| Lemon flavor is an important flavor additive in soft drinks. Citral is the key flavor compound of lemon flavor, with a rich lemon aroma. However, due to the existence of isolated C = C, C = O and carbonyl conjugated C = C, citral is prone to oxidation reaction,dehydrogenation cyclization reaction and rearrangement reaction. Especially in the acidic environment, it will accelerate citral degradation, and result in the production of many undesirable compounds which have poor flavor, thus lost the fresh lemon aroma. The pH of most of the orange juice drink is about 3, the character of citral limits its applications in the beverage and perfume industry. Solid lpid nanoparticlesare prepared from physiologically compatible and biodegradable lipids, which can be used to encapsulate flavors such as citral to improve their solubility and stability.Citral solid lipid nanoparticles (citral-SLNs) were prepared by high shear and high pressure homogenization method. The optimum preparation process was obtained firstly:the high shear homogenization speed was 19000 rpm, the high shear homogenization time was 1 min, the high pressure homogenization pressure was 550 bar, the homogeneous cycle was 2, then the formula was optimized as following: the emulsifier content was 1%, the ratio of citral to lipid was 1:2, the total content of citral and lipid was 3%,the average particle size of obtained citral-SLNs is 215.4 ± 4.32nm,the polydispersity coefficient PDI is 0.35 ± 0.04, the encapsulation efficiency is 60.68 ± 3.52%. Further optimization was done using response surface analysis, and the optimized results were as follows: the content of emulsifier 0.9%, the ratio of citral to lipid 1:2, and the total content of citral and lipid 2.9%.According to the model, the entrapment efficiency is 65.15%, and the entrapment efficiency of the experiment was 63.86%.The performance of the optimal citral-SLNs was characterized, scanning electron microscope results showed that the obtained citral-SLNs were smooth and spherical, and the particle size was consistent with the result of the dynamic laser light scattering. The original ordered crystal structure of GMS was reduced when citral was encapsulated in solid lipids by scanning calorimetry determination. Fourier transform infrared spectroscopy showed that citral was successfully encapsulated in citral-SLNs. X-ray diffraction analysis showed that a new less orderly phase was formed in citral-SLNs. Thermogravimetric analysis showed that the load percentage of citral-SLNs was 22.8%; the gas chromatographic results showed that the degradation rate of citral after entrapment was significantly lower than that of the non-entrapped, the retention rate of citral in the citral-SLNs sample was 66.98%, while that in the blank control was only 8.22% when the samples were stored at 37℃ for 12 days. It indicated that the solid lipid could effectively isolate citral from the acidic medium and reduce its oxidative degradation.Seven kinds of antioxidants (isoascorbic acid, tangeretin, β-carotene, naringenin,quercetin dihydrate, procyanidins and (+) - catechins) were selected from natural products to investigate the effects of solid lipid nanoparticles and antioxidants on the degradation of citral. The physical stability of samples with β-carotene and isoascorbic were better. In the sample using β-carotene, the degradation products p-cymene and acetophenone were significantly lower than those of the blank control and other samples, indicating thatβ-carotene could inhibit the formation of p-cymene and acetophenone, and it showed thatβ-carotene has the best effect on inhibition of citral degradation. |
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