| Sargassum fusiforme is a marine algae with high nutritional value.However,fresh S.fusiforme is perishable due to high water content,and not easy to preserve for a long time.Drying,the primary processing method for agricultural products,can effectively reduce moisture,which facilitate long-term storage and transportation for the agricultural products.However,different drying methods have different effects on the physical and biological activities of the dried samples.In this work,four different drying methods(freeze drying,hot air drying,microwave drying,and sun drying)were used to treat S.fusiforme,and the composition and activity of dried S.fusiforme were analyzed.The results showed that the rehydration rate of freeze drying samples is the highest,and that dried by sun drying is lowest.The color of the freeze drying samples is close to fresh S.fusiforme and the values of L*,a* and b* are the highest.The color of the sun drying samples is black and the values of L*,a* and b*are the lowest.The chemical analysis showed that the samples dried by freeze drying contain the highest contents of polyphenols and total chlorophyll,which is 7.85mg/g and 0.1524mg/g,respectively.Compared with other drying methods,the microwave drying samples show the highest content of polysaccharides(177.72mg/g).Biological activity analysis showed that the samples dried by freeze drying have the highest scavenging activities with DPPH radical and ABTS radical,and FRAP reducing power and ?-glucosidase inhibitory activity.The samples dried by microwave drying show the strongest hydroxyl radical scavenging and DNA protective abilities.The sun drying samples show the lowest antioxidant activity and ?-glucosidase inhibitory activity.The results from this work showed that the different drying methods have different effects on the quality of S.fusiforme.The samples dried by freeze drying exhibit the best appearance quality,antioxidant activity and ?-glucosidaseinhibitory activity.S.fusiforme has strong fishy smell,which affects the consumer acceptance and limits the development of S.fusiforme industry.Fermentation by microorganism is one of the common methods to change odor compounds and improve the nutritional function of agricultural products.In this study,S.fusiforme was fermented by Cordyceps militaris to reduce the fishy smell and improve the nutrition.The results showed the L* value and b* value decreased,while a* value increased with the fermentation process.The scanning electron microscope(SEM)analysis showed that the structure of S.fusiforme is eroded after fermented by C.militaris.During the fermentation,the polysaccharide content decreased firstly from 14.53 mg/g on day 0 to 10.44 mg/g on day 8 and then increased to 13.09 mg/g on day 12.The polyphenols content and the antioxidant activity of S.fusiforme showed a decreasing trend during the fermentation.But the ?-glucosidase inhibitory activity of S.fusiforme was continuously enhanced.HPLC-MS analysis showed that significant differences existed between the original sample and the 6th day fermentation sample.Fishy odor of fresh S.fusiforme is not smelled after fermentation.GC-MS analysis showed that the components and contents of volatile compounds in S.fusiforme decrease significantly after fermentation.For example,the content of trans-?-ionone is 3.312 mg/kg on day 0,but decreases to 1.932 mg/kg on day 4,and the compound cannot be detected after 8 days fermentation.The results of this study showed that fermentation is an effective method to remove the odor of S.fusiforme and enhance its ?-glucosidase inhibitory activity. |
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