Oxidative stability of microparticles based on emulsified linseed oil and plant biopolymers

Oxidation is the main deterioration process affecting oils rich in polyunsaturated fatty acids, such as linseed oil. This process compromises sensory properties and leads to the formation of toxic compounds. Microencapsulation can be used as protective strategies for these oils. Therefore, the aim of this study was to evaluate oil oxidation in spray-dried linseed oil emulsions, investigating the effect of interfacial multilayer systems based on carob protein concentrate or hydrolysate. Four emulsion formulations were studied: multilayer emulsions stabilized by pectin and carob protein concentrate (CPCME) or hydrolyzed carob protein with 2% degree of hydrolysis (CPHME); and their respective single-layer counterparts, without pectin (CPCSE and CPHSE). Four grams of each sample were incubated at 37 °C in sealed tubes for 28 days, and oxidation was evaluated by oxygen consumption, conjugated diene formation (CD), thiobarbituric acid-reactive substances (TBARS), and intrinsic tryptophan fluorescence. Oxidation was also specifically assessed in the surface oil (SO) fraction and compared with the total oil (TO) and encapsulated oil (EO) fractions. After 14 days, CPCME and CPCSE samples consumed approximately 80% of the initial oxygen, while CPHME and CPHSE samples consumed around 30%, indicating a protective effect of the hydrolyzed protein (CPH) on linseed oil. After 28 days, only the CPHME sample showed significantly lower CD (113 ± 15 µmol/g oil) and TBARS (1161 ± 311 nmol MDA eq./g oil) values, compared to the other formulations, which showed CD values around 145 µmol/g oil and TBARS above 3500 nmol MDA eq./g oil, with no statistical difference among them (p < 0.05). The surface oil fraction presented higher CD and TBARS values than the total and encapsulated oil fractions for all samples. For the CPHME sample, CD values after 28 days were 154 ± 27 and 95 ± 27 µmol/g oil, and TBARS values were 2974 ± 384 and 347 ± 260 nmol MDA eq./g oil, for SO, and EO fractions, respectively. Tryptophan fluorescence profiles showed a similar trend: CPHME exhibited a 30% reduction in maximum fluorescence, while the other samples showed around 40% reduction, indicating that protein co-oxidation is directly influenced by lipid oxidation. After 28 days of incubation at 37 °C, all samples showed a high extent of tryptophan fluorescence quenching, indicative of protein oxidation; however, the combined application of protein hydrolysate and multilayer interfacial systems (CPHME) proved effective in protein and lipid oxidation during particle storage.