Properties Of Two Nerica Rice

Published Date: 02 Nov 2017

A. Addo*, G. Bismark and K.A. Dzisi

Department of Agricultural Engineering

Kwame Nkrumah University of Science and Technology, Kumasi, Ghana

*Corresponding author’s e-mail: [email protected]

ABSTRACT

The parboiling effect on the quality properties of Nerica 1 and 2 varieties were studied with samples grown in Ghana. The physical and physic-chemical analyses during steaming at three different temperature period of 100oC at 10mins, 110oC at 15mins and 120oC at 25 mins. The results showed that the effect of parboiling process on the quality indicators through the kinetic parameters followed the first order kinetic model of initial steps of steaming and final reaction rate constant values were dependent on steaming temperature and period. Both Nerica 1 and Nerica 2 showed similar behaviour during steaming process. The Arhenius-type of equation described the strong temperature effect on the physical and physicochemical properties with k-values ranging from 0.188 to 0.530 for lightness; 0.272 to 0.327 for hardness; 0.133 to 0.336 for maximum viscosity; and 0.211 to 0.856 for breakdown value.

Keywords: Paddy rice, Physico-chemical Properties, Steaming, Parboiling, Reaction Rate Value, And Physical Properties

Introduction

The parboiling process is a method used in the world rice processing industry. Generally, the majority of the developing countries consume parboiled rice especially in the Indian Sub-continent where it originated a long time ago. It was reported that about one-fifth of the world’s rice is parboiled (Bhattacharya, 1985). This seems to be increasing day by day, because the growth rate of population in these countries ishigher and the most consumable food value is the rice. Parboiling is a hydrothermic treatment given to rough rice, and consists of soaking, steaming and drying. During the parboiling process, starch gelatinization takes place, a thermo-chemical reaction between the starch granules and heat energy in the presence of water. This starch gelatinization changes the physicochemical properties of rice (Bhattacharya and SubbaRao, 1966; Bhattacharya and Indudhara Swamy, 1967; Raghavendra Rao and Juliano, 1970; Gariboldi, 1972; Kimura, 1983; Bhattacharya, 1985; Itoh and Kawamura, 1985; Kimura, 1991; Kimura et al., 1993; 1995; Islam et al., 2001), which affects the other processing operations of storage, milling, cooking and eatingquality. Islam et al. (2001) evaluated the quality of parboiled rice by its physical properties of maximum viscosity, hardness of brown rice, hardness and adhesion of cooked rice, volume expansion ratio and solid content, utilizing the first-order kinetic model. They identified the rate of change of quality and the quality index of parboiled rice with the reaction rate constant and final values of the quality indicators. The quality of parboiled ricewas greatly affected by the severity of the parboiling treatment; severely treated rough rice produces a product of lesser quality. For wider acceptability of parboiled rice, processing equipment and conditions should be developed to produce a better quality product. Parboiling of rough rice at higher temperatures generally produces a dark coloured product (Bhattacharya, 1985; Kimura et al., 1993). Therefore, parboiling at lower temperatures (80 to 100°C) is preferable to produce a better quality product for consumer acceptance.

Rice (Oryza sativa L.) is considered as a main staple food and is a major source of nutrients in many parts of the world. Consumers prefer to eat unpolished rice because of the nutrient value in the bran. Therefore, demands for brown rice and parboiled rice are increasing because of their high value in nutrition and health importance associatedwith eating this type of rice. However, brown rice has some disadvantages such as slower absorption of liquid into the kernel because the bran contains fibre, which increases cooking time and furthermore, the oil content in the bran shortens its shelf life, as the bran becomes rancid. Therefore, parboiling is one alternative to reduce these problems.

scope of the study

The parboiling process is a world processing industry in which the population of developing countries eats parboiled rice. About one-fifth of the world’s rice is parboiled (Bhattacharya, 1985). So, it can be regarded as one of the most important processing methods in rice industry. These includes soaking either cold or hot water method, steaming with steam at gauge or atmospheric pressure, and drying naturally under sunshine or shade method or artificially by the mechanical dryer with hot air. Parboiling makes rice easier to process by hand, improves its nutritional profile (excepting its vitamin-B content, which is denatured in the process), and changes its texture. Polishing rice by hand, that is, removing the bran layer is easier if the rice has been parboiled. It is, however, somewhat more difficult to process mechanically. The bran of parboiled rice is somewhat oily, and tends to clog machinery. Most parboiled rice is milled in the same way as white rice Parboiling rice drives nutrients, especially thiamine, from the bran into the grain, so that parboiled white rice is 80% nutritionally similar tobrown rice. Because of this, parboiling was adopted by North American rice growers in the early 20th century. The starches in parboiled rice become gelatinized, making it harder and glassier than other rice. Parboiled rice usually has small amounts of milk added to it to prevent the grain from over hardening. Parboiled rice takes more time to cook, and the cooked rice is firmer and less sticky. In North America, parboiled rice is generally partially or fully precooked by the processor. However, pressure and warmer soaking temperature are commonly employed in modern processes to reduce processing time. More recently, the use of fluidization techniques (Soponronnarit and others, 2006) and ohmic heating (Sivashanmugam and Arivazhagan, 2008) to parboil rice have been reported. Parboiled rice accounts for about 15% of the world’s milled rice (Bhattacharya, 2004), and its market has been increasing especially in industrialized countries (Efferson, 1985). It is the staple food in southern Asian countries such as India, Sri Lanka, Pakistan, Nepal and Bangladesh (Juliano and Hicks, 1996; Bhattacharya 2004; Roy and others, 2007). It belongs to the most popular rice products in Europe including Belgium, Germany, Italy and Spain (Efferson, 1985; Bhattacharya, 2004; Fuhlbrugge, 2004; Vegas, 2008). There is also a high demand for parboiled rice in Saudi Arabia, Turkey, Jamaica, Yemen, Ghana, and Nigeria (Otegbayo and others, 2001; Bhattacharya, 2004; Tomlins and others, 2005; Vegas, 2008). Parboiling is accompanied by some profound changes in rice physical, chemical and functional properties. Starch granules undergo irreversible swelling and fusion as a result of gelatinization (Rao and Juliano, 1970; Ali and Bhattacharya, 1980; Juliano and Hicks, 1996). Protein bodies are disrupted (Rao and Juliano, 1970) and protein barriers are inferred to form through disulfide cross-linking (Derycke and others, 2005). Lipids form complexes with amylose, which, along with protein barriers, may contribute to restricted swelling and solubilization of starch during cooking (Biliaderis and others, 1993; Derycke and others, 2005). Parboiling also results in inward diffusion of water-soluble vitamins and other bran components (Juliano and Hicks, 1996). Such changes in chemical components during parboiling, in turn, contribute to harder kernels upon drying, improved milling yields, more translucent but amber coloured head rice, firmer and less sticky cooked rice, higher retention of minerals and water-soluble vitamins, increased health promoting starch fraction (resistant starch), and longer shelf life (Pedersen and others, 1989; Juliano and Hicks, 1996; Kar and others, 1999; Otegbayo and others, 2001; Bhattacharya, 2004; Derycke and others, 2005; Heinemann and others, 2005; Kim and others, 2006). Parboiled rice is most often used in the industrial and food service markets because of its ease of preparation, durability, and stability to overcooking (Juliano and Hicks, 1996; Vegas, 2008). The traditional feedstock for parboiling is rough rice or paddy. The siliceous hulls in rough rice, however, have a poor thermal conductivity and slow down heat transfer to the endosperm (Kar and others, 1999). This makes rough rice parboiling more time and heat energy consuming. Moreover, very little or a few information are available regarding the reaction kinetics of parboiling treatment. Bandyonpadhyay and Ghose (1965), and Bandyipadhyay and Ray (1976) studied the hydration kinetics of paddy during soaking and reported that soaking was influenced by two different mechanisms, one below and other above the gelatinization temperature which reflected in the appreciable difference in the activation energies for these ranges. (Bandyipadhyay and Ray, 1976 cited in Md R. Isalam, 1998). Suzuki et al. (1976) studied the kinetics on cooking of rice and reported that with the cooking temperature range of 75-150°Ċ, the cooking rate constant changed around 110°Ċ. The activation energy of cooking at temperatures below and above 110°Ċ was about 19000 and 8800 cal /mol, respectively. Bakshi and Singh (1980) studied the water diffusion and starch gelatinization during rice parboiling and reported that parboiling process is limited by the reaction of starch with below 85 °Ċ and by diffusion of water above 85°Ċ. They reported the activation energy of 18534 and 85-10470 cal /mol for the temperature range of 50-120°Ċ, respectively. Kimura et al. (1993) and Bhattacharya (1996) studied the reaction kinetics of parboiling treatment on colour value and reported that both reaction rate constant and final colour value increase due to increasing the severity of parboiling treatment. In this respect, for better understanding the reaction kinetics of parboiling treatment on the physicochemical property and cooking quality of parboiled rice, a great-deal of fundamental study is still needed for selecting proper quality indicator for optimizing the parboiling process.

1.3 Objectives

The main aim of this study was:

To determine the thermal properties, i.e. gelatinization parameters of parboiled rice produced locally.

The specific objectives were:

i) To study the effect of parboiling treatment on the physical properties of locally grown rice.

ii) To compare the quality indicators of parboiled rice produced

MATERIALS AND METHODS

Plant Materials

The Nerica 1 and Nerica 2 varieties were obtained from Tamale, Northern region. Milling was carried out at experimental laboratory of Ghana Irrigation Development Authority (GIDA), Ashaiman. Colour measurement, pasting and textural analyses were carried out at Food Research Institute (FRI), Accra, Ghana.

3.1 SAMPLE PREPARATION

The average initial moisture contentof rice grain was 13±1% (w.b). Before conducting the experiment, rough rice packed in a 5 kg polyethylene bag were kept in a laboratory at room temperature.

3.1.1 Preparation of paddy Rice

After removing the stored paddy from the polyethylene bag, samples were brought to roomtemperature by holding for 1 day. Some of the samples were then poured into a basin of water to float unfilled grains and lighter particles and straw particles which were then removed by hand. The water was then poured off for the samples to be at the bottom of the basin.

3.2 PARBOILING PROCESS

3.2.1 Soaking Condition

Initial temperatures were 26oC, 50oC and 70oC. Samples weighing 1000 g of paddy rice were soaked in nylon filter cloth immersed in hot water for 2h, 3h, 4h and 5h and then drained respectively for each soaking temperatures. While another sample 1000 g was soaked at 26oC in nylon filter cloth immersed in cold water or room temperature for 2h, 3h, 4h and 5h and then drained all soaked water from sample.

3.2.2 Steaming Condition

The second step of the parboiling process is steaming to improve rice moisture to 30–35 %

(w.b) (Kimura, et al., 1976; Bhattacharya, 1985) and heat treatment also irreversibly gelatinizes the starch. Steaming was done using an autoclave at 100o C, 110oC and 120oC for 10 min, 15 min and 25 min respectively.

3.2.3 Drying condition

The steamed rice was then dried on trays at room temperature (30±1o C, 60±5 % RH) resulting in the final moisture content of 13±1% (w.b.). After drying, samples were stored in airtight polyethylene bags for moisture equilibration and hardness stabilization (Kimura, 1991). Physicochemical analyses were performed after two weeks. The effects of initial soaking temperature, soaking time and steaming condition on various quality parameters were investigated. Two initial soaking temperatures (50oC, 70oC), four soaking times (2h, 3h, 4 h and 5h) and three steaming times (10, 15 and 25 min) were evaluated. Hence, twenty treatment combinations were tested, as shown in Table 1. Moisture content determination for the varieties (thus Nerica one and Nerica two) was achieved using the oven method.

3.3 MATHEMATICAL MODEL

Food research system usually follows either a zero or first order kinetics as reported by (Arabshahi and Lund, 1985). During food processing, estimation of these kinetic parameters led to understanding of the changes that occur (Arabshahi and Lund, 1985; Rao, 1986; Holdsworth, 1990) and can be used for process maximization, scale-up and for better control of the process and quality of the finished product of parboiled rice. For the first order kinetic reaction, reaction rate constant can be calculated from the equation below:

= k (Me ‒ M) ‒ ―→ (1)

Where, M = quality indicator at any time t

t = Time (min)

k = kinetic reaction rate constant (min-1),

Me= Final value of any quality indicator,

or, = kdt (separating M and t)

or, -Ln (Me-M) = kt + C (Integrating the above equation, where, C = constant of integrating) at initial conditions at,

t = 0, M = Mo

the valve of C becomes

Ln (Me‒Mo)

Substituting for C, equation becomes

-Ln(Me‒M) = kt ‒ Ln(Me ‒Mo)

or, Ln

or, Me‒M = (Me ‒ Mo)*exp(‒kt)

or, M = Me + (Mo ‒ Me)*exp(‒kt) ‒ ―→ (2)

by using nonlinear regression technique, K and Me values can be calculated using equation two(2). For understanding the molecular mechanism of chemical reaction, the effect of temperature on the reaction rate is of at most concern. Arrhenius Equation was used to interperate the influence of temperature on the rates of chemical reaction. According to this equation, a rate constant (K) is the product of a pre-exponential factor A and an exponential factor:

K = Ae-E/RT ‒ ―→ (3)

Or, -LnK = E/RT‒LnA

Where, K = kinetic reaction rate constant (min-1),

A = Frequency factor (min-1),

E = Activation Energy (J/mol),

R = Gas constant (8.314 J/(mol.K)),

T = Temperature (K).

Determination of Moisture content

The moisture content was determined using a duplicate sample of different grams of soaked paddy rice at different soaked temperatures and, an hourly intervals for four samples. They were dried in an oven at 105oc temperature for twenty hours (24hrs) with both their initial and final masses determine using an electronic balance.

Milling

18 samples of dried parboiled with two unparboiled samples were kept in an air tight polythene bag. The samples were then taken to Ghana Irrigation Development Authority for milling. Satake Rice machine was used to milled five hundred grams sample each of the samples to about 100 percent husking ratio. Brown rice was then polished and graded to obtain white rice, head rice and broken rice respectively. The milling yield and degree of milling were done using the following formulas:

Milling yield (%) = ‒ ―→ (5)

Degree of milling = ‒ ―→ (6)

COLOUR MEASUREMENT

A Minolta Chroma Meter Model CR 310(Minolta Camera Co. Ltd., Osaka, Japan) was used to measure the lightness and saturation of the colour intensity value of the whole kernel milled rice flour utilizing the CIE L*, a*, b* uniform colour space procedure. The value of L* expresses the psychometric lightness value, and a* and b* are factors expressing hue and saturation of the colour intensity. The instrument was calibrated with a standard white plate having L*, a* and b* values. Each measurement was replicated five times and theaverage value was used.

The colour intensity value (B) of parboiled grain was calculated using the following formula (Kimura et al., 1993):

B = ‒ ―→ (7)

DETERMINATION OF PASTING CHARACTERISTICS

A smooth paste was made of the prepared flours of parboiled rice (40g) in 420ml distilled water (8.8% slurry) for viscoelastic analysis using Brabender Viscoamylograph (Viskograph-E, Brabender Instrument Inc. Duisburg, Germany) equipped with a 1000 cmg sensitivity cartridge. The smooth paste was heated at a rate of 1.5°Cmin-1 to 95°C and maintained for 15 min. It was then cooled at 1.5°Cmin-1 to 50°C and maintained for 15 min. Viscosity profile indices were recorded for pasting temperature, peak temperature, peak viscosity, viscosity at 95°C, viscosity after 15 min hold at 95°C (95°C Hold), viscosity at 50°C, viscosity after 15 min hold at 50°C (50°C Hold), breakdown and setback as described by Mazaurs, et al., (1957) and Walker et al., (1988).

DETERMINATION OF TEXTURE CHARACTERISTICS

The hardness texture characteristic was determined by cooking a sample for 20-30 min within which the cooked sample was kept in an insulated container. A texture analyzer was then used to determine the grain hardness. A forceps was used to pick five grains of cooked sample and then placed between auxiliary vertical load and sample platform. The setup was then controlled automatically by a software which gives end result hardness graph and values.

RESULTS AND DISCUSSION

4.1 Effect of parboiling treatment on physical properties

4.1.1 Lightness

Parboiling treatment discolours grain and decreases the lightness value but the ultimate aim was to produce whiter parboiled rice. Several researchers measured various kinds of lightness value (Jayanarayanan, 1964; Bhattacharya and SubbaRao, 1966; Kawamura et al., 1982; Kimura et al., 1993). Jayanarayanan (1964) reported that whiteness of parboiled rice was affected by soaking conditions, water temperature and pH value. Others reported that lightness (or whiteness) of parboiled rice was mainly affected by the temperature and period of steaming (Bhattacharya and SubbaRao, 1966; Kimura et al., 1993; Bhattacharya, 1996). Table 4.1 and 4.2 shows the statistical results of lightness value for nerica one (N1) and two (N2) respectively. From these tables, it was observed that steaming temperature and its period had a significant effect (p<0.01) on the whiteness of the grain kernel for both varieties as can also be observed from Table 4.33 and Table 4.35 at appendices showing mean summary of steaming treatment on physiochemical lightness value of varieties and its LSD.

As the steaming temperature and period increases, the lightness value decreases as shown in Fig 4.1 and Fig 4.2. At Figure 4.1, the lightness value decreases for all the steam samples for 100oC, 110oC and 120oC with highest effect on steam 120oC, 110oC and 100oC respectively at period of 10min. As the steaming period increases to 25min, the most affected was steam at 110oC, 100oC and 120oC respectively. Also for steam period of 15min, steam samples 120oC, 100oC and 110oC respectively was most affected with lightness value. At Figure 4.2, the lightness value decreases for all the steam samples with least value for 120oC, 110oC and 100oC respectively at period 10min while at increase steaming period of 25min, the most affected was steaming at 120oC, 110oC and 100oC respectively. Also at steaming period of 15min, the most affected lightness value was steam sample 120oC, 110oC and 100oC respectively. These figures show a scatter diagram of the effect of steaming on lightness value for nerica one and nerica two respectively as temperature and period of steaming increases. These are in agreement with other researchers as mention above. First order kinetic model (Bhattacharya, 1996) was used to analyse the experimental data.

Table 4.3 and 4.4 shows the average lightness value and rate of reaction due to steaming for both varieties. As the steaming temperature increases, the final K-value (thus rate of reaction) increases at high steaming temperature and thus decreases in lightness value. Fig 4.3 and 4.4 shows the temperature dependence of lightness reaction rate constant for nerica one and nerica two. There is significant dependence of K-value on steaming temperature as observed from these figures having significant (p<0.01) positive linear correlation between K-value and 1/T. They also have R2-values of 0.439 and 0.481 for both varieties respectively.

Table 4.1 Statistical results for physical property (ANOVA Table for Lightness L-colour value N1)

SOURCE

DF

SS

MS

F

P

Steam

3

569.3

189.8

8.88

0.006

Error

8

171.0

21.4

Total

11

740.3

Table 4.2 Statistical results for physical property (ANOVA Table for Lightness L-colour value N2)

SOURCE

DF

SS

MS

F

P

Steam

3

624.30

208.10

20.88

0.000

Error

8

79.75

9.97

Total

11

704.05

Table 4.3 Average Lightness (L) and rate of reaction value (K) due to steaming temperature for Nerica 1

Treatment

Steaming

Temperature

100oC

110oC

120oC

Lightness Value N1

62.2825

63.9775

63.0225

K-value, min-1

0.294431

0.205517

0.494314

Table 4.4 Average Lightness (L) and rate of reaction value (K) due to steaming temperature for Nerica 2

Treatment

Steaming

Temperature

100oC

110oC

120oC

Lightness L-value N2

64.0475

67.3625

64.305

K-value, min-1

0.280277

0.188169

0.530106

Figure 4.1 Effect of steaming on lightness value for Nerica 1

Figure 4.2 Effect of steaming on lightness value for Nerica 2

Figure 4.3 Temperature dependence of lightness reaction rate constant for Nerica 1

Figure 4.4 Temperature dependence of lightness reaction rate constant for Nerica 2

4.1.2 Colour Intensity

At high temperature and long steaming time, generally produces a dark colour and harder product (Bhattacharya, 1985; Kimura et al., 1993). These products fetch lower price in the market. In addition, parboiled rice has a peculiar smell and taste. Discoloration of rice due to parboiling treatment is another important quality indicator. It is a negative effect of the parboiling process, because dark coloured parboiled rice loses market value and lowers consumer acceptability in most countries (Bhattacharya, 1985). Many researchers measured the colour intensity value following parboiling treatment (Jayanarayanan, 1964; Bhattacharya andSubbaRao, 1966; Pillai-yar and Mohandoss, 1981; Kimura et al., 1993; Bhattacharya, 1996), and reported that discoloration was mainly caused by the Maillard type of non-enzymatic browning reaction, and that the processing conditions determine the intensity of colour during parboiling.

Table 4.5 and 4.6 shows the statistical results for B-colour intensity for both nerica one and nerica two varieties. From table 4.5 and 4.6, it can be observed that the steaming treatment had significant effect (p<0.01) on colour intensity. As the temperature increases, their mean and standard deviation value increases as compared to their control value (thus steam 0oC) for both varieties. Nerica two was darker in colour than Nerica one after milling. High polishing regulatory value during polishing of parboiled rice compared to unparboiled rice. At appendix, Table 4.34 and 4.36 show mean summary of steaming treatment on physiochemical properties on paddy rice and their LSD. From Table 4.34 it was observed that at highest steam temperature (120oC), highest mean colour value obtained meaning very dark colour of grain as compared to others. This might be the reason why parboiled rice loses market value and lowers consumer acceptability as compared to unparboiled rice. Steaming temperature and period must be controlled during parboiling treatment. Fig 4.5 and 4.6 show the effect of steaming treatment on the colour intensity value for Nerica one and Nerica two respectively. From Fig 4.5 with steam period 10min, the darker rice was at steam 100oC, 120oC and 110oC respectively and at 25min shows most affected colour at steam 120oC, 110oC and 100oC respectively. While at 15min indicate highly affected colour pattern on steam sample 110oC, 120oC respectively with no effect on steam sample 100oC.

From Fig 4.6 with steam period of 10min, steam sample 100oC shows significant effect of colour intensity as compare to steam sample 120oC and 110oC. At steam period 25min, the most affected colour intensity was steam sample 120oC, 100oC and 110oC respectively. This value increased with increase in steaming temperature and period, and increase pattern was severe at higher temperatures. To understand the reaction kinetics of colour intensity, experimental data were fitted to a first-order kinetic model to calculate the kinetic parameter which shows the kinetic parameters of colour intensity value for different temperatures. The final colour intensity value increased with increase in steaming temperature, while k-value also showed changes in pattern as shown in Table 4.11 and 4.12 titled average colour intensity and reaction rate constant value due to steaming for Nerica one and Nerica two respectively.

Figs 4.7 and 4.8 show the temperature dependence of colour intensity reaction rate constant. They also have a significant dependence of K-value on steaming temperature as observed from these figures having significant (p<0.01) positive linear correlation between K-value and 1/T. They have R2-values of 0.307 and 0.794 for both varieties respectively. It was established that the change of yellowish component faster than the reddish component (Kimura, 1989) of parboiled rice due to parboiling. Table 4.7, 4.8, 4.9 and 4.10 shows the anova statistical results for physical property for a* and b* values on the effects of steaming of Nerica one and Nerica two respectively. From these tables, there exist significant effect (p<0.01) of steaming on both a* and b* values for both varieties which affected their colour intensity during parboiling.

These results indicated that the effect of parboiling treatment was greater on the lightness value; therefore, this value can be seen to be a more important quality indicator than colour intensity value. The change in final colour intensity value was found to be greater for higher temperatures of 110oC and 120°C and longer durations. To produce a less coloured product, steaming temperature and period should be controlled, as higher temperature affects colour quality of parboiled rice. It was also reported that colour intensity due to parboiling treatment was controllable at lower temperature (Bhattacharya, 1985; Kimura, et al., 1993). Considering the visual observations and the change of the parboiled rice with temperatures in this study, parboiled rice at high temperatures and period should be avoided.

Table 4.5 Statistical results for physical property (ANOVA Table for colour intensity value for Nerica 1)

SOURCE

DF

SS

MS

F

P

Steam

3

0.611

0.204

1.59

0.267

Error

8

1.026

0.128

Total

11

1.637

Table 4.6 Statistical results for physical property (ANOVA Table for colour intensity for Nerica 2)

SOURCE

DF

SS

MS

F

P

Steam

3

182.3726

60.7909

824.05

0.000

Error

8

0.5902

0.0738

Total

11

182.9627

Table 4.7 Statistical results for physical property (ANOVA Table for hue value thus a-value N1)

SOURCE

DF

SS

MS

F

P

Steam

3

2.235

0.745

5.86

0.020

Error

8

1.016

0.127

Total

11

3.251

Table 4.8 Statistical results for physical property (ANOVA Table for hue value thus a-value N2)

SOURCE

DF

SS

MS

F

P

Steam

3

209.2311

69.7437

844.44

0.000

Error

8

0.6607

0.0826

Total

11

209.8913

Table 4.9 Statistical results for physical property (ANOVA Table for b-value N1)

SOURCE

DF

SS

MS

F

P

Steam

3

3.73

1.24

0.54

0.670

Error

8

18.51

2.31

Total

11

22.24

Table 4.10 Statistical results for physical property (ANOVA Table for colour b-value N2)

SOURCE

DF

SS

MS

F

P

Steam

3

16.8069

5.6023

109.69

0.000

Error

8

0.4086

0.0511

Total

11

17.2155

Table 4.11 Average Colour intensity and reaction rate constant value due to steaming for Nerica 1

Treatment

Steaming

Temperature

100oC

110oC

120oC

Colour intensity( B-value)

6.971828

6.734731

7.067151

K-value, min-1

0.290443

0.367204

0.188671

Table 4.12 Average Colour intensity and reaction rate constant value due to steaming for Nerica 2

Treatment

Steaming

Temperature

100oC

110oC

120oC

Colour intensity(B-value)

9.488492

9.620844

9.568959

K-value, min-1

0.358254

0.335653

0.334684

Figure4.5 Effect of steaming period on colour intensity value of Nerica 1

Figure 4.6 Effect of steaming period on colour intensity value of Nerica 2

Figure 4.7 Temperature dependence of colour intensity reaction rate constant for Nerica 1

Figure 4.8 Temperature dependence of colour intensity reaction rate constant for Nerica 2

4.1.3 Milling Yield

The parboiled product exhibit several advantages over unparboiled product such as the strengthening of kernel integrity, increased milling recovery, prevention of the loss of nutrients during milling and improved shelf life as well as prevention of the proliferation of fungus and insects (Rao and Juliano, 1970a, Bhattacharya, 1985). Table 4.13 and 4.14 shows the statistical results for milling yield. From the tables, it can be observed that steaming treatment had a significant effect (p<0.01) on milling yield on both varieties. At appendices, Tables 4.33 and 4.35 showing mean summary of steaming treatment on physiochemical properties of paddy rice and its LSD, on milling yield shows a significant increase in mean yield as compare to its control but decreases at high temperature and thus shows a significant difference as to its LSD. Parboiling treatment brought about a striking improvement in the milling quality of paddy rice (Bhattacharya and SubbaRao, 1966). The parboiling imparts hardness to the grains so that they resist breakage during milling, minimizing breakage loss and increasing milling yield (Garibaldi, 1974).

Figure 4.9 and 4.10 shows the effect of parboiling treatment on the milling yield of both varieties. From Fig 4.9 with steam period 10min, steam sample 120oC, 110oC and 100oC shows greater milling yield respectively while at steaming period of 15min, the highest milling yield was steam sample 120oC, 100oC and 110oC respectively. Also at steam period 25min, steam sample 100oC, 120oC and 110oC shows greater milling yield respectively. From Fig 4.10, at steam period of 10min, higher milling yield occurred for steam sample 100oC, 120oC and 110oC respectively. It was also high for steam sample 120oC, 110oC and 100oC respectively at steam period 15min. When the steaming period was increase to 25min, steam samples 110oC, 100oC and 120oC also increases respectively but decreases comparatively to the milling yield period of 15min and 10min respectively. It can be seen that as steaming temperature and period increases, there was an increase in the milling yield until the highest steaming temperature and period, and then decreased rapidly.

During parboiling of paddy rice at higher temperatures, severe deformation of the grain occurs along with exudation of endosperm due to husk splitting and absorption of excessive moisture content. The deformed grain loses the exuded part of the endosperm during milling. Thus, with parboiling of paddy rice at higher temperatures for a longer steaming period milling yield decreases, depending on the severity of processing conditions. Since higher steaming temperature is most favourable for grain deformation, which reduces the milling yield, might be the cause for getting almost the same or less milling yield due to steaming temperature and period increases for both figures of the varieties.

Tables 4.15 and 4.12 show the average milling yield (%) and rate of reaction value (K) due to steaming temperature for both varieties. It can be shown from Table 4.12 that milling yield and reaction rate increases at 110oC while it decreases at 120oC for nerica two. While for Table 4.15, rate of reaction and milling yield at 100oC is higher than 110oC but less than values at 120oC. Figs 4.11 and 4.12 show the temperature dependence of milling yield (%) reaction rate constant for Nerica one and two. From these figures, rate of reaction decreases as parboiling temperature increases. These figures show a significant (p<0.01) negative linear correlation between K-value and 1/T for steaming as observed with coefficient of correlation (R2) values of 0.994 and 0.605 respectively. It also shows a significant difference on the temperature dependence of the rate of reaction.

Table 4.13 Statistical results for physical property (ANOVA Table for milling yield (%) N1)

SOURCE

DF

SS

MS

F

P

Steam

3

133.05

44.35

13.63

0.002

Error

8

26.04

3.25

Total

11

159.09

Table 4.14 Statistical results for physical property (ANOVA Table for milling yield (%) N2)

SOURCE

DF

SS

MS

F

P

Steam

3

59.41

19.80

13.29

0.002

Error

8

11.92

1.49

Total

11

71.34

Table 4.15 Average milling yield (%) and rate of reaction value (K) due to steaming temperature for Nerica 1

Treatment

Steaming

Temperature

100oC

110oC

120oC

Milling yield N1

78.035

76.905

78.235

K-value, min-1

0.333475

0.199296

0.336551

Table 4.16 Average milling yield (%) and rate of reaction value (K) due to steaming temperature for Nerica 2

Treatment

Steaming

Temperature

100oC

110oC

120oC

Milling yield N2

76.435

77.935

77.12

K-value, min-1

0.214248

0.338254

0.315604

Figure 4.9 Effect of steaming on milling yield (%) for Nerica 1

Figure 4.10 Effect of steaming on milling yield (%) for Nerica 2

Figure 4.11 Temperature dependence of milling yield (%) reaction rate constant for Nerica1

Figure 4.12 Temperature dependence of milling yield (%) reaction rate constant for Nerica 2

4.1.4 Head Rice Yield

Table 4.17 and 4.18 shows the statistical results for head rice of Nerica one and two respectively. From these tables, it was observed that there was a significant effect (p<0.01) for both varieties due to parboiling treatment. From these tables, as the steaming temperature and period increases, the mean value increases from raw rice to steam 100oC. At higher temperature and period, the mean value decreases at steam 110oC and then raises at steam 120oC. As steaming temperature increases, it decreases degree of milling which improves head rice yield as observed in this study. Thus excessive steaming increases the starch gelatinization which causes exuding of the endosperm from the husk which might be the cause of this effect as reduced head rice yield after milling of parboiled rice steamed at higher steaming temperature and period. Tables 4.34 and 4.36 show mean summary of steaming treatment on physiochemical properties of both varieties and its least significant difference (LSD) respectively. From these tables, it was observed that there was a significant difference (p<0.01) between the mean summary values and its least significant difference (LSD) for both varieties.

Table 4.19 and 4.20 shows average head rice and reaction rate constant value due to steaming for both varieties. From Table 4.19 there was a fluctuation for the head rice values and reaction rate constant (k-values) as the steaming temperature and period increases but the k-values for Table 4.20 shows an increase in values as the steaming temperature and period increases. At highest steaming temperature (120oC), the rate of reaction was highest for both varieties tables. It was observed that head rice yield can be improved by controlling steaming temperature and period as excessive parboiling treatment affects head rice yield. Figs. 4.13 and 4.14 show effect of steaming on head rice for both varieties respectively. From Fig 4.13, head rice increases as steaming period increases. At steam period 10min, steam samples 100oC, 110oC, and 120oC increases respectively. For steam period 15min, slight increase in head rice for steam sample 110oC while greater increase occur for steam sample 120oC, and 100oC respectively. Also steam period 25min shows an increase in head rice for steam sample 120oC, 100oC and 110oC respectively but comparatively lower head rice for steam period 15min and 10min. Fig 4.14 also shows a similar behaviour as Fig 4.13 for steam sample 100oC, 110oC and 120oC as steaming period increases from 10min, 15min and 25min. From these figures, it shows an increase in head rice as at steam 100oC for 10min. Steam 110oC for 15mins shows a decrease in head rice whilst slightly further increase in head rice for steam 120oC for 25min. Figs. 4.15 and 4.16 show temperature dependence of head rice reaction rate constant for Nerica one and two respectively. It shows a negative linear correlation between k-values and 1/T with R2 values of 0.420 and 0.989 respectively.

However, it was found that the steaming of rice variety at the suitable conditions increased the head rice yield of parboiled rice which further caused gelatinization process that brings stronger structure and the denaturation of protein by diffusing into inter-granular space of starch which further increases the binding effect, and is better for milling process (Gariboldi, 1974). In addition, the moisture was removed slowly from parboiled rice in the shade, although it takes longer but gives an excellent milling quality. In addition, head rice yield values decreased with longer time and higher temperature of steaming. It might be that soaking and steaming low amylose content at higher temperature causes severe deformation of the grain that loses the exuded part of the endosperm while absorbing excessive moisture which led to reduced milled yield (Islam et al., 2004; Bello et al., 2006). Therefore, longer duration of steaming is not suitable for parboiled rice.

Table 4.17 Statistical results for physical property (ANOVA Table for head rice (g) N1)

SOURCE

DF

SS

MS

F

P

Steam

3

146969

48990

6.04

0.019

Error

8

64924

8115

Total

11

211893

Table 4.18 Statistical results for physical property(ANOVA Table for headrice N2)

SOURCE

DF

SS

MS

F

P

Steam

3

86387

28796

8.97

0.006

Error

8

25686

3211

Total

11

112073

Table 4.19 Average head rice and reaction rate constant value due to steaming for Nerica 1

Treatment

Steaming

Temperature

100oC

110oC

120oC

Head rice N1

284.3

229.725

263.275

K-value, min-1

0.316438

0.183397

0.592530

Table 4.20 Average head rice and reaction rate constant value due to steaming for Nerica 2

Treatment

Steaming

Temperature

100oC

110oC

120oC

Head rice N2

251.825

295.3

280.225

K-value, min-1

0.196624

0.316537

0.478591

Figure 4.13 Effect of steaming on head rice (g) for Nerica 1

Figure 4.14 Effect of steaming on head rice (g) for Nerica 2

Figure 4.15 Temperature dependence of head rice (g) reaction rate constant for Nerica 1

Figure 4.16 Temperature dependence of head rice (g) reaction rate constant for Nerica 2

4.1.5 Hardness

Hardness is the most important physical properties of parboiled rice among all the physical properties, as it reduces breakage during milling which further makes significant influences in increasing the market value and consumer acceptability. It is generally understood that cooked parboiled rice is harder and less sticky than raw cooked rice (Islam et al., 2001). Hardness value is greatly affected by parboiling condition such as starch gelatinization and amylose content. Table 4.21 and 4.22 shows the statistical results of hardness for both Nerica one and Nerica two which were the local varieties used for the study. From the tables, it can be shown that steaming treatment had significant effect (p<0.01) on hardness in both varieties. Several researchers reported that hardness is greatly affected by parboiling conditions, moisture content after drying, elapsed time, the balance of starch gelatinization and retrogradation and other factors (Ali and Bhattacharya, 1976; Pillaiyar and Mohandoss, 1981; Bhattacharya, 1985; Itoh and Kawamura, 1985; Kimura, 1991; Islam et al., 2001).

Also Tables 4.33 and 4.35 at appendix show mean summary of steaming treatment on physiochemical properties and its least significant difference. From these tables, it was observed that increase in steaming treatment had a significant effect on hardness in both varieties. Figs 4.17 and 4.18 show the effect of steaming treatment on paddy rice varieties and steaming periods on hardness value. Fig 4.17 shows an increase in hardness value as the steaming temperature and period increase. From Fig 4.17, hardness increase as steaming period increases. At steam period 10min, 15min and 25min, hardness increases for steam sample 100oC, 110oC and 120oC respectively as steam temperature increases for samples. Comparatively steam period 25min, 15min and 10min shows greater increase in hardness respectively. Fig 4.18 also shows a similar behaviour of hardness as steam period increases and steam samples temperature increases. But at long steaming period and high temperature, it was observed that the husks of paddy were splitting due to expansion of the endosperm. Fig 4.18 also shows the same trend but as steaming temperature and period increases excessive splitting was observed causing more of the endosperm to be exuded which might have affected its hardness value as shown in the graph. The hardness of the parboiled rice was due to gelatinization of starch granules which occurred at high temperature of steaming and its period. This might also be the reason why excessive exuding of endosperm occurred during the steaming process at high temperature and period. Table 4.23 and 4.24 shows the average hardness and reaction rate constant value for hardening reaction at different steaming processes. From Table 4.23, it can be observed that the steaming process has significant effect on both hardness and rate of reaction. As the temperature increases, hardening of grain kernel also increases with respect to its reaction rate constant.

Comparatively, hardening of nerica two from Table 4.24 also follows the same trend but its reaction rate constant differs. This might be due to excessive hardening of the kernel leading to more splitting of the husk. There are other factors which affect the hardening of the kernel during parboiling which may include the sizes of nerica one being smaller compared to nerica two. Also physical textural hand feeling of the varieties shows more grittiness in nerica two than nerica one which might be the cause of high hardness properties and reaction rate constant values. Hardness of the parboiled rice can depend on temperature of steaming, particle sizes and textural properties of the two varieties as observed in this study. Fig 4.19 and Fig 4.20 show temperature dependence of hardening reaction rate constant for nerica one and nerica two. These figures show a significant (p<0.01) negative linear correlation between K-value and 1/T for steaming as observed with coefficient of correlation (R2) values of 0.849 and 0.989 respectively. It also shows a significant difference on the temperature dependence of the rate of reaction.

Table 4.21 Statistical results for physical property (ANOVA Table for hardness N1)

SOURCE

DF

SS

MS

F

P

Steam

3

15598770

5199590

16.51

0.001

Error

8

2519556

314945

Total

11

18118326

Table 4.22 Statistical results for physical property (ANOVA Table for Hardness N2)

SOURCE

DF

SS

MS

F

P

Steam

3

26441035

8813678

146.43

0.000

Error

8

481512

60189

Total

11

26922547

Table 4.23 Average hardness and reaction rate constant value due to steaming for Nerica 1

Treatment

Steaming

Temperature

100oC

110oC

120oC

Hardness N1

2258.1025

2734.555

3204.883

K-value, min-1

0.272791

0.314784

0.320369

Table 4.24 Average hardness and reaction rate constant value due to steaming for Nerica 2

Treatment

Steaming

Temperature

100oC

110oC

120oC

Hardness N2

3178.245

3257.075

3553.405

K-value, min-1

0.327085

0.312507

0.323663

Figure4.17 Effects of steaming on hardness of Nerica 1

Figure 4.18 Effects of steaming on hardness of Nerica 2

Figure 4.19 Temperature dependence of hardening reaction rate constant for Nerica 1

Figure 4.20 Temperature dependence of hardening reaction rate constant for Nerica 2

4.2 Effect of parboiling treatment on gelatinization properties

4.2.1 Maximum viscosity

The process of starch gelatinisation is called parboiling which depends on the severity of the parboiling process. It was reported that parboiling treatment resulted in decrease in maximum viscosity and breakdown (Kimura et al., 1995) as can be observed by RVA viscograms parameters. In some cases of parboiled rice, distinct peak viscosity was almost identical to final viscosity (RaghavendraRao and Juliano, 1970). Table 4.25 and 4.26 shows the statistical results for maximum viscosity for Nerica one and two respectively. From Table 4.25, it was observed that maximum viscosity for mean value decreases from raw rice to steam 120oC as steaming temperature and period increases. There was no significant difference at steaming temperatures of 100oC and 110oC but significant effect exist at steam 120oC. But from Table 4.26, there exist a significant effect (p<0.01) for all steaming temperatures as it increases. This might be due to amylase or starch granules content at each variety which affected the gelatinization process of Nerica one and two as steaming temperature and period increases.

It was observed that lower maximum viscosity value due to parboiling is a reflection of the decreased swelling ability of gelatinized starch (Priestley, 1976; Ali and Bhattacharya, 1980). Figs. 4.21 and 4.22 show the effect of steaming on maximum viscosity for both varieties of rice respectively. From Figure 4.21, there is a decrease in maximum viscosity as steaming temperature increases from raw rice to steam (120oC) and period 25mins. From Figure 4.22, as the steaming temperature increases and period increases shows a scattily graph representation with an increase in maximum viscosity. At steam 100oC the maximum viscosity remains unchanged at 94.5 RVA units as the period increases. For steam 110oC, as period increase to 15mins, it reduced to 90.05 RVA units and then rose again after that time elapsed to 94.5 RVA units. For steam 120oC, it did not show any significant effect on maximum viscosity as both temperature and period increase. From Figure 4.22, as maximum viscosity increase from 91.05 RVA units to 94.5 RVA units, effect of steaming and period increases had a slight effect on maximum viscosity for Nerica 2 as compared to Nerica one which shows decrease in maximum viscosity.

Tables 4.27 and 4.28 show average maximum viscosity and reaction rate constant value due to steaming. Table 4.27 shows a decrease in maximum viscosity and an increase in reaction rate constant with highest at steam (120oC). From Table 4.28, maximum viscosity for steaming temperatures (100oC and 120oC) was the same but different from steam 110oC, as reaction rate constant values were different but highest for steam 120oC. Figs. 4.23 and 4.24 show temperature dependence of k-values, maximum viscosity and reaction rate constant for Nerica one and two respectively. From these figures, significant (p<0.01) negative linear correlation between k-values and 1/T was obtained with R2 values of 0.723 and 0.839 for steaming both varieties respectively. Also exist a significant difference of temperature dependence of reaction rate constant (k-values) for both varieties. This decreasing pattern agrees well with other researchers in case of RVA parameter (Kimura et al., 1995), as well as amylograph viscosity (RaghavendraRao and Juliano, 1970; Priestley, 1976; Ali & Bhattacharya, 1980c).

The change in quality of parboiled rice with respect to maximum viscosity due to parboiling treatment can be understood from the least squares analysis using the first order kinetic model. It was found that the average value of maximum viscosity was lowest for the higher steaming temperature of 120°C compared with 100oc and 110°C temperature, and that of reaction rate constant value was highest at the higher steaming temperature. The average maximum viscosity and reaction rate constant value indicates the quality index and the rate of change of quality for the respective steaming temperature. The maximum viscosity depends on the swelling behaviour of starch granules during heating stage. Formation of amylose complex (Priestley, 1970a) due to parboiling stabilizes the starch granules (Gray and Schoch, 1962), which restrict swelling and solubilisation of starch. As a result, destruction of starch granules do not occur even at higher temperature, since complexes are thermally stable at temperatures greater than 100oC (Biliaderis et al., 1993).

Table 4.25 Statistical results for physical property (ANOVA Table for Maximum viscosity for Nerica 1)

SOURCE

DF

SS

MS

F

P

Steam

3

1079

360

2.85

0.105

Error

8

1010

126

Total

11

2089

Table 4.26 Statistical results for physical property (ANOVA Table for Maximum viscosity for Nerica 2)

SOURCE

DF

SS

MS

F

P

Steam

3

25.40

8.47

6.04

0.019

Error

8

11.21

1.40

Total

11

36.61

Table 4.27 Average maximum viscosity and reaction rate constant value due to steaming for Nerica 1

Treatment

Steaming

Temperature

100oC

110oC

120oC

Maximum viscosity

88.775

89.425

72.3625

K-value, min-1

0.135600

0.133783

0.253024

Table 4.28 Average maximum viscosity and reaction rate constant value due to steaming for Nerica 2

Treatment

Steaming

Temperature

100oC

110oC

120oC

Maximum viscosity

93.7125

92.7

93.7125

K-value, min-1

0.236635

0.250531

0.336635

Figure.4.21. Effect of steaming on maximum viscosity of Nerica 1

Figure.4.22. Effect of steaming on maximum viscosity of Nerica 2

Figure.4.23 Temperature dependence of maximum viscosity reaction rate constant for Nerica 1

Figure.4.24 Temperature dependence of maximum viscosity reaction rate constant for Nerica 2

4.2.2 Breakdown value

Table 4.29 and 4.30 shows the statistical results for breakdown value for both varieties Nerica one and two respectively. From these tables, steaming treatment had a significant effect (p<0.01) on breakdown values of both varieties. As steaming temperature and period increase, it has a higher effect on the parboiled rice at steam temperature of 120oC for both varieties. The mean summary for both varieties at Tables 4.29 and 4.30 also show a higher effect of steaming on maximum viscosity. It was reported by Kimura et al. (1995), that parboiling treatment also resulted in decrease in breakdown as those of maximum viscosity. Figs 4.25 and 4.26 show the effect of steaming treatment on the breakdown value in this study as already reported by researchers. These figures also show a scatter graph with a decrease in breakdown value from positive values to negative values as parboiling treatment increases.

Tables 4.31 and 4.32 show average breakdown value and reaction rate constant value for Nerica one and two respectively. From these tables, it can be shown that rate of reaction increases at higher temperature (120oC) which implies steaming treatment had a significant effect on the parboiled rice. From this result, breakdown of parboiled rice can be controlled with steaming temperature. Higher effect of steaming on maximum viscosity was also observed. From these tables it can be shown that steaming temperature has significantly affected the rate constant value of breakdown. In case of maximum viscosity, the steaming temperature affected the reaction rate constant value. As mentioned earlier, in some cases maximum viscosity of parboiled rice was almost identical to find viscosity (RaghavendraRao and Juliano, 1970), but in this case minus breakdown value clearly indicated that in some cases viscosity of parboiled rice gradually increased, which did not follow the pattern of raw rice. In this study, for the parboiled rice obtained from longer period and higher temperature of steaming, no pasting time was achieved.

It was also reported that ultimate peak viscosity was not reached even after constant heating at 95oc for 30 min (Priestly, 1976). Figs 4.27 and 4.28 show the temperature dependence of k-values for breakdown rate constant for both varieties. As in case of maximum viscosity, here also significant difference of temperature dependence of k-value was observed for both varieties. Although, significant (p<0.01) negative linear correlation between k-values and 1/T was obtained for steaming with R2-values of 0.814 and 0.588 for Nerica one and two respectively.

Table 4.29 Statistical results for physical property (ANOVA Table for breakdown value for Nerica 1)

SOURCE

DF

SS

MS

F

P

Steam

3

22003

7334

27.73

0.000

Error

8

2116

164

Total

11

24119

Table 4.30 Statistical results for physical property (ANOVA Table for breakdown value for Nerica 2)

SOURCE

DF

SS

MS

F

P

Steam

3

27897

9299

5.68

0.022

Error

8

13107

1638

Total

11

41003

Table 4.31 Average breakdown value and reaction rate constant value due to steaming for Nerica1

Treatment

Steaming

Temperature

100oC

110oC

120oC

Breakdown value , RVA

38.75

42.5

29.25

K-value, min-1

0.240786

0.250889

0.337533

Table 4.32 Average breakdown value and reaction rate constant value due to steaming for Nerica 2

Treatment

Steaming

Temperature

100oC

110oC

120oC

Breakdown value, RVA

51.75

69.25

64.125

K-value, min-1

0.319159

0.211965

0.856640

Figure 4.25 Effect of steaming on breakdown value of Nerica 1

Figure 4.26 Effect of steaming on breakdown value of Nerica 2

Figure 4.27 Temperature dependence of breakdown rate constant for Nerica 1

Figure 4.28 Temperature dependence of breakdown rate constant for Nerica 2

CHAPTER FIVE

5.0 CONCLUSIONS AND RECOMMENDATIONS

5.1 CONCLUSIONS

This study was conducted to generate useful data regarding parboiling process, together with some physicochemical properties with steaming quality of parboiled locally grown rice. This data will be helpful in the parboiling industry in developing countries such as Ghana, where small scale production of parboiled rice is produced utilizing traditional parboiling equipment and process. Experiments were conducted to study parboiling effect on the physicochemical properties of two locally grown varieties of rice. Data were analysed by the non- linear regression method using a first order kinetic model. Efforts were made to know the effect of parboiling and steaming process on the kinetic parameters of some physicochemical properties of parboiled rice.

The following conclusions can be made from this study;

First order kinetic model successively stimulated parboiling process on the quality indicators through the parboiling process.

The reaction constant value for lightness, colour intensity and milling yield is controllable with steaming period.

The final value of head rice yield, hardness, maximum viscosity and breakdown value and their reaction rate constant value is controllable with steaming temperature.

Both varieties of locally grown rice showed similar behaviour during steaming process.

5.2 RECOMMENDATIONS

In this study, temperature dependence of reaction rate constant value due soaking and steaming was achieved taking only three observations which resulted in lower coefficient of correlation value between k-values and 1/T in case of steaming treatment for physical property and physicochemical property. In this regard more than three observations should be considered for more precise results.

Further study should be carried out how microstructure and nutritional composition affect reaction rate values.

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