The use of microbial transglutaminase and soy protein isolate to enhance retention of capsaicin in capsaicin-enriched layered noodles

Abstract

Specialty layered noodles (LN) were prepared by sandwiching a capsaicin-enriched dough (CED) between two gastro-resistant dough layers made up of wheat flour, soy protein isolate (SPI) and microbial transglutaminase (MTG) at 0.5 (0.5MTG LN), 1.0 (1.0MTG LN) and 1.5 (1.5MYG LN) g/100 g of wheat-SPI flour. The textural, tensile and structural breakdown properties, capsaicin retention, microstructures and the sensory characteristics of cooked LN were evaluated. Compared to other LN, 1.5MTG LN exhibited the highest textural and tensile parameters, highest capsaicin retention, densest structure and was the most difficult to breakdown. The sensory quality of all LN was acceptable, even though it was the Control LN (prepared without SPI and MTG) that scored the highest acceptability. In general, increasing the level of MTG in the sandwiching dough layers of MTG LN reduced the release of capsaicin in simulated mouth, gastric and intestinal conditions, and these results could be due to increased protein cross-linking.

Introduction

Capsaicin is the predominate substance responsible for the hot character of chili peppers, which is known to exert the function of anti-obesity through increasing the energy expenditure and decreasing the appetite. After ingestion of capsaicin, the energy metabolism is enhanced via the activation of sympathetic nervous system (Kang et al., 2010; Westerterp-Plantenga, Diepvens, Jossen, Berube-Parent, & Tremblay, 2006). This causes an increased secretion of catecholamine from the adrenal medulla (Yoshioka et al., 1999) and the expression of certain fat degrading proteins (Joo, Kim, Choi, & Yun, 2009). The feeling of satiety is promoted and the energy intake is reduced (Reinbach, Smeets, Martinussen, Moller, & Westerterp-Plantenga, 2009; Westerterp-Plantenga, Smeets, & Lejeune, 2005). However, the application of capsaicin in the food industry for treating or preventing obesity is limited because the effective dose of capsaicin application in food for weight control (10–30 mg) (Reinbach, Martinussen, & Moller, 2010; Yoshioka et al., 2004; Yoshioka et al., 1999) is much higher than the limitation of intake for normal people (1–10 mg) (Craft & Porreca, 1992; Yoshioka et al., 2004; Yoshioka, St-Pierre, Suzuki, & Tremblay, 1998). A product that is directly incorporated with capsaicin may be too hot for most consumers to consume. This calls for products that can deliver capsaicin in a controlled manner. As such, some cutting-edge companies have already introduced delivery systems that are based on encapsulation technologies using capsules that are designed to release capsaicin in the intestine, but not in the stomach, to reduce irritation and pain. While this approach is suitable for nutraceutical applications, more innovation is desirable in order to achieve similar functions in food products.

“Layered Noodle” (LN) is a specialty noodle product that is prepared by sandwiching a capsaicin-enriched dough (CED) layer with two gastro-resistant dough layers, which might be a good candidate to carry the functions of capsaicin (Li, Liong, & Easa, 2011). This idea is possible because many Asian consumers choose to slurp the noodle rather than chewing them extensively during eating. Because a quantity of capsaicin is retained in the middle layer of the LN, consumers should experience reduced pain in the mouth. The release of capsaicin in the stomach and intestine will be expected to be controlled thus reducing irritation (Li et al., 2011).

To achieve the controlled-release properties, the overall structure of the LN should be strong and resistant to breakdown, in order for it to retain capsaicin and release it in a controlled manner. Microbial transglutaminase (MTG) is a thermal stable enzyme, which is isolated from Streptoverticillium sp. and legally to be assessed as a processing aid food enzyme. MTG has great potential to be used in the food industry as an agent to improve firmness, elasticity and water-holding capacity of food through the mild enzyme reactions (Aalami & Leelavathi, 2008; Basman, Köksel, & Arli, 2006). After incorporating MTG, high molecular weight polymers were formed through ε-(γ-Glu)Lys bonds, which reinforce the network structure and modified the properties of the products (Motoki & Seguro, 1998). The effects of MTG can be obtained in various kinds of noodles and pasta, but the degree of change in the physical properties varies with the sorts of products. By adjusting the amount of MTG, the textural qualities of noodles/pasta can be controlled (Kuraishi, Yamazaki, & Susa, 2001). Furthermore, since the cross-links introduced by MTG are heat-stable, the modified structures of noodle are retained for longer even after cooking. Therefore, the use of MTG at different levels might be a safe and efficient way to develop the gastro-resistant properties of LN enriched with capsaicin.

Soy protein isolate (SPI) has been broadly used as the functional ingredient and texture enhancer in the food industry (Tang, Wu, Chen, & Yang, 2006). SPI that is treated with additional food-based protein cross-linking enzyme, such as MTG, has been shown to enhance the network structure and gastro-resistant properties of SPI gels and noodles (Gan, Cheng, & Easa, 2008; Gan, Ong, Wong, & Easa, 2009; Yeoh, Alkarkhi, Ramli, & Easa, 2011). Thus, MTG treated SPI that is incorporated with LN could function as the gastro-resistant layers that enhance the capsaicin retention of LN.

We have described the basic preparation of the so-called layered noodles (Li et al., 2011). Other than this, there is no report in the literature that describes the preparation or evaluation of layered noodles for controlling the release of capsaicin. Thus, the objective of this study was to evaluate the textural and breakdown properties, capsaicin retention, microstructures and sensory characteristics of the layered noodles as a function of MTG concentration.