Diamonds among leaves

• Quince is a low-maintenance plant, yet rich in bioactive compounds, and has a high processing potential
• Research by UPWr scientists has shown that the phenolic compounds contained in quince leaves have antioxidant, anti-inflammatory and anti-hypertensive properties, and also help prevent obesity
• The market for nutraceuticals, supplements and functional food is growing rapidly. This is both a challenge and an opportunity to disseminate products with health-promoting properties to consumers

One such plant rich in bioactive compounds is quince, to which Igor Turkevich devoted four years of his doctoral studies: he studied its fruit, seeds and leaves with regard to their content of health-promoting compounds. He wrote about the impact of his leaf analyses in the article 'UPLC/ESI-Q-TOF-MS analysis of (poly)phenols, tocols and amino acids in Chaenomeles leaves versus in vitro anti-enzyme activities', which appeared in the Elsevier 'Industrial Crops and Products' journal. – I consulted the idea and concept of the research with my supervisor, Professor Aneta Wojdyło, while Paulina Nowicka and Karolina Tkacz also worked on the analyses and preparation of the manuscript for publication – adds the lead author.

Liqueurs and preserves

This short shrub can often be found in parks and residential gardens. In its natural state, quince grows in East Asia, including China and Japan; it also copes well with the climatic conditions in the Baltic countries and is grown, among others, in Lithuania, Latvia, Estonia and Ukraine. There are several known species of quince (Chaenomeles ssp.), but in Poland mostly three are cultivated: the Chinese quince (Chaenomeles speciosa), the Japanese quince (Chaenomeles japonica) and a hybrid of the two (Chaenomeles × superba). It is not very demanding: it can grow in any soil, although it produces better yields on sandy loam soils that are fairly moist, rich in humus and slightly acidic. It prefers sunny, warm and secluded locations, protected from the wind. Diseases and pests are not a threat, so it does not require chemical treatment and is suitable for organic farming.

Gardeners value it for its abundant reddish-maroon flowers and spiky stems that form hardy hedges, while foodies appreciate its fruit, which although too hard and sour to be eaten raw, is perfect for making quince cordial and preserves, as well as for scenting rooms. Of interest to scientists are both the small yellow fruits and the dark green serrated leaves.

– Quince fruit is an example of a raw material with great processing potential, but its high organic acid content makes it unsuitable for direct consumption and limits its use in the food industry – says the author. In earlier studies, he carried out a detailed analysis of the chemical composition and biological potential of fruits of 19 quince varieties. They were found to be low in sugar, but rich in organic acids, especially malic acid and L-ascorbic acid, as well as carotenoids, chlorophylls, phenolic compounds, tocopherols and tocotrienols. The fruits analysed showed antidiabetic and anti-inflammatory activity and can also be used in obesity prevention, due to their potent pancreatic lipase inhibition.

– At the next stage we took a closer look at the leaves, as they had not been analysed in detail before, especially across such a wide spectrum of species and varieties. There are many reports on the chemical composition and biological properties of the leaves of commonly grown plants such as lemons, tangerines, apples, pears and bananas. However, only a few studies have looked at the composition and health-promoting properties of the compounds contained in the leaves of Chaenomeles – adds the scientist.

Hope for diabetics

The leaves of selected species belonging to three cultivars: Chinese quince (Nivalis, Simonii, Rubra), Japanese quince (Cameo, Cido, Red Joy) and hybrid quince (Andenken ans Karl Ramcke, Colour Trail, Crimson and Gold, Nicoline, Pink Lady, Texas Scarlet) were used for the study, which was conducted from June 2020 to September 2021 in the Department of Fruit, Vegetable and Plant Nutraceutical Technology.

Samples were subjected to ultrasound-assisted extraction, followed by analysis using high-performance liquid chromatography conjugated to a high-resolution mass detector. Enzymatic in vitro tests using spectrophotometric methods were used to assess the anti-diabetic and anti-obesity properties.

Karolina Tkacz, the co-author of the research and publications: – We identified 39 phenolic compounds, with the highest amount in the Nicoline variety and the lowest in Colour Trail. These include polymers and monomers of flavanols, phenolic acids, flavanones and flavones. The results of our research indicate a wide range of biological activities of these compounds, including antioxidant, anti-inflammatory, anti-hypertensive and anti-obesity activities. Quercetin and isoramnetin derivatives are highly active compounds in improving cognitive functions and slowing neurodegenerative changes, while flavonol monomers and polymers are effective in inhibiting the activity of α-glucosidase and α-amylase enzymes, and can therefore be a dietary supplement for the treatment of type 2 diabetes.

The analysed leaves contained tocopherols and tocotrienols, as well as 23 amino acids, including all the nine essential amino acids. Endogenous amino acids can be synthesised by the human body on its own, whereas exogenous amino acids are not produced by humans or are insufficient in quantity and therefore require supplementation. These compounds affect the proper functioning of the nervous system, the proper functioning of muscles, and they regulate the metabolism by participating in the formation of hormones. BCAAs are among the essential amino acids identified in quince leaves, and are particularly recommended for people who regularly engage in sport. Their supplementation alleviates unpleasant post-workout conditions, including muscle soreness, increases strength endurance, improves and accelerates the regeneration and recovery processes of muscle tissue. The compounds found in the leaves also have the ability to inhibit the enzymes α-amylase, α-glucosidase and pancreatic lipase.

– In the leaves of the Andenken Karl Ramcke, Nicoline, Pink Lady and Texas Scarlet varieties we obtained stronger inhibition of α-glucosidase than acarbose, which is used in the treatment of type 2 diabetes. Inhibition of this enzyme is crucial for people struggling with impaired sugar metabolism. On the other hand, α-amylase and α-glucosidase are responsible for breaking down polysaccharides, e.g. starch into disaccharides and simple sugars. The inhibition of these enzymes reduces the increase in postprandial glycaemia and therefore improves the carbohydrate metabolism in the body – adds Igor.

Viburnum, hawthorn, rosehip

According to scientists, quince leaves can be treated as a source of natural extracts rich in polyphenols, vitamin E and amino acids, for use in dietary supplements.

– The market for nutraceuticals, supplements and functional food is developing intensively. Scientists are still searching for good sources of them, and in line with the zero waste concept there is a global trend to use what seems useless, such as pomace, seeds or leaves. We are trying to 'squeeze' as much as we can out of plants; hence our research into quince from various angles. Its leaves proved to be rich in health-promoting compounds that could benefit human health, but this still needs to be verified at the level of in vivo research – says Dr. Paulina Nowicka from the Department of Fruit, Vegetable and Plant Nutraceutical Technology at the UPWr, who assisted Igor and Karolina in analysing quince's health-promoting properties.

Professor Wojdyło adds that not only is the financial value of the market increasing, but the volume of functional products has been growing strongly in recent years. - Also domestic companies, such as Maspex, with branches in Tymbark or Olsztynek, are becoming interested in functional food. While carrying out NCRD-funded projects together with them, we repeatedly developed food with health-promoting properties, particularly taking into account the prevention of diseases of civilisation. In an ongoing project we are also researching the use of apples, including red-fleshed apples and quince; we expect such projects to later be implemented. Igor's knowledge and experience from his doctorate on quince fruit is invaluable here - adds Prof. Wojdyło.

– You can isolate the desired ingredients from almost any plant and use it to develop a supplement. In my opinion nutraceuticals seem to have more potential, as the plant simply needs to be dried, crushed and formed into a capsule. Of course, you have to bear in mind cultivation, factors that could result in the accumulation of harmful and poisonous substances and anti-nutritional components. For example, quince seeds have compounds with health-promoting properties, but at the same time contain cyanogenic amygdalin – adds Igor Turkiewicz.

Everyone agrees that there has been a growing interest in lesser-known or somewhat forgotten plants over the past 20 years, with viburnum, hawthorn, rosehip, elderberry, scorzonera and parsnip all making a comeback. We frequently show interest in actinidia, Kamchatka berry, shadbush, blackthorn, rowan, cloudberry, dogwood or barberry. Sea buckthorns, which were the focus of Karolina Tkacz's doctorate, are also becoming an object of considerable attention.

– Consumers are reluctant to use sea buckthorn because of its intense acidity, astringency, pungent berry flavour and lumpy juice consistency, so we have changed its sensory qualities, but without compromising its high health-promoting potential. To achieve this we used a method of bioprocessing the juice through malolactic fermentation to reduce acidity, blending sea buckthorn fruit with other raw materials and microencapsulating the juice to increase the stability of bioactive compounds. The results of this research may contribute to spreading awareness of the plant in Poland and increasing its consumption, including in the prevention of chronic non-communicable diseases – says Karolina Tkacz.

– These are our diamonds, enthusiasts with similar interests. Already during their engineering and master's studies were they very perceptive, real group leaders. They were also strongly involved in the 'Fructus' Students' Society, of which I am the supervisor – says Paulina Nowicka about Karolina and Igor. – I'm glad they decided to pursue their doctoral studies, and I hope they will stay at the university, because they provide us with a lot of support. Together with Prof. Wojdylo, we provide them with methodical support and recommend solutions.

Professor Wojdyło: – I met Karolina and Igor when they were in the third year of their studies, when we cooperated in the research for their master's thesis. We then started talking about their doctoral studies, which allowed us to plan our thesis research accordingly and, more importantly, apply for the Diamond Grant, a Ministry of Science and Higher Education project for active students who want to carry out research. Both projects were the basis for their doctoral thesis research, which is why we call them 'diamonds'. They made the most of their doctoral studies, carrying out research, self-educating, developing their scientific passions and establishing contacts with scientists, among others from Spain, the USA and Portugal. We were able to agree on an important point with them: we shall not keep the results hidden in a drawer, but publicise them. This paid off, helping them gain recognition in the community, and obtain, among others, the Bekker scholarship from NAWA, a scholarship from the Minister of Science, the Wrocław 'Young Scientist Award' in the category of scientist, Karolina's current START FNP scholarship and funding from the National Science Centre for her next research project. Just as at a jeweller's, when a rough diamond has been polished and cut, in science such committed people are worth investing in. I am pleased that there are more and more young people who are active at different stages of their careers at our university.

As part of the 7th edition of the Diamond Grant programme, Igor obtained funding for his research 'Potential use of quince fruit (Chaenomeles ssp.) in obtaining innovative products with programmed health-promoting properties'. Initially, only quince fruit was to be covered, but during the course of the project, together with his supervisor Prof. Aneta Wojdyło, he decided to extend the scope of research to also cover the analysis of seeds and leaves.

– I have developed optimisation of the parameters for drying and osmotic dehydration of the fruit and microencapsulation of quince juice and polyphenol concentrate, which will be the subject of my doctoral thesis – he says. He has no plans for further research in this field, but has some ideas for further research into plant dyes. – I don't want to give away the details, although I will definitely look into nutraceuticals.

– Plant raw materials have enormous potential, sometimes even surprisingly high – admits Prof. Aneta Wojdyło, head of the NSC project 'Fruit tree leaves as a donor of natural bioactive substances in the context of preventive strategies for selected diseases and conditions of civilisation', in which the leaves of apple, pear, quince, apricot, peach, plum and cherry trees are being studied. Their active substances proved to be effective in neutralising free radicals, with significant antioxidant, antimicrobial, anti-inflammatory and anti-obesity potential, and they are also highly active in slowing down neurodegenerative changes, sometimes more than fruit.

– The development of functional products enriched with bioactive compounds isolated from fruit tree leaves, including polyphenolic compounds and chlorophylls, is still to come. I am already thinking about my next project using another unconventional source of bioactive compounds, which might also receive funding. The use of fruit leaves as an unconventional source of bioactive compounds is a topic increasingly being explored by many scientists in their research and publications, and we are actively contributing to it – adds the Professor.