| Broccoli is rich in functional components such as polysaccharides,dietary fibres,phenols,thioglucosides,etc.It has various pharmacological effects such as anti-tumour,antiinflammatory and serum cholesterol lowering.During harvesting and processing of broccoli,60-70% of the total plant stems and leaves are usually discarded,and the protein resources in them are wasted.Therefore,the sensible development and utilisation of broccoli agricultural by-products is in line with the concept of sustainable development.Plant-derived peptides are protein hydrolysis products formed from plant proteins and hydrolysed by proteases,which have the characteristics of small molecular weight,high antioxidant activity and strong safety,and can be used as natural antioxidants in the food industry.In this experiment,broccoli leaf protein was extracted by acid heating method using broccoli waste leaves as raw materials,and the amino acid composition and functional properties were determined.Later,broccoli leaf antioxidant peptides were prepared by ultrasonic pretreatment enzymatic hydrolysis.Finally,using the prepared antioxidant peptides as raw materials,a fruit juice drink with special flavour was developed and its related physical and chemical properties were determined,with the aim of improving the utilisation rate of broccoli agricultural by-products and developing a new way for deep processing of broccoli leaf protein.The main research contents and conclusions of this paper are as follows:(1)Extraction of broccoli leaf protein.In this study,broccoli leaf protein was extracted from broccoli leaves using an acidification and heating method.It was experimentally determined that the magnitude of the influencing factors were: C > A > B.Extraction time >p H > extraction temperature.The best process conditions were p H 4.70,extraction temperature70°C,extraction time 11 min,and the yield of leaf protein under these process conditions was9.80%.(2)The amino acid composition and content of the extracted leaf proteins were analysed and their nutritional value was evaluated.By using LC showed that,the highest amino acid content was glutamic acid,followed by aspartic acid.The result of RAA/RC analysis showed that the essential amino acid content of broccoli leaf protein was highest in leucine,followed by threonine,and the first limiting amino acid was phenylalanine + tyrosine.(3)The functional properties of broccoli leaf protein were determined,including solubility,water-holding capacity,oil-holding capacity,foaming,emulsification and emulsion stability.The analysis showed that broccoli leaf protein has good functional properties.(4)Broccoli leaf antioxidant peptides were prepared by ultrasonic pretreatment enzymatic hydrolysis,with DPPH radical scavenging rate as the index,and the results of univariate test and response surface analysis were obtained,the enzyme addition amount(C)> enzymatic hydrolysis time(D)> ultrasonic power(A)> ultrasonic time(B),the optimal enzymatic hydrolysis conditions were ultrasonic power 280 W,ultrasonic time 20 min,enzyme addition amount 7000 U/g,enzymatic hydrolysis time 160 min,under these conditions the actual value of DPPH radical scavenging was 93.34%.(5)Using beet juice and apple juice combination juice,citric acid,erythritol and broccoli leaf antioxidant peptide as raw materials,and using sensory score as an index,single factorial and orthogonal experiments were used to determine the best process parameters of broccoli leaf antioxidant peptides juice drink: the ratio of beet juice and apple juice combination juice was4:6,the addition amount of citric acid was 0.06%,the amount of erythritol was 5%,the amount of antioxidant peptides was 1.5%,and the sensory score of fruit juice drink was 84.4.(6)The physicochemical and microbiological indices of the broccoli leaf antioxidant peptides juice drink were determined as follows: p H 4.21 ± 0.27,soluble solids content 6.50 ±0.20%,total acid content 0.91 ± 0.09%,sedimentation rate 1.08 ± 0.44%,total bacterial colony<100 CFU/m L,E.coli and pathogenic bacteria were not detected. |
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