Submitted to: Journal of Food Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/15/2009
Publication Date: 8/16/2009
Citation: Liu, K.S., Barrows, F.T. and Obert, D. 2009. Dry fractionation methods to produce barley meals varying in protein, beta-glucan and starch contents. J. Food Sci. 74(6):C487-C499).
Interpretive Summary: Barley is the fourth most important cereal in the world in terms of total production after wheat, rice and corn. A significant amount of barley is consumed as livestock feed, a relatively lower amount for brewing, and very little amount is used directly as human food. However, in recent years, there has been a growing interest in incorporating barley into the human diet since it is naturally healthy, readily available, and relatively inexpensive. In particular, there is considerable interest in producing fractions enriched in protein, beta-glucan (BG), and starch. In this study, successive pearling and two milling methods (abrasive or impact milling) followed by sieving were compared and combined for dry fractionating hulled and hulless barley. The objectives were to determine the effects of barley type, pearling cycle, milling method, and particle size and their interactions on concentrations and recovery rates of three key nutrients, protein, BG and starch in resulting fractions. The present study shows that pearling had significant effects on the efficiency of subsequent milling methods followed by sieving, in term of nutrient enrichment and recovery rates. The milling method also had significant effects on efficiency of sieving for nutrient enrichment and recovery rates, as did the genotype. For protein, pearling alone was the best method to enrich it, but for BG and starch, in order to achieve maximum nutrient shifting, a combination of pearling and milling followed by sieving was necessary. Therefore, although dry fractionation is the method of choice for separating barley into fractions with varying levels of protein, BG and/or starch, selection of a specific single or combined method is needed for achieving maximum shifts of a particular nutrient. The study provides significant insight to these who use dry fractionation methods to enrich protein, beta-glucan and/or starch.
Technical Abstract: Barley contains several valuable nutrients including beta-glucan (BG), protein and starch. Each has additional value when concentrated. Dehulled and hulless barleys were sequentially pearled for 1 to 6 cycles, each with 8% removal. The 6 pearled kernels plus the initial kernel were subjected to impact or abrasive milling, followed by sieving with a series of U.S. standard sieves. Results of pearling fines show that protein was most concentrated in the outer area, and decreased all the way toward the core area (near 100% surface removal). Starch showed an opposite trend. BG followed the starch trend, but reached a peak at about 60% surface removal. Upon milling and sieving of kernel samples, genotype and particle size had significant effects on nutrient contents in sieved fractions. The pearling cycle had significant effects on protein and starch contents but little effect on BG content, while the milling method had significant effects on protein and BG contents but little on starch content. Abrasive milling produced sieved fractions with much higher variation in protein content than impact milling, but the opposite effect was observed for shifting BG content. Mass frequency influenced more on recovery rates of nutrients than their concentrations in individual fractions. When the recovery rate was also taken into consideration, pearling alone was found to be the most effective way to enrich protein in barley kernels. However, a combination of pearling with the method of milling and sieving was needed for maximally shifting BG and starch contents.