Glucosinolates in watercress (Nasturtium Officinale) and their hydrolysis products under different conditions

• Main Author: Nurazilah Farhana Aripin
• Format: Thesis
• Language: English; English
• Subjects: QK710-899 Plant physiology
• Online Access: https://eprints.ums.edu.my/id/eprint/38976/1/24%20pages.pdf; https://eprints.ums.edu.my/id/eprint/38976/2/FULLTEXT.pdf; https://eprints.ums.edu.my/id/eprint/38976/

Watercress or Nasturtium officinale is a cruciferous vegetable that commonly known as a rich source of gluconasturtiin or 2-phenyl ethyl glucosinolates (PEGLS), the type of glucosinolate that abundant in watercress. However, very few studies have been done on PEGLS content thus the first objective of this study is to quantify and qualify glucosinolates content (PEGLS and other GLS if any) in watercress. It is crucial to understand the hydrolysis of PEGLS because (and depending on conditions) phenylethylnitrile (PEN) and / or phenylethylthiocyanate (PEITC) are possible hydrolysis products of PEGLS. Unlike PEITC, these other hydrolysis products are not known to possess anticancer properties. The production of PEITC and any other hydrolysis products are caused by endogeneous myrosinase activity hence, the second objective of this study is to study the myrosinase activity under different conditions. There are many factors that influence the hydrolysis of glucosinolates which are external factors such as temperature, pH, presence of redox agents, and intrinsic factors such as structure of the side-chain of GLS, myrosinase activity and protein specifiers etc. Hence, the hydrolysis products of watercress (PEITC and PEN) also being investigated through this study. The conditions studied for both myrosinase activity and hydrolysis products of watercress were temperature ( 25°C, 45°C and 65°C), pH ( 3, 7, 9), ascorbic acid and ferrous ions with similar concentration (2mM, 4mM, 6mM, 8mM, and 10 mM). Glucosinolates contents (extracted using deionized water) and myrosinase activity (crude myrosinase mixed with known concentration of sinigrin, as substrate) were analysed using HPLC. While GC used in this study was to profile the hydrolysis products that being extracted using dichloromethane after the hydrolysis of glucosinolates and enzyme myrosinase in the presence of water. The results showed that the amount of PEGLS in the watercress plant for 0.5 g is 0.21 μmol/g. The optimum conditions of myrosinase activity showed at 45°C (1.23 mM min s-1), pH 7 and 9 (1.36 mM min s-1) and both 2mM concentration in ascorbic acid (0.67 mM min s-1) and ferrous iron (1.44 mM min s-1) . While for PEITC and PEN, all conditions showed the highest content of PEITC compare to PEN. For ascorbic acid and ferrous iron, the highest content of PEITC showed in the concentration of 2 mM which are 886.8 ppm and 756.1 ppm respectively while 25°C for temperature (601.1 ppm) and at pH 9 for pH conditions (561.1 ppm).The overall aim of this study is to identify the optimum conditions for the production of PEITC in watercress and the activity of the endogeneous enzyme myrosinase. These findings will be beneficial to provide information on how to optimize the uptake of this anticancer secondary metabolite from watercress.