In order to develop simple and adaptable measures to reduce the impact of changing climatic conditions and poor postharvest practices on grain quality, data on temperature and postharvest practices were collected and correlated with physical grain quality parameters for 3 rice development hubs (Ndop, Lagdo and Mbam) in Cameroon. Inter-annual variations in temperature and thermal amplitudes were the highest in Ndop followed by Mbam and the least in Lagdo. When the same rice variety was grown in the hubs and milled with a laboratory hand dehusker, the mean chalky score was highest in Ndop (18%) and least in Mbam (11%). In addition, Ndop recorded higher grain fissures and broken fractions compared to Mbam or Lagdo. Positive correlations were observed between thermal amplitudes, grain fissures and the proportion of broken fractions. However, rice milled using commercial mills located in the hubs recorded the highest broken fractions in Mbam (54% - 63%), followed by Lagdo (43% - 52%) and the least in Ndop (35% - 38%). The type of mills in the hubs was responsible for these differences as Mbam had only Engelberg types mills that recorded higher broken fractions than in Ndop where only rubber roll mills were present (P < 0.05). Lagdo had a mixture of Engelberg and rubber roll mills and recorded intermediate broken fractions. Proper parboiling, recovery and processing of poorly filled and immature grains during parboiling and processing of low-grade and fine broken rice into product generally accepted by the local population were demonstrated as simple adaptation strategies to mitigate the adverse effects of changing climatic conditions and poor postharvest practices on the physical quality of rice especially in sub-Saharan African countries.
Rice (Oryza. sativa L.) and to some extend (Oryza. glaberrima S.) is fast becoming a global staple and its de- mand is on the rise especially in sub Saharan African (SSA) countries. Rice production per hectare has to rise above 12% annually to keep pace with the expected demand. In addition, rice postharvest operations will have to be tailored in such a way as to reduce losses and add value to the crop. This cannot be achieved without taking into considerations the effect of changing climatic conditions on rice production. Climatic factors that affect rice production and quality include heat (temperature and humidity), carbon dioxide levels, drought, salinity and flooding. Several authors have reported on the effects of changing climatic conditions on rice production and strategies for adaptation [
Rice parboiling, if properly carried out can be an effective way of eliminating chalkiness in milled rice grains. In addition, adding value to low-grade broken rice by processing into other products like biscuits may also be an effective strategy of reducing the adverse effects of high temperatures and poor postharvest operations on the physical quality of the rice grain. Parboiled rice is rice that has its starch partially gelatinized by soaking paddy rice or brown rice in water followed by steaming and a drying process [
Rice samples were collected from three “rice development hubs” (RDHs) in Cameroon [
Data on temperature variations for the last six decades (1955-2002) for the 3 RDHs were collected from the Centre for Hydrological Research, Institute of Mining and Geological Research, Yaoundé-Cameroon. Data on temperature amplitudes for the 3 RDHs were also collected.
Samples of the major rice varieties grown in each RDH were collected. These samples (paddy and white milled rice) were collected from farmers and millers. For each farmer, the method used to thresh the rice was recorded. Milled samples were collected from millers at the mill houses. The type of mills used to mill the rice was also recorded. The moisture content of the grains was determined using a Satake Rice Moisture meter (Satake Co. Ltd., Tokyo, Japan) according to manufacturer’s instructions and expressed as a percentage. All determinations were carried out in triplicates.
Rice samples were milled using three different mills; the Engelberg type mill (GFAMO-CIG, Garoua, Came- roon), the Satake commercial rubber roll mill (Satake Co. Ltd., Tokyo, Japan) and the Satake Laboratory hand de-husker (Satake Co. Ltd., Tokyo, Japan).
When part of the milled rice kernel was opaque (white spot) rather than translucent, it was considered “chalky”. Two hundred (200) milled rice grains were placed on a blue cardboard background to visually identify under white light the grains that had white belly, white centre, white back or a combination of these [
Fifty (50) grains of paddy or milled rice were randomly selected from each sample and viewed under HP Pho- tosmart C8100 scanner (Hewlett Packard, Japan). The flatbed million-color option was used to acquire a 600 dpi TIFF format image on a black background. The number of fissures in grains was determined using the image analysis method of [
The images were acquired on a dark background; the software, ImageJ64 was run on a Mac OS X Version 10.6.8 platform, with a 2.4 GHz Intel Core i5 Processor; and analysis of particles options were; size = 200-in- finity, circularity = 0 - 1 and show = overlay outline.
The total number of fissures observed in 50 grains was reported.
The level of broken rice fraction was determined using a sample of 20 g of milled rice. The broken grains were manually selected from the whole grains and weighed and the results expressed as percentage of broken fraction in milled rice.
Rice was parboiled using two procedures: 1) A uniform steam-distributed (USD) parboiling technology [
Fifty (50) kilograms of paddy rice was completely submerged in 100 liters of water. The grains that floated were recovered and weighed rather than discarding as commonly practiced by local processors. The poorly filled grains collected during the washing of paddy rice for parboiling were separately parboiled, dried, milled, weighed and the weight of milled grains expressed as a percentage of milled parboiled rice obtained from com- pletely filled grains.
Completely broken (100%) rice fraction that has been previously shown to have a very low market value [
The data obtained were analyzed using the Statistical Package for Social Sciences (SPSS version 10.1.4 (2002)) at a 5% significance level. For each variable, mean ± 2 Standard Error (SErr) were computed for each RDH and the results plotted on a chart. Data on the physical quality attributes of rice from the different RDHs or pro- cessed using different procedures were compared by one-way ANOVA to determine variations in the means. Pearson correlation was used to determine the relationship between thermal amplitude; number of fissures in grains and percentage broken fractions in rice milled using the Satake Laboratory hand de-husker (Satake Co. Ltd., Tokyo, Japan). Using the least significant difference (LSD), varietal classes for chalkiness, fissures and broken fractions were created for the most popular rice varieties grown in Cameroon.
A total of 13 rice varieties were collected with at least 3 varieties selected per RDH.
. Characterization of rice production site in Cameroon with respect to threshing method, types of mills and major rice varieties cultivated
Site | Threshing method | Type of mills | Rice varieties collected |
---|---|---|---|
Lagdo hub | Beating on a steel drum | Satake commercial rubber rolls and Engelberg | IR-46 NERICA-3 ITA-300 |
Mbam hub | Beating on a steel drum | Engelberg only | Madam Bakala M-13 CICA-8 NERICA-3 |
Ndop hub | Beating on a piece of wood | Satake commercial rubber rolls only | Tainan-5 TOX-3145 NERICA-3 |
JICA* experiment farm Yaoundé | Threshing machine and beating on a piece of wood | Satake laboratory rubber roll only | NERICA-L42 NERICA-8 NERICA-3 |
*Japan International Cooperation Agency.
Between 1955 and 1990, variations in mean annual temperature showed a similar pattern in the three RDHs with inter-annual variations not exceeding ±1˚C except in the following years in Lagdo hub (1972, 1985, 1986, 1987 and 1990), Ndop hub (1987), and Mbam hub (1987, 1988 and 1990). Between 1990 and 2002, Lagdo hub had inter-annual variations >1˚C only in three years (1990, 1998 and 2002) while in Ndop and Mbam hubs, this happened respectively in 9 years (1993, 1994, 1995, 1996, 1997, 1998, 2000, 2001 and 2002) and in 5 years (1990, 1994, 1995, 1998 and 2002). These results show that Ndop hub had the highest inter-annual variations in temperature between 1990 and 2002 followed by Mbam hub and least in Lagdo hub (
There was variation in moisture content of rice samples from different RDHs in Cameroon (F-statistic (F) =73.6, Probability (P) = 0.0001) using one-way analysis of variance (
Inter-annual variation in temperature for three rice development hubs of Cameroon between 1955 and 2002
Thermal amplitudes for three rice development hubs of Cameroon
Moisture content of paddy rice recorded in different rice development hubs in Cameroon and from the Japan International Cooperation Agency (JICA) rice project site in Nkolbisson, Yaounde-Cameroon. *Bars with different letters signify significant difference at 0.05 level
The chalkiness score defined as the percentage of chalky grains in a rice sample was determined as described above. Rice varieties in this study were classified into three distinct chalky classes (F = 140.5, P = 0.0001); highly chalky, moderately chalky and low chalky (
(a) Classification of major rice varieties produced in Cameroon into three classes based on % chalky grains using a pooled sample from three rice development hubs (Ndop, Mbam and Lagdo) of Cameroon. *Bars with different letters signify significant difference at 0.05 level; (b) Rate of chalky rice recorded in different rice development hubs in Cameroon and from the Japan International Cooperation Agency (JICA) rice project site in Nkolbisson, Yaounde-Cameroon. *Bars with different letters signify significant difference at 0.05 level
high % chalky score (82% - 85%), seven varieties-IR46, NERICA-3, Tainan-5, TOX3145, M-13, CICA-8 and NERICA-L42—had moderately chalky score (18% - 25%), and one variety—NERICA-8-had low chalky score (9% - 12%). The mean % chalky score from all RDHs in Cameroon was >20% and could therefore be attributed the score of 9 [
Like chalkiness, the rice varieties were grouped into three distinct classes based on the number of fissures in 50 grains (F = 79.0, P = 0.0001); highly fissured, moderately fissured and low fissured (
Rice produced in Cameroon generally has high levels of broken fraction (35% - 63%). In this study, rice was milled using three different types of mills. The highest proportion of broken fractions as expected was recorded with the Engelberg type mills (50% - 63%), followed by the Satake Commercial rubber roll type mills (36% - 46%) and the least with the Satake laboratory hand de-husker (11% - 17%) (
(a) Classification of major rice varieties produced in Cameroon into three classes based on number of fissures in 50 grains using a pooled rice sample milled using rice mills located in three rice development hubs (Ndop, Mbam and Lagdo) of Cameroon. *Bars with different letters signify significant difference at 0.05 level; (b) Number of fissures in 50 grains rec- orded from NERICA-3 rice collected from different rice development hubs in Cameroon and milled using a laboratory hand de-husker. *Bars with different letters signify significant difference at 0.05 level
(a) The rate of broken fraction recorded for rice milled using different types of mills found in Cameroon; (b) The rate of NERICA-3 broken rice fractions recorded from samples milled using the mills present in the different rice development hubs of Cameroon. *Bars with different letters signify significant difference at 0.05 level
son for the relatively high proportion of broken fractions in Mbam and Lagdo compared to Ndop was the types of mills used in these hubs. In Mbam hub, only the Engelberg type mills that produced very high proportion of broken fractions are available. On the other hand, in Lagdo hub, Engelberg and rubber roll mills are present while in Ndop only rubber roll mills, which produced relatively lower levels of broken fractions were present.
The milled rice obtained from different rice varieties in this study was grouped into three distinct classes (Highly broken, moderately broken and low broken) based on the% broken fractions (F = 120, P = 0.0001). One variety-IR46-was highly broken (75% - 80%), 3 varieties—ITA-300, TOX-3145, CICA-8—were moderately broken (55% - 70%) while 6 varieties—Tainan-5, NERICA-3, M-13, Madam, NERICA-8 and NERICA-L42— had low broken fractions (23-30%) (
(a) Classification of major rice varieties produced in Cameroon into three classes based on broken rice fraction using a pooled sample from three rice development hubs (Ndop, Mbam and Lagdo) of Cameroon. *Bars with different letters signify significant difference at 0.05 level; (b) Rate of broken rice fraction of NERICA-3 collected from different rice development hubs in Cameroon and from the Ja- pan International Cooperation Agency (JICA) rice project site in Nkolbisson, Yaounde-Cameroon and milled using a laboratory hand de-husker
was also observed between thermal amplitudes and the proportion of broken fractions (R = 0.80, P < 0.05) using milled samples from the laboratory hand de-husker.
When the paddy of TOX-3145 rice was parboiled using the improved (uniform steam-distributed, USD) par- boiling technology [
It is common practice in the rice parboiling industry to discard immature and poorly filled grains during par- boiling. In SSA countries, this is done by submerging paddy rice in water and allowing the immature and poorly filled grains to float and subsequently discarded. High temperatures during the ripening stage of rice may cause immature and poorly filled grains [
In Cameroon, low-grade and fine broken rice is used in the Northern part of the country for the production of a local meal “Gniri”. Gniri is made by cooking low-grade or fine broken rice in water and mashing it to produce a paste that is eaten with a local sauce. In addition some local processors use it for the making of rice porridges and rice “doughnuts” after grinding into flour. However, these practices are not common in the Southern part of the country and as such low-grade and fine broken rice is sold very cheaply as a feed for livestock. In this study, fine broken rice (100% broken) was used to produce rice biscuits. The biscuits were highly accepted by a test panel at IRAD confirming earlier results by [
In this study, the level of chalky white rice, fissures in rice grains and broken rice fractions in three contrasting RDHs (Lagdo, Ndop and Mbam) in Cameroon were evaluated. The mean % chalky grains from all RDHs in
. Effect of parboiling on some physical quality parameters of TOX3145 rice variety produced in Cameroon
Quality Attribute | WNP | IP | TP |
---|---|---|---|
Broken fraction (%) | 66.11 (±1.4) | 5.35 (±2.0)* | 44.95 (±1.0) |
Fissures in 50 grains | 6.00 (±1.4) | 1.00 (±0.4)* | 11.00 (±1.7) |
Chalky grains (%) | 35.0 (±1.3) | 1.02 (±0.01)* | 4.56 (±0.4) |
WNP = White nonparboiled rice, IP = Improved parboiled rice, TP = Traditional parboiled rice. *Means are significantly different at 0.05 level.
Cameroon was more than 20% and a score of 9 was attributed to these samples according to [
Thermal amplitudes and the differences between the daily minimum and maximum temperatures were the highest in Ndop hub compared to Mbam and Lagdo. Milled rice produced in Cameroon generally has a high proportion of broken fractions. However, the main factors responsible depend on the hub where the rice is pro- duced. In Mbam and Lagdo, the main factor causing grain breakage is the type of mills used for de-husking and polishing. In Ndop, the main factors responsible are high thermal amplitudes and temperature variations espe- cially during the rice ripening stage. This does not, however, rule out the contribution of other factors such as poor harvesting, threshing and drying methods that are common in all the RDHs. An improved parboiling tech- nology, the recovery and processing of poorly filled and immature grains and the processing of rice with a high proportion of broken fractions into biscuits or other products generally accepted by the local population can be implemented as adaptation strategies to the effects of temperature variations and poor postharvest operations on physical quality of the rice grain especially in SSA countries. These strategies will increase the revenue of rice value-chin actors by reducing quantitative and qualitative postharvest losses.
This work received financial assistance from the Canadian International Development Agency (CIDA) sponsored project on “Enhancing food security in Africa through the improvement of rice postharvest handling, marketing and the development of new rice-based products”.