Preparation of Matcha Fresh Noodles with Stable Color using Embedding Method and Microwave Treatment

Summary

The protocol describes a method for embedding matcha with whey protein and carboxymethyl chitosan and microwave-treating wheat flour to obtain color-stable matcha fresh noodles.

Abstract

Matcha, as a healthy food additive, has been widely utilized in traditional foods such as noodles, cookies, and bread. However, there are several challenges that must be addressed in the quality of matcha-incorporated foods, with the most significant being the prevention of matcha discoloration. In this study, we introduce a novel approach involving the incorporation of matcha with whey protein (0.08 g/mL) and carboxymethyl chitosan (0.04 g/mL), accompanied by microwave treatment at 700 W for 60 s of wheat flour to produce color-stable matcha fresh noodles. All steps involved in the production process of matcha fresh noodles are presented in the article, including matcha embedding treatment, microwave treatment of wheat flour, kneading the dough, leaving to prove, dividing the dough, rolling out the dough and slicing the sheets by noodle press. The findings revealed a 72.13% reduction in discoloration of fresh matcha noodles following embedding and microwave treatment, compared to untreated fresh matcha noodles. Moreover, the combined process did not have any detrimental impact on the sensory attributes of matcha noodles, including their aroma and taste. Therefore, the novel method proposed in this study holds significant potential for enhancing the color stability of fresh matcha noodles during preparation.

Introduction

Noodles are a staple of traditional grain-based cuisine in China, with approximately 40% of the wheat production in Asian countries being utilized for noodle processing¹. Nevertheless, the basic nutritional component of wheat flour is insufficient to satisfy the increasing nutritional needs of consumers. Therefore, several investigators have opted to replace a portion of the wheat flour in noodles with alternative natural ingredients, such as oat bran², milk protein³, sweet potato⁴, and citrus maxima⁵, in order to enhance the nutritional and functional qualities of the noodles. Matcha is an abundant bioactive compound possessing antioxidant and anti-inflammatory properties, which have the potential to mitigate the risk of cardiovascular disease and prevent chronic illnesses⁶. Consequently, there has been a burgeoning interest in investigating the integration of matcha into traditional culinary fare, including Chinese steamed bread, rice cake, and particularly fresh noodles.

However, fresh noodles are prone to time-dependent darkening, leading to unfavorable changes in the visual appearance of the product, which poses a significant challenge to the storage of fresh noodles⁷. It is widely agreed that the discoloration observed during the storage of fresh noodles is mainly caused by the presence of polyphenol oxidase (PPO)^7,8. Additionally, it was indicated that the soluble protein fraction is involved in the process of non-polyphenol oxidase (non-PPO) darkening⁹. Extensive efforts have been devoted in recent years to mitigate the darkening of PPO during storage. Previous studies have suggested that acid inhibitors and heat treatment applied to raw noodles could effectively achieve this objective by denaturing proteins and consequently inhibiting enzyme activity^10,11. Chlorophyll is susceptible to changes in pH, temperature, and heat, and the vibrant green hue of green tea noodles is primarily attributed to chlorophyll¹⁰. It is evident that there are limitations in effectively controlling the color of green tea noodles through the direct addition of acid inhibitors and heat treatment.

In addition to the thermal processing of wheat flour, the preservation of chlorophyll in matcha noodles is a critical factor to consider. Several methods have been proposed to prolong the storage time of chlorophyll and preserve its pigment, including the use of alkalinizing agents, copper complexations, and low-temperature storage¹². Unfortunately, the majority of processes necessitate a pH level close to nature in order to reduce the occurrence of unfavorable chemical reactions. The stability concern may be potentially mitigated by the copper complex of chlorophyll derivatives, which exhibit a green color reminiscent of natural chlorophyll. However, individuals exhibit a preference for natural chlorophyll over artificial colors. Microencapsulation techniques have emerged as a viable solution to the challenge of improving bioactive compounds' stability by providing barriers against environmental conditions such as oxygen, pH, ionic strength, and temperature^13,14,15. Until now, tea extract, catechins, and chlorophyll have been continuously studied for their stability and controlled release properties when embedded in different wall materials¹⁴. However, the incorporation of microcapsules into noodles has not yet been proposed¹⁵.

In this study, we described a method that embeds matcha with whey protein and carboxymethyl chitosan and microwave-treating wheat flour to obtain color-stable matcha fresh noodles. The addition of microencapsulated bioactive compounds to food facilitates the creation of novel functional food products while preserving the inherent qualitative attributes. We present the results obtained using this processing protocol to investigate alterations in color values of matcha noodles following storage. The specific objective of the study was to determine the optimal approach for preparing matcha noodles that demonstrate both exceptional color and flavor.

Protocol

1. Production of matcha-embedded suspension

1. Place 4 g of carboxymethyl chitosan (see Table of Materials) in 100 mL of distilled water to prepare a 0.04 g/mL of carboxymethyl chitosan stock solution. To dissolve carboxymethyl chitosan heat to 60 °C on constant temperature heating magnetic stirrer.
2. Dissolve 4 g of whey protein (see Table of Materials) in 50 mL of distilled water to prepare a 0.08 g/mL of whey protein stock solution.
3. After the solutions cool, store them in a freezer and refrigerate them overnight to fully saturate the polymer molecule.
4. Place 8 g of matcha and 4 g NaCl (see Table of Materials) in a beaker and add 50 mL of sterile boiled water to prepare matcha slurry. Assist the dissolution process using a glass stirring rod. Sterile water is deionized water that has been boiled in a pot for 15 min.
5. Mix matcha slurry with 50 mL of carboxymethyl chitosan solution and blend with a magnetic stirring apparatus at 300 rpm at room temperature.
6. Drip 25 mL of whey protein into the mixture and stir at 300 rpm for 30 min to create an embedded suspension. (see Figure 1). The suspension should be prepared concurrently with the noodle production and stored at a temperature of 4 °C on the same day.
   NOTE: The pH of the matcha-embedded suspension solution was left unadjusted, thus solely influenced by the matcha or wall material.

2. Microwave treatment of wheat flour

1. Distribute 300 g of wheat flour in a round plastic container. Cover the container with plastic wrap and place it in the microwave oven at 700 W for 60 s. Afterward, keep the container with flour outside until it feels cool.

3. Production of matcha noodles

1. Dough mixing: Pour 125 mL of pre-formed matcha-embedded suspension and 15 mL of water into 300 g of microwave-treated wheat flour slowly. Gently pull the flour into the center, bit by bit, until the embedded suspension is incorporated.
   1. For non-microwave-treated wheat flour, use 125 mL of water instead of matcha-embedded suspension to prepare noodles, which are labeled as blank noodles (control). Add 125 mL of water and 8 g of matcha to non-microwave-treated wheat flour to prepare noodles and designate these as matcha noodles (M-noodles).
2. Kneading the dough: Knead the noodle dough with a dough mixer for 7 min. The dough should be smooth and pliable, not wet or sticky when done.
3. Resting: Return the ball of dough to its mixing bowl and cover it with a damp tea towel. Let it rest for 30 min at room temperature.
4. Prepare noodles as described below.
   1. Divide the dough into 4 equal pieces, then rewrap 3 and set aside. Lightly flour the unwrapped piece, lifting it occasionally to ensure that it does not stick.
   2. Adjust the press roller spacing of the dough press to 3.5 mm. Place the dough on a dough press to sheet, and then compound. Press the dough sheet repeatedly until it reaches a smooth and pliable consistency.
   3. Thin the dough sheet to 1 mm. Starting from 3.5 mm, adjust the press roller spacing to 2 mm and then 1 mm. Press the sheet 3x in each roller spacing.
   4. Cover loosely with clingfilm, and then repeat steps 3.4.1-3.4.3 with the remaining dough.
      NOTE: In order to ensure that the pressing process of each batch of samples is consistent, the press roll spacing is adjusted once, and the next spacing is adjusted after each sample is passed.
   5. Slit the noodle strands into 22 cm long, 1 mm thick, and 3.0 mm wide samples (see Figure 2). Dust about 3.75 g semolina to make sure noodles do not stick together.

4. Sensory evaluation and physical property analysis

1. Sensory evaluation
   1. Place 30 g of noodles in 600 mL of boiling water and cook for 5 min. Immerse cooked noodles in cold water immediately, before testing.
   2. Perform sensory evaluation of noodle samples using quantitative descriptive analysis (QDA) as outlined in Li et al.¹². Ensure that the sensory characteristics of the samples are evaluated by 12 trained panelists using a nine-point hedonic scale with 9 denoting like extremely and 1 denoting dislike extremely.
2. Color measurement
   1. Cut cooked as well as fresh samples into pieces of about 10 cm and place them under the instrumental aperture of the colorimeter.
   2. Press the instrumental button to measure the color of the fresh noodles and repeat the test 6x for each sample.
3. Texture analyzer
   1. Determine the texture property of cooked as well as fresh noodles using a texture analyzer and calculate based on texture profile analysis (TPA).
   2. Place five strands of noodles on the test bench and repeat the test 6x for each sample.

5. Data analysis

1. Analyze the data by variance analysis (ANOVA) and consider the difference significant when p < 0.05.

Results

This protocol allowed for the sensory and physical property analysis of processed matcha-incorporated foods and noodles, beginning with matcha treatment and continuing through the intermediate stages of processing to the final product. This protocol was coupled with embedding and microwave to produce matcha noodles (Figure 3). The fresh noodles with unencapsulated matcha, with embedded matcha and microwave treatment, and without any matcha were marked as M-Noodles, ME-Noodle...

Discussion

Compared to instant noodles, fine-dried noodles, and other similar products, fresh noodles have a greater capacity to preserve their original taste and flavor, making them highly promising in the market. A previous study has shown that green tea could enhance the overall quality of fresh noodles to a certain degree¹⁶. Therefore, incorporating tea into the flour product system of fresh noodles aims to prioritize both high quality and health benefits, in line with the contemporary trend of promoting...

Materials

Name	Company	Catalog Number	Comments
Carboxymethyl chitosan	Mackin
Colorimeter	3nh	NH-300+
Dough mixer	ACA	AM-CG108
Freezer	Haier	BCD-252KS
Heating magnetic stirrer	Yuhua	DF-101S
Magnetic stirrer	Keezo	KMS-521D
Matcha	Jinhua Feicui
Microwave	Panasonic	NN-GF351X
NaCl	China National Salt Industry Corporation
Noodle maker	Tianxi	JCD-10
Texture analyzer	Lotun Science	TA-XT plus
Wheat flour	Queen
Whey protein	Yuanye