Cottage Level Cassava Starch Processing Systems in Colombia and ...

Food Bioprocess Technol (2013) 6:2213–2222 DOI 10.1007/s11947-012-0810-0

COMMUNICATION

Cottage Level Cassava Starch Processing Systems in Colombia and Vietnam Guillaume Da & Dominique Dufour & Andres Giraldo & Martin Moreno & Thierry Tran & Gustavo Velez & Teresa Sanchez & Mai Le-Thanh & Claude Marouze & Pierre-André Marechal Received: 13 June 2011 / Accepted: 12 February 2012 / Published online: 7 March 2012 # Springer Science+Business Media, LLC 2012

Abstract In the tropics, cassava starch is produced at artisanal and industrial scales. This paper focuses on a new methodology enabling the technoeconomical comparison of small-scale cassava starch manufacturing process (1–5 t of starch/day) in two markedly different contexts (Colombia and Vietnam). Measurements were conducted during trial runs for each unit operation (washing/pealing, rasping, extraction and separation). Starch mass balance was calculated from sample composition (moisture, starch and crude fiber and ash content). Production capacity, water consumption, electric requirements and capital– labor costs were also measured. The manufacturing processes differed mainly on starch recovery from starch present in washed roots (65 vs. 76%), extraction capacity (0.3 vs. 0.9 t of washed roots/h), water consumption (45 vs. 21 m3/t of dry starch), energy consumption (59 vs. 55 kWh/t of starch) and production costs (1,156 vs. 162 US$/t of starch) for Colombia and Vietnam, respectively. Moreover, the effectiveness of the

starch extraction process could largely be attributed to the differences in the extent of root disintegration achieved with different rasping equipment. Keywords Cassava starch . Extraction efficiency . Water consumption . Colombia . Vietnam Introduction Cassava (Manihot esculenta Crantz) is a major source of starch in the tropics. In Latin America, the northern region of Cauca Department in Colombia provides a good example of rural cassava industry. Previous studies were conducted in Colombia in the 1990s in order to assess the adoption of these technologies for manufacturing fermented cassava starch (Gottret et al. 1997; Rojas et al. 1996). More recently, some authors investigated the

This paper is dedicated in memoriam to our friend Dr. Claude Marouzé. G. Da : P.-A. Marechal Laboratoire GPMA-AgroSup Dijon, Université de Bourgogne, 01, esplanade Erasme, 21000 Dijon, France G. Da (*) CERTES, Université Paris-Est Créteil (UPEC), 61, Avenue du Général de Gaulle, Créteil 94000, France e-mail: [email protected] D. Dufour : T. Tran : C. Marouze CIRAD, UMR QUALISUD, 73 Rue Jean-François Breton, Montpellier, France D. Dufour : A. Giraldo : T. Sanchez CIAT, A.A 6713 Cali, Colombia

M. Moreno Universidad del Valle, Cali, Colombia

G. Velez Deriyuca LTDA, Carrera 89 #10-80 apartamento 323, multicentro, Unidad 20-21, Cali, Valle del Cauca, Colombia

M. Le-Thanh Hanoi University of Science and Technology (HUST), IBFT. 01, Dai Co Viet Road, Hanoi, Vietnam

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energy utilization and some environmental issues in the production of cassava products (Colin et al. 2006; Jekayinfa and Olajide 2007). Despite some figures revealing potential differences between small-scale processes (Westby 2002), comparisons remained difficult because of different methodologies used to estimate their operating conditions and process efficiencies. Consequently, a methodology of diagnosis was developed for assessing small-scale manufacturing processes in northern Vietnam (Da et al. 2008). Results suggested that the main differences between processing types, differing in rasping and extraction stages, were in their capacities, water consumptions, electric requirements and capital–labor costs, with a tendency in adopting continuous processes for the washing and rasping stages. The objective of this study was to apply a similar methodology of diagnosis to compare two types of small-scale manufacturing processes in Vietnam and in Colombia. One ton of extracted starch at 12% moisture (wwb, weight wet basis) was provided as a reference unit. Results could be used and expanded to other starch manufacturing processes in other contexts.

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rasping surface, were employed. The first type of rasper with abrasive metal sheet (RRall) was the local type used within the processing unit (Rallanderia La Zelandia, Cauca Department); the second type of rasper with serrated blades (RCIAT) was used at the CIAT research center (CIAT rasper). The comparison trials between these two rasping technologies consisted only in replacing RRall by RCIAT on the processing line, while all other starch manufacturing equipment remained the same. In Vietnam, rasping and extraction stages were performed in a single equipment (RETC). The operating principle of this rasping and starch milk filtering machine was described previously (Da et al. 2008). Extraction In Colombia, the extraction stage was ensured in two horizontal rotating drum separators operating in parallel as described previously by Rivier et al. (2001). A separator (locally called coladora) consisted of a pivoted feed and discharge hopper, a cylindrical separating drum (0.386 m3 in volume), a water aspersion system and the casing. Sieving and Settling

Materials and Methods Manufacturing Process Technologies This study was conducted in two typical wet starch processing units from Northern Vietnam and in the Cauca Department of Southwestern Colombia. The noncontinuous manufacturing processes were representative of the basic process used in the tropics for cottage level starch extraction from cassava (Balagopalan 2002). Roots were washed and mechanically rasped to a pulp, from which starch was extracted by abundant washing with water. The bagasse was squeezed out, while starch was collected in settling tanks. When the starch granules settled down, the supernatant water was eliminated and wet starch was finally obtained. Processing Equipment Different types of equipment for a small-scale cassava wet starch production unit used in this study have been described elsewhere (Da et al. 2008; Rivier et al. 2001). However, main modifications have been made on the equipment as follows. Rasping In Colombia, two different types of cylindrical raspers, which had the ability to work in a continuous manner but differ in the

For all processes, fine sieves fixed on frames were used for removing remaining fibers before decantation in settling tanks where the extracted starch was separated from its aqueous suspension under gravity (starch slurry). The last stage occurred after collecting the creamy yellow scum layer locally called “black starch” in Vietnam and “mancha” in Colombia. This fraction was collected from the tank, weighed and dried. Sedimented wet starch was finally collected and weighed. Samples of starch were collected in triplicate and dried for analysis. Water Consumption Water previously drawn from the local river and stored in concrete tanks was used. Water consumption was measured by water meters placed on water inlets of the extractors. The volumes of suspensions (starch milk, wastewater) in the settling tanks were also reported. Mass Balance of the Wet Starch Manufacturing Process The diagnosis methodology previously described by Marouzé and Da (2007) was used to evaluate the efficiency of the manufacturing process. The trials were repeated in triplicate within the same processing unit. In Colombia, for each trial, 250 kg of fresh roots from two varieties (Mper 183 and Algodona) were obtained and processed into wet starch in Rallanderia La Zelandia, Cauca Department in June 2007. In Vietnam, up to 2,000 kg of fresh roots from high yield cassava

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varieties (hyv) were obtained from mountainous areas and processed into wet starch in a cluster of craft hamlets from Cat Que commune in the Red River Delta. The high yield varieties (KM60 and KM94) were the renamed Thai varieties Rayong 60 and Kasetsart 50, which were selected from a number of Thai varieties introduced in Vietnam as clonal planting material in 1990. These varieties have a fresh root yield of 25–30 t/ha and starch yield of 5–6 t/ha (depending on growth conditions), and they are now being disseminated to a large number of farm households in Vietnam. Analysis Sample Preparation and Proximate Analysis Samples were collected in triplicate from the manufacturing process, cut into small pieces, mixed and dried at 60 °C for 48 h. Moisture content of the products which did not need further analysis was determined by drying 10 g of sample at 105 °C for 24 h (Gibert et al. 2009). Ash content was calculated following heating to 550 °C for 3 h as per AOAC official method. Crude fiber contents of solid samples were determined for the loss on ignition of dried residue remaining after digestion of cassava flour (2 g) as per AOAC official method. Starch content analysis for solid samples was obtained using enzymatic analysis as described by Sánchez et al. (2009). The results are given in kilogram of starch (or crude fibers) per 100 kg of dry matter. Starch content in starch milk was obtained by a density method as described by Da et al. (2008). Starch extraction in the lab was performed using the technique described by Sánchez et al. (2009). The particle size of fibers produced from different types of raspers was measured by wet sieving. The method previously developed on rabbits feeds (Lebas and Lamboley 1999) was adapted in our study as follows: bagasse samples in triplicate (10–15 g dry basis) were placed in a minimum volume of 250 ml water for initial separation. Thus, the mixture of water and bagasse was filtered on a three-dimensional vibrating sifter (Tyler, Las Vegas, USA) for 10 min with water followed by 2 min without water. The standardized sieves used (Tyler, Las Vegas, USA) had square meshes with open holes of 2,800 (N°7), 2,000 (N°10), 850 (N°20), 600 (N°30), 212 (N°70) and 150 (N°100) μm. The quantity of particles retained on each sieve was expressed as a percentage of the dry matter of the test specimen, and the particle size distribution could be obtained. The particle size was reported in terms of median particle diameter (d50 in millimeter), in which the median is the midpoint of the distribution. In order to compare the particle size distributions of bagasses from RETC, RRall and RCIAT with other bagasse samples, additional samples of bagasses were obtained from the following rasping technologies: an industrial hammer mill and

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rasper (YFACO, Vietnam), an Osterizer blender from CIAT and a wooden cylindrical rasper serrated with fine wires as described previously (Da et al. 2008). The samples in triplicate were analyzed by wet sieving, and they underwent the same procedure described above in order to determine their median particle diameter. Electric Consumption In Colombia, movement for all the equipment was provided by one three-phase electric motor (NP08.95 kW) which transmits the mechanical power through a system of flat belts and pulleys. During the trials, the power of the motor was measured by a current analyzer (Fluke, model 43B, Ontario, Canada). The device was placed on the three-phase electric outlet in order to record the real power while machines were running. The energy per kilogram of feeding material was measured after taking into account the conversion yield from electric power to mechanical power. Production Costs In Vietnam, labor input and production costs described previously (Da et al. 2008) were used. For Colombia, the socioeconomic study by Gottret et al. (1997) was updated with the real cost (financial accounting on a 6-month period) from a local small-scale cassava starch factory (Deriyuca LTDA, Cauca Department). Fixed costs were calculated with the cost of civil works (based on estimates of averages over 15 years of useful life) and equipment (6 years of useful life) and by considering 10% of annual interest. Calculation and Statistical Analysis From the mass balance and composition analyses, the following yield components were calculated: the processing yield (kilogram of recovered dry starch divided by 100 kg of washed fresh roots), the starch recovery from production (Marder et al. 1996) and the rasping effect (YRE) described by Grace (1977). In order to evaluate and compare the different processes in Vietnam and Colombia, a common functional unit (FU) was defined as 1 t of extracted starch at 12% moisture (wwb), in line with methodological guidelines of the life cycle analysis (LCA) approach (Roy et al. 2009). The quantities of materials (fresh roots, bagasses, crude fibers, water, etc.) and the energy consumption were expressed per FU. Statistically significant differences between sample means were determined using Student's test or ANOVA for multiple comparisons at a 95% confidence level. The statistical analyses were performed with Statistica v7.1 software (StatSoft, Inc., Maisons-Alfort).

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Results and Discussion Quality of the Products Table 1 shows the composition of the products collected along the cassava manufacturing process. The quality of the washed roots used for processing in Colombia and Vietnam were within the range for root quality traits (such as starch content and fiber content) (Sánchez et al. 2009). Washed roots from Mper 183 and Algodona varieties did not show a significant difference in dry matter and starch content and had lower dry matter than the washed roots from Vietnam. These differences could be attributed to the fact that varieties are selected for their final uses and consumer preferences, which differ between Vietnam and Colombia. In Vietnam, bitter high yield varieties (hyv) were introduced nationwide (through research and development projects) in order to produce large quantities of starch for food as well as many nonfood uses (Howeler 2010). In Colombia, starch is mainly extracted from sweet cultivars, which contain lower level of starch given their alternative use for table consumption. Nevertheless, some differences observed in dry matter and starch content between the cassava root cultivars used in this study might also be attributed to different harvesting times after planting and overall growing conditions.

Table 1 Composition of the products (% dry matter) collected from particular stages of the cassava wet starch manufacturing process in Vietnam and Colombia Product

Variety

Dry matter (% wwb)

Starch (% wdb)

Crude fibers (% wdb)

Mper 183 Algodona Vietnam hyvc

33.9±1.4b 32.1±0.4b 41.6±2.7a

86.0±5.6a 87.5±1.6a 82.7±2.0a

5.5±0.2a 3.7±0.4b 3.1±0.8b

Mper 183 Algodona Vietnam hyvc

12.5±1.3a 15.0±0.4a 11.6±4.2a

62.1±6.3a 70.2±6.0a 41.0±3.2b

19.7±1.7a 13.7±1.0b 21.4±1.8a

Mper 183 Algodona Vietnam hyvc

11.0±0.4a 4.3±0.6b 11.5±1.6a

82.3±1.9a 62.6±1.4b 61.2±nd

0.3±0.0 1.4±nd 0.7±0.0

Washed roots

Bagasse

Mancha

Granulometry An independent graphic representation of the size of the cassava fibers in the form of a histogram of cumulative mass frequency is proposed as illustrated in Fig. 1. The cumulated percentages on each size class are presented on Fig. 1a. The median particle size (d50) of each bagasse, corresponding to the theoretical sieve through which 50% of the weight can pass, was determined from each curve, and d50 was used as a characterization of the effect of different rasping methods/ technologies on fiber sizes. The analysis revealed that the d50 was significantly lower for fibers obtained from blender as compared to fibers obtained from RRall and RCIAT rasping technologies; with 0.45 (±0.03 mm), 0.83 (±0.09 mm) and 1.18 (±0.06 mm), respectively. A comparison between the median particle size of seven types of bagasses is presented on Fig. 1b. Four significantly different classes of d50 were identified. The lowest particle size class corresponded to processing with a blender or with rasping technologies from Vietnam; the median particle size was obtained with type RETC (0.46±0.04 mm); and the two classes with larger particle size corresponded to processing with types Rrall and RCIAT. These differences in d50 could be attributed to a better rasping followed by a better starch extraction efficiency in processing Vietnamese facilities compared with those from Colombia. Mass Balance of Wet Starch and Yield Components

Standard deviations are indicated with a “±” sign wwb weight wet basis, wdb weight dry basis Statistically significant differences at α05% level for each product and within each column a,b

c

The composition of the “mancha” collected from Mper183 variety revealed a significantly higher starch content than that from Algodona or hyv varieties (Table 1). The dry matter content and the fiber content of the wet starch were in the ranges 49.0–55.3% and 0.2–0.3%, respectively. The three systems from Vietnam and Colombia did not allow for the extraction of all the starch contained in the parenchyma of the roots (Table 1). Nevertheless, the composition of the cassava bagasse revealed that the starch content was significantly lower by 30% with hyv cultivars, compared with the two cultivars from Colombia (41, 62 and 70% dry basis, respectively). Additionally, the crude fiber content of the hyv and mper83 bagasses were significantly higher than those of Algodona cultivar.

Cassava high yield varieties from Vietnam (KM60 and KM94) process with type C rasping-extractor

The washing stage revealed that the loss of peels (kilogram of fresh peels and soil per 100 kg of fresh roots) was significantly higher for Mper183 and Algodona varieties in Colombia compared to hyv varieties in Vietnam, with 6.6% (±0.9), 7.9% (±1.1) and 2.5% (±0.9), respectively. This might be attributed to the larger amounts of water used for the washing stage in Colombia, which was threefold higher than in Vietnam (9±2 and 2±1 m3, respectively).

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Fig. 1 Particle size distributions of the cassava bagasses obtained from different rasping technologies. Cumulated percentages of the different particle size classes (a). Each plot represents an average of triplicate samples with repeated trials (dots with error bars). Median particle diameter d50 of bagasses obtained with different types of raspers (b);

hammer mill (1), CIAT rasper (2), cylindrical rasper from Colombia (3), rasping disc from Vietnam (4), blender (5), cylindrical rasper from Vietnam (6), industrial rasper from Vietnam (7). Levels not connected by the same letter are significantly different

Table 2 shows the mass balance of the cassava manufacturing processes from Vietnam and Colombia. The mass balance (in kilogram of dry weight) of the process from Vietnam revealed the highest quantity of dry matter liberated during the extraction stage, and the highest processing yield as compared to results from Colombia. The rasping effect showed that type C extraction (RETC) was more efficient to liberate starch from rasping and extraction stages than with RRall and RCIAT technologies. The starch yield could be greatly affected by the blade height of the rasping rolls in type RCIAT, the perforation in RRall, or the teeth height of the disc in RETC. The main limiting factor for starch recovery from production (kilogram

of starch recovered divided by total starch in kilogram in washed roots) with the RETC technology was the settling stage because great amounts of total solids were carried in the wastewater rather than the rasping–extraction stage (Table 2). In contrast, the RRall and RCIAT technologies allowed only 58– 65% recovery of the starch present in washed roots from both cultivars; i.e., the RRall and RCIAT technologies were limited both by the efficiencies in rasping and extraction and also at the settling stage. The starch recovery from production with RETC was similar to that from production in two Brazilian plants where a technological assessment was conducted in 1993 (Marder et al. 1996). The authors reported that the starch

Table 2 Balance sheet (kilogram of dry weight) and yield components for three types of small-scale cassava manufacturing processes from Colombia (RRall and RCIAT) and Vietnam (RETC) Processing characteristics

Mass balancea Washed roots Bagasse Mancha Wet starch Total solid carried in wastewater Sun-dried starch Yield components [%] Processing yield Rasping effect Starch recovery from production

Type RRall

Hyv

Algodona

Algodona

100.0 20.7±1.5b 10.0±0.3b 54.6±1.5c 14.7±1.4b 52.3±1.5

100.0 22.1±0.7b 3.6±0.4c 54.5±3.1c 19.8±3.3b nd

100.0 27.0±nd 3.6±nd 50.8±nd 18.6±nd nd

100.0 14.1±1.0c 3.3±3.4c 66.3±0.8b 16.3±1.9b nd

17.1±0.7c 79.5±3.8c 58.8±3.5c

16.3±0.9c 78.1±3.1c 65.8±3.3c

15.1±nd 80.2±nd 58±nd

27.0±1.7b 93.1±0.9b 76.1±1.9b

Kilogram of dry weight

b,c

Type RETC

Mper 183

The data provides the average of three trials. The standard deviations are indicated with a “±” sign a

Type RCIAT

Statistically significant differences at α05% level within each line

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recovery from production was about 71% for plant A and 77% for plant B. Furthermore, our study proved that for the variety mper183 extracted with RRall technology, the starch recovery was statistically lower than from starch recoveries obtained through the RETC technology. Production Capacities and Water Consumption The washing times were significantly higher to process 1 t of fresh roots in Vietnam than in Colombia (Table 3). In both locations, the equipment consisted of batch-operated horizontal hexagonal or cylindrical cages rotating at low speed. Thus, the differences in washing efficiency could be attributed to the use of greater volumes of water in Colombia than in Vietnam (threefold higher) rather than to the type of washing equipment. Moreover, in Colombian agroindustries, the loading and unloading stages are facilitated by plant design which takes advantage of gravity. Observations during our root processing trials indicated that roots in Colombia have less dirt than roots in Vietnam, possibly because of more sandy soils in the Colombian production region, which may contribute to explain the higher washing capacity in Colombia. The rasping efficiency of the RCIAT (Table 3) was seriously limited and the processors rejected it rapidly. Although the RCIAT rasper functioned without adding water, it resulted in great loss of fresh pulp. Consequently, only one trial was performed with this type of rasper. While analyzing processes with system RRall and system RETC, the rotational speed appeared to be a key factor influencing starch recovery, as a higher mechanical energy input

results in finer particle size and better starch extraction. Depending on rasper drum diameter, optimum rotational speeds are in the range 1,000–2,000 rpm (Grace 1977; Rivier et al. 2001), above which energy costs exceed the gains in starch recovery. The design of the rasping plate is a second factor determining starch recovery because a sharper teeth profile can improve the rupture of root cell walls and starch extraction. However, literature is still scarce regarding the optimization of rasping teeth profile. Table 3 shows clearly that the main factor affecting production capacity was the type of extraction technology. In Colombia, despite the use of two coladoras extractors associated in parallel, the extraction stage remains the bottleneck of the manufacturing process in which threefold lower extraction capacities were observed as compared to the process in Vietnam. The starch density profiles in RRall and RCIAT are presented on Fig. 2. The curves had nearly the same shape, and their slopes did not differ much from each other. The extraction stage lasted 18 min, but the density of the starch slurry dropped down from an initial 1,055 kg/m3 to 1,010 kg/m3 (1.4°Be) after only 8 min. The extraction efficiency in system RRall could be improved by increasing the residence time of the reactor (volume of the reactor divided by the average inflow of water). Indeed, a previous study showed that the great extraction efficiency in RETC could be attributed to a shorter time period compared to single-filtering machine rotated at 140 rpm, with 70 s and 16 min, respectively (Da et al. 2010). The main differences in water consumption between the RERall and RETC processes occurred at the rasping and the

Table 3 Production capacities and water consumption for three types of small-scale cassava manufacturing processes from Colombia (RRall and RCIAT) and Vietnam (RETC) Type RRall

Type RCIAT

Type RETC

Processing characteristics

Mper 183

Algodona

Algodona

hyv

Production capacitya Washing

2.0±0.2b

1.7±0.2b

1.92±nd

1.14±0.11c

1.37±0.1 0.28±0.00c

2.42±0.2 0.31±0.06c

0.37±nd 0.39±nd

0.86±0.09b,d

9.1±2.0b 2.8±nd nd nd nd 61.1±14.2b

9.3±0.5b 3.0±0.7b 29.8±6.0b 12.2±6.0b 12.5±1.3 49.0±8.9b

10.1±nd 0.0±0.0c 31.9±nd 18.3±nd 10.3±nd 61.1±nd

Rasping Extraction Water consumptione Washing Rasping Extraction Second sieving Cleaning equipment Volume of starch milk in settling tank

2.0±0.9c 18.8±0.4c,d 0.0±0.0c 0.1±nd 17.8±0.5c

The data provides the average of three trials. The standard deviations are indicated with a “±” sign a

Tons of entering material per hour

b,c

Statistically significant differences at α05% level within each line

d

The data reported for type C during the extraction stage includes the volume of water (or the capacity) used for both rasping and extraction stages which worked simultaneously e

Cubic meter of water per ton of starch at 12% moisture (wwb)

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allowed similar electric and mechanical consumptions for the extraction of starch (Fig. 3) as compared with the singlevertical extractor used in processing clusters in Vietnam (Da et al. 2008). Extraction with RETC revealed that 40% of the demand in power was used for rasping and 60% for extraction. Production Cost

Fig. 2 Starch milk density profile during the extraction of starch from cassava using rasping system RRall and rasping system RCIAT from Colombia. For type RRall, each plot represents an average of triplicate samples with repeated trials (dots with error bars). RCIAT horizontal grating machine with serrated blades from the CIAT research center

extraction stages (Table 3). In Vietnam, the rasping–extractor required 20 m3/FU of water for the simultaneous rasping and single extraction stages. In contrast, the study of the RRall process in Colombia revealed that the three types of equipment (one rasper, two coladoras in parallel and one sieve) used in the three successive operations (rasping, extraction and second sieving) required 44.9 (±4.8) m3/FU of water, with contributions of 7%, 66% and 27%, respectively. Thus, the differences observed in water consumption between the technologies from Vietnam and Colombia were in accordance with the differences previously cited on extraction capacities. The greater velocity of the blades used with RETC as compared to the rotative speed of the coladoras (2,400 rpm and 27 rpm, respectively) leads to higher extraction efficiency and lower water consumption. Energy Consumption Figure 3 presents the electric energy consumption of the main processing equipment used for manufacturing cassava starch. The rasping stage conducted with RCIAT resulted in great irregular electric consumption demand as compared to the rasping stage conducted with RRall (Fig. 3). This difference corresponded to the action of the operators who had to push the roots manually on the rasping surface of RCIAT to increase rasping efficiency and rasping capacities. Consequently, the very high electric energy for rasping with system RCIAT led the operators to reject this technology. The configuration of the agroindustries in Colombia results in electric energy saving, since loading is facilitated by the plant design utilizing gravity. Moreover, the Colombian process was characterized by very low consumption of electric energy used for rasping the roots as compared with energy requirements for rasping/extraction stages in Vietnam (13.6 and 55.3 kWh/t, respectively). In Colombia, mechanical power transmitted to the flat pulleys

The production costs for 1 t of starch from Colombia and Vietnam were dramatically different, with 1,156 US$ and 162 US$, respectively (Table 4). This difference can be explained by raw material contribution which accounted for 90% in Vietnam and 66% in Colombia, while the prices were 43 US$ and 180 US$/t of fresh roots, respectively. In Vietnam, processing costs (labor and electricity) were reduced to a minimum (5% of the production costs). Moreover in Colombia, the production cost was characterized by a higher contribution of the labor costs (up to 9.3%), and the process in Colombia benefited from an economy of scale, with lower contribution of electric costs compared with Vietnam. The latest study of the socioeconomic performance and technical production of sour starch in the Cauca Department of Colombia showed an important adoption of extraction technologies in the late 1990s (Gottret et al. 1997). In our study, a visit of several rallanderias was performed. It was noted that the methods/processes were quite similar between factories and that few changes had been made on equipment by the starch manufacturers. Nevertheless, the great profitability of the Colombian process for manufacturing sour cassava starch was revealed by this study as compared to the Vietnamese process. The factories in Colombia operate almost yearlong with low variable costs (electricity); this results in significant economies of scale compared with Vietnam where numerous transaction costs restrict potential price reduction for raw materials. Finally, it would be helpful to analyze the network of stakeholders and institutions governing the cassava transformation industry in Colombia in order to identify how these might enable and constrain further implementation of greener production practices, as has been done in Asia in the case of cassava agroindustry (Dieu 2006). Equipment Performance and Water Management From a technological perspective, the importance of the design of raspers and extractors used in the production of wet starch has been clearly highlighted in this study. Other authors have previously investigated, at lab-scale, the effectiveness of three different types of equipment for releasing starch from the roots: a meat mincer, a commercially available hammer mill and a belt-driven perforated plate rasper (Marder et al. 1996). These authors showed that the three equipment and the operating parameters led to different rasping effects (39.8, 63.4 and 75.8%, respectively), but they did not correlate these results to

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Fig. 3 Electric and mechanical energy consumption for rasping and extraction stages in small-scale cassava starch manufacturing in Vietnam and Colombia. RCIAT rasper type (top left); RRall rasper type (top

right); five successive extraction batches conducted with RETC rasper/ extractor type from Vietnam (bottom left); one single extraction batch conducted with coladora extractor from Colombia (bottom right)

fiber size reductions. In our study, experiments carried out at a small industrial scale confirmed that none of the rasping technologies used in Vietnam and in Colombia allowed for the extraction of all the starch contained in the parenchyma of

the roots. Moreover, this study shows that the effectiveness of the starch extraction process can largely be attributed to the differences in root disintegration obtained with different machines (a rasping roll with serrated blades, a rasping roll

Table 4 Cost structure, profit and income generation of small-scale units for 1 month in Vietnam and in Colombia

Items

1 2 3

Profit equals total returns (1) minus production costs (6). B/C ratio (8) corresponds to total returns (1) divided by the subtraction of (1) from (7). Income generation (9) is the addition of (5) and (7). Starch is at 12% moisture content (wwb). The production cost was calculated based on 1t of starch at 12% moisture (wet weight basis)

4 5 6 7 8 9

Type RETC

Type RRall

Output: starch By-product Total returns Raw material Other inputs Electricty Contengencies Administrative costs Others

[t] [t] [month] [t]

Fixed costs Laborers Production costs Profit B/C ratio Income generation

[month] [month] [month] [month] [month] [month]

[month] [month]

Quantity

Value (US$)

Quantity

Value (US$)

12 4 1 50

16,665 661 17,326 8,936

19 5 1 66

3,381 85 3,467 2,795

1

90 59

1

1

1 1

131 206 1,547 1,291 161 1,252 13,525 3,802 1.28 5,054

1

1 1

96 79 3,119 348 1.11 427

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with abrasive metal sheet, or a horizontal disc made of wood and serrated with fine recycled wires). The study also showed the effectiveness of the rasping technology: firstly by determining the quantity of unextractable starch remaining trapped with the lignocellulosic fibers after washing out of the freed starch, and secondly, by characterizing the median particle sizes of bagasses, which demonstrated that lower lignocellulosic fiber particle size led to higher quantity of extracted starch. However, the sieving analysis was adapted from animal feed applications, in which dry material were previously rehydrated (Lebas and Lamboley 1999). Processors from Colombia maximize the capacity of the extraction stage by high levels of freshwater consumption compared to the processors in Vietnam which used the type RETC. The huge water consumption in Colombia can be attributed to the awareness of the processors that water is important to produce a good quality edible fermented starch (personal communication). Indeed, sour cassava starch manufacturers in Brazil defined product quality in terms of the starch's degree of whiteness and its acidic taste. The quality was said to improve with several factors including the quality of water used in processing and the quantity used in washing (Marder et al. 1996). In Vietnam, wet starch is not produced for direct food applications, and consequently, has a lower quality standard than in Colombia; increasingly wet starch in Vietnam is an intermediate product which is later purified either locally or within large-scale factories. Moreover, in Vietnam, starch production is conducted in densely populated villages where processors face difficulties expanding their activities, so the availability of and access to water is a problem for most owners (Fanchette and Stedman 2009). Consequently, the development of the manufacturing technologies in Vietnam has been clearly motivated by greater capital-intensive method with a minimization of total water consumption (Da 2008; Da et al. 2010). In Colombia, large space is used for settling channels and fermentation tanks; recent investigations on the use of hydrocyclones to concentrate starch suspensions resulted in a 70% reduction in the overall quantity of fresh water used (unpublished results). This option has not yet been studied at a similar scale in Vietnam where small settling tanks are used for production. People are becoming increasingly aware of the pollution resulting from the disposal of effluents from factories in both Vietnam and Colombia. Some options for environmentally friendly processes have been studied in Vietnam (Dieu 2006). However, they have not been implemented locally, and promoting practical wastewater treatment devices remains a great challenge for small-scale producing starch facilities.

Conclusion The comparison of three rasping technologies indicated that reducing water consumption is a common challenge for small-

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scale cassava starch producers both in Colombia and Vietnam in order to preserve local water resources. The degree of rasping appears to be a key factor for addressing this issue because a more thorough rasping enhances starch extractability and thereby reduces the volume of water needed to achieve economically acceptable yields. The direct comparison of the efficiency of rasping equipment relied on a new method for particle size characterization of wet pulps developed and tested in the course of this study and on the normalization of the processing parameters to the same functional unit (1 t starch) based on the methodological recommendation of the LCA framework. Acknowledgments The work reported in this study was supported by CIRAD as well as AgroSupDijon, CIAT, and HUST. We acknowledge Hernan Ceballos for his assistance in reading the manuscript.

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