Faculty of Food Technology and Biotechnology, University of Zagreb
Abstract
The process of micronisation, a short time high temperature process that utilizes electromagnetic radiation in the infrared region to rapidly heat materials, is often used to improve storage stability of whole grain flour. In this work the consequences of such temperature treatment on the quality and solubility of proteins, viscosity, content of total phenolics, tocopherols, ß-carotene, as well as the antioxidant properties of maize (Zea mays L.) flour are presented. For these studies three maize hybrids were used: the semi-flint hybrid ZP 633 with pronounced yellow kernels, ZP Rumenka with dark red pericarp and yellow endosperm, and ZP 551b hybrid which is characterized by white kernels. The process of micronisation did not change the content of crude protein, the amount of albumin, globulin and zein were decreased, while glutelin remained the same or increased after micronisation. As a consequence of thermal effect on maize protein, tryptophan content was significantly decreased. Micronisation had a significant effect on the pasting properties of the selected maize flour. Viscosity of all micronised flour samples increased constantly, but without reaching a peak during heating of the slurry to 95 °C. At 95 °C it was slightly higher, but final viscosity at 50 °C was significantly lower. The micronisation treatment decreased the content of bioactive compounds (tocopherols, ß-carotene) naturally present in the raw grains. The whole grain flour from micronised grain, with modified nutritional and technological characteristics, represents a good raw material for production of gluten-free products.Mikronizacija, tj. postupak kratkotrajnog izlaganja materijala visokoj temperaturi pomoću elektromagnetskoga zračenja u infracrvenom području, često se primjenjuje za poboljšanje stabilnosti pri skladištenju cjelovitoga brašna žitarica. U radu je ispitan utjecaj takva postupka na kakvoću i topljivost proteina, viskoznost, udio ukupnih fenola, tokoferola i β-karotena, te na antioksidativna svojstva kukuruznoga brašna. Upotrijebljena su tri hibrida kukuruza (Zea mays L.): ZP 633, polutvrdunac izrazito žutih zrna; ZP Rumenka, tamnocrvenoga perikarpa i endosperma žute boje, te ZP 551b bijelih zrna. Mikronizacija nije utjecala na udio sirovih proteina, ali je smanjila udio albumina, globulina i zeina, dok je udio glutelina ostao nepromijenjen ili se neznatno povećao. Nakon toplinske obrade udio se triptofana znatno smanjio. Mikronizacija je također uvelike utjecala na vezivna svojstva brašna. Povećana je viskoznost svih uzoraka brašna, ali nije dosegla vrhunac zagrijavanjem suspenzije do 95 ºC. Na 95 ºC viskoznost je bila nešto veća, dok je pri završetku mikronizacije na temperaturi od 55 °C bila kudikamo manja. Mikronizacijom se smanjio udio bioaktivnih spojeva (fenola, tokoferola i β-karotena) prisutnih u sirovom zrnju. Cjelovito brašno dobiveno mikronizacijom zrnja žitarica zbog svojih je hranjivih i tehnoloških svojstava dobra sirovina za dobivanje bezglutenskih proizvoda
