Capture the pungency of horseradish products (Armoracia rusticana) study on glucosinolates and myrosinase

Armoracia rusticana (Horseradish, Brassica family) is a root characterized by a pungent taste and smell that is released from glucosinolates (GLSs) hydrolysis. GLSs are hydrolyzed by the endogenous enzyme myrosinase (MYR) upon cells damage, producing volatile breakdown products, such as isothiocyanates (ITCs) [1]. ITCs are also known to have anticarcinogenic properties, thus their formation has a health benefit for consumers [2]. Horseradish is widely consumed freshly grated or mixed with vinegar as sauce. Due to its very long growing season, horseradish is only available for few months a year, and the storage affects pungency of horseradish. The aim of this study is to investigate how different horseradish preparations and storage temperatures affect the GLSs, MYR and ITCs levels. Horseradish was collected from Basilicata (Italy) and investigated as (1) grated and (2) grated with vinegar and olive oil (sauce). Both products were stored for 2 months at 4˚C and - 20˚C. GLSs, MYR and ITCs were measured in the untreated, fresh prepared and stored samples. No MYR activity was detected in the sauce, probably due to the low pH of vinegar (pH =2.8). Whereas in grated radish 10 % MYR activity was retained upon two weeks of storage at 4 °C. The storage temperature that most preserved the MYR activity was -20 °C with 50 % of retention after two months. Sinigrin, the most abundant GLS in horseradish [1], show the highest stability storing the samples at 20 °C, regardless the type of product. The sinigrin degradation was explained by the hydrolytic activity of MYR. In fact, in samples in which MYR was still active and in which the conditions were favorable for the hydrolysis, the sinigrin degradation was higher. For the allyl ITCs, which are the ITC of the sinigrin, very low levels were detected in all samples regardless the storage temperatures, probably because these compounds were lost during the grating of the radish due to their volatility. A supplementary experiment was conducted to evaluate the taste and flavor of the graded horseradish during storage, to associate the low levels of allyl ITC detected with the pungency of the samples. The sensory test (6 participants) showed that the storage severely affected the pungency of the samples, especially by storing at 4 °C. This work shows that the storage decreases the release of the allyl ITCs reducing the healthy effect and also its taste and flavor. New researches should be conducted to optimize the preparation of horseradish to preserve the sensory attributes and its biologically active compounds upon storage. References 1. Li X and Kushad MM. 2004. Correlation of glucosinolates content to myrosinase activity in horseradish (Armoracia rusticana) roots. Journal of Agricoltural and food chemistry 52, 6950-6955. 2. Zhang Y. 2010. Allyl isothiocyanate as a cancer chemopreventive Phytochemical. Molecular Nutrition & Food Research 54, 127-135.