Comparison of the Physicochemical Properties of Clear Beetroot Juice-Enriched Noodle with Different Amounts of Alkali
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Abstract:
Beetroot juice, rich in bioactive substances, is a good source of food colorings and functional ingredients. In this study, clear beetroot juice (CBJ) was added to the formulated noodle to improve the nutritional value, antioxidant properties and color of the noodle. The 10% CBJ-noodles was used as the research object to study the effects of added alkali level (0~0.40%) on the texture, color and antioxidant properties of the resultant noodles. Texture and color of the noodles were measured by a texture analyzer and a colorimeter, respectively. Total contents of betalains and polyphenols, and the 1, 1-diphenyl-2-picrylhydrazyl (DPPH) radical scavenging capacity were determined by spectrophotometry. The research results showed that compared with the control noodle (without alkali), increasing the alkali level (0.10~0.40%) significantly increased the breaking force (11.07~33.35%) and the content of free polyphenolics (2.26~25.28%) of the dried CBJ-noodles, whilst decreasing significantly total betalains (3.77~43.20%) and DPPH radical scavenging capacity (1.08~18.20%). In addition, increasing the level of added alkali increased significantly the cutting force (10.88~29.23%) and tensile strength (47.78~137.21%) of cooked noodles. In terms of color, the redness (a* value) of dried raw and cooked CBJ-noodle with 0~0.40% alkali ranged from 16.59 to 1.98 and from 7.39 to 1.76, respectively. These results indicate that the betalains in CBJ were unstable at a high pH and temperature. Therefore, this research proposes the use of a low alkali level (0.10%) for the preparation of alkaline noodles, which makes the noodles not only having a pink appearance but also possessing higher contents of retained betalains and polyphenols and higher antioxidant activity.
