Starch granule properties as a potential indicator of nutritional quality of cereals.

Abstract

39A Starch granule properties as a potential indicator of nutritional quality of cereals M.R. Zarrinkalam1,2, D.R. Tivey2, M. Choct3 and R.J. van Barneveld 1,4 1 2 3 4 South Australian Research and Development Institute, P.P.P.I, Rosewor thy SA 5370 Depar tment of Animal Science, The University of Adelaide, Rosewor thy SA 5370 School of Rural Science and Natural Resources, The University of New England, Armidale NSW 2351 Barneveld Nutrition Pty Ltd, 19_27 Coonan Road, South Maclean Qld 4280 zarrinkalam.reza@pi.sa.gov.au The nutritional quality of cereals for pigs and poultry is known to vary considerably (Hughes and Choct 1999; van Barneveld 1999) and assessment of basic nutritional values (e.g. available energy and amino acids) is important to optimise production efficiency. The cost and time associated with in vivo assays have prompted renewed interest in development of in vitro alternatives. Moran (1982) and van Barneveld (1999) suggested starch granule (SG) structure and composition could influence digestive processes in pigs and poultry, and available energy supply to the animal. This paper examines SG properties as indicators of nutritional differences between cereal grains. Grain samples, 16 barley, 10 wheat and 15 sorghum, were obtained from the GRDC feed grain project. Two replicates per sample were prepared for assessment of SGs by light microscopy using a modification of the method developed by Fulcher et al. (1997) that employed a 0.5 mg sample instead of 0.1 mg, and pre_incubation of sorghum with protease. The diameter and area of SGs (~ 2000 SG/sample) were measured using an image analyser. In the barley and wheat grains, SGs were categorised as A (area >100�m2) or B (area <100�m2 ). Sorghum SG areas were classified as A (>10�m2) or B (<10�m2). Only the duplicates varying by <10% were utilised in the calculation of frequency, mean, median and ratio of the B to A granules (Table 1). There was a high degree of variation in the SG properties of all grains, and between duplicate measurements. Consequently the technique, in its current form, appears to hold little potential for rapid, reliable prediction of nutritional quality. The accuracy of measurement of SG properties might be improved in wheat and barley by decreasing the sample area under the microscope and de_husking milled samples. Fulcher, R.G., Churchill, K., Peterson, D., and Medin, T. (1998). Rapid analysis of starch granule characteristics in wheat and barley using digital image analysis. Proceedings of the 47th Australian Cereal Chemistry Conference 1997, pp. 129_32. Royal Australian Chemical Institute, Sydney. Hughes, R.J. and Choct, M. (1999). Chemical and physical characteristics of grains related to variability in energy and amino acid availability in poultry. Australian Journal of Agricultural Research 50, 689_701. Moran, E.T. Jr. (1982). Starch digestion in fowl. Poultry Science 61, 1257_1267. van Barneveld, R.J. (1999). Chemical and physical characteristics of grains related to variability in energy and amino acid availability in pigs: a review. Australian Journal of Agricultural Research 50, 667_87. Table 1 Characteristics of starch granules in samples of barley (n = 16) wheat (n = 10) and sorghum (n = 15). Barley Range in area means of A (�m2) Range in area means of B (�m2) Ratio of B/A granules Range of median for A (�m2) Range of median for B (�m2) 188.5_347.0, 68.75%* 6.69_8.73, 68.75% 6.83_17.04, 18.75% 164.5_299.55, 75% 4.89_5.83, 50% Wheat 241.45_320.3, 70% 13.63_18.14, 40% 9.12.39, 20% 207.9_273.1, 30% 10.26_18.89, 40% Sorghum 12.98_15.82, 93.33% 3.07_3.33, 13.33% 3.9**, 6.67% 12.18_14.77, 86.67% 1.31_2.44, 13.33% * Percentages show propor tion of samples for which duplicates varied by <10% ** Only one sample had a duplicate which varied <10% for ratio of B/A granules Recent Advances in Animal Nutrition in Australia, Volume 13 (2001)