Submitted to: Journal of Food Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/8/2008
Publication Date: 9/1/2008
Citation: Liu, K., Moreau, R.A. 2008. Concentrations of functional lipids in abraded fractions of hulless barley and effect of storage. Journal of Food Science. 73(7):C569-C576.
Interpretive Summary: Barley kernels contain very high levels of vitamin E, and barley is one of the few seeds that contain all eight natural forms of vitamin E, four tocopherols and four tocotrienols. Tocopherols and tocotrienols alleviate the symptoms of vitamin E deficiency and promote health through their antioxidant activity and cholesterol-lowering ability. In previous reports, we showed the total levels of tocopherols, tocotrienols, and phytosterols in milled fractions from barley were probably not high enough to justify use of barley as a functional food but their levels in the oil extracted from kernels and milled fines were sufficiently high to consider potential use of barley oil as a new health-promoting oil. In the current study, we abraded 4-40% of the surface layers of two hulless barley varieties and stored the samples under two different conditions, a 3-week experiment at elevated temperature and humidity, and a 6-month experiment at ambient temperature and moisture. Storage caused no change in the amounts of oil and tocopherols but significant reductions in the levels of tocotrienols and phytosterols. Grinding kernel samples before storage caused further degradation of phytosterols but had a limited effect on the deterioration of tocotrienols. This information should be very useful for those who want to produce a milled barley product or barley oil. For example, based on the results of this study, if one wants to produce a barley oil that contains tocopherols, tocotrienols and phytosterols, then the oil can be obtained by extracted the abraded outer layers, and the proportions of tocotrienols will increase as more of the surface of the kernel is abraded. Also, in both milled barley fractions and in barley oil, the tocopherols and phytosterols were found to be quite stable, but tocotrienols were more susceptible to degradation during storage.
Technical Abstract: Hulless barley kernels were sequentially abraded to achieve 4, 8, 16, 24, 32 and 40 % removal. Abraded fines, kernels and powered kernels were stored at 35 deg C and 75% relative humidity for three weeks. Stored samples were extracted and levels of oil, free phytosterols, tocopherols (Ts) and tocotrienols (T3s) were analyzed and compared with freshly abraded fractions. The results revealed that oil, sterols and Ts were concentrated in the outer layers, particularly in the germ layer. In kernel fractions with 32% or more removal, Ts were absent but oil and sterols were present in substantial portions. In contrast, T3s were lowest in the germ layer and they increased to highest concentrations in aleurone and maintained high in the endosperm region. In whole kernels, homologues of both Ts and T3s show the same ranking order in concentrations as alpha > gamma > beta > delta. The homologue composition of Ts remained the same but that of T3s changed across the kernel. The % T3 in total tocols increased in fractions with increasing endosperm tissue. Storage caused no change in oil and Ts but significant changes in sterols and T3s. The changes were differential among T3 homologues, with alpha-T3 decreasing and delta-T3 increasing. The degradation of alpha-T3 was accelerated in fractions with more endosperm tissue. Grinding kernel samples before storage accelerated sterol degradation but had a limited effect on changes of T3s. A second experiment using a different hulless barley line and ambient storage for 6 months confirmed all the findings. These results provide practical information to those who wish to produce a barley fraction enriched with a particular functional lipid and maintain stability of their products.