Identification and assessment of nutritional relevance of antioxidant compounds from soft fruit species

Transcription

1 UDK: 634.7: riginalan nau~ni rad riginal scientific paper Identification and assessment of nutritional relevance of antioxidant compounds from soft fruit species Derek Stewart Scottish Crop Research Institute, Dundee, Scotland, UK Abstracts: Raspberry, strawberry and black currant exhibit a significant range of antioxidant capacities. ur studies suggest that for the whole fruit phenolic compounds are the determinant factors for antioxidant capacity and that, not surprisingly, the major phenolics compounds vary from species to species. This presents significantly different targets for breeding should antioxidant status be deemed to be a quality trait to aim for. In addition, we have shown that the relative protective effects of vitamin C and phenolics could be separated and compared at least with regard to LDL oxidation and, by inference, the initial stages of atherosclerosis. These initial studies suggest that the chemistries representative of Rubus, here Rubus ideaus, are the most promising target for more detailed in vivo studies. Keywords: Soft fruit species, antioxidants. Introduction Premature deaths in Scotland substantially exceed those in most Western countries with coronary heart disease, strokes and cancers the major causes. Free radicals are implicated in the pathogenesis of these diseases and it s now thought that an insufficient intake of antioxidants is a contributory factor. It is likely that the health of the population would improve if antioxidant status were enhanced by consumption of foods rich in antioxidant nutrients. Potentially important sources of antioxidant-rich food are the locally grown soft fruits; strawberries (Fragaria), raspberries (Rubus) and blackcurrant (Ribes). Isolated studies with compounds derived from these fruit have been shown to exhibit in vitro antioxidant (free radical scavenging) ability and the sparse biomedical studies have focused on inhibiting cancerogenesis and the initiation, and progression, of cardiovascular disease. For example, extracts of strawberries, raspberries and blueberries have been shown to inhibit cancerogenesis in breast Jugosl. vo}ar. Vol. 38. br (2004/1 2),

2 and cervical cell line studies. In addition, specific berry compounds, flavonoids, have been reported to exhibit vasoprotective abilities in animal studies (Trewavas and Stewart, 2003). However, the relevance of these fruit to human nutrition is still not clear and consequently we aim to address this by studying their antioxidant capacities, the derivation of this ability and the associated ability to inhibit the initial stages of atherosclerosis in a model system. Materials and methods Juices were extracted from Rubus ideaus (Glen Ample), Ribes nigrum (Ben Lomond) and Fragaria (Symphony) and filtered. Vitamin C (Vit C) and phenolic contents, and antioxidant capacities were measured as described by Deighton et al. (2000). Ellagitannins were determined as described by Mullen et al., (2002). LDL oxidation experiments were performed as described by Gray et al (2002) using Cu2+ as the oxidant and juices at a dilution in the range 1:1000. xidation was measured spectrophotometrically and experiments were performed in replicates of 5 and the averages presented. The fruit compositional data were measured as described by Kähkönen et al. (2001). Results and discussion Colourometric (FRAP) and spectroscopic (ESR) methods for the assessment of the antioxidant potential of soft fruits were developed, validated and applied to over 100 soft fruit varieties (Graf. 1). verall, blackcurrants had the greatest activity fol- Fe (II) Produced (mm) Fe(II) Dobijeno (mm) Raspberry / Malina Strawberry / Jagoda Black currant /Crna ribizla Sample No. Uzorak broj Grph 1. The antioxidant potential (FRAP) of extracts of selected raspberry, strawberry and black currant varieties Graf. 1. Antioksidantski potencijal (FRAP) u ekstraktima odabranih sorti maline, jagode i crne ribizle 74 Jugosl. vo}ar. Vol. 38. br (2004/1 2), 73 80

3 lowed by strawberries then raspberries. In general, significant varietal variation in the antioxidant potential was confined to blackcurrant although a wild variety of raspberry displayed an antioxidant potential almost double that of any of the cultivated varieties. Vitamin C made varying contributions to the total antioxidant potential; blackcurrant (50%), strawberry (40%) and raspberry (15%). LC/MS analysis indicated that the soft fruit contained several polyphenols including catechins, flavonoids, anthocyanins and ellagitannins, although the latter was largely confined to Rubus (Tab. 1). Anthocyanins accounted for about 20-30% of the antioxidant capacity of the soft fruit whereas the contribution from flavonol/flavanones was minimal (<5%). The contribution from catechins was least in raspberry (5-10%), greater in blackcurrants (25-20%) and greatest in strawberries accounting for 30% of the total antioxidant potential. The relationship between the total phenolic content of the extracts and the antioxidant potential was found to be a direct one (Graph 2) for all methods of measurement (including TEAC, data not shown). This means that phenolic content may be treated as a antioxidant trait and could be a target for enhancement to provide more nutritious fruit The LDL oxidation model is now widely accepted as a simple yet effective way of representing the initial stages of atherosclerosis. Briefly, in vivo circulating LDL is oxidised by the day-to-day processes of, and chemicals in, the body resulting in oxidised LDL which is accumulated by foam cells in the arteries. ver time this leads to a thickening, or hardening, of the arteries; atherosclerosis. The ability to retard this oxidation should reside, at least partially, in the diet and fruit, as shown above, are known to be readily available sources of antioxidants. There were clear differences in the abilities of very dilute (1:1000) extracts of the three fruits at inhibiting the oxidation of LDL (Graph 3). Clearly all the fruit extracts acted as more potent antioxidants than an equivalent amount of vitamin C alone (Graph 3). In addition, species differences were exhibited; Rubus>Fragaria>Ribes>Vit C. It is already known that the three fruit studied here vary in Vit C content (Tab. 1) and this means that extracts diluted to obtain equivalent Vit C levels will have magnified differences with respect to the other components, such as the phenolic compounds. This clearly accounted for the efficacy ranking. However when the experi- Tab. 1. Compositional data for the main antioxidants in raspberry, blackcurrant and strawberry Strukturalni podaci glavnih aktioksidanasa u malini, crnoj ribizli i jagodi Fruit Anth 1 Flav 2 HCA 3 HBA 4 Elllag 5 Phenols 6 Vit C 7 Plod Raspberry Malina Black currant n.d Crna ribizla Strawberry Jagoda 1 7 Anth - anthocyanins, Flav - flavonol, HCA - hydroxyl-cinnamic acids, HBA - hydroxyl benzoic acid; Ellag ellagic acid and ellagitannins. Values are expressed as mg/100 g fresh weight. Jugosl. vo}ar. Vol. 38. br (2004/1 2),

4 Radicals per kg Radikali po kg Fe (II) produced (mm) Fe(II) Dobijeno (mm) 5E+22 4E+22 3E+22 2E+22 1E (a) Total Phenols / Ukupni fenoli (b) Total Phenols / Ukupni fenoli Graph 2. Correlation of total phenol concentration with antioxidant capacity, determined by (a) ESR and (b) FRAP assays Graf. 2. Korelacija ukupne koncentracije fenola i kapaciteta antioksidanasa odre ena po (a) ESR i (b) FRAP metodama LDL xidation (A 234 ) LDL oksidacija (A 234 ) Control (Vitamin C only) Kontrola (samo vitamin C) Ribes Fragaria Rubus Time (mins) / Vreme (mins) Graph 3. Inhibition of LDL oxidation by soft fruit extracts with an equivalent Vitamin C content Graf. 3. Inhibicija LDL oksidacije ekstratima sitnog vo}a sa ekvivalentnim sadr`ajem vitamina C 76 Jugosl. vo}ar. Vol. 38. br (2004/1 2), 73 80

5 LDL xidation (A 234 ) LDL oksidacija (A 234 ) Control (Vitamin C only) Kontrola (samo vitamin C) Fragaria Ribes Rubus Time (mins) / Vreme (mins) Graph 4. Inhibition of LDL oxidation by soft fruit extracts with an equivalent phenolic content Graf. 4. Inhibicija LDL oksidacije ekstraktima sitnog vo}a sa ekvivalentnim sadr`ajem fenola H H Cyanidin-3--sophoroside H + H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H H Sanguiin H-6 Sheme 1. Cyanidin-3--sophoroside and SanguiinH-6 the major anthocyanin and ellagitanin, respectively, in raspberry (Rubus ideaus) [ema 1. Cyanidin 3--sophoroside i samguiin H-6 Glavni antocijanin i eleganin u malini (Rubus ideaus) Jugosl. vo}ar. Vol. 38. br (2004/1 2),

6 ment was repeated, this time on an equivalent phenolic content basis, Rubus again came out as the most potent source of antioxidants, but this time with the relative efficacies of Ribes and Fragaria interchanged (Graph 4); Rubus>Ribes>Fragaria>Vit C. Given that Vit C and phenolics are essentially the only significant sources of antioxidant ability in these fruit the difference must lie with the corresponding chemistries (Tab. 1). It is evident that with Rubus (ideaus) the predominant phenolics are the anthocyanins and ellagitannins (Sheme 1) with the latter largely confined to Rubus. The preponderance of tri-phenolic acid groups (gallate) in ellagitannins ensures their antioxidant ability and almost certainly is the source of raspberry s potent ability to inhibit LDL oxidation. Conclusion Raspberry, strawberry and black currant exhibit a significant range of antioxidant capacities. ur studies suggest that for the whole fruit phenolic compounds are the determinant factors for antioxidant capacity and that, not surprisingly, the major phenolics compounds vary from species to species. This presents significantly different targets for breeding should antioxidant status be deemed to be a quality trait to aim for. In addition, we have shown that the relative protective effects of vitamin C and phenolics could be separated and compared at least with regard to LDL oxidation and, by inference, the initial stages of atherosclerosis. These initial studies suggest that the chemistries representative of Rubus, here Rubus ideaus, are the most promising target for more detailed in vivo studies. Acknowledgement The author acknowledge funding by the Scottish Executive Rural Affairs Department. 78 Jugosl. vo}ar. Vol. 38. br (2004/1 2), 73 80

7 References Deighton, N., Brennan, R., Finn, C., Davies, H.V. (2000): Antioxidant properties of domesticated and wild Rubus species. J. Sci. Food Agric., 80: Gray, D.A., Clarke, M.J., Baux, C., Bunting, J.P., Salter, A. (2002): Antioxidant Activity of at Extracts added to Human LDL Particles and in Free Radical Trapping Assays. J. Cereal Sci., 36: Khkönen, M.P., Hopia, A.I., Heinonen, M. (2001): Berry Phenolics and Their Antioxidant Activity. J. Agric. Food Chem., 49: Mullen, W., Stewart, A.J., Lean, M.J., Garner, P., Duthie, G.D., Crozier, A. (2002): Effect of freezing and storage on the phenolics, ellagitannins, flavonoids and antioxidant capacity of red raspberries. J. Agric. Food Chem., 50: Trewavas, A., Stewart, D. (2003): Paradoxical effects of chemicals in the diet on health. Curr. pinion Plant Biol., 6:1-6. Primljeno: Prihva}eno: Jugosl. vo}ar. Vol. 38. br (2004/1 2),

8 IDENTIFIKACIJA I CENA NUTRICINE VA@NSTI ANTIKSIDANTSKIH JEDINJENJA IZ SITNG V]A Derek Stewart Škotski institut za biljna istra`ivanja, [kotska, UK Rezime Dijete koje podrazumevaju obilje vo}a i povr}a štite od mnogih bolesti, naro~ito od kardiovaskularnih oboljenja i epitelijalnih malignih oboljenja (izuzev onih povezanih sa hormonima). Jedna od osnovnih komponenti za koje se smatra da pru`a pomenutu zaštitu su antioksidansi. To su jedinjenja koja uklanjaju slobodne radikale stvorene tokom oksidacije i time umanjuju ošte}enja. Poznato je da je sitno vo}e, poput crne ribizle, maline, jagode bogato antioksidansima. Cilj rada je odre ivanje potencijala antioksidanasa upotrebom divljih i gajenih sorti pomenutog vo}a, i kona~no, ustanovljavanje da li je antioksidantski potencijal sam po sebi nasledna osobina koja se mo`e mapirati i koristiti kao marker u oplemenjivanju. Author's address: Dr Derek Stewart Scottish Crop Research Institute Dundee DD2 5DA, Scotland The United Kingdom 80 Jugosl. vo}ar. Vol. 38. br (2004/1 2), 73 80