THE EFFECT OF RAW MATERIAL COMPOSITION ON A SOLUBLE SUBSTANCES CONTENT AS WELL AS THE DIRECTION AND EXTEND OF CHANGES IN SACCHARIDES DURING EXTRUSION PROCESS

Wiktor Obuchowski¹, Aleksandra Chalcarz², Hanna Paschke^2
1 Institute of Food Technology of Plant Origin, University of Life Sciences in Poznań, Poland
² Faculty of Food Science and Nutrition, The August Cieszkowski Agriculture University of Poznan, Poland

ABSTRACT

The aim of this study was to evaluate the effect of raw material composition in conditions of gentle extrusion cooking on so-called sugar profiles and the increase of water soluble substances content.

Five samples of extruded potato chips differing in raw material composition were examined. Sugar profiles were determined on the basis of HPLC method.

The results show that during extrusion cooking starch is decomposed into shorter chains, mainly dextrins consisting of 7 to 10 joined glucose molecules. There is no increase in simple sugars (glucose, fructose) and disaccharides (maltose) content. The degradation of starch does not go too far but rather gentle shortening of glucose chains to compounds of lower molecular weight occurs.

Key words: extrusion cooking, sugar profiles, soluble substances, wheat flour, potato flour.

INTRODUCTION

In the last years extrusion cooking process is used wider and wider in various branches of carbohydrate raw material processing. Nowadays it is used to produce instant noodles, snack foods, crisp bread and breakfast cereals. Recent research revealed it can also be successfully used in a production of tasty chips on the basis of mixture of potato flour, wheat and oat flour and other components [1, 2, 3].

The quality of the product expressed in terms of desirable consumption properties is formed by the proper selection of raw material and the conditions of the extrusion process. Extremely intensive effect of heat, pressure and mechanical shear in conditions of permanent moving and homogenization of material occurring during this process causes a number of changes, reactions in raw material leading to a change of the physicochemical characteristics improving nutritive value of the product, its taste, colour and structure [4, 5, 6]. As a result the final product has definitely different physical, biochemical and nutritional features from the raw material used.

Depending on the parameters of the extrusion process it is possible to differentiate the degree of raw material processing. Nevertheless it should be assumed that the crucial influence on occurring changes has the chemical composition, especially quantity and type of saccharides in the processed material [3, 4, 5]. The research conducted so far indicates that during this process there is a noticeable soluble substances content increase. A part of starch may undergo degradation into polysaccharides of lower molecular weight which causes slightly sweet taste of the product. On the other hand high-molecular-weight complexes of starch and lipids may also develop leading to formation of unsusceptible to digestion, so-called resistant starch.

However some informations about the degree of the increase of soluble substances and the saccharides involved and produced in those changes can be found. Therefore, the aim of the present work was to evaluate the effect of raw material composition on so-called sugar profiles and the increase of water soluble substances content as a result of high-molecular-weight compounds degradation in conditions of gentle extrusion cooking.

MATERIAL AND METHODS

Five samples of mixtures used to produce potato chips of relatively low (in comparison with ones produced in traditional way) content of fat, differing in raw material composition were examined. Raw material mixture included potato flour from “SOLAN” Co. Głowno and also (in different proportions) wheat flour type 550, oat flour, maltodextrin 18DE, vegetable oil (kujawski), salt and a leavening agent. Table 1 presents the basic physicochemical characteristic of main starch ingredients used in the experiments. The composition of different raw material mixtures is shown in Table 2.

The ingredients were thoroughly mixed in a laboratory mixer (Type GM-2, produced by ZBPP) at the final moisture level of 25%. Such prepared material was subjected to an extrusion cooking in a twin-screw extruder (ZSK-25P made by Krupp Werner-Pfleiderer) at the following parameters of the process: L:D = 20; a temperature of the 1 zone 115°C; a temperature of the 2 zone 130°C; a temperature of the head 90°C; corotating screw revolutions = 50/min, a nozzle equipped with an insert which shaped the product into a ribbon 1.5 mm thick and 8 mm wide. Extruded product was gently dried in a blow-dryer at the temperature not exceeding 45°C to water content of 4-5%. Next it was crumbled and water soluble substances content according to Rohrlich [7] was determined.

Sugar profiles were determined in Cargill (Poland) according to the following procedure: 9 g samples were dissolved in 50 ml of water. The obtained mixture was filtered using a filter paper and a sugar profile was determined on the basis of HPLC method applying Bio-Rad 300 mm x 7.8 mm HPX-42A column. The eluent was demineralised water at a flow rate of 0.6 ml·min^-1. A temperature of the oven was 85°C. The calibration of the equipment gives the possibility to determine contents from a single molecule of glucose (DP₁) or fructose up to 10 glucose molecules joined together (DP10).

RESULTS AND DISCUSSION

The raw materials used in the experiments are extremely rich in starch (potato flour and wheat flour), with an average for this type of raw materials protein content and a low fat content (Table 1). Oat flour presents considerably lower carbohydrate content and relatively high fat content. Oat flour, in spite of unfavourable from technological point of view characteristics, is willingly used as a valuable component of snack foods owing to its high nutritive value [1, 2] and for these reasons it was used in the experiments.

These raw materials are characterised by various soluble substances content. The highest amount, more than 13% of these compounds, contains granulated potato flour, definitely lower water soluble substances content, not exceeding the level of 4% showed wheat and oat flour. The addition of other ingredients in various proportions (maltodextrin, baking powder, NaCl) to a mixture prepared for extrusion, as presented in Table 2, brought about an increase in soluble substances content in particular mixtures up to the values presented in Table 3.

As the effect of the extrusion process the quantity of soluble substances in extrudates increased by 3.1%–4.7% depending on a mixture composition. Taking the process condition: high temperature (at the level of 100°C), moisture and pressure into consideration, it may be assumed with high certainty that the increase in soluble substances content is a result of changes occurring in polysaccharides: gelatinisation and degradation of starch to sugars of shorter glucose chains.

Data presented in Table 4 and Figures 1-5 show that during extrusion cooking starch is decomposed into shorter chains, and within the range of water soluble substances they are mainly dextrins consisting of 7 to 10 joined glucose molecules. There is however no increase in the simple sugars (glucose, fructose) and disaccharides (maltose) content. On the contrary, the content of these components slightly decreases which may suggest that they are used to build high molecular complexes with other mixture ingredients. It is especially noticeable in the mixture containing maltodextrin (variant C), where the extrusion process caused considerable decrease of the maltose and glucose level accompanied by a relatively higher content of sugars consisting of 7 to 10 glucose molecules.

The results presented in Table 4 and Figures 1 to 5 indicate the complexity of carbohydrate components conversion, which take place during gently conducted extrusion cooking process. The degradation of starch does not go too far but rather gentle shortening of glucose chains to compounds of lower molecular weight occurs. At the same time in the case of high level of simple sugars content their reactions with other components (most probably in changes leading to formation of Maillard’s compounds) take place.

CONCLUSIONS

Extrusion cooking leads to degradation of starchy raw materials. Effect is more pronounced in the case of wheat flour and maltodextrin than in oat flour and pure potato. As a result of starch and maltodextrin degradation mostly the amount of longer-chain sugars with 7-10 joined glucose units increases. Simple sugars and maltose units during the extrusion process are involved in Maillard reaction, and in effect their content in the product slightly decreases. It could be assumed, that in the case of more severe extrusion process parameters the changes in sugar profiles would be more evident.

ACKNOWLEDGEMENTS

The authors wish to express their thanks to staffs of Cargill (Poland) Ltd. for carrying out the sugar profiles determination for the present paper.

REFERENCES

1. Huang D., 2001. Selecting an Optimum Starch for Snack Development. Cereal Foods World 6, 237-239.

2. Jones J.M., 2001. The benefits of eating breakfast cereals. Cereal Foods World 10, 461-464.

3. Kasper A., Rajkowska N., 2005. The effect of raw material and technological parameters on sensory profile of extruded products. M.Sc. Thesis, Faculty of Food and Nutrition Sciences, Agric. Univ. Poznań.

4. Majcher M., Jelen H., 2005. Identification of potent odorants formed during the preparation of extruded potato snacks. J. Agric. Food Chem. 53, 16, 6432-6437.

5. Mercier C., Linko P., Harper J.M., 1989. Extrusion cooking. Am. Assoc. Cereal Chem. Inc. St. Paul, Minnesota, USA.

6. Obuchowski W., Majcher M., 2003. The characteristic of volatile aroma substances of the extruded products contained of oat flour. Przegl. Zboż.-Młyn. 2, 14-16.

7. Rohrlich M., Bruckner G.: Das Getreide. Teil II. Paul Parey, .Berlin. 1967.

Accepted for print: 25.01.2007

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