Ultrafine Grinding Of Mulberry Leaf And Its Application In Biscuit

Mulberry leaves are the major component of mulberry trees,which are rich in carbohydrates,amino acids,cellulose,vitamins and mineral compounds.Meanwhile,there are also many bioactive compounds in mulberry leaves,including flavonoids,phytosterin,y-aminobutyric acid(GABA),1-Deoxynojirimycin(DNJ)and organic acids.These bioactive compounds result in anti-aging,anti-cancer,anti-oxidation,anti-obesity,anti-atherosclerosis,anti-inflammation and anti-diabetes properties.Fresh leaves cannot be preserved for a long time,due to the high water content.Thus,it is importan to process mulberry leaves to various products,in order to extend its application in the food industry.In this thesis,the effects of different pretreatments before drying on the quality of mulberry leaves powder were studied.According to the results,ultrasound was selected as a proper pretreatment method.After that,ultrasound-treated mulberry leaves were grinded into powders by using ball grinder.The influence of various ultrafine grinding times on the quality of mulberry leaves powder was analyzed.Meanwhile,the effect of high temperature baking on the bioactive compounds of mulberry leaves powder was studied.Furthermore,mulberry leaves powder was appropriate to be added on the surface of biscuits after baking.The manufacturing process was optimized.In addition,the quality and safety of biscuits containing mulberry leaves powder was evaluated.The main outcomes are shown below:1.Investigation of various pretreatments on the quality of mulberry leavesThe effects of bleaching and ultrasound treatment before drying on the bioactive compounds,water content and ash of mulberry leaves were studied.Specifically,bleaching(100?,90 s)reduced the water content,as well as the contents of ash,flavonoids and chlorophyll(chlorophyll decreased by 50.3%and flavonoids decreased by 38.9%)(p<0.05).Meanwhile,the effect of bleaching on GABA and DNJ contents was insignificant(p>0.05).On the other hand,ultrasound pretreatment(20 kHz)resulted in the increase of mulberry leaf weight.Weight gain first increased with the increase of ultrasound intensity and then decreased gradually.After sonication at 117.6 W/L for 15 min,solid loss due to sonication reached maximum,being 0.367%.The drying time of ultrasound-treated(63.0 W/L,20 ?and 10 min)mulberry leaves was reduced by 27.5 min.However,there were no significant differences in the contents of flavonoids,GABA,DNJ,total phenolic and chlorophyll between ultrasound-treated and non-ultrasound treated samples(p>0.05).Therefore,ultrasound was selected as a proper pretreatment before drying of mulberry leaves.2.Effects of ultrafine grinding and baking on the quality of mulberry leaves powderMulberry leaves powder was produced through ultrasound pretreatment(63.0 W/L,20 ?and 10 min),drying and ultrafine grinding.Ultrafine grinding at 480 r/min for 3 h did not affect water content,ash and color of mulberry leaves powder.However,particle size of the powder decreased with increasing of grinding time.The contents of chlorophyll,flavonoids,DNJ increased slightly after grinding for 9 h.The contents of DNJ,total chlorophylls and flavonoids were 2.87?3.66 and 74.94 mg/g,respectively after 11h grinding.On the other hand,the investigation was done by adding 20%powder into the biscuit dough and passing through baking process at 200 ? for 3 min 20 s.The contents of DNJ,total chlorophylls and flavonoids decreased significantly(p<0.05).The color of powders turned darker simultaneously.In summary,the optimal way to produce mulberry leaves powder was ultrasound,drying and grinding successively.Due to the loss of bioactive compounds in mulberry leaves powder,high temperature baking was not suitable for mulberry leaf application in Food Industry.3.Application of mulberry leaves powder during biscuit manufacturingBiscuits were mainly produced by roll-in,molding,baking and cooling.After that,Mulberry leaves powder was added to the surface of biscuits.It was found that when the addition of mulberry leaves powder was 1%(w/w),the quality of resulting biscuits was satisfactory.Meanwhile,the timing of mulberry leaf powder addition was investigated.When mulberry leaves powders were added before and after oil spray,the sensory scores of biscuits were 1.5 and 0,the sensory criterion was a 5-scale system from-2 to 2.When mulberry leaves powder was mixed with palm oil and then added,the sensory score was-1.5.Therefore,mulberry leaves powder was added before oil spraying at a ratio of 1%.Furthermore,the physicochemical and microbiological properties of resulting biscuits were determined.According to the results,the water content of biscuits containing ultrasound-treated mulberry leaves powder was 0.016 g/g,which was lower than that specified by the national standard 0.040 g/g.The microbiogical parameters were all within the range of national standards.In addition,the good products were packed with PET composite films.After being stored at 52 ?&75%RH for 8 weeks,the biscuits were slighted oxidized but still accepted;whilst,storage in ambient condition(25 ?)lasted 9 months and all test items were within the range of national standards.In summary,the shelf-life of biscuits containing mulberry leaves powder can reach 9 months.