In the present study, rice noodles known as koay teow were prepared from a locally grown, popular, organic rice variety Bario rice of Malaysia and were compared with Basmati rice (imported from Pakistan). The quality criterion's evaluated included: determination of physical (colour and texture), cooking and organoleptic properties. Additionally, microbial quality of fresh and stored noodles (stored for 3 days with 0 day as control) was also determined. Results showed tensile strength and elasticity modulus of rice noodles to decrease on storage with Bario rice showing the lowest value for both the parameters analyzed (24.11 kPa and 7.89kPa), respectively. The cooking loss of rice noodles increased with storage for both rice varieties with Basmati rice having higher range of 5.9-7.14%. With regard to colour, significant differences was observed between storage days for all three parameters of L*, a* and b*value. L* value of noodles prepared from Bario as well as Basmati rice showed a decrease on storage (became darker). With regard to microbial quality, total plate count as well as yeast and mold counts increased significantly during storage. The colour (6.67), appearance (6.8) and texture (6.67) of fresh rice noodles was much higher in Bario rice than in Basmati rice. From the results obtained it can be concluded that the physical, cooking and microbial quality of rice noodles deteriorated with storage.
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Today, consumers' expectation and demand for healthy and nutritious food has increased tremendously. In addition, consumers are constantly looking for novel food products wherein local produce (cereals, grains, legumes, etc) are incorporated. This has rendered food manufactures to explore and formulate new food products (with improved taste, texture and appearance) based on the local traditional knowledge available.
Rice noodles are traditionally prepared popular dish, broadly consumed in most of the South-East Asian Countries (Fiedler et al. 2009). The main ingredients for rice noodles are just the rice and the water, mixed at appropriate concentration. Rice noodles have a very smooth texture, mouth feel and are white in colour. It has been reported that adequate functional and cooking properties are essential to produce a high quality starch based noodle (Chen et al. 2003; Cui 2005; Purwani et al. 2006). As the quality of noodles (cooked or uncooked) are generally assessed by its physical (colour and texture), cooking and organoleptic properties, it is highly imperative to provide these details when developing a noodle from an unreported rice variety. In this study, to prepare rice noodles, we used 'Bario' rice which is considered as an exotic local variety of rice with a distinctive taste, soft texture, and exhibiting a mild and delicate aroma on cooking. This rice is as an organic produce and are grown at high altitudes (1000 meters above sea level). Based on these, the present study was undertaken to prepare a new noodle formulation using the local, Bario rice variety and were compared with one of the most popular rice varieties, the Basmati rice, which is preferred by consumers worldwide due to its aroma, tenderness, and taste (Bhattacharje et al. 2001). It was envisaged that the results generated from this study will be useful to popularize this local rice variety for international market.
MATERIALS AND METHOD
Samples and Noodle Preparation
The rice varieties used in the present study were purchased from the local Supermarket (Penang, Malaysia). Bario rice was origin from Sabah, East Malaysia, while Basmati rice was imported from Pakistan. Rice grains without any apparent physical or insect damage were selected for analysis.
For preparation of noodles, approximately 300 g of rice grains were individually weighed (in replicates of 3) and soaked overnight (16 ± 1h) in 300 ml potable quality water (to soften the grains). Further, it was blended in a Waring blender (Panasonic Model MX-898, Malaysia) for 10 min until a thick and uniform batter was formed. Cooking oil (0.5 ml, sunflower) was brushed onto a baking pan (6 x 2 inch round pan) and the batter (120 ml) was poured gradually and smoothly unto the oiled baking pan. The baking pan was placed into a steamer (Well Company Model 288128, Made in China), closed with a lid and steamed for 5-6 min., until cooked. Once done, the freshly steamed noodles were again coated with the cooking oil. This process was again repeated (until 3 more layers are formed) with another 120 ml of batter poured on top of the first layer of noodles and then steamed for another 5-6 min. The last layer of batter was steamed for 8-9 min. On cooling, the baking pan was removed from the steamer and the fresh noodles prepared were cut into 15cm x 1cm (l/b) slices. The noodles prepared were used immediately for various analysis (0 day), while those noodles placed in air tight containers and were stored at room temperature (25 ± 1°C) for 3 days for storage analysis.
Colour Measurement, Tensile Strength and Elasticity
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Colour analysis was carried out on rice noodles using a colourimeter (Minolta Spectrophotometer model CM-3500d, USA). Initially, the colourimeter was calibrated by using the zero calibration plate, followed by the white calibration plate. Three individual measurements of L*, Chroma and Hue values were taken for each noodle. L*, a* and b* values were chosen as it represents lightness (brightness), a* (redness when positive and greenness for negative) and b*(yellowness when positive and blueness when negative). Colour analysis were performed on the samples between day 0 (control) up to day 3 ( storage).
The texture of cooked noodles was determined using a Texture Analyzer, -TX2 model (Stable Micro Systems, Surrey, England), which was pre-calibrated using a 2.5 kg load cell. For tensile strength analysis, the settings included: Mode, Measure force in tension; Option, Return to start; Pre-Test Speed, 1mm/s; Test Speed, 3.0mm/s; Post Test Speed, 15mm/s and Distance, 100 mm. Initially, the cooked noodles were maintained at room temperature for 10 min and were tested by placing one end into the lower ring arm slot and the other end to the upper arm. From the force and displacement curve obtained from the TA machine, informations such as tensile strength and elasticity of the noodle strands were calculated. Tensile strength was calculated as σ = F/A,
Where σ is the tensile strength (Pa), F is the maximum load or peak force (N) and A represents the cross sectional area of the noodle strand (m2).
The elasticity modulus (EM) of noodle strands was calculated based on the formula:
EM = Flo x 1
Where, F/t is the initial sloe (N/s) of the graph (Force vs Time), lo is the initial length of the noodles between the limit arms (10mm), Ao represents the original cross section are of the noodles and v is the movement rate of the upper arm (0.0003m/s).
The cooking loss of noodles were determined following the method described by AACC (2000) with slight modifications. In brief, approximately 250 mL of potable water in a beaker was brought to a boil on a hot plate. When the water started boiling, 25 g of noodles, (cut into 3 ï‚´ 5 cm) length was placed in the beaker and cooked for 5-6 minutes until no white core was observed (visually). Cooking process was confirmed by pressing a single noodle between two sterile and clean glass plates. The noodles were then drained, rinsed and cooled with water. An evaporating dish containing 20 ml of the filtrate was then dried in an oven at 105ËšC (Memmert UL 40) until a constant weight was attained.
Cooking loss (%) = Weight of drained residue in cooking water (g) - 100
Weight of noodles before cooking (g)
Rehydration Ratio The rehydration ratio of noodles was evaluated based on the method described by Von Loesecke (1945) with slight modifications. In brief, a strainer is used to hold 3 g of noodles, which is then dipped into boiling water in a 250 ml beaker. The noodles were cooked for approximately 10-12 min., before being drained in a strainer (for 2 min.). After this, the noodles surface were dried using a paper towel to remove the excess water adhering to the noodles. Rehydration ratio was calculated as the weight of the cooked noodles compared to the weight of the dried noodles.
Microbiological quality evaluation
Total Plate Count (TPC) and Yeast and Mould Counts (TYMC)
Determination of TPC and TYMC, was based on spread plate method described by Jay (1986). Freshly prepared rice noodles (10 g) was homogenized in a stomacher bag with 90 ml of sterile peptone water (Buffered peptone water, EMD Chemicals, Inc, Ginnstown, NJ; 1 g/L) in a stomacher blender (Stomacher® 400 Circulator, Seward Ltd., West Sussex, UK). Appropriate serial dilutions were prepared and 0.1 ml of each dilution was spread on Merck Plate Count Agar plates using disposable spreader (SPL Labware). Further, agar plates containing samples were inverted upside down followed by incubation at 37°C for 48 h. After incubation, the colonies were counted manually and results were expressed as log CFU/g of rice sample. The same procedure was repeated for stored noodles wherein samples were collected on day 1, 2 and 3.
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For TYMC, potato dextrose agar (Dehydrated potato dextrose agar, EMD Chemicals Inc, Gibbstown, NJ). In brief, 25 g of rice noodle samples were mixed with sterile peptone-water solution (0.1%, 225 ml) of in a stomacher bag and homogenized in a stomacher blender. Serial dilutions of the sample were prepared upto 10-4, after which, 1 ml from each dilution was transferred onto a corresponding Petri dish and spread-plated. The plates were incubated for 5-6 days at 25±1°C. The same procedure was repeated for stored noodles wherein samples were collected on day 1, 2 and 3.
Sensory quality examination of the fresh noodles was carried out with the help of 30-trained panelists consisting of both students and staff of the Food Technology Division, University Science Malaysia (USM). The sensory laboratory consisted of isolated sensory booths to minimize the panelists bias as well as maximize their sensitivity for evaluation. Hedonic ratings using 9-point scale was adopted to determine the sensory quality. Panelist were required to evaluate the noodles based on the colour, odour, appearance, texture, overall appearance and overall acceptability. The scale used is verbally anchored as follows: like extremely, like very much, like moderately, like slightly, neither like nor dislike, dislike slightly, dislike moderately, dislike very much and dislike extremely. The higher ratings indicated good quality attributes (1 indicated dislike extremely, and 9 indicated like extremely).
All the data generated in the present study was analyzed using SPSS version 17.0 (SPSS Inc., Wacker Drive, Chicago, IL, USA). Triplicates of readings were used and presented as mean ± standard deviation (S.D.). Tukey's HSD post-hoc test was performed and statistical significance was considered at P < 0.05.
RESULTS AND DISCUSSION
Colour is one of the important parameter used to evaluate by the consumers for marketability of noodles. (Asenstorfer et al. 2010). The colour of fresh noodles is a clear indicator on its quality as fresh noodles needs to maintained its white-ish appearance. Based on the results obtained in the present study (Table 1), the L* value of rice noodles decreased in fresh noodles prepared from both Bario and Basmati rice samples. With an increase in storage days the noodles got darker. The L* value reduced from 69.13 (day 0) up to 64.21 (day 3) in Bario rice. Whereas in noodles prepared from Basmati rice, the L* decreased from 77.13 (day 0) to 73.98 (day 3).
It has been reported that after being stored for two to five days, fresh noodles have a tendency to darken (Hatcher et al. 2010), which holds true for our observations too.
With regard to a* value, there was no significant difference recorded between day 0 and 1 for noodles prepared from either Bario or Basmati rice varieties. The b* values were significantly different between storage days. For Basmati rice, the b* increased from 10.57 to 12.51 to 13.91 and 16.21 after 3 days of storage. Colour analysis is done and measured throughout storage as it provides vital information to food manufactures on the stability and strength of colour ( Hatcher et al., 2010).
Tensile Strength and Elasticity
Texture is an important attribute of cooked noodles as it determines consumer acceptance of the product (Dexter et al, 1985; Hatcher et al, 2010). In the present study, texture of cooked noodles was assessed as tensile strength and elasticity (figure 1A).
In this study, noodles prepared from Bario rice had higher tensile strength as compared to Basmati rice (46.33 kPa and 36.33kPa on day 0). After 3 days of storage, less force was needed to tear noodles prepared from both Bario and Basmati rice. Tensile strength assesses the capability of noodles to endure a longitudinal force without tearing. The cooking quality of noodles can also be determined based on the results of tensile strength as it indicates how the noodles can stay intact during cooking (Bhattacharya et al. 1999; Ross 2006). Amylose content of rice varieties is reported to have significant effect on the strength of noodles (Guo et al., 2003; Fari et al. 2011;). The higher the amylose content (22.63 for Bario rice and 9.43 for Basmati rice), the higher the tensile strength, which holds true in this study also.
Elasticity is defined as the ability of deformed noodles to return to its initial shape and size when the force creating the deformation is removed. Results from this study showed noodles prepared from Bario rice to have a higher elasticity modulus as compared to Basmati rice (13.19 and 7.89 on day 3 of storage). Overall, Elasticity modulus of rice noodles decreased significantly after storage in noodles prepared from both rice varieties. High quality noodles are usually associated with noodles which possessed high elasticity modulus ( Chen et al., 2002).
Cooking loss is an important attribute in noodles as it evaluates the amount of irrecoverable solid content in cooking water. It is highly vital that the structural integrity of noodles need to be maintained throughout the cooking process. In the present study, noodles prepared from Basmati rice had a higher value for cooking loss, which was found to increase on storage (Figure 2A). After 3 days of storage, Basmati rice noodles had a cooking loss of 7.14%, while Bario rice cooking loss was 3.89%. High cooking loss is unacceptable as there can be high amount of solubilized starch present which leads to cloudy boiling water and 'sticky' mouth feel with lower tolerance (Jin et al. 1994; Chen et al., 2002; Chakraborty et al. 2003;).
Rehydration ratio for Bario and Basmati rice noodles is shown in Figure 2B. Overall, no significant differences were observed on storage of noodles prepared from Bario rice on day 0 and 1 and on day 2 and 3. However there was a significant difference in Basmati rice on day 2 and 3.
Bario rice noodles had a higher rehydration ratio (3.89) compared to Basmati rice noodles (3.71) after 3 days of storage. High rehydration ratio tends to make noodles limp and sticky whereas low rehydration ratio causes noodles to have a hard and unrefined texture (Collado et al., 2001; Yoenyong-buddhagal and Noomhorm 2002;). Our results on decrease in rehydration ratio of rice noodles on storage time are in agreement with the findings of Zhang (2006) on instant rice noodles.
Microbial Quality Evaluation
Results obtained for microbial quality is depicted in Fig. 3A. Based on the results, the TPC of noodles prepared from both Bario and basmati increased significantly during storage. Overall, Basmati rice had a higher TPC as compared to Bario rice. The TPC for Bario rice ranged between log 2.63 CFU/g on day 0 and log 6.02 on day 3 whereas for Basmati rice the TPC content ranged from log 3.54 CFU/g to log 6.89 CFU/g. The acceptable amount of total microbes in fresh rice noodles should be less than or equal to log 7 CFU/g (ANZFA, 2001; Thai Industrial Standard, 2005). Based on results on TPC, both Bario and Basmati noodles were still acceptable even after 3 days of storage at room temperature.
The TYMC for Basmati rice was higher compared to Bario rice (figure 3B). Initial TYMC for Basmati rice was log 1.12 CFU/g and log 0.98 CFU/g for bario rice. By the 3rd day, the TYMC in Basmati rice noodles was log 3.51 CFU/g and log 2.98 CFU/g for bario rice, respectively. Generally, yeast and molds optimum temperature of growth is around 25-37oC, where it grows luxuriantly. This temperature range is commonly encountered in most of Asian countries. Thai Industrial Standard (2005) states that the acceptable amounts of TYMC for fresh rice noodles should be equal or less than log 2 CFU/g. However, in the present study, after being stored for 2 day at ambient temperature, both samples were above the recommended amounts and hence the noodles are recommended to be consumed within 48 hours of preparation (stored at room temp.).
Sensory quality evaluation is vital whenever a new food product is developed. This is also important when consumer acceptability towards the food product need to be forecasted (Hutchings, 1999). Results obtained on sensory evaluation in terms of colour, odour, appearance, texture, appearance and overall acceptability is presented in Figure 4.
From the results, the colour acceptability score for Bario rice were 6.67 and Basmati rice was 5.87. Determining visual color as a part of sensory quality is important because the first parameter which is assessed visually by a consumer is color (Blouin et al. 1981; Hutchings 1999.Odour of food has an effect on the amount of food consumed by consumers (Stevenson et al., 1999). The odour of rice noodles prepared from Basmati rice was slightly higher than Bario rice (5.87 and 5.73 respectively). However in terms of appearance, Bario rice had a higher score of 6.8 as compared to Basmati rice (4.3).
Texture has been recognized as the second most assessed sensory property of food (Rakosky 1989). Bario rice had the more preferred texture and a higher acceptability score of 6.67 compared to 4.8 of Basmati rice. In terms of overall appearance and acceptability Bario rice faired much better implying that it was the more preferred noodles compared to Basmati rice.
Overall, based on the results generate in this study, the tensile properties, cooking properties, colour and microbial count of rice noodles started to deteriorate after 3 days of storage. Rice noodles made from Bario rice had good tensile properties. Basmati rice had a low rehydration ratio but high cooking loss. For sensory analysis, panellist preferred Bario rice noodles over Basmati rice noodles as it had the higher overall acceptance and appearance. The suitability of Bario rice in the preparation of fresh rice noodles should be explored even further due to its good cooking and physical properties. Improvement in rice noodles quality especially in terms of storage by selecting suitable packaging material, incorporating various preservatives or pre treatments may help extend the shelf life of fresh rice noodles. Hence,helping manufacturers to market it commercially.
The first author would like to thank Universiti Sains Malaysia, for the financial support provided (as graduate assistantship) rendered throughout the study.