MAIARA PEREIRA MENDES

Título da Dissertação: EFEITO DAS MODIFICAÇÕES FÍSICAS INDIVIDUAIS E COMBINADAS NAS PROPRIEDADES DO AMIDO DE MILHO

Orientadora: Prof. Dr. Antonio Roberto Giriboni Monteiro
Data da Defesa: 17/02/2017

RESUMO GERAL

INTRODUCTION
Corn is mainly composed of starch, with about 70%. Corn starch is the starch most world widely used. Native starches have limiting characteristics in some applications. For this reason, the modification of starch has been an alternative to produce foods with specific characteristics. The modifications may be chemical, physical or enzymatic. Physically modified starches can be considered as a natural product and a safe ingredient, a
great advantage compared to other types of modification.
Heat-moisture treatment (HMT) and annealing (ANN) are physical processes for the starch modification which require moisture, temperature and heating time controls and changes the physical-chemical properties of the starch without destroying its granular
structure. The difference between them is in the percentage of moisture and the process temperature. Extrusion is widely used in the snacks food, breakfast cereals and animal feed production. The high temperature and the short process time have important effects on the physical-chemical properties of starch-based raw materials. The combined modifications have been successfully studied when regarding to HMT-ANN combinations, but when it comes to combined treatment with extrusion there are a lack of studies, principally using a single-screw extruder.
OBJECTIVE
To evaluate the corn starch changes, the single-screw extruder efficiency and the best applications for modified starches through individual and combined physical processes.
MATERIAL AND METHODS
The corn starch was purchased from the popular market in the city of Maringá-PR. The starches underwent four independent and three combined modifications. The independent variables were: heat-moisture treatment by oven-dry (HMT), heat-moisture
treatment by autoclave (HMTA), annealing (ANN) and extrusion (E). The combined modifications were the same as before, but followed by extrusion: HMT followed by extrusion (EHMTE), HMTA followed by extrusion (EHMTA) and ANN followed by
extrusion (EANN). Native starch was used as standard.
HMT treatments were performed with 25% ± 0.5% moisture. HMT was carried out in an oven at 110 °C for 16 hours. In the HMTA it was autoclaved at 121 °C for 1 hour. In the ANN treatment, a 1: 4 starch:water ratio was used at 50 °C ± 2 °C for 16 h under magnetic stirring. For the extrusion, a sample pre-treating was necessary to increase the particle size. The extrusion treatment was performed by an IMBRA RX50 extruder (INBRAMAQ,
Ribeirão Preto - SP), equipped with a single screw of 0.05m in diameter and 0.2m in length, a screw speed of 41.89 rad / s and feed rate of 42 kg / h. All samples were oven dried at 40 °C
for 24 h after modifications. The swelling power and solubility was performed according to Leach, Mcoowen and Schoch (1959). The transparency methodology was carried out according to Morikawa and Nishinari (2000). The X-ray diffraction was evaluated in X-ray diffractometer (D8 Advance - Bruker). The pasting properties were assessed through Pumacahua-Ramos et al. (2015) proposal. The starch granules morphology was analysed by scanning electron microscopy (SEM) (SHIMADZU, SS-550). Statistical analyses were ascertained by ANOVA using the Assistat software (Federal University of Campina Grande, Campina Grande - PB, Brazil)
version 7.7 beta.
RESULTS AND DISCUSSION
The NAT and ANN starch samples presented higher swelling values than the other modified samples. This behaviour can be explained because the NAT had no initial changes and the ANN treatment temperature was not high enough to alter the swelling properties. The samples NAT, ANN, HMT and HMTA had higher swelling values than the ones that underwent extrusion process and the inverse occurred with the solubility where the extruded
samples revealed higher percentages. Native starch prior to extrusion had a lower transmittance index compared to the
ANN, HMT and HMTA modifications however, when the modifications became pretreatments for extrusion, it was observed that native extruded starch had a higher
transmittance index than the extruded ones after the treatment. The transmittance percentage presented similar behaviour for the samples NAT, ANN, HMTA and HMT. ENAT and EANN samples showed similar behaviour after 48 and 96 hours, and the EANN sample had similar transmittance to the EHMTA sample after 96 hours The starches NAT, ANN, HMT and HMTA showed strong peaks at 15.2° and 23.2° 2Ɵ, and a hesitant doublet between 17.9° and 18.1°, this profile indicates type A starch.
Modified starch HMTA had more intense peaks than the other samples. After the extrusion process the appearing double peak in the samples between 17.9° and 18.1° 2Ɵ collapsed and
originated a singlet around 18.4° 2Ɵ. At 7.0°, 12.1° and 13.2° 2Ɵ small peaks appeared in all extruded samples, losing their characteristic of type A starch and presenting characteristic of
type V starch. The HMTA sample had the highest pasting temperature, highest breakage and highest retrogradation. The highest viscosity peak was the ANN sample. The highest strength
and final viscosity was of the starch NAT. The extruded samples had low pasting temperature and low viscosity.
In relation to the morphological analysis it was observed that corn starches that were modified by ANN, HMT and HMTA formed agglomerates with spherical and polygonal granules. ANN starch granules are more polygonal and smooth, with few pores. The HMT and HMTA samples, however, present less uniformity and more porous granules. The starches structure after extrusion was partially destroyed generating irregular, relatively large, rough and almost amorphous particles.
CONCLUSIONS
In general, the ANN, HMT and HMTA modifications did not presented such relevant differences compared to the NAT starch. Extrusion modified more intensely. Besides pregelatinization, altered the characteristics of crystallinity and viscoamylographic properties. The single-screw extruder was efficient at modifying, producing a starch with novel characteristics for various applications.
Keywords: physical modification, pregelatinization, extrusion.

Artigos Publicados Vinculados a Dissertação:

https://doi.org/10.4025/actascitechnol.v40i1.35118