Influence of emulsifying starches on dough technological characteristics and bread quality

Prema najnovijim istraživanjima modifikovanim skrobovima može se pripisati još jedna uloga – aditivi u pekarstvu, s obzirom da utiču na poboljšanje kvaliteta hleba i usporavaju proces starenja. Međutim, prema saznanjima autora ove disertacije, ne postoje istraživanja na temu uticaja emulgujućih skrobova (skrob-natrijum oktenilsukcinata, OSA skrobova) na kvalitet testa i hleba od pšeničnog brašna. Uzimajući u obzir činjenicu da druge vrste modifikovanih skrobova ispoljavaju dobre osobine u smislu poboljšanja kvaliteta hleba i da je OSA skrob nutritivno vredna sirovina, s obzirom da se u organiznu ponaša kao prehrambeno vlakno, od velike je važnosti ispitati ulogu OSA skroba kao aditiva u pekarstvu. Međutim, usled kompleksne prirode testa kao sistema, bilo je teško odrediti relativni uticaj pojedinačnih komponenti (proteina, pšeničnog skroba, OSA skroba) i njihovih međusobnih interakcija na osobine testa. Stoga je, u cilju rasvetljavanja uticaja različitih OSA skrobova na viskoelastične osobine testa i retrogradaciju skrobne komponente (fenomen povezan sa starenjem hleba), pšenično brašno frakcionisano na gluten i skrob, i vršena su ispitivanja strukturnih, reoloških i termičkih osobina hidratisanog glutena i skrobnih gelova sa dodatkom OSA skroba. Takođe su pripremani i model sistemi testa. Ispitivanja na realnim sistemima (testo i hleb) izvođena su zamenom 2,5; 5 i 10% pšeničnog brašna, jednim od tri vrste OSA skroba: skrob-natrijum oktenilsukcinatom (OSA-ST), preželatiniziranim skrob-natrijum oktenilsukcinatom (Pregel OSA-ST) i hidrolizovanim sušenim u spreju skrob-natrijum oktenilsukcinatom (Hydrol OSA-ST). Cilj je bio da se ispita uticaj dodatka OSA skrobova na strukturu testa (SEM), empirijske (miksolab, alveograf i reofermentometar) i fundamentalne (oscilatorna merenja i testovi puzanja i deformacije) reološke osobine, kao i parametre kvaliteta hleba (specifična zapremina, boja kore i sredine hleba, vlaga sredine hleba, parametri raspodele veličine pora i tekstura sredine). Pored pomenutog, praćena je i promena kvaliteta hleba tokom skladištenja, kako bi se dobio uvid u kinetiku starenja hleba. Rezultati dobijeni u ovoj disertaciji ukazali su da reološko ponašanje testa sa dodatkom OSA skrobova zavisi od strukture skrobnih granula, tj. od stepena dezintegracije i depolimerizacije granule tokom procesa modifikacije. Stoga je dodatak OSA-ST doveo do ojačavanja glutenske mreže što se odrazilo na porast modula elastičnosti i testa i glutena. Nasuprot tome, Pregel and Hydrol OSA-ST uticali su na kontinualnost glutenske mreže koja je u njihovom prisustvu bila poroznija, a time su i dobijena testa bila mekša i rastegljivija. Istraživanja na realnim i model sistemima (pšenični skrob sa dodatkom OSA skroba) ukazala su da sva tri OSA skroba usporavaju retrogradaciju pšeničnog skroba. Takođe je dokazano da svi ispitivani emulgujući skrobovi povećavaju specifičnu zapreminu hleba u poređenju sa kontrolnim, pri čemu je Pregel OSA ispoljio najjači efekat. To se odrazilo i na strukturne osobine sredine hleba, a posledično i na mehaničke osobine sredine, čija promena je praćena u cilju određivanja kinetike starenja hleba. Prema dobijenim rezultatima, vrednosti čvrstoće sredine hleba koji je sadržao OSA-ST i Pregel OSA-ST su i nakon 24 h bile slične ili značajno niže od vrednosti čvrstoće kontrolnog uzorka određene 2 h nakon pečenja.Recent studies have demonstrated that modified starches can be used as novel additives in breadmaking since they improve bread quality and retard stalling. However, up to the author's knowledge, there are no investigations concerning the influence of emulsifying starches (starch sodium octenyl succinates - OSA starches) on wheat flour dough and bread quality. Taking into account the fact that other modified starches have exhibited significant bread improving properties and that OSA starch has special nutritional value since it can act as functional fibre, it is of a great importance to investigate the feasibility of OSA starch as bread improver. However, due to the complex nature of dough, it was difficult to determine the relative contributions of protein, native and modified starch components and their interactions on dough properties. Therefore, in order to resolve the influence of different OSA starches on dough viscoelastic properties and starch retrogradation (the phenomenon related to bread stalling), wheat flour was fractionated into gluten and starch; and the structural, rheological and thermal behaviour of the hydrated gluten samples and starch gels supplemented with emulsifying starches was also studied. Dough model systems were also prepared. Experiments on real systems (dough and bread) were performed by incorporating starch sodium octenyl succinate (OSA-ST), pregelatinized OSA starch (Pregel OSA-ST) and hydrolysed spray-dried OSA starch (Hydrol OSA-ST) at 2.5, 5 and 10 % into wheat flour. The aim was to investigate the effect of incorporating OSA starches on dough structural (SEM imaging), empirical (Mixolab, Alveograph, Rheofermentometre) and fundamental (oscillatory and creep measurements) rheological properties as well as bread quality parameters (specific loaf volume, crust and crumb colour, crumb moisture, crumb grain features, crumb texture). In addition, the bread quality attributes during storage were also monitored in order to get insight into bread stalling kinetics. The results obtained in this thesis revealed that the rheological behaviour of OSA starch supplemented dough depended on the OSA starch granule rigidity, i.e. extent of OSA starch granule disintegration and polysaccharide degradation during modification. OSA-ST starch caused a reinforcement of the gluten network, as shown by the increase in storage modulus of doughs and gluten. On contrary, Pregel and Hydrol OSA-ST affected the continuity of gluten network which became porous and thus produced softer and stickier doughs in comparison to control. Investigations on real dough and model systems containing wheat and OSA starches revealed that all three types of OSA starches reduced starch retrogradation. In general, all the examined emulsifying starches increased bread loaf volume in comparison to control bread with no added polymers, while Pregel OSA starch has expressed the greatest impact. It also reflected on bread crumb structural features and consequently on the crumb mechanical properties which were used for bread stalling monitoring. Firmness values of OSA-ST and Pregel OSA-ST starch supplemented bread crumbs, after 24 h of storage, were similar to or significantly lower than those of control determined 2 h after baking