Study On Nutritional Characteristics Of Hempseed And Effect Of Processing On Its Quality

China has a tradition of using hempseed as edible and medicinal material since ancient times.Hempseeds from six main growing regions of China were selected,marked as ALHS,GBHS,GTHS,HBHS,HSHS,YDHS,and their facades,the content of basic nutrients,fatty acids,amino acids,mineral elements,total phenolic contents,total flavonoid contents and antioxidant activity were investigated.In addition,the effect of four kinds of thermal processing methods steaming,frying,hot air roasting and microwaving on the sensory,color,main nutrition components,fatty acid composition,fat oxidation and antioxidant activity of YDHS were analyzed.At last,the fermentation conditions of hempseed milk were explored to provide technical support for the further processing and utilization of hempseed.The main findings are as follows:(1)The appearance and content of each component of hempseed from different places were obviously different.The weight of hempseeds were 4.87?7.29 g/(100 grains),and the kernel yields were 45.57%?54.92%.YDHS showed the maximum weight with the smooth surface and full grain.GBHS had the highest kernel yield.The color of the shells gradually became lighter with the latitude increased,and the color overall were brownish gray.The content of lipid(47.40?53.06%),protein(11.15?19.18%),total sugar(2.72?4.98%)and ash(3.37?5.26%)varied considerably in hempseed from different growing regions.The results indicated that YDHS showed the highest protein content and total sugar content.ALHS had the highest fat content and GTHS had the highest ash content.Hempseeds had high level of unsaturated fatty acids(85.89?90.56%),which detected as 17 amino acids and 7 essential amino acids.P,K,Mg,Ca and Na were the highest constant elements and Fe,Zn,Mn and Cu were the highest trace elements.The total phenolic and total flavonoids content respectively ranged from1.71 to 2.57 mg GAE/g and from 0.41 to 2.92 mg QE/g,and the highest contents were detected in YDHS.The results of antioxidant tests showed that YDHS revealed the highest DPPH free radical scavenging ability and FRAP value,and GBHS revealed the highest ABTS~+free radical scavenging ability.(2)During the thermal process,the raw smell of hempseed gradually decreased,the grain flavor,the burnt paste smell and the greasy rancidity gradually increased.Scoring based on the combination of the raw smell,the roasted grain flavor,the burnt smell and the greasy rancidity of thermal processed hempseed,conditions for steaming,frying,hot-air roasting and microwaving were:atmospheric pressure steaming 8 min,150°C frying 15 min,130°C hot-air roasting 40 min,and 600 W microwaving 4 min.The protein,total sugar and ash content of thermal processed hempseeds were decreased.In addition,the fat content of microwaved hempseeds increased,the steamed,fried and hot-air roasted hempseeds all decreased.The content of total phenol and total flavonoids of fried hempseeds decreased,while the hempseeds treated by the other three thermal processed had no significant change.The proportion of unsaturated fatty acids of thermal processed hempseeds were reduced to varying degrees.Among them,the fried hempseeds were most obviously reduced,while the hot-air roasted hempseeds had the smallest effect.In addition,the thermal processes had different degrees of influence on the color of hempseeds.After thermal processing,the AV,POV,p-AV and TOX of hempseed increased in varying degrees.The steamed hempseeds had the largest increase in AV.The fried hempseeds had the largest increase in POV.The p-AV and TOX of the fried and microwaved hempseeds had the max and min increase respectively.In addition,the activity of lipoxygenase in hempseed was reduced effectively by thermal processing,among which the activity of lipoxygenase in the roasted hempseeds had the greatest decrease,and the activity of hot-air roasting had the smallest decrease.The antioxidant activities of steamed hempseed increased,while the antioxidant activities of fried hempseed reduced.The DPPH free radical scavenging ability and FRAP of hot-air roasting hempseed and microwaved hempseed increased,but the ability of scavenging ABTS~+free radical were reduced.(3)Through Box-Behnken response surface design,the regression model of the fermentation conditions was obtained as follows:Y=0.91-2.333E-003A-5.121E-004B-8.647E-003C-0.033D-7.293E-003AB-4.784E-003AC-0.01AD-0.029BC-7.5E-004BD-0.022CD+7.438E-003A2-0.029B2-0.02C2-0.015D2.The optimal fermentation conditions were as follows:Lactobacillus bulgaricus:Streptococcus thermophilus:Lactobacillus casei:Streptococcus acidophilus=2:2:1:1.7841,inoculation amount 6.21%,fermentation temperature39.42°C and fermentation time 7.12 h.In actual operation,Lactobacillus bulgaricus:Streptococcus thermophilus:Lactobacillus casei:Streptococcus acidophilus=2:2:1:1.8,inoculation amount 6%,fermentation temperature 39°C and fermentation time 7.2 h,the number of viable bacteria of hempseed fermented milk was 1.9×10~8 CFU/m L,the acidity was78°T,the sensory score was 8.74,the fuzzy comprehensive evaluation value was 0.927,and the comprehensive quality was good.Compared with raw hempseed milk,the contents of total sugar and total solids of fermented hempseed milk were significantly reduced(p<0.05)under optimal fermentation conditions,and the contents of total acids,total phenols and total flavonoids were significantly increased(p<0.05).The results of antioxidant tests showed that DPPH free radical scavenging rate,ABTS~+free radical scavenging rate and FRAP of fermented hempseed milk were improved,and the DPPH free radical scavenging ability and ABTS~+free radical scavenging ability were respectively equivalent to those of 9.51 mg/m L and 17.86mg/m L Trolox solution.