Australian canola oil quality – the influence of varietal traits and other parameters on valuable minor components

Clare Flakelar^1,2, David Luckett^2,3, Julia Howitt^1,4, Gregory Doran^1,2 and Paul D. Prenzler^1,2,

¹School of Agricultural and Wine Sciences, Charles Sturt University,  Wagga Wagga; ²Graham Centre for Agricultural Innovation (an alliance between Charles Sturt University and NSW Department of Primary Industries), Wagga Wagga; ³NSW Department of Primary Industries, Agricultural Institute, Wagga Wagga; ⁴Institute for Land, Water and Society, Charles Sturt University, Wagga Wagga.

GRDC project code: GRS10664

Keywords: canola, carotenoids, tocopherols, sterols, health-benefits.

Take home messages

• Canola oil in its crude form is a source of many bioactive compounds including carotenoids, tocopherols and sterols that have considerable health benefits.
• GRDC funded research conducted in 2013 investigated general seed and oil quality traits, including analysis of bioactive components (tocopherols and carotenoids), for commercial canola cultivars grown in South-Eastern Australia.
• The study illustrated large concentrations of these bioactive compounds in the Australian cultivars and a large varietal influence for bioactive components was indicated.
• A related study is now underway to verify the varietal influence, and to quantify and processing effects on bioactive compounds, with results providing valuable information for farmers, breeders and the canola industry.

Background

Since its introduction in the late 1970s, canola has grown to become the most important oilseed crop produced in Australia. Its production has increased steadily, with approximately four million tonnes now produced each year (NSW Department of Primary Industries, 2014). Seed and oil quality parameters such as, oil content, free fatty acid (FFA), moisture content, seed weight, as well as contaminants and seed defects, are routinely used by agricultural buyers and exporters to assess the quality of canola seed and provide an indication of the quality of the resulting oil, as well as to dictate pricing (Australian Oilseeds Federation Inc, 2011).

In addition to its desirable fatty acid composition, canola is a rich source of health-beneficial bioactive compounds including: tocopherols, carotenoids and sterols. In its crude form, canola oil contains high concentrations of these bioactive components (Alander et al., 2002; Przybylski et al., 2005).

Current commercial processing heavily degrades these bioactive components, with losses of 40% for sterols, 50% for tocopherols and, 90% for carotenoids (Dunford and Dunford, 2004). Processors have used the current processing techniques for several decades due to their ability to achieve optimum oil yield and profit, as well as the desirable oil quality, with low levels of impurities and maintaining a satisfactory fatty acid composition (Dunford and Dunford, 2004). Correspondingly, the primary focus for breeders has been to produce canola varieties that overcome the main economic challenges by ensuring optimum seed and oil yield and resistance to blackleg, drought and herbicides.  Additionally, fatty acid composition has become a recent target for breeding programs and several new varieties have been released with benefits of higher stability and an enhanced nutritional profile in terms of fat composition (Abbadi and Leckband, 2011). Research has already begun overseas to investigate breeding on the basis of minor components in the oil, including tocopherols and sterols (Fritsche et al., 2012; Vlahakis and Hazebroek, 2000). However, there remain opportunities to assess the potential for maximizing bioactive components in canola and its oil and whether or not we can breed new varieties targeting these compounds. The bioactive compounds could then be deliberately extracted for use as a valuable food additive, or processing methods could be modified to retain more of the bioactives in the canola oil giving it a market advantage.

Studies conducted in 2013 and 2014 on current Australian commercial genotypes, indicated there is potential to breed new Australian genotypes based on carotenoids and tocopherols. The GRDC-funded study focused on commercial canola varieties commonly grown in south-eastern Australia. Important relationships between seed quality parameters and oil components were identified and will be used to guide further research into enhancing minor components in canola oil.

Methodology

A total of 156 commercial canola seed samples were obtained from Southern NSW from the 2011 and 2012 harvests. Samples included 32 commonly-used commercial varieties received at nine different locations across Southern NSW (Figure 1).  Samples were analyzed for the quality parameters listed in Table 1 and some samples were analysed in duplicate (total n=207, duplicates averaged n=156).

Figure 1. Sampling locations (●) for canola at commercial grain receival sites in southern New South Wales, Australia. Stockgb = Stockinbingal (NSW Government Bureau of Transport Statistics, 2011).

Figure 2. Frequency plot illustrating sample spread with respect to location and variety for each season.

Table 1. Measured traits and their respective units and classes analysed in the study. General seed parameters were measured on whole seed, the remainder on extracted oil.

Results and Discussion

The values in Table 2 denote the influence (as a percentage of total variation of that parameter) to several factors, variety, location and season in which the canola samples originated as calculated using Restricted Estimate Maximum Likelihood analysis. A larger % indicates more influence of the factor on the respective trait. Canola cultivar was found to be the dominant influence on many traits, particularly on carotenoid and tocopherol concentration (Table 2, highlighted). A much smaller degree of influence was attributed to location and season. This will be particularly beneficial, if it is discovered that these bioactive compounds can be retained in the oil through modified processing. Further research has commenced to verify this varietal influence, and to determine the processing parameters that are most detrimental to the retention of bioactives in the oil.

Table 2. Influence of season, site and variety on measured seed and oil traits (expressed as a percentage of total variance). Site*Variety is the interaction between these two factors. See text for an explanation of the highlighted numbers.

Concentrations of the bioactive components in crude canola oil are of sufficient quantity to present benefits to human health. The Australian canola varieties examined possessed similar levels of tocopherols to those previously reported in literature (Table 3). Fewer studies have reported the levels of carotenoids however, and our averages were slightly lower than those reported on varieties grown in central China (Yang et al., 2013). Yang et al., (2013) employed a cold pressed method and did not use solvent extraction (which is the standard commercial method), so lower concentrations are expected.

Table 3. Average concentration (ppm) of carotenoid and tocopherol compounds as measured in the current study, n = 156.

Furthermore, relationships between traits and also amongst variety and location were found. Similar results for oil, protein, glucosinolates and kernel weight were discovered for locations close to one another. The variety Fighter-TT was found to have consistently higher levels of α-tocopherol and, Fighter-TT and Bravo-TT were discovered to have higher γ-tocopherol when compared to other varieties. A relationship between the two main carotenoids found in canola oil, β-carotene and lutein, was also discovered in the analyzed samples, indicating biochemical interactions may affect both similarly and this relationship will be further investigated in a new study. The detailed results of this work have been submitted for publication and are currently under review.

Conclusion

Canola oil in its crude form is a valuable source of many bioactive compounds that have large, potential health benefits. These compounds include: carotenoids, tocopherols and sterols. The research has shown that many of the routinely-analysed seed and oil traits were associated with cultivar type, and further research was required to verify this relationship. Additionally, the study illustrated that high concentrations of these bioactive compounds were present in the Australian cultivars examined. The results of this work have led to new research now underway to verify the relationship between cultivar and bioactive compounds (tocopherols, carotenoids and sterols), and, to investigate ways in which to retain or recover these valuable compounds in the oil through storage and processing. Outcomes for this work may include a higher export demand for Australian-grown canola, the opportunity for new genotypes to be developed within Australia targeting minor oil components, a potential new marketing advantage for oil processed within Australia, and the potential for increased future profit for the canola industry.

References

Abbadi, A., & Leckband, G. (2011). Rapeseed breeding for oil content, quality, and sustainability. European Journal Lipid Science Technology, 113 (10), 1198-1206.

Alander, J., Andersson, A.-C., Bagge, C., Bringsarve, K., Hjorth, M., Johansson, M., Granroth, B., Norberg, S., Pedersen, M., Persson, M., Wennermark, B., & Wennermark, M. (2002). Handbook: Vegetable oils and fats. In). Sweden: Alfaprint.

Australian Oilseeds Federation Inc. (2011). Quality Standards, Technical Information & Typical Analysis In  Vegetable Oil Quality Standards,  (pp. 61). Australia Square: Australian Oilseeds Federation

Dunford, N. T., & Dunford, H. B. (2004). Nutritionally enhanced edible oil and oilseed processing. Illinois: AOCS Press.

Fritsche, S., Wang, X., Li, J., Stich, B., Kopisch-Obuch, F. J., Endrigkeit, J., Leckband, G., Dreyer, F., Friedt, W., Meng, J., & Jung, C. (2012). A candidate gene-based association study of tocopherol content and composition in rapeseed ( Brassica napus ). Frontiers in Plant Science, 3.

NSW Department of Primary Industries. (2014). Quality of Australian canola 2013-14. In N. D. o. P. Industries (Ed.),  (pp. Australian Oilseeds Federation). Wagga Wagga.

NSW Government Bureau of Transport Statistics. (2011). Travel Zone Shape Files in ESRI Format - NSW In N. G. BTS (Ed.)). Haymarket.

Przybylski, R., Mag, T., Eskin, N. A. M., & McDonald, B. E. (2005). Canola oil. In F. Shahidi (Ed.), Bailey's Industrial Oil and Fat Products 6th ed., vol. 2 (pp. 63 of 749). United Kingdom: Wiley-Blackwell.

Vlahakis, C., & Hazebroek, J. (2000). Phytosterol accumulation in canola, sunflower, and soybean oils: Effects of genetics, planting location, and temperature. Journal of the American Oil Chemists' Society, 77(1), 49-53.

Yang, M., Zheng, C., Zhou, Q., Huang, F., Liu, C., & Wang, H. (2013). Minor components and oxidative stability of cold-pressed oil from rapeseed cultivars in China. Journal of Food Composition and Analysis, 29(1), 1-9.

Contact details

Clare Flakelar
School of Agriculture and Wine Sciences,
Locked Bag 588,
Charles Sturt University,
Wagga Wagga, NSW 2650

0400608957
cflakelar@csu.edu.au
@clflake