Researchers from University of SÃo Paulo Investigate Ozone Processing to Enhance the Performance of Different Starch Sources, Creating New Ingredients for Different Industries

Edited from a write-up provided by Pedro E. D. Augusto, University of São Paulo

The Problem: 

Starch is a natural biopolymer synthetized and stored in vegetables as an energy source. It is also a versatile industrial ingredient that is widely used in various sectors such as: food, feed, chemical, petrochemical, adhesive, paints, paper, textile, and pharmaceuticals. Although many different properties of starch are demanded by industry, the available sources of starch are limited by nature. Consequently, different starch modification processes are being developed to achieve new properties and applications to enhance starch performance. Currently the modification technologies that are most frequently applied involve chemical substances such as hypochlorite, acetates, phosphates, and acids. These techniques generate a large volume of effluents which causes concerns for both the consumer and the environment. Therefore there is a rising demand for starch modification alternatives using environmentally friendly technologies.

The Solution:

The Process Engineering Research Group (Ge²P) of University of São Paulo has been studying ozone technology as an alternative to starch modification for 6 years. Different starch sources have been studied such as: maize, cassava, potato, wheat and arracacha. The combination of ozone processing to modify starch with other technologies have also been studied, particularly ozone combined with ultrasound and dry heating treatments.

Ozone is produced by the coronal-discharge method from industrial oxygen and can reach concentrations of 40-50 mg O₃ L⁻¹ in the gas stream. The starch is suspended in water and the reaction occurs at room temperature, where the gas stream is bubbled in the starch suspension in a glass reactor. The system is multiphase with three different phases and physical states: gas (O₂ + O₃), liquid (water), and solid (starch granules). The concentration of ozone is continuously monitored in both the reactor inlet and outlet using an ozone monitor (2B Technologies, Model 106-H, Boulder, USA) to evaluate the reaction. Different ozone concentrations, gas flows and reaction times were evaluated.

Figure 1. The ozone processing system used in the starch modification studies.

Despite the different sources, the main modifications in relation to starches’ structure are the increase of carbonyl and carboxyl groups content (as a consequence of oxidation of hydroxyl groups) and partial depolymerization (decreasing of the molecular chain length) of both amylose and amylopectin molecules. These structural changes result in different molecular interactions that affect the starch properties and possible applications.

For example, hydrogels are 250-300% stronger than those produced from native starch. The hydrogels were also resistant to acidic conditions. Additionally weaker gels can also be obtained by changing the process conditions. Gel formation is the most important property of starch for different industrial applications. The stronger hydrogels improve 3D printing performance, an emerging technology in food processing.

The different molecular interactions of ozonated starches resulted in better oven expansion. This allowed for the production of gluten-free doughs and biodegradable plastics with enhanced properties such as stronger and more transparent films.

The research has shown that the combination of technologies also improved starch modifications. Pre-treatment with ultrasound affected the subsequent ozone processing, while the order of combination of ozone + dry heating treatment influenced the final properties.

Results: 

The ozone process is highly efficient to promote starch modifications, however its effectiveness varies depending on the starch source. Even when the same ozone system and processing conditions are applied, different properties can be observed depending on the starch source that is being evaluated. This indicates the starch structure plays an important role in the final results.

For example, hydrogels are 250-300% stronger than those produced from native starch. The hydrogels were also resistant to acidic conditions. Additionally weaker gels can also be obtained by changing the process conditions. Gel formation is the most important property of starch for different industrial applications. The stronger hydrogels improve 3D printing performance, an emerging technology in food processing.

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