Study on Nutrients and Texture of Pickled Huangzhou Radish

Ying ZHANG Zhenyan TIAN Xin LIU Shisheng LI Quan KUANG

Abstract [Objectives] The changes in the nutrient contents and texture of pickled Huangzhou radish with pickling time were studied to further improve its edible value and improve its sensory evaluation. [Methods] Huangzhou radish as a raw material was pickled， and exploration was conducted through the following aspects： with the extension time of pickling time， the changes in nutrient contents such as reducing sugars， free amino acids and ascorbic acid were detected in pickled Huangzhou radish， and the changes in the texture characteristics of pickled Huangzhou radish such as hardness， viscosity， elasticity， recoverable deformation， compression power and chewiness were detected. [Results] As the pickling time became longer， the reducing sugar content in pickled Huangzhou radish gradually increased， and when the pickling time exceeded 13 d， the reducing sugar content showed a downward trend; the ascorbic acid content gradually decreased， and the decreasing rate was relatively lower after the pickling time exceeded 7 d; and the amino acid content first increased and then decreased， and when the pickling time exceeded 13 d， the content exhibited basically no change. The hardness of the radish gradually decreased; the viscosity first decreased and then slowly increased; the recoverable deformation first increased and then decreased; the elasticity first increased and decreased; and the chewiness first increased and then decreased. Through this experiment， it is concluded that the pickled Huangzhou radish has richer nutrients and the best taste when the pickling time is 7-10 d. [Conclusions] This study provides a theoretical reference for producing and processing pickled Huangzhou radish， improving the quality of pickled Huangzhou radish and increasing the nutritional value of the product.

Key words Pickled Huangzhou radish; Nutrients; Texture characteristics; Edible taste

Pickled radish is a kind of pickled vegetable prepared from fresh radish as raw material by infused with salt water with auxiliary materials under the action of various microorganisms. It tastes salty， refreshing， natural and pure. It can be eaten as an assistant food or as a seasoned dish[1-4]. Pickled radish has intestine cleaning， antibacterial， anti-cancer， anti-aging， anti-arteriosclerosis， anti-obesity， anti-mutation activity and cerebral hemorrhage-preventing effects[3]. It is one of the world's three recognized healthy fermented vegetable pickles. Huangzhou radish not only has a crisp taste， but is also rich in Vc and trace element zinc， which helps to improve the body's immune function[5-9]. During the pickling process of Huangzhou radish， the nutritional quality and commercial value of the food itself change greatly. At present， there are few reports on the analysis of the changes in the nutritional composition and browning kinetics of Huangzhou radish during the pickling process[10-11]. In this study， the changes in nutrient content and texture of pickled Huangzhou radish with the passage of pickling time under normal temperature conditions were investigated， so as to explore the change laws of amino acids， reducing sugars， ascorbic acid and other nutrients during pickling of Huangzhou radish. Moreover， the texture indicators such as chewiness， viscosity， elasticity， recoverable deformation and hardness were measured， aiming to provide a theoretical reference for producing and processing pickled Huangzhou radish， improving the quality of pickled Huangzhou radish and increasing the nutritional value of the product.

Materials and Methods

Materials

Huangzhou radish from the Dabie Mountain Biological Resource Library was used as the experimental material.

Experimental methods

Methods and steps of pickling Huangzhou radish

The Huangzhou radish was first washed， sliced and air-dried to remove the surface water， for later use. Then， a kimchi jar was disinfected and washed with boiling water， and a jar of water was boiled， added with 5% edible salt and 5% white sugar， and stirred thoroughly， to make the salt and sugar dissolve completely. After the water was cooled， the processed radish slices were added into the kimchi jar， which was finally added with garlic， ginger and other auxiliary materials and sealed for storage[12].

Determination of reducing sugars， ascorbic acid and amino acids

The reducing sugars， ascorbic acid and amino acids in pickled Huangzhou radish were determined by the 3，5-dinitrosalicylic acid reagent （DNS reagent） colorimetric method[13]， the 2，6-dichlorophenol indophenol titration method[14] and ninhydrin colorimetry[15]， respectively.

Texture analysis of Huangzhou radish during pickling

The test parameters of a texture analyzer were set as follows： test target type： TPA mode， target value： 5 mm， test speed： 1.00 mm/s， and probe specification： TA44 Cylinder/4 mm D cylindrical probe. Based on pre-experiments and references， the pickled Huangzhou radish was placed on the base of the texture analyzer and tested in TPA mode[16]. The texture indicators included the hardness of pickled Huangzhou radish， the stickiness of pickled Huangzhou radish， the elasticity of pickled Huangzhou radish， the recoverable deformation of pickled Huangzhou radish， the chewiness of pickled Huangzhou radish， etc.

Statistics and processing of experimental data

Excel 2010 and SPSS-13 were used to process the required observation data of each treatment group， and perform analysis of variance and multiple comparisons.

Results and Analysis

Variation of reducing sugar content in Huangzhou radish during pickling

From Fig. 1， with the passage of pickling time， the reducing sugar content gradually increased. When the pickling time exceeded 13 d， the reducing sugar content showed a downward trend. The main reason was that as the pickling time increased， the salt content in pickled Huangzhou radish was fully absorbed， and lactobacillus fermentation in the radish also affected the reducing sugar content. When the pickling time exceeded a certain value， the reducing sugar content decreased. Combined with the effect of pickling time on reducing sugar in radishes， the appropriate pickling time was 7-13 d.

Analysis of the variation of ascorbic acid content in Huangzhou radish during pickling

It can be seen from Fig. 2 that with the extension of the pickling time， the ascorbic acid content gradually decreased. The main reason was that as the pickling time increased， the fermentation of pickled Huangzhou radish had an impact on the ascorbic acid content， and as the pickling time became longer， the ascorbic acid content decreased accordingly. Combined with the effect of the pickling time on the ascorbic acid in the radish， the appropriate pickling time was 7-10 d.

Analysis on the variation of amino acid content in Huangzhou radish during pickling

It can be seen from Fig. 3 that as the extension of the pickling time， the amino acid content first increased and then decreased. When the pickling time exceeded 13 d， the amino acid content exhibited basically no change. The main reason was that the radish would absorb salt water with the passage of pickling time; and lactobacillus fermentation also affected the amino acid content， and when the pickling time exceeded a certain value， the amino acid content decreased with the change of fermentation speed， and finally reached a balance. Combined with the effect of pickling time on reducing sugar in radish， the appropriate pickling time was 7-10 d.

Analysis of the texture changes of Huangzhou radish during pickling

It can be seen from Fig. 4-Fig. 6 that with the extension of the pickling time， the hardness gradually decreased， the recoverable deformation first increased and then decreased， and the viscosity first decreased and then slowly increased. The main reason might be that as the pickling time was prolonged， the salt in the radish was fully absorbed， the hardness of the radish was changed by the influence of salt， and the moisture content of the radish increased， which changed its recoverable deformation and affected the viscosity change of the pickled Huangzhou radish; and the fermentation of radish also had a great influence on various parameters， and when the pickling time exceeded a certain value， the changes of various factors gradually became slow. Considering texture parameters of the first cycle from Huangzhou radish during pickling， the appropriate pickling time was 7-10 d.

Conclusions and Discussion

In the pickling process of pickled radishes， the amount of sucrose added[17] and the duration of the pickling time[18-19] are also important factors. The amount of sucrose added has an impact on the acid production of lactic acid bacteria and yeast during the pickling process， which affects the taste and flavor of pickled radishes[17，20]. The duration of the pickling time has a greater impact on the taste， flavor and nitrite content of pickled radishes. As the pickling time becomes longer， the nitrite content in pickled radishes will gradually decrease， which is more beneficial to human health and the improvement of food safety， but a too long pickling time will affect the taste and flavor of food[21-22]. Therefore， it is more reasonable to consider the plan of pickling radishes in combination with the control of the addition of salt and sucrose during the pickling process and the pickling time[21-23]. In this study， we could draw the following conclusions： ① in terms of nutrients， as the pickling time became longer， the reducing sugar content of pickled Huangzhou radish gradually increased， and when the pickling time exceeded 13 d， the reducing sugar content of pickled Huangzhou radish showed a downward trend; the ascorbic acid content of pickled Huangzhou radish gradually decreased， and the decreasing rate was relatively slow after the pickling time exceeded 7 d; and the amino acid content of pickled Huangzhou radish first increased and then decreased， and when pickled for more than 13 d， the content exhibited basically no change. Therefore， from the perspective of changes in nutrient content， when the pickling time is 7-10 d， pickled Huangzhou radish is more nutritious， which is more beneficial to the human body. ② In terms of texture， combined with the changes in the parameters of the first cycle， the hardness of pickled Huangzhou radish gradually decreased （too high hardness makes the radish more difficult to chew， while too low will reduce brittleness and affect the taste）; the viscosity first decreased and then slowly increased （too high viscosity makes the radish more sticky and affects the mouthfeel， while too low will affect the chewing effect）; the recoverable deformation first increased and then decreased （the higher the recoverable deformation， the better the elasticity and the better the taste when eating）; the elasticity first increased and then decreased （The higher the elasticity value， the better the elasticity and the better the taste）; and the chewiness first increased and then decreased （the higher the chewiness， the better the texture when eating）. Therefore， from the perspective of texture analysis， pickled Huangzhou radish has the best taste when the pickling time is 7-10 d. Combining above two aspects and considering actual situation， the most suitable time for pickling Huangzhou radish is 7-10 d.

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