Eur Food Res Technol (2005) 220:20–24 DOI 10.1007/s00217-004-1038-7 ORIGINAL PAPER Iwona Konopka · Daniela Rotkiewicz · Malgorzata Tan ´ska Wheat endosperm hardness. Part II. Relationships to content and composition of flour lipids Received: 7 July 2004 / Published online: 28 October 2004  Springer-Verlag 2004 Abstract In Part I we analysed hardness and colour of wheat endosperm and stated that these features are quite well correlated among kernels of individual varieties. In order to enhance knowledge of the biochemical basis of endosperm hardness, this study aimed at determining how the content and the composition of free and starch lipids influence it. Wheat samples (used previously in Part I) were milled in a way that reduced the number of non- endosperm particles in flour. Simple linear correlation coefficients between endosperm hardness and its lipid composition indicated that hardness was positively cor- related with the content of free glycolipids (r=0.82) and negatively with the content of surface lipids of starch, especially with their non-polar fraction (r=-0.83). The typical feature of harder wheat varieties was a substan- tially higher content of oleic acid in lipids of the starch surface. Keywords Wheat · Endosperm hardness · Free lipids · Starch lipids Abbreviations -NL: Non-polar lipid · -GL: Glycolipid · -PhL: Phospholipid · -FNL: Free non-polar lipid · -FGL: Free glycolipid · -FPhL: Free phospholipid · -STPhL: Starch total phospholipid · -SSL: Starch surface lipid · -SSPL: Starch surface polar lipid · -SSNL: Starch surface non-polar lipid · -TLC: Thin layer chromatography · -TAG: Triacylglycerols · -PN: Polish Standard Introduction Studies into biochemical determinants of the structure of wheat endosperm, reviewed by Turnbull and Rahman [1], have linked hardness with the occurrence of low-molec- ular-weight proteins, referred to as puroindolines a and b, on the surface of starch. Their synthesis in the kernel is controlled by genes located on a short arm of chromo- some 5D [2]. A majority of hard wheats have a glycine- to-serine mutation in puroindoline b, or they are devoid of puroindoline a [3, 4]. The presence of leucine and tryp- tophane, instead of proline and arginine in puroindoline b also determines the occurrence of a soft phenotype of wheat [4, 5]. Wheat lipids are also found to influence endosperm hardness but this relationship has not been fully recog- nised so far. Panozzo et al. [6] found that flours of ex- traction rate in the range 72.4–73.7% from hard grained wheats grown in Australia demonstrate higher levels of free lipids. At the same time Morrison et al. [7] stated that harder wheat lines had less free polar lipids. They dis- covered also that the level of free polar lipids is controlled by at least two genes (one of these genes could be allelic to Ha, or is closely linked to it) and that wheat lines lacking the short arm of chromosome 5D were much harder. In summing up these observations, it may be as- sumed that flours of harder wheat varieties contain more free non-polar lipids (FNLs). Their origin is worth con- sidering. Most of the FNLs of grain and flour are repre- sented by storage triacylglycerols (TAGs). Their sources are oil bodies, the so-called spherosomes. A majority of spherosomes are located in the aleurone layer and germ and their concentration in starchy endosperm is consid- erably lower [8]. Higher contents of free lipids in flour from harder wheat grains [6, 7] can be explained by its larger “contamination” with non-endosperm lipids de- pendent on milling conditions [9]. Forming explicit con- clusions on the impact of lipids on endosperm hardness without a detailed control of the milling process is diffi- cult. Correlation of these features should be performed only for “pure” endosperm flour that can be distinguished, for example, by ash content [10]. More accurate results are obtained in an analysis of starch lipid profile. Greenblatt et al. [11] have pointed to quantitative and qualitative diversification of lipids oc- I. Konopka ( ) ) · D. Rotkiewicz · M. Tan ´ska Chair of Food Plant Chemistry and Processing, University of Warmia and Mazury in Olsztyn, Pl. Cieszyn ´ski 1, 10-957 Olsztyn, Poland e-mail: Iwona.Konopka@uwm.edu.pl Fax: +48-89-523-3466