoids, pigments that are also potent antioxidant compounds that could play a role in preventing disease. Tomatoes are a particularly rich source of lycopene, a fat-soluble carotenoid that could help to regulate lipid metabolism and reduce the risk of diabetes and stroke. “This makes tomatoes a useful starting point as a functional food,” says Liao. Functional foods provide additional health benefits beyond meeting basic nutritional needs.

For all the benefits of eating plenty of tomatoes, making them widely accessible to consumers is tricky. Their high water content and thin skins make them susceptible to damage during picking, sorting and transportation, Liao explains, resulting in the loss of 10-20% of harvests. Their high respiration rate and release of ethylene gas, a potent plant hormone, means that they must be stored at low temperatures to prevent premature ripening. However, not at temperatures below 7°C, which can spoil them. This narrow temperature window means that a specialized cold chain transport is required over long distances, increasing costs and energy consumption.

Processing power
One solution is to turn fragile fresh tomatoes into everything from canned products to juices and purees near to the source of their harvesting. Although the consumption of ultra-processed food has been linked to disease, lightly processed fruits and vegetables could be part of the answer to improving human health without damaging planetary health.

Mechanical tomato picking in northwest China. Tomatoes are a valuable food source, being rich in antioxidant compounds, but they are susceptible to damage during picking and processing.

Food processing is crucial for more people to have access to healthy food,” Liao says. “Techniques such as freezing, heat treatment, drying and packaging not only prolong shelf life and help reduce food waste, but ensure food safety by reducing contamination with harmful substances such as mycotoxins,” which are toxic compounds that are produced by moulds in poorly stored foods, he adds.

Heat is commonly used to kill bacteria and to inactivate enzymes that would otherwise spoil processed tomatoes. But even a brief exposure to heat — 110°C for 9 seconds — is enough to lower total lycopene levels in tomato juice by about 8% compared to fresh juice, Liao and his team have found.

When high hydrostatic pressure (HHP) during processing is used to kill bacteria instead, lycopene and total carotenoid levels are not reduced compared to fresh juice, the study found. The team’s metabolomic approach used ultra-performance liquid chromatography-mass spectrometry to analyze 425 metabolites, 14 carotenoids and 56 volatile compounds. It found that HHP preserved ascorbic acid, amino acid derivatives, and alcohols, as well as lycopene. This helps tomato juice to retain its nutritional profile, taste and colour, says Liao.

Energy saver
Liao also has an eye towards the sustainability of the wider industry that is still using traditional processing.

For example, the Liao team have shown that during cold crushing, which is often used to produce tomato juices, reducing temperatures from 65–75°C to 10–55°C saves energy and also inhibits enzymatic and thermal degradation of tomato pectin, a source of natural dietary fibre, explains Liao. A similar effect is seen when the temperatures for ‘hot chopping’, used to produce sauces and pastes, are reduced from 100–105°C to 80–90°C. The reduction in temperatures, which has been taken up by industry, also increases sauce viscosity by 38%, says Liao.
Tomato cleaning prior to processing at the COFCO Tunhe Tomato Co., Ltd.

The team has also developed a fast-drying method that extracts more than 85% of the lycopene in tomatoes. “We are pioneers in the highly efficient extraction of lycopene from tomato skins, reducing solvent residues while improving product purity,” says Liao.

New ways to process the end-product — crystals that are 90% lycopene — have been developed to produce capsules, powders, drinks and food colorants. “By adopting microencapsulation and emulsification technology, we have created new high value products of stabilized and water-soluble lycopene, expanding the scope of applications,” says Liao.

While Liao’s processing techniques were first developed for tomatoes, they are now being used to reduce waste while processing other fruits and vegetables. For example, his team’s highly efficient methods are used commercially to extract capsanthin, capsaicin, and capsicum oleoresin, which are used as natural coloring and flavoring agents.

The average daily intake of vegetables in China is 250g, far below the 300–500g recommended in our dietary guidelines,” Liao says. “In the future, we will focus on developing tomato products with better flavour and texture, such as probiotic-fermented juice, freeze-dried tomato cubes and other snack foods.” Liao points out that Chinese eating habits are changing with a shift towards convenience foods. “We will also expand into fresh tomato products, such as juice and tomato chunks,” he says. “Our goal is to improve intake of vegetables.”

Source: nature.com
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