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Two different types of rice noodles were made from Bario rice local and Basmati rice imported. The cooking, physical, organoleptic and microbial attributes of the noodles were evaluated. The cooking loss of rice noodles increased with storage for both rice varieties with basmati rice having the higher range of (5.9-7.14%). The L* value of glass noodles decreased for both samples, with an increase in storage days causing noodles to get darker. Significant difference (P ≤ 0.05) was observed between storage days for all three parameters of L*, chroma and hue. The tensile strength and elasticity modulus of rice samples decrease with storage with bario rice having the lowest value for both analysis after 3 days of storage (24.11 kPa and 7.89) respectively. Total plate count and yeast and mold count increased significantly with storage, with total plate count having a maximum value of log 6.89 CFU/g and log 4.51 CFU/g for basmati rice.
Keywords: Rice noodles, storage, cooking quality, tensile strength, sensory analysis
With consumer expectations and demands rising for healthy food, food manufactures are having a tough time formulating popular food products which still maintains its appeal in terms of taste, texture and appearance but with different ingredients used. Rice noodles are conventional and a very common dish which is broadly consumed in many Southeast Asian Countries (Panlasigui et al., 1990). The main ingredients for rice noodles are rice and water. Hence the starch found in rice is has to possessed adequate functional and physiochemical properties to produce a high quality starch based noodle (Chen et al., 2003). Partial starch gelatinization is needed to form an amylose network which helps improve the texture of the batter. Rice noodles have a very smooth texture, mouth feel and are white in colour. Apart from that, noodles made from starch is required to have high tensile strength and low cooking loss to maintain the integrity of its eating quality (Purwani et al., 2006).The quality of cooked or uncooked noodles is usually assessed by its visible characteristics.
Materials and Method
Basmati rice was chosen to make into rice noodles compared to black and glutinous rice because it had good cooking properties in terms of cooking time, gruel solid loss, length to breadth ratio. It is the more preferred rice by consumers worldwide due to its aroma, tenderness, and taste (Bhattacharje et al., 2001). Even though black rice had better proximate composition, the amylose content of rice was low and it tends to become sticky after cooking. Basmati had intermediate antioxidant and functional properties, hence it was chosen to be maked into rice noodles.
Bario rice was chosen compared to white rice or brown rice as it is has intermediate amylose content, which is the more preferred characteristic. Apart from that, It had a high protein and low fat content. The cooking properties of bario rice were also much better compared to brown rice which takes a longer time to cook. Bario rice had better antioxidant properties and functional properties compared to white rice making it the better choice to make into rice noodles.
Approximately 500 g of rice is weighed and soaked overnight in water to soften the grains. It was later blended in a Waring blender (Panasonic MX-898 M, Malaysia) for 10 min until a thick and uniform batter is formed. Oil is dripped unto a baking pan which was then placed into a steamer (Well, 288128, China) for 2 min to heat it. A measuring cup is used to measure 120 ml of the batter which is then poured gradually and smoothly unto the oiled baking pan. The baking pan containing the batter was closed with a lid and placed in a steamer for 5 min. Once done, the freshly steamed noodles were then coated with vegetable oil. The process in then repeated with another 120 ml of batter poured on top of the first layer of noodles and then steamed for another 5 min. The same procedure is done with the remaining batter except for the last layer, which was steamed for 9 min. Once cooled down, the baking pan is removed from the steamer. The noodles are then removed from the baking pan and cut into 2.5cm x 15cm slices. The noodles is either than used immediately for analysis or wrapped in cling wrap and stored at room temperature for 3 days for future analysis.
Cooking loss was determined following the method described by AACC (2000) with slight modifications. Approximately 250 mL of tap water in a beaker was brought to a boil using a hot plate. When the water started boiling, 25 g of noodles, cut into 3 to 5 cm lengths was added into the beaker. The cooking process lasted for about 5 minutes until no white core was observed and was then pressed between two glass plates. The noodles were then drained, rinsed and cooled with distilled water. An evaporating dish containing twenty millilitres of the filtrate was then dried in an oven at 105ËšC until a constant weight was attained.
Cooking loss (%) = Weight of drained residue in cooking water - 100
Weight of noodles before cooking
The rehydration ratio was evaluated based on the method of Von Loesecke (1945) with slight modifications 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 11 min before being drained in a strainer for 2 min. After which, the noodles surface was wiped dry with a paper towel to remove the excess moisture. Rehydration ratio was calculated as the weight of the cooked noodles compared to the weight of the dried noodles.
Colour analysis was carried out on rice noodles using a colorimeter (Minolta Spectrophotometer model CM-3500d, USA). The colorimeter was calibrated first by using the zero calibration plate, followed by the white calibration plate. Three measurements of L*, Chroma and ΔH were taken for each noodle sample to obtain consistent results and mean value. L*, Chroma and ΔH were chosen as it represents lightness (brightness), saturation (vividness) and hue (colour). Samples were measured on different days from day 0 to day 3.
Tensile Strength and Elasticity
The texture of cooked noodles were determined using a Texture Analyzer, -TX2 model (Stable Micro Systems, Surrey, England) and was a calibrated with a 2.5 kg load cell. For tensile strength analysis, the settings were: Mode: Measure force in tension; Option: Return to start; Pre-Test Speed: 1mm/s; Test Speed: 3.0mm/s; Post Test Speed: 15mm/s; Distance: 100mm. The cooked noodles was stored for 10 min at room temperature 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 recorded by the TA machine, other information such as tensile strength and elasticity of the noodle strands can be calculated.
Tensile strength was calculated as σ = F/A where is the tensile strength (Pa), F is the maximum load or peak force (N) and A is the cross sectional area of the noodle strand (m2). Elasticity of noodle strands was calculated based on this formula: Flo x 1
t Ao v
Where F/t is the initial sloe (N/s) of the graph (Force vs Time), lo is the original length of the noodles between the limit arms (10mm), A is the cross-sectional area of the noodles (m2) and v is the rate of movement of the upper arm (0.0003m/s).
Total Plate Count (TPC)
Determination of total plate count was performed according to aerobic spread plate method as described by (Jay, 1986). Rice sample (10 g) was homogenized with 90 ml of sterile peptone water (1 g/L) in a laboratory homogenizer (Bag Mixer, Interscience, France) and serial dilution were prepared. Then 0.1 ml of each dilution was spread with disposable spreader (SPL Labware) on triplicate plates of Merck Plate Count Agar (PCA). The agar plates containing the samples was inverted upside down and incubated at 37°C for 2 days (48 hours). The noodles were stored at room temperature and the analysis was then repeated for day 1, 2 and day 3. After incubation, the colonies were counted manually and results were expressed as log 10 CFU/g of rice sample.
Yeast and Mould Count
Total mould and yeast count was conducted by the aerobic spread plate described by ( Jay, 1986), which uses potato dextrose agar (PDA). About 25g rice samples mixed with 225b gaqq ml of sterile peptone-water solution (0.1%) homogenized sample. Dilutions of the sample were prepared for 1 to 1x 10-4 and an amount of 1 ml from every dilution was transferred onto a corresponding labelled Petri dish and spread-plated over the agar surface. Inoculation PDA plats were incubated at 25°C for 2 days (48 hours). The noodles were stored at room temperature and the analysis was then repeated for day 1, 2 and day 3.
The plates with 30-300 colony forming unit (CFU) for TPC and 10-100 CFU for mould and yeast counts were counted and average values were taken after a duplicates count. The number of CFUs was multiplied by the dilution factor and was divided by the inoculation amount in order to determine the CFU per gram of sample. The CFU numbers were transformed into corresponding logarithmic numbers. Sensory Analysis
Sensory examination was carried out by 30 panellists consisting both students and staff of the Food Technology Division, USM. The sensory laboratory consists of six isolated sensory booths to minimize the subject's biases and to maximize their sensitivity. Hedonic ratings using 9-point scales were adopted. Panellist was 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, dislike extremely and 9, like extremely).
All the data 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 of mean. Tukey's HSD post-hoc test was performed and statistical significance was considered at P < 0.05.
Results and Discussion
Cooking loss is an important attribute in noodles as it evaluates the amount of solid content irrecoverable in cooking water. The structural integrity of noodles needs to be maintained throughout the cooking process. Noodles made from basmati rice had a higher value for cooking loss and it continue to increase with storage days (Table 1). After 3 days of storage, basmati rice noodles had a cooking loss of 7.14%.No significant difference (P < 0.05) was observed between basmati rice for day 2 and day 3. High cooking loss is unacceptable as there is a higher amount of solubilized starch present which leads to murky boiling water and gluey mouth feel and lower tolerance (Jin et al., 1994; Chakraborty et al., 2003).
Rehydration ratio for basmati and bario rice noodles is shown in Table 2. No significant difference (P <0.05) was observed in storage of Bario rice between day 0 and 1 and day 2 and 3. Bario rice noodles had a slightly 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 (Yoenyong-buddhagal and Noomhorm, 2002). The rehydration ratio of rice noodles decrease with storage time and the results are in agreement with the findings done by (Zhang, 2006Physical Analysis
Colour is one of the dominant parameter evaluated in helping to boost noodle marketability. (Asenstorfer et al., 200). After being stored for a few days, fresh noodles have a tendency to darken (Hatcher et al., 2010). Based on the results obtained from table 3, the L* value of glass noodles decreased for both samples, with an increase in storage days causing noodles to get darker (table 3). Significant difference (P ≤ 0.05) was observed between storage days. It reduced from 59.13 to 57.09 to 56.18 to 54.21 after three days of storage for Bario rice. The storage of rice noodles at room temperature could have accelerated the darkening of noodles.
There was no significant difference at (P ≤ 0.05) in the Chroma values between day 2 and 3( table 4). As the storage day increases, the Chroma values (dullness) decreases which is in agreement with (Hatcher et al., 2002) as discoloration happens during storage. The hue angles were significantly different between storage days (table 5). For basmati rice, the hue angle decreased from 146.21 to 142.11 to 136,51 and 132.57 after 3 days of storage.
Tensile Strength and Elasticity
Texture is a very important attribute of cooked noodles as it determines consumer acceptance of the product (Dexter et al., 1985).The texture of cooked noodles was assessed using tensile strength and elasticity as shown in Table 6. The most extensively accepted instrumental method in assessing texture of cooked noodles is texture profile analysis (Hatcher et al., 2010). Tensile strength assesses the capability of noodles to endure a longitudinal force without tearing. The cooking quality of noodles can also be determined from tensile strength as it shows how the noodles stay intact during cooking (Bhattacharya et al., 1999). Noodles made from Basmati rice had higher tensile strength as compared to bario rice (46.33 kPa). After 3 days of storage less force was needed to break noodles for both samples. All samples were significantly different at (P ≤ 0.05). Amylose content of rice varieties has an effect on the strength of noodles (Lii et al., 1981, Fari et al., 2011). The higher the amylose content, the higher the tensile strength as observed in this study.
Elasticity is 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 show that Basmati rice had a higher elasticity modulus as compared to Bario rice. Elasticity modulus of rice noodles decreases after storage. All samples were significantly different at (P ≤ 0.05) in terms of storage. Elasticity of basmati rice noodles decrease rapidly with longer storage time.
Figure 1 shows the total plate count of steamed rice noodles during a 3 day storage period at room temperature. Based on the results obtained, the total plate count of noodles increased significantly during storage. The total plate count for Bario rice was log 2.63 CFU/g on day 0, log 4.04 CFU/g on day 1, log 4.63 CFU/g on day 2 and log 6.02 for day 3. Basmati rice had a higher total plate count as compared to Bario rice. The acceptable amount of total microbes for fresh rice noodles is less than or equal to log 7 CFU/g (Thai Industrial Standard, 2005). Both samples were still acceptable after 3 days of storage at room temperature.
The yeast and mold count for basmati rice was higher compared to Bario rice (figure 2). Yeast and mold's optimum temperature of growth is around 25-37oC. Initial yeast and mold count for basmati rice was log 2.12 CFU/g and log 1.98 CFU/g for bario rice. By the 3rd day, basmati rice was log 4.51 CFU/g and log 3.98 CFU/g for bario rice when stored at ambient temperature. Thai Industrial Standard (2005), states that the acceptable amounts of yeast and mold counts for fresh rice noodles should be equal or less than log 2 CFU/g. After being stored for 3 days at ambient temperature, both samples were way above the recommended amounts.
Sensory evaluation is done to help researchers develop new food products, study storage life of food products as well as determine consumer acceptability towards the food product (Hutchings, 1999) .Results of sensory evaluation in terms of colour, odour, appearance, texture, overall appearance and overall acceptability are presented in Figure 3. Colour acceptability scores for bario rice were 6.67 and basmati rice was 5.87. The first parameter which is assessed by consumer is most probably colour ( Blouin et al., 1981).
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 for basmati rice. In terms of overall appearance and acceptability Bario rice faired was better implying that it was the more preferred noodle compared to Basmati rice. Hence the panellist preferred the rice noodles with the intermediate amylose content rice
Rice noodles made especially basmati rice had good tensile properties. However after 3 days of storage, tensile properties, cooking properties, colour and microbial count started to deteriorate. For sensory analysis, panellist preferred bario rice noodles over basmati rice noodles as it had the higher overall acceptance and appearance. Improvement in rice noodles quality especially in terms of storage may help manufacturers sell it commercially