Effects of thermal treatment on colour and texture of Typha latifolia L.

Abstract

A b s t r a c t. Through the analysis of the residual activity of peroxidase (POD), chromatic aberration, shear intensity and shear power, the effects of different thermal treatment times at 100°C on the POD, surface colour and texture of Typha latifolia L. were evaluated. The results showed that the activity of POD decreased with the increasing thermal treatment time at 100°C. The regeneration amount of POD increased first for some time and then started to decrease with the treatment time. Thermal treatment times 1.0 and 1.5 min at 100°C exhibited maximum regeneration of POD for the samples stored at 20 and 37°C, respectively. The sample had acceptable texture and surface colour when they were treated at 100°C for 4 min because the POD in the sample was inactivated to an acceptable level.K e y w o r d s: colour, texture, regeneration of POD, pretreatment, vegetable processing INTRODUCTION Typha latifolia L., which is called 'pucai' vegetable in China, belongs to Typha genus. This vegetable is distributed all over the world. Typha latifolia L. is also growing in Poland, and its name is 'pa³ka szerokolistna'. It is used for industrial purposes. In English it is also called 'Bulrush, Common Bulrush, Broadleaf Cattail, Common Cattail, Great Reedmace'. In China, Typha latifolia L. is mostly grown in the lakes, canals or ponds in the south of the Yangtze River. The young stem of Typha latifolia L. is used as edible vegetable in traditional Chinese cuisines, while in other nations or regions it is often used as water-growth plant for landscaping and purification of water or as herb (Ke, 1998). In famous Huai-Yang Cuisine, belonging to Chinese 'Eight Great Cuisines', Typha latifolia L. is one of the most important vegetables for some famous dishes in Chinese restaurants and family meals (Zhou and Zhang, 2004). At present, the production of Typha latifolia L. reaches to about 20 000 tons each year in Southern China (Huai-an City Statistics Bureau, 2003). Unfortunately, it is very difficult to preserve the colour and texture of fresh Typha latifolia L. in cold or room storages (Li and Duan, 2004). Therefore, it is important to develop a preservation technology based on thermal treatment.Peroxidase (POD) enzyme affects the quality of vegetable products in postharvest storage and processing (Han, 1999). POD is a redox enzyme which can catalyze four different reactions: -peroxidation, -oxidation, -peroxide reaction -hydroxylation.The main reaction that POD catalyzes is peroxidation in which the substrates are peroxide and reducing agents (Wang, 1988). The main roles of POD in reducing vegetable quality include: enzymatic browning, development of offflavour especially in low acid vegetables during storage, and lipid oxidation. In the processing of Typha latifolia L., severe enzymatic browning and off-flavour would take place if the activity of POD in the products is not prohibited. Therefore, inactivation of POD in vegetables is necessary for the retention of product quality. In processing vegetables, thermal treatment is a ...

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