Preparation Of Spray-dried Mulberry Leaves And The Changes Of The Phenolic Compounds During In Vitro Digestion

Mulberry leaves are traditional Chinese medicine for the treatment of diabetes.With the potential antihypertensive,antihyperglycemic,antioxidant,and antiinflammatory activities,consuming mulberry leaves as a health food has become more and more popular.The phenolic compounds are the major component in mulberry leaves that exert biological activities.However,the phenolic compounds decreased in the extraction of mulberry leaves with ethanol or water during processing.Therefore,whole mulberry leaves are beneficial to retain phenolic compounds during processing nutraceuticals when compared with their extract.At the same time,phenolic compounds are unstable in the gastrointestinal tract,which results in a low absorption rate in human gastrointestinal tract.Previous studies have reported that thermal processing could increase the bioaccessibility of phenolic compounds.However,the phenolic compounds are sensitive when exposed to oxidants,light and heat.Therefore,selection of thermal processing method and appropriate conditions is crucial for mulberry leaves processing.Spray drying is a thermal treatment and the time of thermal treatment is shorter in the process of spray drying than most thermal processing methods.Meanwhile,the addition of drying aids can protect the thermosensitive components in raw materials during processing.In this study,the status of raw materials and drying aids formulation for spray drying mulberry leaves were optimized,and the effects of spray drying on the metabolism of phenolic compounds in the gastrointestinal tract were determined through in vitro gastrointestinal digestion and colonic fermentation.The sensory evaluation and major nutrient composition of spray dried whole mulberry leaves powder were investigated to evaluate the potential of spray-dried mulberry leaves to be developed as a health food.The results of this study are as follows:1.The retention of phenolic compounds in spray-dried whole mulberry leaves and spray-dried mulberry leaf extracts were compared.The results showed that The retentions of phenolic compounds in spray-dried whole mulberry leaves were higher than spray-dried mulberry leaf extracts(p < 0.05),which indicated that the whole mulberry leaves were more appropriate to be used as raw materials during processing of spray-dried mulberry leaves.2.The spray-dried products with different proportions of maltodextrin and whey protein isolate were prepared,and the physical and chemical properties of products were investigated.The optimal drying aids formulation was selected via principal component analysis.The results showed that with the increase of whey protein isolate content,the water solubility of the product increased,hygroscopicity decreased and the color of products became brighter.Moreover,the total polyphenol content,total flavonoids content and antioxidant capacity of products were also increased.At the same time,the content of whey protein isolate was significantly positively correlated with the content of total phenols,total flavonoids and antioxidant capacity.Finally,the product 6 which possessed the highest content of whey protein isolated(38.7%maltodextrin,3.8% soybean lecithin,24.2% whey protein isolate)had the highest comprehensive score in principal component analysis.Therefore,the product 6 was chosen as the optimal product.3.In vitro gastrointestinal digestion and colonic fermentation were carried out to analyze the stability of phenolic compounds in spray-dried whole mulberry leaves in the gastrointestinal tract.In the gastrointestinal digestion stage,the bioaccessibility of phenolic compounds in spray-dried mulberry leaves was significantly higher than that in fresh mulberry leaves,which proved that spray drying could improve the stability of phenolic compounds of mulberry leaves in the gastrointestinal digestion stage.In the stage of colonic fermentation,the degradation rate of phenolic compounds of spraydried mulberry leaves was higher than that in fresh mulberry leaves,which indicated that spray drying could enhance the utilization efficiency of phenolic compounds of mulberry leaves by intestinal microorganism.4.The major nutritional components of spray-dried mulberry leaves were determined,the sensory evaluation and the in vitro digestion was carried out to evaluate its potential to be developed as a health food.Compared with the freeze-dried mulberry leaf powder,the spray-dried whole mulberry leaf powder prepared in this study had higher contents of three macro-nutrients.Moreover,spray-dried products possessed higher solubility when holding the original flavor and aroma of mulberry leaves.Meanwhile,the bioaccessibilities of phenolic compounds in spray-dried mulberry leaves were higher than those in freeze-dried mulberry leaves.Therefore,the spraydried mulberry leaves prepared in this study has the potential to be deveoped as a health food.