Study of the crosslinking of wall materials in the microencapsulation of omega-3 rich oils

GIMENEZ PAOLA ALEJANDRA; BERGESSE ANTONELLA ESTEFANÍA; CAMACHO NAHUEL MATÍAS; RIBOTTA PABLO DANIEL; MARTÍNEZ MARCELA; GONZÁLEZ AGUSTÍN

Congreso; GEP-SLAP 2022; 2022

Chia seed oil, with 61-70% alpha linolenic acid (18:3) is the vegetable richest sources of omega 3 fatty acids. Although a higher consumption of these is favourable from a nutritional and health point of view, some drawbacks are presents due to it less oxidative stability and a shortened shelf life. One of the main challenges for the use and incorporation of these fatty acids in processed foods, lies in the need to be stabilized by incorporating antioxidants and conveyed in a polymeric matrix that contains and protects them. A competent technology for this purpose is icroencapsulation in solid and polymeric matrices [1]. The use of plant proteins as wall material is being widely developed, however, it is necessary to study strategies that make it possible to obtain better microcapsules compared to those reported so far [2]. Due to the above, this work will study a challenging and novel methodology such as the chemical modification of the proteins used as wall material through cross-linking reactions with natural polyphenolic compounds. Its influence on the quality of the omega 3 rich-oils containing microcapsules (MC) will be analysed, focusing on their morphological characteristics and the degree of protection on the oil contained. Aqueous dispersions of isolated soy protein (SPI) 8% w/w were made, and brought to pH 10. Natural crosslinkers such as tannic (TA) and gallic acid (GA) and a heat-treated tannic acid (130 ° C for 15 and 30 min for increasing its antioxidant capacity [3]) (TA 15 and TA 30) were studied. Different amounts of the crosslinking agents were added (1, 5, 10, 20 and 40% w / w) and allowed to react with stirring at 60 °C at different reactions times. The degrees of crosslinking were quantified. Crosslinked materials were also studied by FTIR spectroscopy and rheology. Chia oil was incorporated dropwise into the dispersions at a 2:1 ratio (wall materials:oil) for 15 min at 18,000 rpm, using an Ultraturrax homogenizer. The resulting emulsions were dried in a Mini Spray Dryer Büchi B-290 with a two-fluid nozzle. Color measurements were obtained in the CieLab Scale using a colorimeter (Konica-Minolta CM600d, Japan). Moisture content was measured for each sample with a moisture analyzer with halogen heating (model MB45 OHAUS, United States). Particle size were determined by laser diffraction with a LA950 V2 Horiba analyser and morphology were evaluated by scanning electron microscopy (SEM) and fluorescence confocal microscopy using nile red as fat dye. Total oil (TO) determination was carried out by Soxhlet extraction with n-hexane and superficial or free oil content (SO) of MC was determined with rapid extractions with petroleum ether. These assays were performed in quadruplicate and the encapsulation efficiency (EE) was determined by calculating the percentual ratio of the total oil contained in the microcapsules and the free oil located on its surface [4]. During the preparation of the wall materials, a dark green color, characteristic of the formation of quinones responsible for covalent bonds with soy proteins, was observed. The reaction crudes were washed by dialysis with portions of distilled water. In order to estimate the achieved crosslinking percentages, the released polyphenols were quantified by UV spectroscopy. A positive correlation was observed between the amount of reacted TA and GA with the amount initially added and the reaction time, reaching a maximum of 200 mg of crosslinker for each g of SPI. A reaction time of 20 h was selected as optimal. FTIR and rheological studies also showed covalent interactions between both components. The rheological tests carried out on the suspensions showed that in all cases they were Newtonian fluids. The effect of crosslinking could be observed by the increase in viscosity in the samples. Microcapsules containing chia oil were obtained by spray-drying with solid yields around 50 to 70%. Moisture content of the obtained powders were around 2.9 and 5.8%. Colour determinations showed that powders become greener and darker with increasing the amount of crosslinker. EE results showed no statistical variations between samples. SEM images showed that powders are formed by deflated and spherical particles around 2 and 8 µm diameter without pores and fissures. By staining with Nile Red, the presence of oil was observed homogeneously distributed in the particles, without free oil outside the microparticles or in areas where there are no MC. The protective effect of the wall materials of the microcapsules on the oxidative stability of the encapsulated oils was demonstrated by obtaining very high induction times in the Rancimat test (greater than 25 hours in the cases that contained 40% of the polyphenols), which gives protection factors greater than 20.The effect provided by the oil microencapsulation with cross-linked wall materials (more rigid and less permeable to oxygen) added to the antioxidant effect provided by the polyphenols used as cross-linkers allowed to obtain a very effective protection of the omega-3 rich oils, greatly increasing its shelf life and enabling its use as an ingredient in processed foods.