MACROMOLECULAR CHARACTERISTICS AND BREAD MAKING PROPERTIES OF ITALIAN WAXY WHEAT LINES

This PhD thesis aims to analyse the waxy (amylose-free) wheat (Triticum aestivum L.) properties and the role in the textural characteristics and staling kinetics of bread and bakery products. Moreover, waxy genes effects on qualitative and agronomic characteristics of autochthonous lines selected by a breeding project aimed to obtaining waxy genotypes suitable for cultivation in Italy have been evaluated. The present PhD thesis, therefore, was divided into six chapters: 1.STATE OF THE ART: WAXY WHEAT ORIGINS, CHARACTERISTICS AND APPLICATIONS. Food industry is increasingly interested in waxy (amylose-free) starch because its application to bakery products seems to be able to naturally induce retardation of staling and to extend shelf-life. The starch retrogradation is indeed believed to be the major cause of bread staling and amylose content is assumed to be the main contributor to bread firming. This section offers an overview related to waxy wheat properties and briefly describes how first waxy wheat varieties have been obtained. Moreover, the main composition and thermal properties of waxy starch are illustrated together with the main waxy wheat applications in food products. 2. AGRONOMICAL AND TECHNOLOGICAL PROPERTIES OF ITALIAN WAXY WHEAT.The high influence of different environments on wheat productivity and quality may in principle impede that waxy wheat lines produced in other countries can be successfully cultivated in Italy. In the perspective of developing waxy wheat lines suitable for cultivation in Italy, various research activities have been accomplished since ten years in this country. Aim of the present study has been the evaluation of agronomic and technological performances of a set of 18 Italian waxy wheat lines (IWWL), derived from a breeding program started in 2000 and set up at CRA-SCV (Italy) from partial-waxy cultivars belonging to Italian germplasm. This study shows that, despite the supposed high influence of different environments on wheat productivity and quality, agronomical tests repeated during three years did not allow detecting significant differences between IWWL and two American waxy wheats as well as between IWWL and not waxy wheat in relation to their agronomical characteristics. On the contrary, important differences related to technical characteristics have been observed. Almost all IWWL showed higher bread making qualities with respect to the Amirican waxy and non-waxy wheats used as controls. Six out of eighteen IWWLs analysed showed particularly good performances. In particular, these lines resulted characterized by higher values of gluten index, SDS sedimentation volume, farinograph stability and bread specific volume. Some of these six lines will be further tested during the next growing seasons in three different locations in order to confirm the results achieved.3.PHYSICOCHEMICAL AND STRUCTURAL CHARACTERISTICS OF STARCH FROM ITALIAN WAXY WHEATS. Starch is the most abundant constituent in wheat flours and plays an extremely important role in their pasting properties. The differences in starches amylose/amylopectin ratio result in different pasting properties of flour, and, therefore, in the texture and quality of bakery products. This study aimed to investigate some of the main physicochemical and structural characteristics of waxy starch. In particular, the analyses have focused on thermal and pasting properties of flour from some waxy wheat lines adapted to the Italian environmental conditions, which have been compared with two American waxy wheats and one non-waxy wheat, taken as reference. Results allowed to highlight how the low amylose content of all IWWL (resulted markedly below 1.7% d.b) influences the characteristics of both suspension and dough systems. Waxy wheat samples resulted having a higher number of small starch granules, often with deformities and small cracks with respect to non-waxy wheats. Regarding starch gelatinization, this phenomenon was observed at higher temperatures (as estimated by DSC analyses) in waxy starch with respect to non-waxy starch. Nevertheless, gelatinization temperature is strongly affected by the conditions applied (e.g. water availability, presence/absence of shear-stress, etc.) in the approach used for its evaluation. As the retrogradation extent resulted highly reduced in all the IWWL flours, these types of flours could be usefully exploited for baking processes.4. PROTEIN CHARACTERIZATION AND RHEOLOGICAL PARAMETERS OF ITALIAN WAXY WHEAT LINES. Except for starch properties, there is still limited information about the quality characteristics of complete waxy wheat cultivars and there is a need to better understand how waxy wheat protein composition could affect the physical properties of dough and bakery products. This study analysed the molecular characteristics of proteins from IWWL, comparing the results with those obtained for two samples of American waxy flour and two non-waxy flours with good bread-making quality. The protein content of IWWL flours resulted on average quite high, ranging from 12.0% to 15.4%. The composition observed for the high-molecular weight-glutenin subunits (HMW-GS) of IWWL was generally associated with medium bread-making quality and the electrophoretic analysis indicated that all IWWLs considered have a similar gliadin composition. Differential-solubility data did not show any significant difference between waxy and non-waxy proteins and also the accessibility of sulfhydryls groups seemed to be comparable between IWWL and non-waxy wheat proteins. Front-face fluorescence analyses allowed instead to highlight an interesting difference between IWWL and non-waxy wheat proteins: in fact, dough from IWWL flours needed more water to completely hydrate their proteins, probably as a consequence of the relevant water-retaining capacity of waxy wheat starch. Moreover, the peculiar properties of waxy wheat starch seemed to affect the interactions between protein hydrophobic regions and amylopectin partially solvated regions. Finally, non-waxy flour dough resulted having a much more solid elastic-like behavior with respect to waxy flour dough whereas IWWL flour dough resulted having higher elasticity and consistency indices with respect to American waxy dough. 5. BREAD MAKING CHARACTERISTICS AND STALING KINETICS OF ITALIAN WAXY WHEAT LINES. Waxy wheat is considered to have superior functional properties for bread-making, resulting in the formation of a soft bread-crumb and improving bread shelf-life due to staling retarding. This study focused on the Italian context and considered three Italian waxy wheat lines (IWWL). The properties of dough and the quality of fresh bread obtained by these lines were compared with those of two American waxy wheat samples and a non-waxy flour with high bread-making quality. Bread-making quality has been analysed also in relation to shelf-life. The specific volume of bread samples from IWWLs resulted significantly higher than that of the controls: in fact, the estimated mean area for the large cells of crumb resulted significantly higher for most of the IWWL samples with respect to non-waxy samples. As expected, breadcrumb firmness of all samples from IWWLs resulted lower than commercial flour breadcrumb firmness for 7 days after baking at least. Among IWWLs, bread from wx123 line achieved the highest volume. Its breadcrumb presented the lowest firmness while its breadcrumb moisture was about 3% over that of the commercial flour bread after 7 day storage. During this storage time, the moisture decrease in wx123 bread resulted of 27% against 35% registered for the samples from commercial flour, whereas the decrease in water activity (6%) was the same among all bread samples. This different behavior could partially explain the lower bread firmness detected for wx123 samples. In general, the waxy wheat lines adapted to the Italian environmental conditions showed better bread-making qualities with respect to American standard waxy lines. 6 INFLUENCE OF FLOUR BLENDS ADDED WITH ITALIAN WAXY WHEAT LINE ON BREAD MAKING QUALITY AND STALING KINETICS. Bread samples from waxy flour were typically characterized by higher volume and retarded staling; nevertheless dough from waxy flour had higher stickiness (and consequently a lower machinability) with respect to non-waxy flour. This study aimed at investigating how this negative characteristic could be decreased by using blends of “normal” wheat flour and IWWL flour, without compromising the other above mentioned good bread-making qualities. Flour blends contained 20% and 40% of commercial flour from non-waxy wheat; the dough and bread properties were compared to American waxy wheat lines used as reference. This approach allowed reducing adhesiveness increasing farinograph stability and dough consistency. The starch retrogradation kinetics wasn’t affected by the presence of commercial flour, as assessed by measuring the firmness of gels stored at low temperatures for long time periods. As regards dough rheological properties, the values registered for the elastic modulus and the viscous modulus in case of waxy dough samples with blends of non-waxy flour varied within the same ranges observed in case of dough samples from pure waxy or pure non waxy flours confirming a solid elastic-like behavior with the elastic modulus prevailing over the viscous modulus also for flour blends dough samples. Concerning bread properties from IWWL flour blends, the specific volumes resulted significantly higher than those of bread samples from non-waxy and American waxy flours. Crust color did not significantly change with respect to breads from 100% IWWL flour excepting for crust redness. The lightness of crumbs increased significantly but remained significantly lower than that of breadcrumb from pure non-waxy flour. As regards bread cells area, the addition of commercial flour in IWWL flour did not determine on average a significant increase in the ratio between cell area and total area of bread cells due to an increase in the density of small cells. Breadcrumbs from blends with 20% of non-waxy flour resulted having good bread-making qualities and maintained low firmness values till 7 days of storage.