Hydrolysis of this portion is different according to the a-amyla- se used: bacterial amylase causes the fragmentation of the granule while outer resistant layers remain after hydrolysis by pancreatic a-amylase. In this case, the filamentous thin and long structures observed here are very different from the structures already described elsewhere for potato as well as the other starches [8, 121. These results confirm the need of direct electron diffraction on thin cross section of starch granules as already carried out for spherolytes by Helberr et al. [19].

Acknowledgement

The authors are indebted to Dr. L. Degras from CRAAG (I. N. R. A., Guadeloupe, French West Indies) who furnished the tubers.

Bibliography

[ l ] Banks, S. W., and C. T. Greenwood: Starch and its components.

[2] Robyt, J. E , and W. J . Whelan: In “Starch and its derivatives”, 4th

[3] Mercier, C.: In “Hydrolases et dCpolymCrases”, Gauthier Villars.

[4] Delpeuch, E , and J. C. Favier: Ann. tech. agric. 29 (1980), 53. [5] Gallant, D. J. , H. Bewa, Q. H. Buy, B. Bouchet, 0. Szylit, and L.

[6] Rasper, V., G. Perry, and C. L. Dutschaever: Can. Inst. Food Sci.

Edinbourgh University Press, Edinburgh 1975.

ed., Chapman and Hall, London 1968.

Paris 1985.

Sealy.: Starkelstarch 34 (1982). 255.

Technol. J. 7 (1974). 166.

[7] Leach, H. W., and T. J . Schoch: Cereal Chem. 38 (1961), 34. [8] Guilbot, A., and C. Mercier: In “The polysaccharides” Vol. 3,

Academic Press, New York 1984. [9] Fuwa, H,, M. Nakajima, and A. Hamada: Cereal Chem. 54 (1977).

230. [ 101 Fuwa, H., Y. Sujimoto, and T. Tanaku: Carb. Hydr. Res. 70 (1979).

233. [ 111 Gallant, D. J., C. Mercier, and A. Guilbot: Cereal Chem. 49 (1972),

354. 1121 Gallant, D. J . , A. Derrien, A. Aumaitre, and A. Guilbot: Starch/

Starke 25 (1973), 56. [13] Tollier, M. T., and J. P. Robin: Ann. Technol. Agric. 28 (1979),

1. [14] AOAC Officials Methods of Analysis. Association of Official

Analyticals Chemists: Washington, DC, 1984. 1151 Thivend, P., C. Mercier, and A. Guilbot: “Determination of starch

with glucoamylase”. In: Methods in Carbohydrate Chemistry, Vol. VI, Academic Press, New York 1975.

[16] Larson, B. L., K. A. Cilles, andS. R. Jenes:Anal. Chem. 25 (1953), 802.

[17] Gallant, D. J., and A. Guilbot: StarchlStarke 21 (1969). 156. [lS] Svensson,’B.: FEBS Letts. 230, (1988), 72. [19] Helberr, W., H. Chanzy, V. Planchot, A. BulCon, and P. Colonna:

Carbohydr. Polymers, accepted (1 992).

Address of authors: Jean-Claude Valerudie*), Paul Colonnu**), Bri- gitte Boucher, and Daniel J. Gallant*). Institut National de la Recherche Agronomique. BP 527 - 44026 Cedex 03 (France).

*) Laboratoire de Technologie Appliquee i la Nutrition. **) Laboratoire de Biochimie et Technologie des Glucides.

(Received: March 16, 1993).

Development of Starch Based Plastics - A Reexamination of Selected Polymer Systems in Historical Perspective

Randal L. Shogren, George F. Fanta, and William M. Doane, Peoria, IL (U.S.A.)

Recent patents in the starch-based plastics area have claimed melted or “destructurized” starch as a new type of material. The term “de- structurized starch” has apparently been coined after the physically modified state of starch obtained by the disruption of the granular state, resulting in the loss of order and crystallinity. A brief literature review is presented which shows that, in the 1970’s, starch containing low (10-30%) water contents was extruded at elevated temperatures to give a thermoplastic melt exhibiting no residual starch crystallinity. Differential scanning calorimetry studies of starch-g-polymethyl acry- late and blends of starch with poly (ethylene-co-acrylic acid) are also presented. These data indicate that these materials, prepared in the 1970’s. also contain starch which was partially or completely de- structurized. Thus, although ideas and uses for destructurized starch in plastic items have proliferated in recent years, completely melted or “destructurized” starch had been conceived and used much ear- lier.

Die Entwicklung von auf Stiirke basierenden Kunststoffen. Eine Uberpriifung ausgewahlter Polyrnersysterne aus historischer Perspektive. Neuere Patente auf dem Gebiet der starkebasierenden Kunststoffe erforderten geschmolzene oder ,,destrukturierte“ Starke als neues Material. Der Begriff ,,destrukturierte Starke“ wurde offen- bar gepragt nach dem physikalisch modifizierten Status von Stake, die nach dem ZerreiBen des kornigen Zustandes erhalten wurde unter Verlust der Ordnung und der Kristallinitat. Ein kurzer Litera- turuberblick wird aufgezeigt, welcher darlegt, daR in den 1970er Jah- ren Starke mit geringem Wassergehalt (10-30%) bei erhohten Tem- peraturen extrudiert wurde, um eine thermoplastische Schmelze zu ergeben. die keine restliche Kristallinitat enthielt. Differential-Ra- ster-Kalorimetrie-Untersuchungen von Stake-g-Polymethylacrylat und Mischungen von Starke mit Poly(ethy1en-co-Acrylsaure) werden ebenfalls aufgezeigt. Diese Daten zeigen, daR diese in den 1970er Jahren hergestellten Materialien ebenfalls teilweise oder vollstlndig destrukturierte St2rke enthielten. Somit haben sich in den vergange- nen Jahren Vorstellungen und Verwendungen fiir destrukturierte Starke in plastischen Artikeln entwickelt, obwohl vollstandig ge- scbmolzene oder .,destrukturierte“ Starke schon vie1 fruher verwen- det worden waren.

* The mention of firm names or trade products does not imply that they are endorsed or recommended by the U. S. Department of Agriculture over other firms or similar products not mentioned.

276 starch/stirke 45 (1993) Nr. 8, S. 276-280 8 VCH Verlagsgesellschaft mbH. D-69451 Weinheim, 1993 0038-9056/93/0808-0276$05.00+.25/0

1 Introduction

1 .I The development of starch-plastic composites

In recent years, most countries of the world have recognized the need to reduce the amount of plastic waste discarded in landfills. Although improved efforts to recycle discarded pla- stics would help accomplish this goal, recycling would be neither practical nor economical for certain end-use applications such as agricultural mulch films, planting pots and garbage bags. For applications such as these, plastics are needed that will fragment or degrade into benign by-products under composting condi- tions. The maritime industry also requires degradable plastics in order to comply with the MARPOL treaty, which prohibits the dumping of non-degradable articles into the sea after January 1, 1994. The incorporation of starch into plastics to enhance their fragmentation and degradability in the environment has gene- rated considerable interest [l]. Starch is inexpensive (about 10 cents per pound). is totally biodegradable and is available in large quantities from certain crops (i. e. corn and wheat) produ- ced in abundance beyond available markets. Replacement of petroleum based plastics with starch is also attractive from the standpoint of conserving our petrochemical resources. This publication will center on starch-containing plastics prepared by extrusion processing. Use of granular starch as a filler in plastics began with the work of Griffin [2-41 in the 1970’s. Starch-containing polyethylene films and other consumer items based on this technology are currently being marketed. Since whole starch granules are used in this technology, the level of starch addition is generally limited to about 10% or less, by weight. Starch is dried to < 1 % moisture to inhibit steam formation during extrusion proces- sing, and starch granules have also been surface-treated (for example with silanes) to increase the compatibility of hydrophi- lic starch with the hydrophobic plastic matrix. Pro-oxidants can also be added to promote degradation of the synthetic poly- mer. At about the same time period as Griffin’s research, Otey and coworkers at the National Center for Agricultural Utilization Research (NCAUR) were studying starch-plastic systems in which the starch granule structure was totally disrupted [5-lo]. For example, a process was developed to extrusion-blow films from mixtures of starch and poly (ethylene-co-acrylic acid (EAA) in the presence of aqueous ammonium hydroxide and urea [lo]. Polyethylene could be incorporated into these formu- lations as a partial replacement for EAA in order to reduce raw material costs and in some instances improve film properties. In these systems, starch can form a continuous phase rather than merely being present as a particulate filler. Starch loadings as high as 50% by weight can thus be obtained in these composites and still obtain acceptable properties. The Ferruzzi Group of Italy (Novamont) [ll-131 is marketing composites of this general type. In these materials, starch is alloyed with various low molecular weight hydrophilic polymers, such as vinyl alcohol-containing copolymers and the EAA polymer first used by Otey et al. in starch based plastics. Starch-thermoplastic polymer composites have also been pre- pared by graft polymerization [14]. Treatment of starch with ceric ammonium nitrate in water yields free radical sites on the starch backbone that can act as macroinitiators in the presence of various monomers to yield polymer grafts of high molecular weight. Extensive research has been carried out at NCAUR on polymers of this type, particularly starch-g-poly (methyl acryla- te) (S-g-PMA) [lS, 161. Graft copolymers have been prepared from both granular and cooked starch, and extruded plastics with good properties are obtained from S-g-PMA containing

40-60% PMA by weight. A study of granular S-g-PMA showed that PMA is the continuous phase when extrusions are carried out under low moisture conditions [16]. Phase reversal can take place if the level of PMA in the polymer is sufficiently low and if there is sufficient water present to yield a starch melt during extrusion. Extruded S-g-PMA ribbons showed only small starch melting peaks when examined by differential scanning calori- metry (DSC), and these were only for samples extruded at the lowest moisture content. Areas of crystallinity were therefore largely disrupted during extrusion. Since starch will biodegrade to carbon dioxide and water in a relatively short time compared with most synthetic polymers, much of the research in recent years has centered on increasing the amount of starch in starch-plastic composites to the highest possible level. The ultimate goal of these research efforts is to prepare consumer items for one-time use from substantially pure starch and to exclude synthetic polymers from the formu- lation. For materials such as these, starch must contain enough water so that it will melt below its decomposition temperature and yield a final product in which the polysaccharide forms a continuous polymeric phase. Wiedmann and Sfrobel[ 171 refer to starch in this form as “thermoplastic starch” and discuss the conditions necessary to form and process this type of material in a twin screw extruder. A good example of the commercial potential of these extruded starch plastics is the starch based expanded packaging material recently patented by National Starch and Chemical Corp. and now marketed as a biodegrada- ble replacement for Styrofoam [18]. Another example of the preparation of single-use items from a starch melt is the Novon technology patented by Warner Lambert Co. [19-201. Starch, containing 5-30% water, is processed at elevated temperatures in an extruder or injection molder to form a melt in which the molecular structure of starch is completely disordered. Evidence for disordering suggested in these patents is the disappearance in the DSC thermogram of a high temperature endotherm attributable to starch melting [21]. For potato starch, the endotherm was observed at moisture contents of 12-40% in the range of 190-160°C. This so-called “destructurized starch” is claimed as a new material. substan- tially comparable to melts formed from well-known hydropho- bic thermoplastics. To modify and improve its physical proper- ties, destructurized starch has also been compounded with a variety of different polymers that are sufficiently hydrophilic to afford some degree of compatibility with the aqueous starch system.

1.2 Thermal transitions in starch

Thermal analysis of native starch granules using DSC and differential thermal analysis (DTA) has provided some insight into the behavior of starch when it is heated in the presence of limited amounts of water. DSC showed a single endotherm at 66°C for potato starch containing a volume fraction of water greater than 0.7 [22]. At lower water levels, a second higher temperature endotherm developed, which was attributed to the melting of starch crystallites. This endotherm became the only one observed with volume fractions of water less than 0.45. As the water concentration decreased, this endotherm shifted to higher temperatures and also decreased in size. When a cooled sample was reheated (in both the presence and absence of added water), DSC showed no endothermic transitions, indica- ting that crystallinity had been lost. Takahashi et al. [23] used differential thermal analysis (DTA) to study thermal transitions in corn, waxy corn, wheat, kuzu and potato starches at low moisture contents. For moisture contents of 0.7-12 wt%. two strong endothems were observed, one at about 190-230°C (Peak A) and the other (Peak B) at

starchlstiirke 45 (1993) Nr. 8. S. 276-280 277

230-250°C. Peak B was presumed to be due to starch decom- position. Microscopic examination of starches at different sta- ges of the heating process showed the disappearance of granule birefringence along with cohesion of individual starch granules at the temperature of Peak A. At the endpoint of Peak A, granules were completely fused. Since there was insufficient water present to cause granules to hydrate and swell, loss of birefringence and granule fusion were assumed to be due to granule melting. Peak A occurred at a different temperature with each starch variety examined. Although this endotherm shifted to higher temperatures with decreasing moisture con- tent, the position of the decomposition peak B was relatively moisture-independent. Maurice et al. [24] and Russell [25] have published DSC studies of waxy maize starch at various moisture levels. They found three distinct endotherms which were referred to as G (gelati- nization) and M1 and Z (melting). The G endotherm was observed only at 50% moisture and above while the Z endo- therm, a sharp peak appearing at temperatures slightly higher than the M1 endotherm. was observed at 20-50% moisture. The origin of the Z endotherm is uncertain although it was suggested that it resulted from annealing of the amylopectin crystallites during heating.

1.3 Extrusion processing of starch in foods

As correctly stated by Wiedmann and Strobe1 (17), “Technolo- gically, starch extrusion know-how for the extrusion cooking of food complements that for compounding plastics.” Furthermo- re, this know-how, which was largely obtained in the 1970’s and 1980’s seems to form the basis for much of the “new” technology now being reported for starch-based plastics. Food extruders can be regarded as high temperature, short time reactors, in which granular starch having a moisture content of roughly 10-25% ist first compressed into a dense, compact solid and is then converted into a molten, amorphous mass by the high pressure, heat and mechanical shear forces encounter- ed during processing. Excellent reviews on the subject of starch extrusion related to food processing have been published by Mercier and coworkers [26-281, by Lai and Kokini [29], and by Harper [30]. The transformations of starch that occur during extrusion are influenced by extruder geometry as well as by processing variables such as extrusion temperature, screw speed, feed rate and moisture content of the starch. Temperature and moisture content have been cited as the two most important variables affecting physical properties of the extruded starch [29]. Chemical modifications of starch during extrusion processing are minimal, although degradation into lower molecular weight components has been demonstrated using gel permeation chro- matography and intrinsic viscosity measurements [29]. Degra- dation increases as extrusion temperature is increased and as the moisture level in starch is reduced [30]. Extruded starches absorb water at room temperature to form pastes composed of soluble starch and swollen gel particles. The absence of ethanol-soluble material in extruded cornstarch indicated that there is little degradation to maltodextrins [27]. In contrast to cereal starch, potato starch yields a fraction soluble in 80% ethanol, suggesting the formation of oligosaccharides having a molecular weight iower than about 2000 [26]. Starch extrudates tend to expand upon exiting the extruder die, and this phenomenon has resulted in the widespread use of extrusion for the preparation of snack foods [27,30]. Expansion of starch extrudates is caused not only by flash-off of internal moisture but also by die swell,due to the elastic character of the molten extrudate (i. e. the Barus effect [31]). The observance of die swell provides evidence that the granular structure has been

destroyed and that a polysaccharide melt, analogous to a conventional polymer melt, has indeed been produced. The destruction of native starch granules in molten extrudates has also been confirmed by scanning electron microscopy [27]. As expected, expansion at the die is reduced when extrusion temperatures are not high enough to convert starch granules into a continuous melt. Starch extrudates are largely amorphous glasses at room tem- perature, and polymer chains are thus frozen in a random configuration; a small amount of crystalline amylose-lipid complexes is also present [26]. Water acts as a plasticizer to depress the glass transition temperature (Tg); slow reassocia- tion of polysaccharide chains, increased hydrogen bonding and recrystallization (i. e. annealing) are observed above Tg [28]. Cornstarch extruded at a number of different temperatures and moisture contents showed no endothermic transitions when examined by DSC [32, 331, indicating the loss of crystallinity during the extrusion process. I t thus appears that starch crystal- lites have been totally disrupted by melting, as in the “destructu- rized starch” claimed at a later date in the patent literature

Structural changes that occur in starch during extrusion proces- sing have also been studied by X-ray diffraction [26]. Native cereal starches exhibit the A-type diffraction pattern, whereas potato starch exhibits the B-type. These diffraction patterns are either partially or completely destroyed during extrusion, de- pending on the moisture in the starch as well as the temperature and the amount of shear used during processing. Extrusion of cornstarch at 135°C and a moisture content of 22% produces a V-type diffraction pattern due to complex formation between amylose and the small amount of lipid present in the native starch [27]. When extrusion is carried out at 185,200 and 225”C, a final water content of only 13% is obtained, and a new structure called the “extruded” or E-type is observed. This structure is characterized by three diffraction peaks slightly displaced from those of the V-structure and is transformed back into the stable V-type, if the starch extrudate is conditioned to a water content of 30%. Similar behavior has been observed with wheat, rice and amylomaize starches containing 55 and 70% amylose. It has been proposed that the E-type structure is helical and, like the V-structure, has six glucose residues per turn. Differences between the two structures have been attribu- ted to different interaxial distances between helices. The V-type and E-type structures have not been observed with potato starch (which is lipid free) or with waxy maize starch (which contains no amylose) [28]. With these two starches, X-ray diffraction patterns showed reduced crystallinity at extru- sion temperatures as low as 70°C. At higher temperatures, the crystalline structure was completely destroyed, and the X-ray diffraction pattern was typical of an amorphous state [27]. The literature published on starch extrusion over roughly the last two decades (mainly in relation to food processing) clearly shows that a melt is formed under high temperature, low moisture conditions and that none of the original starch crystal- linity remains after processing. From the data presented, it is difficult to see how the physical state of starch in these extruda- tes is substantially different from that in the so-called destructu- rized starch claimed in recent patents. Since research at NCAUR over the last 20 years has dealt with the preparation and extrusion processing of starch-polymer composites. we wished to determine whether the original crystalline structure of starch in some of our previously prepa- red products was completely lost during processing. Products chosen for this study were extruded starch, polymer composites containing starch and EAA and, finally, a graft copolymer prepared from granular starch and methyl acrylate (S-g-PMA). DSC was used to study phase transitions in these materials.

~ 9 1 .

278 starchlstarke 45 (1993) Nr. 8, S . 276-280

2 Experimental

2.1 Sample preparation

Cornstarch was Buffalo 3401 from CPC International Inc. Cornstarch, adjusted to 25% water content, was extruded into a ribbon at 175°C as described earlier [34]. Starch was also dissolved by passing 20% aqueous suspensions of cornstarch through a steam-jet cooker (Penick & Ford, Cedar Rapids, IA) at 140°C [35] and the resulting solution was dried on a steam- heated. double-drum drier heated to 150°C. Granular starch containing 55% (by weight) grafted PMA was synthesized according to Bugley et al. [15] as modified by Trimmell et al. [16]. Starch-g-PMA, containing 30% water based on starch. was extruded at 110°C following example 11 B of Bugley et al. 1151. Starch-EAA films. containing 50% starch, were prepared by Orev and coworkers using the following three techniques: a) heating starch with an aqueous suspension of the ammonium salt of EAA (20% total solids) in a flask at 80°C and casting a film onto a heated plate [6,7], b) by pasting starch, EAA and ammonia at 50% solids in a Readco mixer followed by multi- ple-pass extrusion film blowing at 120- 130°C to reduce water content to 5-10% [8, 91 and c) by multiple-pass extrusion of starch and E A A with 15% urea and 20% water at 8O-ll0"C Wl. 2.2 DSC Analyses

Prior to DSC analysis, the above samples were pulverized by shaking in a stainless steel vial with two steel balls at liquid nitrogen temperature. The starch-EAA film prepared by the above method (c) was extracted with water before pulverizing to remove urea. Samples (29-30mg) were adjusted to the desired moisture level by placing them in a desiccator contai- ning water, and samples were then sealed in stainless steel, high-pressure DSC pans (Perkin-Elmer Corp., Norwalk, CT). DSC analyses were carried out using a Perkin-Elmer DSC7. Samples were heated from 2 to 220°C at a rate of 10"C/min.

3 Results and Discussion

DSC thermograms of granular, unprocessed cornstarch at 11 and 20% moisture (A and B respectively) are shown in Fig. 1. Peak numbers 2 and 4 correspond to the melting of amylopectin

F E

ii m P) I

v

c

42 44i 40-

0 50 100 150 250

Temperature ('C)

Figure 1. DSC thermograms of granular cornstarch at 11% moisture (A), granular cornstarch at 20% moisture (B). extruded cornstarch at 20% moisture (C) and jet cooked and drum dried cornstarch at 20% moisture (D).

~ ~~

while peak 5 corresponds to the melting of amylose 1341. The second, sharper melting endotherm (#4) for amylopectin is only seen at moisture contents of 16-30% [34]. This is appa- rently the sharp endotherm referred to in the Warner-Lambert patents [20, 211 and in earlier work [24, 251 (i.e. the Z endo- them). The melting temperature of endotherm #4 in Fig. 1 B is 165°C similar to that found for waxy maize starch (170°C) [24] and potato starch (179°C) [25] at 20% moisture. Its origins are unclear, although it may represent the melting of larger crystal- lites of amylopectin formed by annealing during the heating cycle. Figure 1 also shows thermograms of starch processed by extru- sion at 175°C (C) and starch solubilized by jet cooking and then drum dried (D). These two samples were also equilibrated to a moisture content of 20%. The disappearance of peaks 2 and 4 indicates that the native crystalline structure of starch has been destroyed or melted by each of these treatments. The small melting endotherms corresponding to amylose suggest that amylose, which is known to be in an amorphous state in the starch granule, has partially crystallized during the heating process. X-ray diffraction studies have shown that extruded starch usually contains amylose-lipid V-type complexes [32,36]. These complexes likely melt and then recrystallize into the crystalline B-form during heating in the DSC. Peak 1 corre- sponds to enthalpy relaxation (physical aging) of amorphous starch [34]. Figure 2 shows similar DSC thermograms for (A) granular S-g-PMA, (B) S-g-PMA extruded at 110°C with 10% moisture

z 2

P

E

ii

v

c m

347

331

29-

28-

27-

26 - 25 -

0

' c,"

I I 1 I 50 100 150 200 2

Temperature ('C)

I0

Figure 2. DSC thennograms of granular S-g-PMA, 55% PMA (A), S-g-PMA extruded at 110°C and 10% moisture (based on starch content) (B). and S-g-PMA extruded at 110°C and 30% moisture (C). AU samples were adjusted to 20°/0 moisture based on starch content for DSC runs.

(based on starch) and (C) S-g-PMA extruded at 110°C with 30% moisture. Samples were adjusted to 9.5% moisture (20% water based on starch) for the DSC runs. These thermograms indicate that about 30% of the starch has been melted after extrusion at 10% moisture, while essentially all the starch has been melted at 30% moisture. These results suggest that the S-g-PMA samples generated previously in the examples of Bugley et al. [15] also contained partially or completely melted (or "destructurized" st arch. Figure 3 shows thermograms for starch EAA films prepared by methods a. b and c, as described in the Experimental Section. All three thermograms are similar with melting peaks for EAA at 40-100°C and exothenns in the 150-180°C region. No melting peaks for starch are evident, indicating that the starch component of these materials is completely melted and that all

-

starch/starke 45 (1993) Nr. 8. S. 276-280 279

F E

ii

- c m P

3:

I “ I I I 1 I

Temperature (‘C) 0 50 100 150 200 250

Figure 3. DSC thermograms of starcNEAA films containing approxi- mately 50% starch prepared by procedures a (A), b (B) and c (C) as described in the experimental section. All samples were adjusted to 20% moisture based on the starch content for DSC runs.

structure and crystallinity originally present in starch has been lost during processing. The exotherms may be due to the heat released during the hydration of the carboxyl groups of EAA.

4 Conclusions

Although recent research on starch-based plastics has provided new information on the behavior of starch during extrusion and injection molding, a major criticism of some of this work is the terminology used to describe physical changes that occur within the starch granule during processing. New terms, such as “destructurized starch” have been coined to describe physical states that are already well-known in the literature under other names, such as melted starch, molecularly dispersed or disrup- ted starch, etc. Over the past two decades, scientists studying the processing of starch-containing foods have been major contri- butors to research related to starch extrusion and have publis- hed a body of literature that encompasses many of the so-called new principles set forth in publications related to starch-based plastics. DSC studies of extruded starch, starch-EAA composites and S-g-PMA graft copolymers prepared in the 1970’s and 1980’s at .NCAUR show that the original crystalline structure of the starch component has been lost through processing. It thus appears that the physical state of starch in these systems is substantially the same as that of destructurized starch. This leads one to conclude that destructurized starch is not a new or novel entity but is merely another term used to describe the well-known disordering of starch chains and the melting of crystallites that takes place when starch is heated in the presen- ce of limited amounts of water.

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Cereal Chem. 57 (1980), 4.

Address of authors: R. L. Shogren, G. F. Fanta, and W. M . Doane, Research Chemists, Plant Polymer Research, National Center for Agricultural Utilization Research, Agricultural Research Service, U. S. Department of Agriculture, 1815 N. University St., Peoria, IL 61604, (U. S. A.).

(Received: May 15, 1993).

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