| Sažetak | Ciljevi ovoga istraživanja bili su: (a) prirediti modifikate škroba kukuruza i tapioke
primjenom acetilacije acetanhidridom, (b) istražiti reološka i termofizikalna svojstva nativnih
škrobova i dobivenih modifikata te (c) istražiti utjecaj pektina, karagena, guara, brašna
sjemenki rogača, glukoze, fruktoze, saharoze, trehaloze, laktoze i sirutke na reološka i
termofizikalna svojstva nativnih škrobova kukuruza i tapioke. Reološka svojstva te svojstva
želatinizacije i retrogradacije pripravljenih modificiranih i nativnih škrobova bez i sa
dodacima mjerena su pomoću Brookfield-ovog rotacijskog viskozimetra i diferencijalnog
motridbenog kalorimetra (DMK).
Rezultati su pokazali da dodatak hidrokoloida znakovito utječe na porast viskoznosti
tijekom zagrijavanja suspenzija škroba kukuruza i tapioke, te konzistenciju škrobnih pasti.
Viskoznost navedenih škrobova, također je porasla dodatkom glukoze, fruktoze, saharoze,
trehaloze, laktoze te sirutke.
Dodatak glukoze, fruktoze, saharoze, trehaloze, laktoze i sirutke u prahu doveo je do
porasta temperature želatinizacije nativnih škrobova kukuruza i tapioke. Nasuprot tome,
hidrokoloidi nisu imali značajniji utjecaj na temperaturu želatinizacije ispitivanih škrobova.
Škrob tapioke imao je manju tendenciju retrogradacije u usporedbi sa kukuruznim
škrobom. Pektin, karagen, guar i brašno sjemenki rogača usporili su retrogradaciju škroba
kukuruza i tapioke, pri čemu je efikasnost ovisila o vrsti hidrokoloida, vrsti škroba te vremenu
i temperaturi skladištenja. Dodatak glukoze, fruktoze, saharoze, trehaloze, laktoze i sirutke u
prahu utjecao je na porast ili sniženje retrogradacije škroba kukuruza i tapioke, ovisno o vrsti
škroba, vrsti dodatka te vremenu i temperaturi skladištenja.
Acetiliranje škroba provedeno je dodatkom 4, 6 i 8 % acetanhidrida. Postotak
acetiliranja pripravljenih škrobova povećavao se srazmjerno s povećanjem koncentracije
acetanhidrida. Tako su postoci acetiliranja iznosili 1,257, 1,739 i 2,212 % za kukuruzni škrob
te 1,065, 1,532 i 1,979 % za škrob tapioke
Acetilirani škrobovi želatinizirali su pri nižim temperaturama i imali su nižu entalpiju
retrogradacije u usporedbi sa nativnim škrobovima. Također, imali su i znatno manju
tendenciju retrogradacije tijekom skadištenja i pri 4 i pri 25 °C.
Acetiliranjem škrobova kukuruza i tapioke dobiveni su modifikati s višim kapacitetom
bubrenja i topljivosti, a od njih pripravljeni gelovi imali su manju čvrstoću, silu pucanja te
adheziju. |
| Sažetak (engleski) | The objectives of this work were to: (a) prepare modified maize and tapioca starches
by acetylation with acetic anhydride, (b) analyse the rheological and thermophysical
properties of native and prepared modified maize and tapioca starches and (c) investigate the
effects of pectin, carrageenan, guar, locust bean gum, glucose, fructose, sucrose, trehalose,
lactose and whey on the rheological and thermophysical properties of native maize and
tapioca starches. Gelatinisation, retrogradation and rheological characteristics of prepared
modified and native starches with and without additives were studied with differential
scanning calorimeter (DSC) and Brookfield rotational viscometer.
Results showed that the addition of hydrocolloids to maize and tapioca starch
suspensions resulted in increased viscosity during starch pasting and consistency of starch
pastes. Viscosity of mentioned starches increased on the addition of glucose, fructose,
sucrose, trehalose, lactose and whey also.
It was observed that addition of glucose, fructose, sucrose, trehalose, lactose and whey
increased gelatinisation temperature of native maize and tapioca starches. In contrast,
gelatinisation temperature did not vary significantly in starch-hydrocolloid systems.
Maize starch had higher tendency of retrogradation comparing to tapioca starch.
Pectin, carrageenan, guar, locust bean gum slowed the retrogradation process of maize and
tapioca starch, where efficiency depended on type of hydrocolloid, storage time and
temperature of storage. Addition of glucose, fructose, sucrose, trehalose, lactose and whey
increased or decreased retrogradation of maize and tapioca starches, depending on type of
starches, type of additives, storage time and temperature of storage.
Acetylation was carried out with 4, 6 and 8 % (w/w) of acetic anhydride. The
acetylation percent increased proportionally with the concentration of acetic anhydride used.
The percentages of acetylation were 1.257, 1.739 and 2.212 % for maize starch and 1.065,
1.532 and 1.979 % for tapioca starch.
Acetylated starches gelatinised at lower temperatures and had lower values of
gelatinisation enthalpy in comparison with native starches. Comparing to acetylated starches
(stored both at 4 °C and 25 °C), native starch had significantly higher tendency of
retrogradation.
The acetylation increased the swelling power of starches, and the similar behaviour
was found for solubility, but decreased hardness, fracturability and adhesiveness of starch
gels. |
