Large amounts of broccoli by-products are generated every year, which are excellent sources of health-promoting isothiocyanates (ITCs). To explore the influence of pretreatments and starter cultures on ITC production during fermentation of broccoli by-products, the dynamics of the glucosinolate (GSL) profile, the formation of total ITCs, the shifts in physicochemical parameters, and the survival of lactic acid bacteria (LAB) were systematically investigated in two batches of broccoli stalks. Three aliphatic, three indolic, and one aromatic GSLs were identified in fermented broccoli. Aliphatic glucoerucin and indolic 4-methoxyglucobrassicin were the main GSLs in both batches of broccoli. The degradation of GSLs and pH change primarily depended on pretreatments; more than 80% of total GSLs degraded in all groups within 10 days of fermentation, while it only takes one day for raw blended groups to degrade more than 97% of total GSLs, and two days for heated blended groups to have 61.1–82.7% degradation. The decrease in pH and increase in LAB in raw cube groups were slower. When it comes to ITC production, the starters played a more important role. Significantly higher ITCs level was detected in Lactobacillus agilis and Companilactobacillus farciminis fermented combined with heat-pretreated groups and Lactobacillus plantarum fermented heated puree group, which could be attributed to the favored pH (3.6–4.2). Overall, our results indicate that LAB fermentation contributed to the production of ITCs from GSLs in broccoli stalks. Pretreating the broccoli stalk with heating and blending favors both the degradation of GSLs and the production of ITCs.
Song et al. (Sat,) studied this question.