Program report 95-96

Program 6

Enhancing the Role of Small-Scale Sweetpotato Starch Enterprises in Sichuan, China
C. Wheatley¹, Lin Liping², and Song Bofu³

Materials and Methods
Results and Discussion
Conclusions
Selected Reading

Sweetpotato, Ipomoea batatas (L.) Lam., is a major component of small-scale Chinese farming systems, which produce more than 100 million t of fresh roots annually. Since the 1960s, use of the crop has shifted from direct human consumption toward animal feed and industrial uses. Shandong and Sichuan provinces, with annual sweetpotato root production of over 20 million t each, have developed important starch industries based on small-scale extraction of starch and its use in transparent noodles, which also are produced largely on a small to medium scale. In Shandong, some 30-40% of sweetpotato production is used for starch extraction; in Sichuan, about 15%.

In Sichuan Province, where CIP has worked with the Sichuan Academy of Agricultural Sciences (SAAS) for over 7 years, significant progress in upgrading the technology level of small-scale enterprises has been achieved. Manual processing of the roots has been largely replaced by small- and medium-scale mechanized equipment (root washers, grinders/raspers, horizontal and drum separators, and inclined channel sedimentation). The introduction of small-scale, single-screw extruders has allowed increases in productivity and output of sweetpotato starch noodles. Several items of equipment also used for potato starch processing are now manufactured commercially and distributed beyond Sichuan Province.

Sichuan is an inland province, distant from the booming coastal regions of China. The province is densely populated (110 million people). Incomes are below the national average: rural per capita annual income in Sichuan was US$85.00 in 1993 (75% of national average rural income, and only 29% of national average urban income). Consequently, Sichuan is now a major source of economic migrants.

Increased use of sweetpotatoes in Sichuan, whether for feed or starch, offers real potential for rural income generation in those areas where sweetpotatoes are grown, and where the need for poverty alleviation is acute. SAAS and CIP research has, since 1994, focused on evaluating the status of sweetpotato starch enterprises and identifying opportunities for their further development. This has entailed integrating market and technical research.

Materials and Methods

Starch enterprise appraisals
Three starch enterprises in Santai County were selected as case study units on the basis of ownership type (private or collective), scale of operation (0.2-0.8 t fresh roots per h), whether manual or mechanized, and the starch sedimentation method used (natural sedimentation in tanks, sour liquid, or inclined channels). Three batches of fresh roots were followed through the normal process operations for each enterprise.

During November 1994, a participatory appraisal of the small-scale starch extraction enterprises was carried out. Data on the technical operation of the process, through direct measurement and observation of normal operations, were complemented by relevant information on the food system in which each enterprise operated.

Fresh roots of Xushu 18 from one field plot were used as raw material for all appraisals. To determine the effects of differing raw material quality on technical performance and process economics, at Guanqiao enterprise fresh roots of Mianfen 1 were also processed. Mianfen 1 has a high fresh-root starch content, but lower fresh-root yield, than Xushu 18.

Technical performance of the enterprise was evaluated on a batch basis (per kg fresh roots processed), and then recalculated on a product basis (per ton dried starch produced). Most (60-80%) of the starch was sold or used immediately as wet starch cakes (moisture content 45%) for noodle production. For the purposes of analysis and comparison, however, results are presented as dry starch equivalents.

On a dry matter basis, prices for wet and dry starch are nearly the same. Drying is worthwhile only if the starch is to be marketed or stored.

Economic performance was determined on a per metric ton dried starch basis plus additional revenues from the sale of moist residues. In many cases the residues are used directly for pig feed by the same household, but for the purposes of enterprise analysis the 1994 market price ($2.40/ton wet residue) has been used.

Market research
A 1995 market survey, conducted jointly by the Center for Integrated Agricultural Development (CIAD) of Beijing Agricultural University and SAAS assessed the potential demand for sweetpotato starch in both food and nonfood industries.

We used secondary information to develop an inventory of Sichuan enterprises that use starch as a raw material for the manufacture of food and other products, for selecting a representative sample of enterprises for interviews, and for estimating starch demand in Sichuan. The field study included sweetpotato starch and wholesale markets, sample starch enterprises, and key informant interviews with scientists and industry leaders in Sichuan.

Process research for quality improvement
During 1996, SAAS process research scientists studied two ways in which small-scale enterprises could improve the quality of the starch they produce through (1) process modifications appropriate to their scale, and (2) use of different sweetpotato varieties.

Using Nanshu 88 in an orthogonal experimental design, the effects of varying the ratio of water to weight of fresh roots (3:1, 6:1, and 8:1), mesh size during separation of starch suspension from fibrous residue (80, 100, and 120 mesh), and sedimentation time (8, 16, and 24 h) on starch yield and quality were studied. Starch yield was calculated at standard 14% moisture content.

Analyses of starch (Layne and Eynon method), lipid (Soxhelet extraction), ash (incineration at 525oC for 1 h), and protein (macro-Kjeldahl) of the dried starch samples were carried out by SAAS Central Analytical Laboratories. Whiteness was determined by fluorescence analysis, and by a sensory panel.

Similar analyses were carried out in a second experiment to determine the variation in starch purity across 10 sweetpotato varieties or promising selections.

Results and Discussion

Starch enterprise appraisals
The appraisal data showed that all enterprises were profitable with high returns on investment, despite low use of installed capacity (Table 1), caused by problems in raw material supply. In 1994, drought lowered sweetpotato production in Sichuan, and reduced the length of the processing season.

The dry starch yield (14% moisture content) ranged from 10% to 18%, depending on both process and variety (Table 2). Improvements to process efficiency, especially at the separation stage, would increase profitability since more starch would be produced per unit of roots processed.

At Guanqiao enterprise, where two varieties were compared, Mianfen 1 yielded more dry starch and greater profits, allowing the enterprise to pay farmers a higher unit price for Mianfen 1 roots. The low labor costs, as a proportion of total costs, in the two mechanized enterprises are encouraging. Any future increases in labor costs should have a small effect on overall enterprise profitability. Use of higher starch varieties (such as Mianfen 1) by farmers should be encouraged by the processing industry, and adequate price incentives should be given, as justified by process economics.

Demand for starch processing equipment is high. One of four starch processing equipment manufacturers in Santai County, Sichuan, reported that from 1992 to 1996 sales of sweetpotato processing equipment more than doubled (240%) for starch extruders, and nearly tripled (288%) for root washers. The sales value of root washers, starch separators, and extruders totaled over US$180,000 in 1996, 85% of total agricultural equipment sales. Between 1992 and 1996, sweetpotato processing equipment sales were valued at $630,000.

Although neither sweetpotato production area nor volume changed appreciably between 1989 and 1995 (production in Santai County varied between 82,000 and 93,000 t/yr), the proportion of sweetpotatoes that were processed increased from 36% to 76%. Of 91,000 t produced in 1995, 69,000 t were processed. That was accompanied by an increase of 70% in the number of pigs produced in the area during the same period (110,000 in 1995). Pig production is closely linked to starch processing through use of residues for feed.

Market research
The results of the market survey were surprising. Companies complained of severe shortages of maize starch (the major starch used) because of (1) insufficient maize production in Sichuan itself, with demand for maize starch exceeding local supply by over 100,000 t in 1995, (2) competition from the feed industry for raw materials, and (3) difficulties in importing starch or maize from other provinces. This last problem was due to congested transport infrastructure and the unavailability of maize elsewhere in China because the richer coastal provinces bought up available supplies for themselves.

This situation represents an opportunity for sweetpotato starch to fill a supply gap. Sweetpotato starch in Sichuan has consistently been priced below maize starch (Figure 1). But sweetpotato starch extraction on a small scale is more profitable than maize extraction on a large scale. At 1994 prices, the net profit on maize starch extraction was $35/ton compared with $60/ton for sweetpotato, even after including the income from maize starch by-products.

Sweetpotato starch product quality, however, was rated poorly by industry. The starch contains impurities such as excessive moisture and ash (Table 1), and is not sufficiently white. Impurities can be reduced through process improvements. Shandong Province produces refined sweetpotato starch using equipment similar to that in Sichuan by additional purification and drying steps.

Research for quality improvement of sweetpotato starch
Mesh size and volume of water used were found to significantly (P=0.0001) affect starch extraction rate and ash content of the extracted starch. All treatments produced starch that met maize starch standards for lipid and protein impurities. Starch whiteness increased with increased volume of water used and finer mesh sizes, but decreased with increased sedimentation time. The ash content of even the best starch samples, however, exceeded acceptable limits (lowest sample value: 0.38%) (Table 2).

For both starch yield and product quality, the optimum processing conditions were found to be 1:6 ratio of root weight to process water, 120 mesh (finest size), and 8 h precipitation. More efficient root washing to ensure more efficient soil removal before processing could reduce ash content of the starch.

Starch was also extracted, under standard conditions, from 10 different sweetpotato varieties/promising selections, from the SAAS Breeding Section. Significant differences were found between the 10 varieties tested for starch content percentage, and lipid and ash content of the extracted starch (Table 3). This suggests a potential to improve starch purity through a varietal approach if the fresh-root and starch yields remain attractive to farmers.

Conclusions

Any diversification of markets for sweetpotato starch in Sichuan will depend upon producing a product with greater purity than that currently available in the market. Such a high-grade starch would also permit the production of noodles of higher quality and value. Recent private-sector investment in Shandong Province points to improved starch quality as a prerequisite for producing export-quality noodles.

The starch and noodle agroindustry in Sichuan is predominantly small scale. These rural entrepreneurs have made significant investments in equipment during the last few years, despite the strong seasonal nature of the business. The processing season may last only a few weeks from late October to mid-November each year. Such seasonality is unfavorable for the establishment of large-scale starch extraction plants, which would remain idle for most of the year unless they were involved in processing other raw materials. That situation provides an opportunity for smaller-scale enterprises to benefit from the expansion of market demand for starch in Sichuan, and for the development of noodle products of higher quality and value.

The technical and market research activities between CIP, the Chinese Academy of Agricultural Sciences (CAAS), and SAAS will feed into these and other efforts. Finally, close links have been established with regional centers of excellence in starch research (Hong Kong University and National University of Singapore), which will assist in relevant technical research and professional development of project collaborators in China.

Selected Reading

CIAD and SAAS. 1995. Potential for market diversification of sweetpotato starch and flour in Sichuan Province. Center for Integrated Agricultural Development (CIAD) and Sichuan Academy of Agricultural Sciences (SAAS), Beijing Agricultural University, Beijing, China. 28 p.

Collado, L.S. and H. Corke. 1997. Properties of starch noodles as affected by sweetpotato genotype. Cereal Chem. 74:182-187.

Marter, A.D. and W.H. Timmins. 1992. Small-scale processing of sweetpotato in Sichuan Province, China. J. Trop. Sci. 32:241-250.

1 CIP, Bogor, Indonesia.
2 Crops Research Institute, Sichuan Academy of Agricultural Sciences (SAAS), Sichuan, China.
3 Chinese Academy of Agricultural Sciences (CAAS) and CIP.