Variation Of Sulfur Compounds During Air-Borne Ultrasound Assisted-Air Drying Of Broccoli Florets And Product Development

Broccoli(Brassica oleracea L.var.Italica)belongs to the genus of Cruciferous Brassica.It is a rich source of protein,glucosinolates,isothiocyanates,phenolics,vitamins,minerals and others.Broccoli not only exerts promising chemoprotective effects and reduces cholesterol or lipid levels,but also may improve insulin resistance in type II diabetes.Recently,broccoli has achieved many attentions and affections for its high nutritional value.Ultrasound as an emerging technology has been combined with drying and applied for fruit and vegetable dehydration gradually.It is meaningful to explore the effect of air-borne ultrasound drying on the changes of physicochemical qualities and sulfur compounds in broccoli,as well as investigate the storage conditions on dried broccoli quality.In this thesis,the broccoli variety "You Xiu" was used as an experimental material to study the influences of microwave drying and air-borne ultrasound assisted air drying on the quality of broccoli.On this basis,the changes of sulfur compounds and the correlations of related factors were further investgated.Last but not least,the storage stability of dried broccoli was also evaluated.The results were shown as follow:1.The drying kinetics and detailed phytochemical profile of broccoli under microwave drying(500 and 900 W)and air-borne ultrasound(125.2 and 180.1 W/dm2)assisted air drying at 70? were compared.The results showed that,together with the higher drying speed,microwave performed better than ultrasound for the protection of chlorophylls and ascorbic acid.On the other hand,ultrasound-dried broccoli samples showed higher contents of carotenoids(lutein,zeaxanthin,?-carotene and ?carotene),glucosinolates(glucoraphanin,glucobrassicin and 4-methoxyglucobrassicin)and sulforaphane compared to the microwave-dried samples.The contents of lutein,glucoraphanin,glucobrassicin and sulforaphane in the ultrasound-dried samples at 180.1 W/dm2 were 56.5%,13.7%,24.9%and 53.0%higher than that in microwavedried samples at 900 W.Taking the aforementioned results and literature survey into consideration,it can be concluded that microwave drying has a higher drying efficiency,whereas ultrasound-assisted drying could be a better technology for the preservation of phytochemicals in fruits and vegetables.2.The current study investigated the evolution of sulfur compounds in broccoli florets during air-borne ultrasound(60?,125.2 W/dm2 and 180.1 W/dm2)assisted air drying.The factors associated with the systhesis and catabolism of glucosinolate were also explored.The results showed that the ultrasound treatment not only accelerated the drying kinetics(drying time were decreased by 11.1%at 125.2 W/dm2 and 17.8%at 180.1 W/dm2)and removed free and bound water faster than air drying alone,but also accelerated the heat transfer within broccoli,especially samples sonicated at 180.1 W/dm2.On the other hand,ultrasound treatment could increase glucobrassicin content and myrosinase activity,and promoted the degradation of glucoraphanin to sulforaphane with less Fe2+ interference.The content of glucobrassicin,sulforaphane,Fe2+ and myrosinase activity in ultrasound-dried samples at 180.1 W/dm2 were 10.7%,26.0%and 15.4%higher than that in air drying samples,while Fe2+ content was 8.1%lower than control sample.Although ultrasound application had no significant influence on total phenolics,free phenolic acids,ascorbic acid and antioxidant capacity(p<0.05),the pearson correlation coefficients indicated that ascorbic acid and phenolic compounds had significantly positive correlation with Fe2+.Amino acid could not facilitate the synthesis of glucosinolates,due to no significant correlation between amino acid and glucosinolates.Therefore,it can be concluded that air-borne ultrasound assisted air-drying is a promising technology for the production of dehydrated broccoli florets with accelerating drying process,promoting the transformation of sulfur compounds,and preserving phytochemicals.3.The adsorption isotherms at different temperatures(20,40,60?)and the storage stability in different humidity environment(11.3%,32.9%,57.4%)of broccoli powders were studied.Meanwhile,the quality of broccoli powder during storage for 90 d was also evaluated.The results showed that the adsorption isotherm of broccoli powder was featured as a ? type.The M0 value fitted by GAB model at 20,40,60?were decreased with temperature rising,whereas K values increased with temperature.After 90 d of storage,broccoli powders stored at 11.3%humidity had better color and less colonies,and no caking problem was observed.Although there were no significant differences in the content of glucosinolate among samples at these three humidiies,the loss of sulforaphane in broccoli powders stored in the humidity of 11.3%was reduced by 31.1%as comparison to the loss in powders stored in humidity of 5 7.4%.Therefore,the quality of broccoli powder stored in a humidity of 11.3%was the best.