Effects Of Different Drying Processes On The Quality Of Spirulina Platensis

Drying process is essential for the product quality and throughput of Spirulina. To obtain in-depth understanding of the effects of different drying processes on the quality of Spirulina, four approaches of drying process, including microwave drying, microwave vacuum freeze drying, hot air drying and vacuum freeze drying, were investigated by measuring organoleptic qualities, moisture content, packing state, flowability and the content of phycobiliprotein and p-carotene in different drying samples.The results indicated that the vacuum freeze-drying powder was bottle green, with a strong fishy smell, which was similar to fresh Spirulina; the samples dried by microwave vacuum freeze method and hot air method were slightly dark green with a mild fishy smell; the colour of microwave drying was dark green and a mild fishy smell. The vacuum freeze-drying sample was relatively loose with a bulk density of0.303g·cm-3and porosity of0.283respectively; the bulk density of microwave drying, microwave vacuum freeze drying and hot air drying were1.007g·cm-3,0.791g·cm-3,1.638g·cm-3respectively, and the porosity of them were0.167,0.155,0.229respectively. All of the four kinds of drying powders had a good flowability, but the vacuum freeze-drying sample was slightly worse than the other three with an angel of repose of26.50°nd an angel of slide of58.33°.The contents of phycobiliprotein and β-carotene in vacuum freeze-drying powder were11.7%and2600μg·g-1, which was the highest one of the four drying methods, while the microwave drying sample had less than2%phycobiliprotein and1770μg·g-1β-carotene. The contents of phycobiliprotein and (3-carotene in microwave vacuum freeze drying and hot air drying were close by about9.5%and1100μg·g-1Although the vacuum freeze-drying had a high content of bioactive compositions, the stacking state and flowability were worse than those of the other three processes. The powder by microwave vacuum freeze drying had a better stacking state and flowability, but the deficiency was that it only had1110μg·g-1β-carotene. However, the drying time of microwave vacuum freeze process reduced nearly two-thirds compared with that of the vacuum freeze process. In summary, the microwave vacuum freezing drying with an optimization would become a suitable method for the drying processing of Spirulina.