| Broccoli(Brassica oleracea L.var.italica)is a very popular cruciferous vegetable.The main ediable part of broccoli is the top flower and nearly 70%of stems and leaves are discarded as waste at harvest,which results in a waste of resource and environmental pollution.On the other hand,broccoli stems and leaves are rich in protein,vitamins,ketones and other substances with bioactivity.Particularly for sulfur glucoside glucosidase(also known as glucosinolates),it can be degraded by myrosinase to form isothiocyanates.According to epidemiological studies,isothiocyanates have anti-tumor activity.Therefore,the studies about isothiocyanates are growing continousaly in recent years.In this paper,the transfers of glucosinolates to isothiocyanates under different stress treatments were investigated.After that,the lactic acid bacteria that can degrade glucosinolates were selected.Furthermore,the fermentation process to produce broccoli kimchi was optimized.The effect of low-temperature plasma sterilization on the quality of broccoli kimchi,as well as its storage stability was also studied.The main results are shown as follows:The effects of mechanical segmentation,low-temperature storage at 4?,heat shock and maceration on the contents of glucosinolates and isothiocyanates(ITCS)in broccoli stems were investigated.The results showed that when the size of broccoli stem was 1.0 cm ×0.2 cm×O.5 cm,the content of glucosinolate is the lowest,being 22.85?mol/100gDW.Meanwhile,The highest content of isothiocyanates(653.74mg/gDW)was obtained.During storage at 4?,both the degradation rate of glucosinolates and the generation rate of isothiocyanates were lower than that during storage at 25?.Furthermore,broccoli stems were immersed in phosphate-citrate buffer solutions at different pHs,ZnSO4 solutions with various concentrations and ascorbic acid solutions for 2 h at 25?,respectively.It was found that when pH of phosphate-citrate buffer solution reached 7.5,both the lowest content of glucosinolate and the highest content of isothiocyanate were obtained in broccoli stems,being 19.09 ?mol/100gDW and 654.36 mg/gDW,respectively.When Zn2+ concentration was 100?mol/L,the content of glucosinolate was the lowest and the content of isothiocyanate was the highest,being 19.09 ?mol/100gDW and 608.32 mg/gDW,respectively.For ascorbic acid,when its concentration was 50?mol/L,the content of the content of glucosinolate was the lowest and the content of isothiocyanate was the highest,being 9.96 ?mol/100gDW and 291.06 mg/gDW,respectively.In addition,when the temperature was 35?,the glucosinolate content in broccoli stem was the lowest.16 strains of lactic acid bacteria were isolated from natural fermented broccoli leaves.After primary and secondary screening,a strain named B2 was slelected,which had a high ability to degrade glucosinolate and enrich isothiocyanate.According to API identification system,B2 was identified as lactobacillus.Lactic acid bacteria fermentation was conducted in broccoli flower stem and leaf,respectively.Single-factor and orthogonal experiments were performed to optimize the fermentation process.The optimal fermentation conditions were 7%for salt concentration and 8%,7%and 9%for inoculum in flower,stem and leaf,respectively.Furthermore,the optimal concentrations of ascorbic acid and Zn2+ for broccoli stem were 150 and 210 ?mol/L.For broccoli flower,the optimal concentrations of ascorbic acid and Zn2+were 140 and 160 ?mol/L.As regarded to broccoli leaf,the optimal concentrations of ascorbic acid and Zn2+ were 110 and 150 ?mol/L.Atmospheric-pressure plasma sterilization was used to process brocooli stem,leaf and flower for 0,30,60,90 and 120 s,respectively.It was found that the total numbers of bacteria,mold and coliform decreased with sterilization duration.After plasma sterilization for 120s,the numbers of bacteria,mold and coliform in untreated samples were 24.51,26.80 and 38.37 times higher than that in plasma treated samples.No bacteria,mold and coliform were detected in broccoli stem,flower and leaf after plasma sterilization for 120 s.Furthermore,the contens of glucosinolates and isothiocyanate in broccoli kimchi did not change significantly(P>0.05).However,glucosinolates and isothiocyanate contents decreased gradually during storage at 4?and ambient temperature.The decreasing rate at 4? was significantly lower than that at ambient temperature.After storage for 120 d,the content of isothiocyanate in broccoli stem pickles stored at 4? was 1.77 times higher than that in samples stored at ambient temperature.In addition,the total numbers of bacteria,mold and coliform in smaples stored at low temperatures were all lower than that in samples stored at ambinent temperatures. |
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