Orientador: Prof. Dr. Antonio Roberto Giriboni Monteiro

 Data da Defesa: 20/08/2020



Starch is one of nature's most abundant macronutrients and one of the most used polymers in the food industry, as its physicochemical characteristics are versatile and embracing. It is present in abundance in corn, cassava, wheat, rice. Corn starch is the most used worldwide. Corn starch is by far the most produced and used worldwide. However, in their native form, starches may not withstand industrial processing such as: high temperature, freezing, pH change, among others. Thus, there is a need to carry out the modification of starch so that it can be used in various food processing. The starch modification can be physical, chemical or enzymatic, individual or combined. Starch fermentation in considered an enzymatic modification and is widely used in the production of sour starch. Chemical modifications are the most used in starch, among them crosslinking using phosphorylation stands out for its efficiency, low cost and for generating starches suitable for human consumption. Phosphorylation crosslinked starch has been used mainly to enhance the viscosity and stability of starch. To carry out the crosslinking of the starch it is common to use the method of heating by oven-heating, however, at the end of the reaction it is necessary to wash the starch a few times to remove the excess residual phosphorus from the starch from the phosphorylation reagents, as it is limited by the Food & Drug Administration. This washing uses excess water, generates effluents and requires more time for the production of modified starches. As an alternative to the common crosslinking method, has reactive extrusion. The extruder is an equipment that combines temperature, pressure and shear force and is considered an HTST (high-temperature short-time) process, does not use excess water and has the ability to modify starches, produce various starch-based foods, among other functions. AIMS The objectives of this research were to verify the effects of fermentation modifications and the modification by the crosslinking method using reactive extrusion and oven heating on the characteristics of corn starch. MATERIAL AND METHODS MODIFICATION OF STARCHES BY THE FERMENTATION PROCESS The fermentations of cassava starch (FM) and corn starch (AM) were carried out separately. In starch fermentation, 3 kg of each sample was added to 4.8 L of water. The mixtures were incubated to BOD at 30 ° C. During fermentation, the acidity of the sample was analyzed weekly. The end of the fermentation was determined according to the acidity following the Brazilian legislation that determines the maximum acidity for the sour powder of 5.0 mL of NaOH.100g-1 (Brasil, 1978). The fermentation of FM lasted 21 days and the AM lasted 28 days. At the end of the fermentation, the excess water was drained and the samples were dried in the sun until reaching a moisture content <14% (Brasil, 1978). 10 MODIFICATION OF STARCHES BY CROSSLINKING METHOD Six samples were produced, namely: native starch (NAT), starch cross-linked by greenhouse at pH 9 (PH9), starch cross-linked by oven-heating at pH 11 (PH11), starch extruded without cross-linking (ENAT), starch cross-linked by pH extrusion 9 (EPH9) and cross-linked starch by extrusion at pH 11 (EPH11). The modifications were made using the crosslinking method proposed by Kerr and Cleveland (1959), with the modifications by Lim and Seib (1993). The choice of using pH 9 and pH 11 was in accordance with the study by Muhammad et al. (2000). The mixing of the reagents with the starch was carried out according to the paste mixing method proposed by Landerito and Wang (2005a). To carry out the cross-linking by oven-heating, the prepared dry starch was heated for 2 hours at 130°C in a conventional oven. For the modification by extrusion, it was necessary to perform a sample pre-treatment to increase the starch granulometry according to Mendes, Demiate and Monteiro (2017). After pre-treatment, the starches were extruded by an IMBRA RX50 extruder (INBRAMAQ, Ribeirão Preto - SP), equipped with a single screw. After extrusion, the samples were dried at 40 ° C until less than 10% moisture, crushed and stored. DETERMINATION OF PHYSICOCHEMICAL CHARACTERISTICS OF MODIFIED STARCHES The acidity was determined according to AOAC (1990) and the results are expressed in mL of NaOH.100g-1 . The phosphorus content P (%), was determined according to the technique described by AOAC (1995a and 1995b). The degree of substitution was calculated according to the equation proposed by Wongsagonsup et al. (2005). The amylose content present in the samples was determined using the colorimetric method proposed by Martinez and Cuevas (1989). The swelling power and solubility of starches were determined according to the method described by Leach, Mcoowen and Schoch (1959). The clarity of paste was performed according to the method of Morikawa and Nishinari (2000). The paste properties of the samples were determined according to Pumacahua-Ramos et al. (2015) using an RVA-4 rapid viscosity analyzer (Newport Sci., Australia). The FTIR spectra of the samples were obtained using a Fourier transform spectrophotometer (Vertex 70V, Germany) coupled with a diamond ATR accessory. The spectral region used was 900 - 1200 cm-1 . The results obtained were subjected to analysis of variance (ANOVA) followed by the Tukey test at a significance level of 5% using the Sisvar 5.6 software (Ferreira, 2014). RESULTS AND DISCUSSION MODIFICATION OF STARCHES BY THE FERMENTATION PROCESS Evaluating the results of the paste properties, the FM (cassava starch) samples showed higher values of peak viscosity. In the resistance attribute, when comparing the AM (corn 11 starch) and FM samples, those that had the same fermentation time did not show significant differences between them. The AM samples did not show any significant difference between the break results, but they differed when compared to the FM samples. Only FMN (native cassava starch) showed greater retrogradation compared to AM samples. However, the initial samples AMN (native corn starch) and FMN did not show differences in the final results of viscosity, but showed the highest values for this parameter with results of 171.50 and 180.50 RVU, respectively. Correlating the results of acidity with the properties of the paste, it was observed that, with the fermentation time and consequent increase in acidity, the properties of the paste showed important changes. MODIFICATION OF STARCHES BY CROSSLINKING METHOD The phosphorus residue of the sodium tripolyphosphate (STPP) and sodium trimetaphosphate (STMP) reagents is limited to 0.4% in starches in accordance with current legislation (Code of Federal Regulation 2019). In this way, the starches were prepared so that after the modification it was with phosphorus content in accordance with the legislation. In this sense, reactive extrusion was the method that proved to be most effective, the phosphorus content of the extruded samples were within the established limit. The samples modified by the conventional method exceeded the residual limit of phosphorus that would require washing to remove the residual, would require water consumption, would generate effluents and would consume energy and time. The higher alkalinity of the modification and the extrusion process had a great influence on the characteristics of the starch, mainly on the paste properties, where these samples presented low viscosity and low paste temperature. With the results of spectroscopy in the infrared region, it can be seen that the starches showed peaks in the same regions, but with different intensities according to their respective modifications. CONCLUSIONS It is concluded that the modification of corn starch by natural fermentation is feasible and some properties are similar, being able to replace in some specific products the use of FMF (fermented cassava starch) by AMF (fermented corn starch). The crosslinking via reactive extrusion is rapidly produces starches with phosphorus content within the permitted by legislation produces starches with different physicochemical characteristics that can be useful for industry and does not use excessive water consumption and does not generate waste. Key words: fermentation; crosslinking; phosphorylation; reactive extrusion.


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