Anti Cancer Potential of Asian Brassicas

Anti-cancer Potential of Asian Brassicas

RIRDC Project No DAQ-307A, June 2004 Dr Tim O’Hare Queensland Department of Primary Industries and Fisheries,

Queensland Horticulture Institute, Gatton Research Station

 

Objectives

  •  Identification of key crucifer species which could form the basis of industry sales on health rather than culinary issues, similar to broccoli sprouts in the USA. Identification and quantification of demonstrated anti-cancer glucosinolates in Asian crucifers. Provision of advice or recommendations on a pathway for addressing the regulatory issues relating to anti-cancer claims.
  • The research has an aim to promote the consumption of Asian vegetables by broadening the consumer base through sales to people who would not have purchased Asian vegetables on a culinary basis (ie. flavour). A second and underlying issue is to identify products that will reduce the incidence of internal cancers in the Australian community.

 

Current Progress (June 2004)

An accurate and replicable HPLC procedure has been optimised for the identification and quantification of glucosinolates in seed material, and is being presently optimised for sprouts and mature tissue. To date, 25 crop species have been analysed for glucosinolate composition, identifying a total of 21 glucosinolates present in significant quantity.

 

The number of glucosinolates identified in each species was variable (1- 10), with a median value of 4. Glucosinolates included 10 alkylthioalkyl-, 6 olefin-, 3 aryl-, and 2 indole-glucosinolates. The anti-cancer potential of each of these compounds (based on the concentration of a compound required to double the quinone reductase specific activity in Hepa 1c1c7 murine hepatoma cells) has been determined from the scientific literature. Species investigated included 12 east-Asian species, 2 west-Asian species, 9 European/Mediterranean species, and 2 American species.

 

 

Anti-cancer Potential of Asian Brassicas

RIRDC Project No DAQ-307A, June 2005 Dr Tim O’Hare Queensland Department of Primary Industries and Fisheries,

Queensland Horticulture Institute, Gatton Research Station

 

Objectives

  • Identification of key crucifer species which could form the basis of industry sales on health rather than culinary issues, similar to broccoli sprouts in the USA. Identification and quantification of demonstrated anti-cancer glucosinolates in Asian crucifers. Provision of advice or recommendations on a pathway for addressing the regulatory issues relating to anti-cancer claims.
  • The research has an aim to promote the consumption of Asian vegetables by broadening the consumer base through sales to people who would not have purchased Asian vegetables on a culinary basis (ie. flavour). A second and underlying issue is to identify products that will reduce the incidence of internal cancers in the Australian community.

Current Progress (June 2005)

Horticultural members of the Brassicaceae (apart from broccoli) that appear most promising anti-cancer potential include radish, daikon, rocket, kale and kohl rabi. Glucosinolate levels are generally highest in seed and sprouted-seed, and lowest in mature vegetables.

 

We are currently assessing effect of sprout age and growing temperature on glucosinolate concentration in daikon and radish, and also the effect of refrigeration on glucosinolate stability. Ideally, we would like to test the anti-cancer potential of candidate species using a quinine reductase assay, but this is dependent on access and availability.

 

We presented/published our preliminary results with seed at the AuSHS Conference held at Coolum in August 2004. We submitted an update article in Jan 2005 regarding our work with sprouts to the Asian Foods Newsletter (published monthly), following on from an earlier article in October 2003. We plan to present further work at the Australasian Postharvest Conference in Sept 2005.

Anti-cancer Potential of Asian Brassicas – Glucosinolates and Chemoprevention

2005  Rural Industries Research and Development Corporation

RIRDC Publication No 05/ Project Number DAQ-307A

O’Hare, T.  DPI&F, Gatton Research Station, LMB 7, MS437, Gatton Qld 4343

The aim of the current project was to investigate the anti-cancer potential of a range of Asian vegetables belonging to the brassica family.  There is increasing evidence that glucosinolates, or more specifically their isothiocyanate hydrolysis products are associated with a lower incidence of certain cancers, particularly those of the gastrointestinal tract (eg. colorectal cancer).

Glucosinolates, of which there are over 120 types, are almost exclusively found in members of the brassica family (or Brassicaceae).  Asian vegetables represent a large number of horticultural brassicaceous species, and therefore hold particular potential as anti-cancer vehicles.  Examples include both members of the Brassica genus (pak choy, tatsoi, choy sum, Chinese broccoli, Chinese mustard, komatsuna, mizuna, Japanese turnip) as well as rocket (Eruca), daikon (Raphanus) and wasabi (Wasabia).

Over the last 10-15 years, considerable research has been conducted in relation to the anti-cancer potential of broccoli.  From a range of mature vegetables, broccoli appeared to be one of the best inducers of mammalian detoxification enzymes, also known as phase 2 enzymes.  Phase 2 enzymes act by binding with or inactivating certain carcinogens, making them more readily excretable from the body.  The current project optimised an HPLC technique for extraction and identification of glucosinolates, followed by identification of 25 glucosinolates in significant amounts.  Identification was tentatively based on compound molecular weight and published scientific literature, and in the case of 11 glucosinolates, confirmed with standards.

It has been already established that different glucosinolates vary in the ability to induce phase 2 enzymes, with the potency of a glucosinolate gauged by its in vitroability to induce quinone reductase.  Using this information and the concentration of glucosinolates present in various plant tissues, we were able to calculate an anti-cancer index, by which we could estimate the relative potential of different species to induce phase 2 enzymes.  Seeds are by far the most concentrated source of glucosinolates, although the presence of erucic acid in brassicaceous seeds has potential health issues in regard to cardiovascular disease.  On the other hand, mature vegetables (which vary greatly in form) tended to have mainly low levels of glucosinolates, increasing the amount required to be consumed to have a chemopreventive effect. Sprouts by comparison have a high level of glucosinolates (however lower than seeds), but the level of erucic acid is negligible making them a good candidate as an anti-cancer product.

Sprouts which had the highest anti-cancer potential included daikon, radish, broccoli, rocket, kohl rabi, wasabi, kale, garden cress, and Chinese broccoli.  This varied slightly with mature vegetables, as the plant part varied, as did the mature glucosinolate profiles.  Mature vegetables with highest anti-cancer potential included rocket, broccoli, daikon and wasabi.

A complicating issue affecting anti-cancer potential was the question as to how much glucosinolate present in plants gets converted to anti-cancer isothiocyanates when it is eaten.  Unfortunately, cooking is often an effective way of stopping conversion, because the enzymes responsible for conversion is inactivated by heat.  Most of the sprouts studied in the current project would be eaten raw though, so this is less of an issue than for mature vegetables such as broccoli.  Many brassicaceous species however have a secondary issue relating to the conversion of glucosinolates to nitriles, rather than isothiocyanates.  The compound responsible for this is known as epithiospecifier protein (ESP), which can reduce anti-cancer potential by 50-80%.  Fortunately, ESP is not present in all species, including radish and daikon sprouts.  In a closer examination of daikon sprouts, sprout growth stage was found to significantly influence glucosinolate level, with younger sprouts being the most potent.  Growing temperature was found to have less impact on glucosinolate profile, although this varied between cultivar.

As sprouts are normally purchased and then stored in a domestic refrigerator, the impact of low temperature on glucosinolate levels for a range of sprouts was examined.  In most cases, glucosinolate levels remained stable at 4°C for up to 4 weeks, although glucosinolate levels in rocket sprouts declined significantly after one week.

Issues other than anti-cancer potential were also investigated in relation to commercially growing and marketing different species of sprouts.  Important issues included public awareness of a species (how many people are familiar with kohl rabi), seed price and availability, flavour, and growing characteristics.  Of the sprouts identified, the two most promising species were daikon (radish) sprouts and broccoli sprouts, the latter of which is not an ‘Asian’ vegetable.  Daikon sprouts (which are a form of radish sprouts) are presently on the market and are actually sold as ‘radish’ sprouts.

The final issue addressed by the current project was regulatory restrictions in regard to what can be claimed on food labelling in regard to health.  Although the regulatory standard is currently under review, producers are likely to be restricted to content claims.  Producers can say that a product is a natural source of glucosinolates, and then list the amount present on a nutrient content label, but they will not be able to say a product is a ‘good’ source of glucosinolates.  This is because the exact amount of glucosinolate required for a physiological effect has not been unequivocally established. Similarly, claims relating to reducing cancer risk are not yet able to be made on food labelling in Australia.

This report, an addition to RIRDC’s diverse range of over 1200 research publications, forms part of our Asian Foods R&D program, which aims to foster the development of a viable Asian Foods industry in Australia.

 

 

Anti-cancer Potential of Asian Brassicas

RIRDC Project No DAQ-307A, June 2006 Dr Tim O’Hare Queensland Department of Primary Industries and Fisheries,

Queensland Horticulture Institute, Gatton Research Station

Objectives

  •   Identification of key crucifer species which could form the basis of industry sales on health rather than culinary issues, similar to broccoli sprouts in the USA.

  •   Identification and quantification of demonstrated anti-cancer glucosinolates in Asian crucifers.

  •   Provision of advice or recommendations on a pathway for addressing the regulatory issues relating to anti-cancer claims.

  •   The research has an aim to promote the consumption of Asian vegetables by broadening the consumer base through sales to people who would not have purchased Asian vegetables on a culinary basis (ie. flavour). A second and underlying issue is to identify products that will reduce the incidence of internal cancers in the Australian community.

Current Progress (June 2006)

Analysis of glucosinolate profiles of horticultural members of the

Brassicaceae was expanded, with the acquisition of wasabi (seed and seed-sprouts), an important Asian species particularly in Japan. Studies on refrigeration of sprouts from broccoli, white radish, kohl rabi and rocket, indicated stability of glucosinolate profiles for at least 21 days in all species except rocket. The effect of growing temperature, sprout developmental stage and cultivar was assessed for white radish sprouts.

All factors significantly affected glucosinolate composition and could be used to optimize glucosinolate yield and anti-cancer potency. Further study into cultivar variability in glucosinolate composition has been initiated. Further study into the role of proteins inhibiting conversion of glucosinolates to their anti-cancer derivatives is underway.

We presented our results in 2 oral presentations at the biennial Australasian Postharvest Horticulture Conference (October 2005), one oral presentation at the First International Symposium on Human Health – Effect of Fruits and Vegetables (August 2005), and one poster presentation at the 5th Annual Health and Medical Research Conference of Queensland (November, 2005).

Anti-cancer Potential of Asian Brassicas

RIRDC Project No DAQ-307A, June 2007, Dr Tim O’Hare Queensland Department of Primary Industries and Fisheries,

Queensland Horticulture Institute, Gatton Research Station

Objectives

To establish anti-cancer potential of Asian horticultural brassicaceous species (based on glucosinolate profile and potential ability to induce phase 2 detoxification enzymes) which could provide the basis of industry sales on health in addition to culinary issues (ie. flavour),

Background

Consumption of brassica vegetables has been linked to reduced incidence of certain cancers. Part of this has been attributed to the presence of glucosinolates that are found almost exclusively in the brassica family. There is increasing public interest in maintenance of health, and diet plays a major role in this area. Asian vegetables constitute a significant number of horticultural brassica species which could contribute to health maintenance. The emergence of a broccoli sprout industry in the

United States based on health rather than culinary characteristics has shown that industry expansion may be achieved in this area.

Research

Asian vegetable species belonging to the brassica family were assessed for glucosinolate composition and concentrations in seed, sprouts and mature vegetables and subsequent anti-cancer potential estimated. Promising species were tested for glucosinolate stability during domestic refrigeration. Effect of growing temperature, physiological stage of development, and cultivar effect were evaluated. Industry assessment of different species was conducted. Advice surrounding regulatory issues and health claims is provided.

Outcomes

In general, sprouted seed had higher levels of glucosinolates than mature vegetables and consequently had greater anti-cancer potential. Asian vegetable spouts with most potential included daikon (radish), rocket and wasabi, along with ‘Western’ sprouts of broccoli, kohl rabi and kale. Most promising mature vegetables were rocket, daikon and wasabi. Daikon (radish) sprouts appeared to be the most marketable species based on consumer awareness, availability of seed, flavour, and growth habit. Current food regulations permit labelling terms such as ‘source of glucosinolate’, but not ‘rich source of glucosinolate’. Reference to a reduction in cancer incidence is not currently permitted.

Implications

The most promising Asian vegetable in regard to anti-cancer potential is daikon (radish) sprouts. It is possible that they may have up to five times the potency of broccoli sprouts, which are currently marketed on perceived health benefits. Current regulations permit content claims, but not direct health claims, so consumer awareness at this stage will depend on general media

 

Publications

  • O’Hare, TJ, Wong LS and Irving DE, 2005. Asian and Western horticultural species of the brassica family with anti-cancer potential. Acta Horticulturae, 694: 457-462.
  • O’Hare, TJ, Wong LS, Force LE and Irving DE, 2008. Glucosinolate Composition and Anti-cancer Potential of Seed-sprouts from Horticultural Members of the Brassicaceae. Acta Horticulturae (in press).
  • O’Hare, TJ, Wong LS, Force LE and Irving DE, 2005. Glucosinolate Composition and Anti-cancer Potential of Seed-sprouts from Horticultural Members of the Brassicaceae. 5th Annual Health and Medical Research Conference of Queensland (abstract).
  • Force LE, O’Hare, TJ, Wong LS and Irving, DE, 2007. Impact of cold storage on glucosinolate levels in seed-sprouts of broccoli, rocket, white radish and kohl-rabi. Postharvest Biology and Technology, 44: 175-178.

 

Daikon, a promising anti-cancer vegetable

RIRDC Project No DAQ-342A, June 2007,  Dr Tim O’Hare Queensland Department of Primary Industries and Fisheries,

Queensland Horticulture Institute, Gatton Research Station

 

Objectives

Identify daikon and radish varieties with highest anti-cancer activity, following on from DAQ-307A which identified daikon and radish sprouts as having extremely high anti-cancer potential. Provide labelling advice in relation to the strongest possible claims that can be made.

 

Current Progress (June 2007)

Daikon and radish were analysed at the seed and sprouted-seed stage to identify cultivars high in the anti-cancer glucosinolate, glucoraphenin. Of the cultivars tested, ‘Cherry Belle’ and ‘Black Spanish’ maintained highest levels of glucoraphenin. Levels were highest in seed, and decreased with increasing sprout age. Decline in concentration was largely due to dilution associated with cell expansion, and partly due to other mechanisms. Differences in the latter appear to have impact on anti-cancer potential.

 

Analysis of mature daikon and radish tissue (roots and shoots) indicated that the principal glucosinolate in roots of all cultivars was glucodehydroerucin, which is estimated to have one tenth the potency of glucoraphenin, the principal glucosinolate found in seeds and young sprouts. By contrast, the principal glucosinolates present in mature shoots were glucoraphanin and glucoraphenin, both potent anti-cancer agents. Shoots were estimated to have approximately 20 times the anti-cancer potential of roots.

 

A scientific paper was presented at the International Horticultural Congress in Seoul (Korea) in August 2006 entitled: “Glucosinolate Composition and Anti-Cancer Potential of Daikon and Radish sprouts”. A poster presentation was made at the 6th Annual Health and Medical Research Conference of Queensland

(November, 2006).

 

 

Glucosinolate Compostition and Anti-Cancer Potential of Daikon and Radish Sprouts

ISHS Acta Horticulturae 765: XXVII International Horticultural Congress – IHC2006: International Symposium on Plants as Food and Medicine: The Utilization and Development of Horticultural Plants for Human Health

T.J. O’Hare, L.S. Wong, L.E. Force, C.B. Gurung, D.E. Irving, D.J. Williams

 

Abstract:
Daikon and radish sprouts contain high levels of glucoraphenin, a glucosinolate which hydrolyses to form sulphoraphene. Sulphoraphene, like sulphoraphane from broccoli, is a potent inducer of phase 2 detoxification enzymes and consequently has potential anti-cancer action. Unlike broccoli however, daikon and radish do not possess epithiospecifier protein, a protein that inhibits conversion of glucosinolates to isothiocyanates, and consequently they may represent more suitable sources of phytochemicals with anti-cancer potential. Concentrations of glucoraphenin were highest in the seed, declining exponentially with sprout development. The rate of decline was observed to vary considerably between varieties of daikon and radish, with some varieties maintaining significantly high levels of glucoraphenin. Varieties maintaining a high level of glucoraphenin included ‘Cherry Belle’ and ‘French Breakfast’.

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