A study published in Nature Food from the Food Sciences Unit at the University of Turku has shown that different processing methods significantly affect the biochemical compositions of plant-based foods, and that the current food classification system does not sufficiently acknowledge the changes to the biochemical composition of the products.
Not all plant-based products are equal
Science indicates that a largely plant-based diet is beneficial for health, and with population growth and environmental pressures, following a largely plant-based diet should be emphasized. However, not all plant-based products are the same when it comes to healthfulness, and due to processing methods, what a plant product started as turns into something completely different biochemically.
Some plant-based products can be processed in different methods to try and improve nutritional or organoleptic quality. These commercially available products range from whole beans to those that are more processed, to even ultra-processed products, which may only contain small portions of the protein part isolated from the plant.
“Plants and plant-based products are known to contain phytochemicals, which are bioactive compounds that can have health benefits. Phytochemicals are a very large group of different compounds found only in plants, of which there are thousands of different types. On average, we consume 0.5-1 g of phytochemicals per day, depending on our diet. However, until now, there has not been enough research on how different processing methods affect these compounds,” says Professor of Food Development Kati Hanhineva.
Processing methods have significant effects on biochemical composition
Using non-targeted metabolomic techniques, researchers analysed commercially available plant-based products, including those made from fava beans, soy, peas, and wheat, showing that different processing methods have significant effects on the biochemical composition of the products.
Focusing particularly on products prepared using soy-based products and their isoflavonoids or isolates, such as plant-based burgers and steaks, the analysis revealed that these products contained very little isoflavonoids. However, products made using significantly lighter processing techniques, such as tofu and soy chunks, maintained a high level of isoflavonoids from the original soybean.
“Fermentation was highlighted as an important processing method in the results. We found that in tempeh, for example, these isoflavonoids were in a form that is more readily absorbed due to the activity of the microbes used in fermentation,” says Doctoral Researcher Jasmin Raita.
Classification does not adequately indicate food composition
Using existing processing classification systems for the plant-based products in the study revealed that some of the fermented tempeh products fell into the ultra-processed category, which is typically considered harmful, as did products made with extrusion, even though they contained high levels of isoflavonoids.
The researchers noted that the current classification systems are limited when it comes to being applied to plant-based products, and their findings highlight the need for new classification systems to reflect the significant changes caused by different processing methods.
“Processing food is common, and even unprocessed food is often eventually processed at home, for example by cooking. Classification systems primarily take into account the processing technique used for the product and the type and number of added ingredients, rather than the biochemical composition of the product. It cannot be assumed that all processing makes a product unhealthy, because ultimately it is only the nutritional components of the edible product that matter, and how they are absorbed by our bodies. These determine the nutritional value and healthiness of food products,” says University Research Fellow Ville Koistinen.
Future food classification systems should take into account the effects of processing on the biochemical composition of the products to recognize the loss of useful compounds in the processing procedures, along with the value of all added ingredients such as herbs and spices.
Ultra-processed food is unhealthy, even if it is plant-based
According to the researchers, ultra-processed food products are classified as unhealthy and should be avoided; some plant-based foods fall into this category, and they are no exception to this rule. Even if the ultra-processed plant-based food still contains some of the compounds found in the original unprocessed plant part, the overall biochemical composition has been changed, and it should be avoided.
“The phytochemical compounds identified in the study may have health benefits, although they are currently not included in the nutrition labelling of food products. Phytochemicals could also indicate how well the original composition of the plant-based raw material has been preserved. If there are no phytochemicals left in the product, it indicates that the product has undergone heavy industrial processing, after which the biochemical composition is completely different to that of the original plant used as a raw material. This perspective is not fully supported by current food processing classification systems,” says Hanhineva.
“It is also important to note that food processing should not be seen as exclusively harmful, as fermentation, for example, can even improve the nutritional value of a product,” adds Raita.
“Highly processed plant-based protein-rich foods have been on the market for such a short time that it is too early to say anything for certain about the healthiness of all processed plant-based products as a whole, but research on this topic is active. What is known, however, is that in population-based epidemiological studies, all food groups rich in phytochemicals are healthy, while unhealthy food categories typically do not contain them. Therefore, it is justified that the range of phytochemicals should be better recognised in the categorisation of foods,” says Hanhineva.
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