Effects of storage time and temperature on quality of blueberry anthocyanin microcapsules

Abstract: Blueberry has a very rich source of bioactive compounds, including vitamin C and E, and phenolic compounds (anthocyanins). Many studies indicated that anthocyanins are beneficial to human health by reducing the risk of cardiovascular disease and improving vision. However, anthocyanins have a poor stability. Microencapsulation is an effective and promising method to prevent the degradation of functional ingredients. In order to explore the effect of storage time and temperature on the quality of blueberry anthocyanin microcapsules, and find out the appropriate storage conditions, quality evolution of microcapsules stored for 6 months under ?18, 4 and 25 ℃ was investigated respectively. The results revealed that there were no significant differences in water activity, hygroscopicity and encapsulation efficiency of encapsulated powders during the storage (P>0.05), which meant that anthocyanins were coated successfully in microcapsules using protein-polysaccharide as wall material. However, with the increase of storage time, the caking degree showed a gradual increasing trend (P<0.05), although the differences under different temperatures were insignificant (P>0.05). It was also found that the glass transition temperature decreased during the storage. One of the most remarkable things was that there was a sharp decrease in the glass transition temperature of anthocyanins stored for more than 4 months. During the storage, the total anthocyanins and total phenolics of microcapsules showed a decreasing trend (P<0.05), while the latter declined less. Storage under ?18 ℃ could increase the stability of anthocyanins and total phenolics obviously (P<0.05). It needed to be emphasized that the presence of whey proteins may improve the stability of malvidin-3-glucoside. Scanning electron microscopic images of encapsulated powders showed that particle size increased gradually due to the glass transition temperature declining. This led to antioxidant capacities, measured by ABTS radical scavenging assay and ferric iron reducing antioxidant power, decreased significantly (P<0.05). The peak intensity at 1 637, 1 508 and 1 030 cm?1 was weakened, which was associated with the possible weakening of the interactions between core and wall materials as well as the interactions among wall materials. Moreover, with the extension of storage time, encapsulation productivity of encapsulated powder and its release rate in water decreased gradually (P<0.05), and the encapsulated powder stored under ?18 ℃ had a higher encapsulation productivity and release rate in water than others (P<0.05). It could be due to that low temperature inhibited the weakening of intermolecular force. In addition, there existed an interaction effect of storage time and temperature on glass transition temperature, encapsulation productivity, release rate in water, value of ABTS and content of monomeric anthocyanins including malvidin-3-glucoside, peonidin-3-glucoside together with cyaniding-3-O-glucoside. Compared with the storage time, storage temperature was a less important factor affecting the stability of blueberry anthocyanin microcapsules. In general, whey protein isolate, maltodextrin, β-cyclodextrin and gum arabic are combined as wall materials, for encapsulation can benefit blueberry anthocyanins through alleviating their quality decrease during the storage. Moreover, the weakened interaction force between the molecules possibly causes a decline in the quality of blueberry anthocyanins during the storage. The suitable storage time and temperature are 3 months and -18 oC, respectively. This research provides the theoretical basis for the application of blueberry anthocyanin encapsulates.